IL Foundation Grade 10 - Biology

IL FOUNDATION SERIES

BIOLOGY

IL Foundation Series - Biology Class 10

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Second Edition

LIFE PROCESSES IN PLANTS 1

1.1 INTRODUCTION TO LIFE PROCESSES

Within the bodies of living things, a variety of physiological processes occur, including photosynthesis, respiration, excretion, and nourishment. These physiological activities that are essential for the survival of living organisms are known as life processes. These are also called metabolic activities.

1.2 NEED FOR LIFE PROCESS IN PLANTS

Unicellular organisms consist of a single cell that houses all their biological functions. In multicellular organisms, distinct organs are assigned distinct roles in various life processes. One of the most important life processes, nutrition is necessary for the development of immunity, growth, reproduction, energy production, and other functions.

1.3 NUTRITION

Nutrition is defined as a process by which living beings procure nutrients (food) or synthesise them and change them into simple, absorbable forms through a series of biochemical processes.

1.3.1 Types of nutrition

There are two basic modes of nutrition: autotrophic and heterotrophic.

Autotrophic nutrition

A series of processes by which an organism prepares its own food from simple inorganic materials collected from the environment is called autotrophic nutrition. Organisms involved in autotrophic nutrition are called autotrophs.

Autotrophs can be further classified into two types based on the source of energy utilised.

1. Photoautotrophs: Green plants are photoautotrophs as they prepare their food through the process of photosynthesis.

2. Chemoautotrophs: The organisms that produce their food by utilising energy from chemical reactions and not by sunlight are called chemoautotrophs, for example, Archaebacteria, Cyanobacteria, and more.

Heterotrophic nutrition

A mode of nutrition in which an organism depends on other organisms for its food is called heterotrophic nutrition. Organisms involved in heterotrophic nutrition are called heterotrophs. All animals and non-photosynthetic plants are heterotrophs. Unicellular organisms are also heterotrophs, for example, Amoeba, Paramecium, etc.

S. No.

Autotrophic Nutrition

i. It occurs in green plants, in some bacteria and, in some protists.

Heterotrophic Nutrition

It occurs in animals and in plants, which do not have chlorophyll.

ii. Chlorophyll is necessary for trapping the solar energy. Chlorophyll is absent; as such, they do not trap solar energy.

iii. Food is self-manufactured using CO2 and water as raw materials.

iv. Digestion of food does not take place.

v. Autotrophs are placed at the bottom of the food chain as producers.

Food is obtained directly or indirectly from autotrophs.

Digestion is required to convert complex organic substances present in the food into simpler and soluble forms.

Heterotrophs are placed above autotrophs in the food chain as consumers.

1.4 PHOTOSYNTHESIS

Green plants make their food by the process of photosynthesis. It is the process of conversion of solar energy into chemical energy. It takes place in the leaves of the plant. Within a leaf, photosynthesis occurs particularly in specialised cells, called mesophyll cells, that contain chloroplasts.

1.4.1

Definition

Photosynthesis may be defined as the synthesis of carbohydrates by plants in the presence of sunlight from CO2 and H2O taken up from the air and soil, respectively. Photosynthesis may also be defined as the capture of photons of light and the conversion of their energy into chemical energy, during which water oxidises, and CO2 is reduced.

An overall chemical equation for photosynthesis may be represented as:

Table 1.1 Difference between autotrophic and heterotrophic nutrition

1.4.2 Significance of photosynthesis

Photosynthesis is important for several reasons such as:

i. Food: Through photosynthesis, green plants synthesise food from simple raw materials, CO2 and H2O. Thus, it sustains life on Earth.

ii. Oxygen: Oxygen released during the process of photosynthesis is needed by animals and humans for respiration. It is also required for the respiration of microbes. Oxygen also supports the combustion of fuels.

iii. Fuels: Fossil fuels like coal, oil and natural gas are forms of stored solar energy synthesised by photosynthesis millions of years ago.

1.4.3 Where does photosynthesis take place?

Photosynthesis occurs in a specialised intracellular organelle called the chloroplast. Pigments and enzymes are grouped together in a biological membrane, enabling the necessary series of chemical reactions to be carried out efficiently.

There are about half a million chloroplasts per square millimetre of a leaf surface Chloroplasts contain double-membrane envelopes. It encloses a proteinaceous fluid called stroma. Darkphase enzymes are present in it. These enzymes reduce CO2 to glucose by a series of biochemical reactions. They turn volatile and functionless if the chloroplast is isolated. An elaborate system of interconnected membrane sacs called thylakoids is present in the stroma. These sacs are stacked in columns called grana. Chlorophylls and the other pigments responsible for the light phase are present on thylakoids.

Fig. 1.1 Photosynthesis in plants

1.4.4 Mechanism of photosynthesis

Photosynthesis is a biphasic process. The two stages of photosynthesis are known as the light reaction and the dark reaction.

Light reaction (Hill reaction)

Light reaction, also known as the photochemical phase or light-dependent reaction, occurs in the grana of the chloroplast. It includes:

1. Light absorption

2. Water splitting (photolysis)

3. Oxygen release

4. Release of high-energy chemical intermediates (ATP and NADPH).

Light reaction is the first stage of photosynthesis in which solar energy is converted into chemical energy in the form of ATP and NADPH. The protein complexes and pigment molecules help in the production of NADPH (reduced nicotinamide adenine dinucleotide phosphate) and ATP (adenosine triphosphate).

The main purpose of the light reaction is to generate organic energy molecules, such as ATP and NADPH, which are needed for the subsequent dark reaction.

Chlorophyll absorbs the red and blue wavelengths of white light, and photosynthesis occurs most efficiently at these wavelengths. When the light falls on the plant, chlorophyll is first activated by absorbing sunlight. This light-activated chlorophyll splits the water molecule (photolysis).

H2O → 2H+ + 2e- + 1 2 O2 (Protons) (Electrons) (Oxygen)

The oxygen, which is a byproduct, is released by the plant into the atmosphere.

Thylakoid membrane

Thylakoid space (lumen)

Chloroplast DNA

Stroma

Thylakoids

Ribosome

Fig. 1.2 Structure of the chloroplast

Dark reaction (Calvin cycle)

The dark reaction, also known as the light-independent reaction or Calvin cycle, occurs in the stroma of the chloroplast. ATP and NADPH, produced in the light phase, are used as assimilatory powers in this reaction. Light is not required directly. Hence, it can be summarised that dark-phase reactions do not depend on light but depend on the light phase.

For ease of understanding, the Calvin cycle can be described under three stages:

1. Carboxylation

2. Reduction

3. Regeneration

Carboxylation: Carboxylation is the fixation of CO2, the most crucial step of the Calvin cycle, where CO2 is utilised for the carboxylation of RuBP (Ribulose bisphosphate). This reaction is catalysed by the enzyme RuBP carboxylase, which is a universal enzyme.

Reduction: This step involves the utilisation of ATP and NADPH for the production of glucose molecules.

Regeneration: Regeneration of the CO2 acceptor molecule RuBP is crucial.

1.4.5

Factors of photosynthesis

The rate of the photosynthetic process is affected by several external (environmental) and internal factors.

The light reaction totally depends on the availability of light, water, pigments, etc., and the dark reaction depends on temperature and available CO2. Thus, all the factors are important in affecting the rate of photosynthesis.

External factors

Light: In photosynthesis, light energy is converted to chemical energy. It can be studied under three headings, i.e., light intensity, light quality, and light duration.

Chloroplast

Fig. 1.3 Calvin cycle

i. Light intensity: Usually, with an increase in light intensity, an increase in the rate of photosynthesis is noticed. It also affects the opening and closing of stomata, thereby affecting gaseous exchange.

ii. Light quality: The blue and red wavelengths of the spectrum are most effective for photosynthesis. Maximum photosynthesis occurs in the red region of the spectrum, with the next peak in the blue region.

iii. Light duration: The rate of photosynthesis is higher in intermittent light than in continuous light. The necessity of light for photosynthesis can be demonstrated by a light screen experiment.

Carbon dioxide: CO2 is the natural limiting factor of photosynthesis, especially on a sunny day. If the concentration of CO2 is increased from 0.03% to 0.05%, the rate of photosynthesis increases. However, a concentration of CO2 above 1% reduces the rate of photosynthesis due to the closure of stomata.

Water: Water deficiency may decrease the rate of photosynthesis, as it is one of the prime substrates.

Temperature: As temperature increases, the rate of photosynthesis also increases. At very high temperatures, denaturation of enzymes occurs, resulting in a decrease in photosynthesis.

Internal factors

The plant factors include the number, size, age and orientation of leaves, mesophyll cells, chloroplasts, internal CO2 concentration, and the amount of chlorophyll. The plant's internal factors are dependent on the genetic predisposition and growth.

1.5 TRANSPORTATION IN PLANTS

The food that is produced in the plant leaves must be transported to different parts of the plants. The transported food, water, and minerals are not only absorbed by the roots but also transported to different sites of the plant’s body for different purposes. Hence, transportation of water, minerals, and food is an important life process. The process of transportation of water and minerals is preceded by the absorption of these substances by the roots.

1.5.1 Absorption of water and minerals by the roots

The roots absorb most of the water that goes into plants with the help of the root hairs that are present in millions at the tips of the roots. Root hairs are thin-walled, slender extensions of root epidermal cells that greatly increase the surface area for absorption. The absorption of water, along with mineral solutes, by the root hairs is purely by diffusion.

Root Hair

Epidermal Cell Cytoplasm

Cell Wall Vacuole

Cell Membrane Nucleus

FullyGrownRootHair

Newly Growing Root Hair

Substances move throughout the plant through diffusion, facilitated diffusion, active transport, and mass or bulk flow.

Bulk transport

There are several means of transport required to transport substances in plants. The process of diffusion alone is not enough to transport substances in the plants. Sometimes, the site of production or absorption and sites of storage are too far from each other; other processes like diffusion and active transport would not suffice.

Special long-distance transport systems become necessary to move substances across long distances and at a much faster rate. Water, minerals, and food are generally moved by a mass or bulk flow system.

Mass flow is the movement of substances in bulk or en masse from one point to another because of pressure differences between the two points.

The bulk movement of substances through the conducting or vascular tissues of plants is called translocation. Xylem is associated with the translocation of mainly water, mineral salts, and some organic nitrogen and hormones from roots to the aerial parts of the plants.

The initial driving force that causes the transportation of water and minerals to the xylem from root hair is called root pressure. Stocking defined root pressure as a pressure developing in the tracheary elements of the xylem due to the metabolic activities of roots. The pressure is caused by the diffusion pressure gradient and is maintained by the activity of living cells. The cortical cells of the root become turgid when water from root hair enters the cortex. Water and minerals are driven into the xylem by the pressure generated in turgid cortical cells. As the cortical cells turn flaccid, they continue to absorb water.

Fig. 1.4 Root hair

1.5.2 Transport of water and minerals in plants

Water is conducted upwards by tracheary elements. i.e., tracheids and vessels. In young herbaceous plants, almost all the tracheary elements participate in this process, but in large woody trees, the tracheary elements of only sapwood are functional and participate in the ascent of sap.

The upward movement of the xylem sap is called the ascent of sap. The various driving forces for the ascent of sap are as follows:

1. Capillarity

2. Cohesive force

3. Transpiration pull

All the three mechanisms mentioned above together help in the transportation of xylem sap. The diameter of xylem vessels is very minute. It ranges from 20 - 400 micrometres. Hence, water capillarity is exhibited here due to the adhesive force between the cell wall of the xylem and water. Then, the role of cohesive force comes into existence. The force of attraction among similar molecules is called the cohesive force. Cohesive forces are very strong in water. This helps in the formation of a long water column without any air gap. Next, the transpirational phenomenon pulls the water column strongly in the upward direction.

1.5.3 Transport of food in plants

The vascular tissue, phloem, is concerned with the transportation of food from leaves to the other parts of the plant. Phloem tissue transports sugar, amino acids, and other organic substances in both directions, upward and downward, to fulfil the requirements of all parts of the plants.

The translocation of these substances, which constitute the phloem sap takes place from leaves to phloem by the mechanism of active transport. The source of the energy required for this process is ATP, which is produced during the process of respiration.

Two types of specialised cells of phloem tissue are involved in the translocation of photosynthetic products. They are sieve tube elements and companion cells. Sieve tube elements are tube-like

Fig. 1.5 Phloem transport

structures connected one above the other. There are porous sieve plates between two sieve tube elements. Companion cells surround the sieve tube elements. Sugar, amino acids, and other organic molecules are transported to sieve tubes through companion cells. The adjacent positions of the xylem and the phloem tissues facilitate the movement of water molecules from the xylem to the sieve tubes of the phloem. The movement of water molecules from the xylem to the phloem takes place through the process of osmosis, which is a passive transport. Thus, high pressure is developed inside the sieve tube elements, and phloem sap can be transported in both directions through highly porous sieve plates.

Due to the difference in pressure between the sieve tubes and the surrounding tissues, phloem sap is translocated to the surrounding cells. Thus, a photosynthetic product reaches different parts of the plant for storage, growth, and generation of energy requirements to conduct different biological processes.

1.6 RESPIRATION IN PLANTS

All living organisms, be it plants or animals, are required to perform certain essential functions to ensure the survival of species. Like animals, plants also require nourishment, a way to excrete waste material (transpiration), a way to breathe (take in oxygen), ways to reproduce and create new plants, and other essential life processes. Similar to respiration in humans and animals, plants also respire to produce energy by using nutrients and oxygen and giving out carbon dioxide and water as by-products. It is opposite to photosynthesis, a process by which plants produce oxygen.

1.6.1 Types of respiration

Respiration can be divided into two categories based on its occurrence in the presence or absence of oxygen. Two types of respiration are:

1. Aerobic respiration

2. Anaerobic respiration

Aerobic respiration

This type of respiration leads to a complete oxidation of stored food (organic substances) in the presence of oxygen and the release of carbon dioxide, water, and a large amount of energy. Such a type of respiration is generally found in higher organisms. The overall equation is:

C6H12O6+6O2+6H2O → 6CO2+12H2O+energy(686 kcal)

If this energy is to be useful to the cell, it should be able to utilise it to synthesise other molecules that the cell requires. The strategy that the plant cell uses is to catabolise the glucose molecule in such a way that not all the liberated energy goes out as heat. The key is to oxidise glucose not in one step but in several small steps, enabling some steps to be just large enough such that the energy released can be coupled to ATP synthesis.

Anaerobic respiration

This type of respiration occurs in the absence of oxygen. Such respiration is observed mostly in bacteria and fungi. In the absence of oxygen, many deep-seated tissues of higher plants, seeds, fleshy fruits, and succulent plants such as cacti undergo anaerobic respiration. Facultative anaerobes are Bacillus, yeast, etc., and obligate anaerobes are Clostridium. The equation of fermentation is as follows:

C6H12O6 → 2C2H5OH + 2CO2 + Energy (56 Kcal)

1.7 EXCRETION IN PLANTS

Excretion is the life process through which waste and toxic products are expelled from the body of an organism. Plants generate different excretory products during the execution of their life processes.

Carbon dioxide is the product obtained during respiration. This gas is consumed in the process of photosynthesis during the daytime, but at night, it is expelled through the stomata. Oxygen gas generated during photosynthesis is partially consumed during respiration, but most of it is excreted through the stomata. Certain waste products in plants accumulate in the vacuoles of cells of old leaves. These wastes are eliminated when these leaves get detached from the plants.

Resin, gum, latex, etc., are the excretory products of plants that ooze out of the bark of trees and are shed in due course of time. Another process of excretion in plants is transpiration. The excess water is eliminated from the plant through the process of transpiration.

1.8 TRANSPIRATION

Transpiration is the process by which the elimination of water takes place from the aerial parts of the plant in the form of water vapour.

1.8.1

Significance of transpiration

1. Creates transpiration pull for absorption and transport of plants.

2. Supplies water for photosynthesis.

3. Transports minerals from the soil to all parts of the plants.

4. Cools leaf surfaces, sometimes 10 - 15 degrees, by evaporative cooling.

5. Maintains the shape and structure of the plants by keeping cells turgid.

1.8.2 Types of transpiration

Transpiration can be categorised on the basis of the aerial parts of the plant involved in transpiration. Different types of transpiration are as follows:

1. Stomatal transpiration

2. Cuticular transpiration

3. Lenticular transpiration

Stomatal transpiration: About 90 per cent of the total water from the plants is eliminated through stomata. Stomatal transpiration depends on the structure of the leaves and the number and distribution of stomata on the surface of the leaves.

Cuticular transpiration: Transpiration through the cuticle, a waxy coating over the epidermal layers of leaves, is called cuticular transpiration. About 5-10 per cent of water loss takes place through the cuticles. Cuticular transpiration is inversely proportional to the thickness of the cuticle.

Lenticular transpiration: Water from plants can also evaporate through small openings present in the woody stems. This is called lenticular transpiration. Plants transpire about 0.1 per cent water through lenticels.

1.8.3 Factors affecting transpiration

External factors

Light: Light indirectly affects the rate of transpiration. It affects the stomatal movement. Stomata opens in the presence of light and the phenomenon of transpiration occurs.

Humidity of the air: The rate of transpiration is higher at relatively lower atmospheric humidity, and the rate of transpiration is lower at relatively higher atmospheric humidity. Hence, the rate of transpiration increases during the summer and decreases during rainy days.

Temperature: The increase in temperature increases the rate of transpiration by increasing the rate of evaporation of water from the cell surface.

Wind velocity: The higher the velocity of wind, the more transpiration there is. The transpiration is faster in the breeze. The wind of much higher velocity, however, retards the rate of transpiration by closing stomata.

Internal factors

The effects of morphology and anatomy of leaves are mentioned below. Larger leaves transpire more water. Inadequate absorption of water by the root causes wilting of leaves. Wilting of leaves reduces transpiration. The transverse arrangement of leaves increases transpiration, while the perpendicular arrangement reduces transpiration.

Succulent leaves contain latex in their tissues, and hence, transpiration gets reduced. Different anatomical features such as a smaller number of stomata, sunken stomata, presence of cuticle, compact mesophyll, etc., reduce the rate of transpiration.

QUICK REVIEW

• Photosynthesis may be defined as the synthesis of carbohydrates by the green organs of a plant in the presence of sunlight from carbon dioxide and water taken up from the air and soil, respectively.

• An overall chemical equation for photosynthesis may be represented as:

• The energy is locked in sugars and is obtained in a useful form by living organisms by the process of respiration.

• The organic compounds that are oxidised during respiration are called respiratory substrates. Glucose is the most favoured respiratory substrate.

• Plants, unlike animals, have no specialised organs for gaseous exchange, but they have stomata and lenticels for this purpose.

• Both aerobic and anaerobic respiration starts with glycolysis.

• The process of translocation of water and minerals from the root tip to the stem top of the plant is called the ascent of sap.

• The bulk movement of substances through the conducting or vascular tissues of plants is called translocation.

• Root pressure is largely responsible for the ascent of sap in herbaceous plants.

• Loss of water vapour from the leaf by diffusion and evaporation is called transpiration.

• Cohesion is the mutual attraction between water molecules.

• Adhesion is the attraction of water molecules to polar surfaces.

• The direction of movement in the phloem can be upwards or downwards, i.e., bidirectional.

MULTIPLE CHOICE QUESTIONS WITH SINGLE CORRECT ANSWER

I. Nutrition

1. Processes that are vital for survival and are required to maintain body functions are called:

a. Ecological processes

c. Revolutionary processes

b. Life processes

d. Evolutionary processes

WORK SHEET - 1

2. Which of the following statements is/are correct?

i) All green plants can prepare their own food.

ii) Most animals are autotrophs.

iii) Carbon dioxide is not required for photosynthesis.

iv) Oxygen is liberated during photosynthesis.

a. i and ii

II. Photosynthesis

b. ii and iii

c. ii and iv

1. What other substance is evolved in photosynthesis besides oxygen?

d. i and iv

a. CO2 b. Water vapours c. H2 d. N2

2. Which one of the following is not essential for the process of photosynthesis?

a. Light and chlorophyll

b. CO2 and light

c. Oxygen and glucose

d. Water and minerals

3. Photosynthesis takes place ______________.

a. Only in sunlight

b. Only in yellow light

c. In the visible light obtained from any source

d. Only in very high-intensity light

4. Which of the following statements about photosynthesis is not true?

a. All green plants photosynthesise.

b. Only green plants photosynthesise.

c. Carbon dioxide is reduced during photosynthesis.

d. Some bacteria also photosynthesise.

5. Which light range is most effective in photosynthesis?

a. Blue

Green

Red

6. During the light reaction in photosynthesis, what all are formed?

a. ATP and sugar

c. ATP, hydrogen donor, and O2

Violet

b. Hydrogen, O2 and sugar

d. ATP, hydrogen, and O2 donor

7. In higher plants, the by-product of photosynthesis is ____________.

a. O2

b. H2O

c. Carbohydrates d. ATP

8. Photosynthesis is a/an ____________.

a. Physico biochemical process

c. Endergonic reaction

b. Anabolic process

d. All the above

9. The first event in photosynthesis is the ______________.

a. Synthesis of ATP

c. Photolysis of water

b. Photoexcitation of chlorophyll

d. Release of oxygen

10. For the process of photosynthesis, which one of the following is not essential?

a. Light and chlorophyll

c. Oxygen and glucose

b. Carbon dioxide and light

d. Water and minerals

11. Stroma in the chloroplasts of higher plants contain ____________.

a. Light-independent reaction enzymes

c. Coupling factor

b. Light-dependent reaction enzymes

d. Chlorophyll

12. In photosynthesis, oxygen is liberated due to the ______________.

a. Reduction of carbon dioxide

c. Photolysis of water

b. Hydrolysis of carbohydrate

d. Breakdown of chlorophyll

13. The light reaction of photosynthesis occurs inside the ___________.

a. Stroma b. Grana

c. Endoplasmic reticulum d. Cytoplasm

14. Statement I: Dark-phase enzymes are present in the grana of the chloroplast.

Statement II: Photosynthetic pigments are present in the grana of the chloroplast.

a. Both statements are true.

b. Both statements are false.

c. Statement I is true, and statement II is false.

d. Statement I is false, and statement II is true.

III. Transportation in plants and transpiration

1. Which of the following is correct regarding the translocation of substances in the vascular tissues of plants?

a. Organic substances, for example, sugars, are transported upward in the xylem.

b. Organic substances move up and down the phloem.

c. Salts and other inorganic substances move downward only through the xylem.

d. Inorganic substances move upward only through the phloem.

2. Water will be absorbed by the root hairs when the ____________.

a. The concentration of salts in the soil is high.

b. The concentration of solutes in the cell sap is high.

c. Plant is rapidly transpiring.

d. They are separated from soil by a semi-permeable membrane.

3. Choose the incorrect option for why plants can get along without respiratory organs, as plants, unlike animals, have no specialised organs for gaseous exchange.

a. The respiration rate is faster in roots, stems and leaves than in animals.

b. O2 released during photosynthesis is utilised for respiration.

c. The loose packing of parenchyma cells in leaves, stems, and roots facilitates respiration.

d. There is very little transport of gases from one plant part to another.

4. A column of water within the xylem vessels of tall trees does not break under its weight because of the ____________.

a. Positive root pressure

c. Tensile strength of water

b. Dissolved sugars in water

d. Lignification of xylem

5. The root pressure develops due to a/an ____________.

a. Increase in transpiration

c. Low osmotic potential in soil

b. Active absorption

d. Passive absorption

6. Assertion (A): In angiosperms, the conduction of water is more efficient because the xylem contains vessels.

Reason (R): Conduction of water by the xylem vessel elements is an active process with energy supplied by xylem parenchyma rich in mitochondria.

a. Both the Assertion and the Reason are true, and the Reason is the correct explanation for the Assertion.

b. Both the Assertion and the Reason are true, and the Reason is not a correct explanation of the Assertion.

c. The Assertion is true, but the Reason is false.

d. Both the Assertion and Reason are false.

7. Assertion (A): The rate of transpiration is indirectly proportional to relative humidity. Reason (R): If the outer air is humid, it will reduce the diffusion of water vapour from intercellular spaces of the leaf to the outer atmosphere.

a. The Assertion and the Reason are true, and the Reason is the correct explanation for the . Assertion.

b. The Assertion and the Reason are true, and the Reason is not a correct explanation for the . Assertion.

c. The Assertion is true, but the Reason is false.

d. Both the Assertion and the Reason are false.

8. Assertion (A): Light is a very important factor in transpiration. Reason (R): It induces stomatal opening and darkness closing. Therefore, transpiration increases in light and decreases in the dark.

a. The Assertion and the Reason are true, and the Reason is the correct explanation for the . Assertion.

b. The Assertion and the Reason are true, and the Reason is not a correct explanation of the . Assertion.

c. The Assertion is true, but the Reason is false.

d. Both the Assertion and the Reason are false.

9. The root pressure is maximum when _____________.

a.Transpiration is high, and absorption is low.

b. Transpiration is very low, and absorption is high.

c. Both are very high.

d. Both are very low.

10. Which of the following contributes the most to the transport of water from the ground to the leaves of a tall tree?

a. Breakdown of ATP

c. Capillary rise of water in xylem

b. Root pressure

d. Cohesion of water and transpiration pull

11. Wilting of plant occurs when the _____________.

a. Xylem is blocked

c. Epidermis and few roots are removed

b. Phloem is blocked

d. Pith is removed

12. The continuity of the water column in the xylem is maintained due to the ___________.

a. Evaporation power of water

c. Presence of air bubbles

b. Cohesive property of water

d. None of the above

13. Water absorption through roots can be increased by ____________.

a. Increased transpiration

c. Decreased transpiration

b. Increased rate of photosynthesis

d. Decreased absorption of ions

14. The absorbed water can rise to the highest point by:

a. Root pressure

c. Force of capillarity

IV. Respiration in plants

1. Stored energy of carbohydrates is released during

a. Respiration

c. Fat metabolism

b. Imbibition force

d. Transpiration pull

b. Photosynthesis

d. Photophosphorylation

2. The conversion of complex substances to simple substances involves the ___________.

a. Catabolic and exergonic methods

c. Anabolic and endergonic methods

b. Catabolic and endergonic methods

d. Anabolic and exergonic methods

3. Respiration in plants is important as it ____________.

a. Provides oxygen to plants

c. Liberates CO2

b. Liberates energy in the form ATP

d. All the above

4. The main substrate of respiration in plants is _____________.

a. Lipids

b. Fats

5. The ATP contains _____________.

a. Adenosine, ribose sugar, and phosphate

c. Adenine, ribose sugar, and phosphate

c. Organic acids d. Carbohydrates

b. Adenosine, deoxyribose, and phosphate

d. Adenine, deoxyribose, and phosphate

6. The original source of energy released in respiration is ____________.

a. Starch b. Glucose

7. Cellular respiration is absent in ___________.

a. Bacterial cells b. Plant cells

c. Fats d. Sunlight

c. Intestinal cells d. Viruses

8. Respiration in bacteria takes place at the ___________.

a. Cell wall

b. Plasma membrane

c. Nucleus d. Cytoplasm

9. Nearly every living organism uses glucose as a nutrient source of energy. Why?

a. Glucose is the only molecule capable of providing the energy to produce ATP.

b. The structure of glucose is very similar to that of ATP.

c. Glucose has more potential energy than any other respiratory substrate.

d. The ability to harvest energy from glucose appeared very early in biological evolution.

10. Read the following statements and choose the correct one.

a. Respiration is purely a catabolic process.

b. Reduction of food results in the release of energy.

c. Chemical energy is broken down during respiration to release energy.

d. Fungi can make their own food and derive energy by respiration.

11. Aerobic and anaerobic respirations differ from each other in all except a. Involvement of oxygen

c. End products

WORK SHEET - 2

b. Output of ATP molecules

d. Method of glucose breakdown in cytosol

MULTIPLE CHOICE QUESTIONS WITH SINGLE CORRECT ANSWER

1. In which of the following plants will there be no transpiration?

a. Aquatic submerged plants

b. Plants living in deserts

c. Aquatic plants with floating leaves d. Plants growing in hilly regions

2. The rate of transpiration will be very low in a situation where the ____________.

a. Environment is very hot and dry. b. Relative humidity is very high.

c. Groundwater is sufficiently available d. Wind is blowing with a very high velocity.

3. Which of the following statements is not true?

a. Transpiration is increased when the root-shoot ratio is increased.

b. Transpiration is increased when the latex and mucilage are increased in the tissue.

c. Transpiration is decreased when the stomata are sunken.

d. Transpiration is decreased when the leaves become leathery or hairy.

4. Why is the transport of organic food through phloem bidirectional?

a. The roots serve as the source, while the leaves are the sink region.

b. The relationship between the two regions is variable.

c. The translocation of organic solute is regulated by energy.

d. The source and sink regions are irreversible.

5. Regarding root pressure, which one is not correct?

a. It is sufficient to raise water above ground-level root pressure.

b. It is positive in all except the tall trees.

c. It does not act as a driving force for the mass flow of sugar.

d. It is not able to push water up to a small height in the stem.

6. Which of the following statements about the movement of water through xylem tissue is false?

a. Evaporation power of water

b. Water is pulled up in the plants by evaporation of water from the leaf surfaces.

c. Water has a strong tendency to be pulled into air by evaporation.

d. Continuous column of water in xylem tissue resists breaking even when exposed to the forces of evaporation and gravity.

7. In the following question, a statement of assertion is followed by a statement of reason. Mark the correct choice.

Assertion (A): Transpiration lowers plant temperature.

Reason (R): Transpiration reduces the

a. Both (A) and (R) are true, and (R) is the correct explanation of (A).

b. Both (A) and (R) are true, but (R) is not the correct explanation of (A).

c. (A) is true, but (R) is false.

d. Both (A) and (R) are false.

8. In plants, respiration takes place

a. Only in leaves during the night b. Only in leaves during the day

c. In all living cells

d. Stroma

9. Where does the light reaction occur in chloroplast?

a. Membrane system (grana) b. Stroma c. Both a & b d. None of these

10. The membranous sytem within the chloroplast is made up of _____________.

a. Grana

b. Stroma lamellae c. Stroma d. Both a & b

11. Which among the following is not a part of chlorophyll?

a. Carbon

b. Iron c. Hydrogen d. Nitrogen

12. The light trapping reaction takes place in the___.

a. Thylakoids

b. Cisternae c. Lamellae d. Stroma

13. Th light energy is converted into chemical energy in the presence of _____________.

a. Pyrenoids

b. Chloroplasts c. Ribosomes d. Mesosomes

14. The stroma in the chloroplasts of higher plants contain _____________.

a. Ribosomes b. Chlorophyll

c. Light-independent reaction enzymes d. Light-dependent reaction enzymes

15. The first reaction of photosynthesis is:

a. Photolysis of water

c. Formation of ATP

b. Excitation of chlorophyll molecule

d. Fixation of CO2

16. Which factor is not limited to normal conditions for photosynthesis?

a. Air b. CO2

c. Water d. Chlorophyll

17. Which factor affects the process of photosynthesis indirectly?

a. Light b. Temperature

c. CO2 concentration d. Water

18. Oxygen, which is liberated during photosynthesis, comes from:

a. Carbon dioxide

c. Chlorophyll

b. Water

d. Phosphoglyceric acid

19. The internal factors affecting photosynthesis are the _______________.

a. Number and size of leaf

b. Age of leaf and orientation

c. Internal CO2 concentration and the d. All of these amount of chlorophyll

20. The external factors affecting photosynthesis are the _______________.

a. Sunlight and temperature

c. Water

b. CO2 concentration

d. All of these

21. Photosynthesis is maximum during ________________.

a. Intermittent light

c. Continuous dim light

b. Continuous strong light

d. None of these

22. The rate of photosynthesis is independent of the ______________.

a. Intensity of light

c. Temperature

b. Duration of light

d. Quality of light

23. Which of the following is true for photosynthesis?

a. Reduction of CO2 and water

b. Reduction of CO2 and oxidation of water

c. Oxidation of CO2 and water

d. Oxidation of CO2 and reduction of water

24. Aerobic respiration is more advantageous because it __________________.

a. Does not require sunlight

b. Produces oxygen as a waste product

c. Does not require molecular oxygen and hydrogen

d. Releases more energy from an equal amount of nutrients

25. The stomatal movement is not affected by ___________. (NEET-2018)

a. Temperature b. Light c. O2 concentration d. CO2 concentration

26. A column of water within the xylem vessels of tall trees does not break under its weight because of the ______________________. (AIPMT-2015)

a. Positive root pressure

c. Tensile strength of water

b. Dissolved sugars in water

d. Lignification of xylem

27. The root pressure develops due to _____________. (AIPMT -2015)

a. Increase in transpiration

c. Low osmotic potential in soil

b. Active absorption

d. Passive absorption

28. Assertion (A): In angiosperms, the conduction of water is more efficient because the xylem contains vessels. (AIIMS-2013)

Reason (R): The conduction of water by the xylem vessel's elements is an active process, with energy supplied by the xylem parenchyma rich in mitochondria.

a. The Assertion and Reason are true, and the Reason is the correct explanation of the Assertion.

b. Assertion and Reason are true, and the Reason is not a correct explanation of the Assertion.

c. Assertion is true, but the Reason is false.

d. Assertion and Reason both are false.

29. Assertion (A): The rate of transpiration is indirectly proportional to relative humidity.

Reason (R): If the outer air is humid, it will reduce the diffusion of water vapour from the intercellular spaces of the leaf to the outer atmosphere. (AIIMS-2012)

a. Assertion and Reason are true, and the Reason is the correct explanation of the Assertion.

b. Assertion and Reason are true, and the Reason is not a correct explanation of the Assertion.

c. Assertion is true, but the Reason is false.

d. Assertion and Reason both are false.

30. Assertion (A): Light is a very important factor in transpiration. (AIIMS- 2011)

Reason (R): It induces stomatal opening and darkness closing. Therefore, transpiration increases in light, and decreases in the dark.

a. Assertion and Reason are true, and the Reason is the correct explanation of the Assertion.

b. Assertion and Reason are true, and the Reason is not a correct explanation of the Assertion.

c. Assertion is true, but the Reason is false.

d. Assertion and Reason both are false.

31. Read the given statements and select the correct option.

Statement 1: Xylem transport is unidirectional.

Statement 2: Phloem transport is bi-directional.

a. Both statements 1 and 2 are correct, and statement 2 is the correct explanation of statement 1

b. Both statements 1 and 2 are correct, but statement 2 is not the correct explanation of statement 1

c. Statement 1 is correct, and statement 2 is incorrect.

d. Both statements 1 and 2 are incorrect.

32. Two factors that are inversely proportional to transpiration are the _________________.

a. Atmospheric pressure and the relative humidity

b. Atmospheric pressure and the temperature

c. Relative humidity and the light

d. Relative humidity and the root-shoot ratio

33. The ascent of sap in tall trees is helped by the _______________.

a. Cohesion of water

c. Transpiratory pull

b. Adhesion of water with walls of xylem

d. All the above

34. The pressure that develops in the xylem vessels during active transpiration is ______________.

a. Negative and push

c. Negative and pull

b. Positive and pull

d. Positive and push

35. Read the following statements and find out the incorrect statement.

a. Transpiration pull does not account for the majority of water transport; most plants meet their need by root pressure.

b. The water loss in the liquid phase is called guttation, while in the vapour phase, it is called transpiration.

c. Besides the loss of water vapour in transpiration, the exchange of oxygen and carbon dioxide in the leaf also occurs through the stomata.

d. When the guard cells become flaccid, the stomata closes, and if turgid, the stomata opens.

LIFE PROCESSES IN HUMAN BEINGS 2

2.1 INTRODUCTION TO LIFE PROCESSES IN HUMAN BEINGS

Living organisms, whether unicellular or multicellular, perform some basic functions or processes for the maintenance of their lives. All the processes that perform this maintenance job together and are essential for sustaining life are called life processes. To sustain the life processes, various biochemical reactions take place inside the living organisms, which are collectively called metabolism

Important life processes we are going to study in this chapter are:

• Nutrition (obtaining and utilising nutrients)

• Respiration (obtaining and utilising energy)

• Transportation (transport of nutrients)

• Excretion (elimination of body wastes)

2.2 NUTRITION IN HUMANS

The process of conversion of complex food substances to simple absorbable forms is called digestion and is carried out by our digestive system by mechanical and biochemical methods.

2.2.1 Introduction

The digestive system of a human being includes the alimentary canal and the digestive glands.

The alimentary canal includes the mouth, pharynx, oesophagus, stomach, small intestine, large intestine, rectum, and anus.

Digestive glands include salivary glands, liver, pancreas and more.

2.2.2 Alimentary canal

The gastrointestinal (GI) tract, or alimentary canal (alimentary = nourishment), is a coiled muscular tube that extends from the mouth to the anus through the thoracic and abdominopelvic cavities. It is about 5-7 metres long and consists of many specialised regions. Arranged sequentially, these are as follows:

Mouth à Pharynx à Oesophagus à Stomach à Small intestine à Large intestine à Anus

Oral cavity

Mouth

Sublingual gland

Liver

Gallbladder

Duodenum

Small intestine

Ascending colon

Rectum Appendix Caecum

Parotid gland

Pharynx

Submandibular gland

Oesophagus

Stomach

Pancreas

Transverse colon

Descending colon

Sigmoid colon

Anal canal

Anus

Mouth

The mouth is an opening and is surrounded by upper and lower lips. It leads into the buccal cavity or oral cavity. The roof of the oral cavity is formed by the hard palate (anterior roof), and the soft palate (posterior roof). The oral cavity has teeth and a muscular tongue on its floor.

Teeth

Teeth are hard structures present in the mouth cavity and are specially developed for efficient mastication, i.e., mechanically breaking the ingested food into smaller pieces. In humans, teeth appear in two sets during a lifetime. The first set of milk teeth is twenty in number. It includes eight incisors, four canines, and eight molars (premolars are absent). The dental formula of the milk teeth and the permanent teeth of humans are given below. Milk teeth Permanent teeth

Fig. 2.1 Human digestive system

The milk teeth are completely replaced by the permanent teeth by about twelve years of age. The permanent teeth in each jaw are four incisors (used for biting), two canines (used for tearing), four premolars (used for grinding), and six molars (used for grinding).

Tongue

The tongue is a muscular, sensory organ that bears taste buds. It helps in tasting the food, mixing the food with saliva (that contains the enzyme ptyalin), and swallowing the food.

Pharynx

The buccal cavity opens into the pharynx. It is the common passage for food and air. It connects the buccal cavity to the oesophagus (food pipe) and the nasal cavity to the larynx (part of the respiratory system).

Oesophagus

The oesophagus (food tube) is a thin, long, muscular tube that lies posterior to the trachea. (It is lined by non-keratinised stratified squamous epithelium). The oesophagus extends inferiorly passing through the neck and thorax. It then pierces the diaphragm and leads into the stomach.

Nasal cavity

Larynx

Trachea

Nasopharynx

Oropharynx

Hypopharynx

Oesophagus

Fig. 2.3 Pharynx and oesophagus

Socket of jaw

Fig. 2.2 Different types of teeth

Stomach

The stomach is a 'J' shaped bag-like structure located in the upper left portion of the abdominal cavity, inferior to the diaphragm. It serves as a mixing chamber and holding reservoir.

A sphincter of smooth (involuntary) muscle called the gastro-oesophageal sphincter/cardiac sphincter regulates the opening of the oesophagus into the stomach. The stomach has three main regions: the cardia, fundus and pylorus. The cardia receives the oesophagus. The fundus is the large central portion of the stomach. The pylorus is the region of the stomach that connects to the duodenum. When the stomach is empty, the mucosa lies in large irregular folds called rugae (= wrinkles).

Small intestine

The small intestine is a long tube of about 3 m in length and averages 2.5 cm in diameter. It begins at the pyloric sphincter of the stomach, coils through the central and inferior part of the abdominal cavity, and eventually opens into the large intestine. The small intestine is distinguishable into three regions: the duodenum, jejunum and ileum.

Small Intestine

Duodenum

Jejunum

Illeum

2.5 Anatomical regions of human small intestine

Fundus

Body

Pyloric Antrum

Pylorus

Cardia

Fig. 2.4 Anatomical regions of human stomach

Fig.

Duodenum

The duodenum is short (0.3 m) and 'U’ shaped. The opening of the stomach into the duodenum is guarded by the pyloric sphincter, which is made of smooth muscle. The duodenum receives chyme from the stomach and digestive secretions from the pancreas and liver. The submucosa of the duodenum contains duodenal (Brunner's) glands, which secrete alkaline mucus that helps neutralise HCl in the chyme.

Jejunum

The jejunum is the long (1 m) coiled middle portion. The bulk of chemical digestion and nutrient absorption occurs in the jejunum.

Illeum

The ileum is the longest (2 m) and highly coiled region of the small intestine that joins the large intestine. The opening from the ileum into the large intestine is guarded by the ileocaecal valve.

Large intestine

The large intestine is about 1.5 m long and 6.5 cm in diameter. It plays a role in the completion of absorption, the production of certain vitamins, the formation of faeces, and the expulsion of faeces from the body. The four major regions of the large intestine are the caecum, colon, rectum and anal canal.

The caecum is a small blind sac which hosts some symbiotic micro-organisms. A narrow finger-like tubular projection with lymphoid tissue called the vermiform appendix (vermiform = worm-shaped; appendix = appendage) arises from the caecum. It was considered a vestigial organ. The caecum opens into the colon.

Appendix

Cecum

Rectum

Anal canal Transverse colon

Ileum

Fig. 2.6 Anatomical regions of human large intestine

Caecum

Colon

The colon (= food passage) is divided into four parts: an ascending, a transverse, a descending, and a sigmoid colon, which then terminates into the rectum.

Rectum

The rectum (20 cm long) is a straight muscular tube. It is an expandable organ for the temporary storage of faeces.

Anal canal

The terminal portion (2-3 cm) of the rectum is called the anal canal. The anal canal opens to the exterior by the anus, which is guarded by an internal anal sphincter of smooth muscle (involuntary) and an external anal sphincter of skeletal muscle (voluntary).

2.2.3 Digestive glands

There are many digestive glands associated with the alimentary canal. These are the salivary glands, the pancreas, the liver, and the gastric and intestinal glands. All these glands play an important role in the digestion of food.

Salivary glands

There are three pairs of salivary glands present in the mouth: the parotid (cheek), the submaxillary or submandibular (lower jaw), and the sublingual (below the tongue).

These glands secrete saliva, which performs two functions:

• Lubricates food and helps in swallowing.

• Its enzyme, salivary amylase (previously known as ptyalin), acts on starch and digests it partially.

Salivary gland duct

Sublingual gland

Submandibular gland

Parotid gland

Fig. 2.7 Types of salivary glands

Pancreas

It is a lobed, yellow-coloured gland situated between the stomach and the duodenum. This gland secretes pancreatic juice, which contains three enzymes, lipase, trypsin, and pancreatic amylase, which act on fats, proteins, and starch, respectively.

Liver

It is the largest gland of the body and is present in the abdominal cavity immediately below the diaphragm. On the undersurface of the liver, a gall bladder is present. Bile is secreted in the liver and is stored temporarily in the gall bladder. Bile is released into the duodenum (small intestine) through the common bile duct when food enters it. It lacks enzymes but contains bile salts (sodium bicarbonates, sodium glycocholate and sodium taurocholate), which help in the emulsification of fats.

Gastric glands

These are present in the wall of the stomach and secrete gastric juice

Intestinal glands

These lie in the wall of the small intestine and secrete intestinal juice (or succus entericus).

2.2.4 Digestion of food

Digestion is the breakdown of food into molecules that are small enough to be absorbed into the circulation. The process of digestion is accomplished by mechanical and chemical processes. Mechanical digestion breaks large food particles down into smaller ones. The teeth cut and grind food before it is swallowed, and then smooth muscles of the stomach and small intestine churn the food. As a result, food molecules become dissolved and thoroughly mixed with digestive enzymes. Chemical digestion is the breaking of chemical bonds in the organic molecules by digestive enzymes. Digestive enzymes produced by the digestive glands catalyse these reactions.

Bile ducts

Common bile duct

Pancreas

Pancreatic ducts

Main pancreatic duct

Duodenum

Gall bladder Liver

Fig. 2.8 Bile ducts

Digestion in mouth

The buccal cavity performs two major functions, mastication of food and facilitation of swallowing. The teeth and the tongue with the help of saliva masticate and mix up the food thoroughly. Mucus in saliva helps in lubricating and adhering the masticated food particles into a bolus (soft rounded ball of digestive contents).

The chemical digestion is initiated in the oral cavity by the hydrolytic action of the salivary amylase. About 30% of starch is hydrolysed here by this enzyme (optimum pH 6.8) into a disaccharide, i.e., maltose.

Starch Salivary amylase

Maltose (Polysaccharide) (disaccharide)

Lingual lipase digests triglycerides into diglycerides and fatty acids in the acidic environment of the stomach.

Lysozyme present in the saliva acts as an antibacterial agent that prevents infections.

Digestion in stomach

As the food reaches the stomach, it is mixed with the gastric juice secreted by the gastric glands. The content of the stomach is churned by the action of the muscles of the stomach. The gastric juice contains dilute hydrochloric acid, mucus and two enzymes, rennin and pepsin. A small amount of gastric lipase is also present in gastric juice.

i. Mucus lubricates the food and protects the lining of the stomach from the action of other components of gastric juice.

ii. Rennin coagulates the milk into curd. This action helps further its digestion by enzymes. Rennin is present in the infant's stomach and is absent in the adults.

iii. Pepsin gets activated in an acidic medium and acts upon the proteins to convert them into peptones (an intermediary product).

iv. HCl present in gastric juice kills the bacteria swallowed along with the food and makes the medium acidic for activation of pepsin.

v. Gastric lipase partially breaks down lipids.

While still in the stomach, the food is churned by the muscular movements of the stomach to a creamy semi-pulp fluid called chyme. The food remains in the stomach for about three hours and is periodically poured through the pyloric sphincter into the duodenum in small amounts.

Digestion in small intestine

Duodenum

When the sphincter muscles relax, the chyme (acidic in nature) enters the duodenum, the first part of the small intestine, which receives two juices:

i. bile from the liver

ii. pancreatic juice from the pancreas

Bile is a yellowish fluid produced in the liver and stored in the gall bladder. Pancreatic juice contains a number of enzymes which act in an alkaline medium. The medium is made alkaline by bicarbonate ions secreted by the duodenal wall. The enzymes are:

i. Trypsin, which converts remaining proteins into peptones and the peptones into peptides and amino acids.

ii. Amylase, which converts the undigested starch into maltose (continues the process that begun in mouth).

iii. Lipase, which converts fats into fatty acids and glycerol.

Ileum

From the duodenum, the food is slowly moved down to the last part of the small intestine, the ileum, where more digestive changes come into action. The intestinal juice called succus entericus secreted by intestinal glands contains the following enzymes which act in an alkaline medium:

i. Trypsin converts peptones into amino acids.

ii. Maltase converts maltose (complex sugar) into glucose (simple sugar).

iii. Lactase converts lactose into glucose and galactose.

iv. Sucrase converts sucrose into glucose and fructose.

v. Lipase converts fats into fatty acids and glycerol.

The digestion, which begins in the mouth, is completed in the small intestine. The digested food comprises soluble products such as monosaccharides, amino acids, fatty acids, and glycerol, which can be absorbed into the bloodstream. Digestion and absorption occur along the entire length of the small intestine as the contents gradually move down through peristalsis.

Digestion in large intestine

No significant digestive activity occurs in the large intestine. The functions of the large intestine:

i. Absorption of some water, minerals and certain drugs;

ii. The secretion of mucus helps adhere the waste (undigested) particles together and lubricate them for easy passage.

Absorption of food

Absorption is the process by which the products of digestion are taken into the bloodstream. Most absorption of food material takes place in the jejunum, except for iron (absorbed in the duodenum), Vitamin B12 and bile salts are absorbed in the terminal ileum. The absorption surface is greatly increased by the presence of millions of finger-like projections called villi. Each villus is covered

by epithelium and contains blood vessels and lymph vessels. The villi are bathed in digested food products that contain the lumen of the intestine, and the food diffuses through the epithelium into the blood vessels. Glucose, acids, minerals and vitamins are absorbed in the blood vessels of the villi; the fatty acids and glycerol are absorbed by lacteals, which are carried to lymph vessels to the point where the lymph vessels empty in the bloodstream.

No enzymes are secreted in the large intestine. This part is concerned with the absorption of water. The undigested semi-solid food which remains in the small intestine is passed into the large intestine. The undigested waste called faeces is stored in the rectum from where it is egested through the anus. The process of elimination of undigested food is called defecation. The roughage in the diet helps promote the movement of the bowels.

2.3 RESPIRATION IN HUMANS

2.3.1 Introduction to respiration in humans

Animals take in high-energy organic molecules in the form of food. The macromolecules in the food (e.g. proteins, carbohydrates, and fats) are digested into micromolecules (e.g. amino acids, glucose, and fatty acids). These are transported to the body cells through the circulatory system. These molecules are catabolised (oxidised) to obtain energy. During this process, adenosine triphosphate (ATP) is synthesised, and energy is trapped by forming bonds between adenosine diphosphate (ADP) and inorganic phosphate (Pi). When required, ATP breaks into ADP and Pi and releases bond energy for utilisation in the cellular processes.

Fig. 2.9 ATP-ADP cycle

2.3.2 Parts of respiratory system

The human respiratory system consists of the nose, pharynx, larynx (voice box), trachea (windpipe), bronchi, and lungs. Structurally, the respiratory system consists of two parts:

1. The upper respiratory tract/system includes the nose, pharynx, and associated structures.

2. The lower respiratory tract/system includes the larynx, trachea, bronchi, and lungs.

Nasal cavity

Nostril

Soft palate

Hard palate

Oral cavity

Larynx

Trachea

Carina of Trachea

Right main bronchus

Right lung

Nose and nostrils

Nasopharynx

Oropharynx

Tongue

Epiglottis

Oesophagus

Left main bronchus

Bronchi

Left lung

Diaphragm

We have a pair of external nostrils opening out above the upper lips. It leads to a nasal chamber through the nasal passage which is lined by mucous membrane. The hard palate forms the floor of the nasal cavity and separates the nasal cavity from the oral cavity. A vertical partition called the nasal septum divides the nasal cavity into the right and left sides.

The nose warms, moistens, and filters air, and functions in olfaction and speech. Posteriorly, the nasal cavity communicates with the nasopharynx through two openings called the internal nares, or choanae.

Pharynx

The pharynx (throat) is a muscular tube that lies just posterior to the nasal and oral cavities, superior to the larynx. Its wall is composed of skeletal muscles and is lined with a mucous membrane. The pharynx can be divided into three anatomical regions.

1. Nasopharynx is the upper portion of the pharynx into which internal nares and eustachian tubes open. It is located above the soft palate and helps in the passage of gases.

2. Oropharynx is the intermediate portion of the pharynx. The oral cavity opens into the oropharynx.

Fig. 2.10 Parts of the human respiratory system

3. Laryngopharynx is the inferior portion of the pharynx. At its inferior end, it opens into the oesophagus posteriorly and into the larynx (through the glottis) anteriorly. The oropharynx and the laryngopharynx serve to pass food and air.

Nasal cavity

Larynx

Nasopharynx

Oropharynx

Hypopharynx

Oesophagus

Larynx

The larynx (voice box) is a passageway that connects the pharynx with the trachea. It is a cartilaginous box which helps in sound production.

The epiglottis is a leaf-like elastic cartilage that prevents food from entering the larynx during swallowing.

Food

The glottis consists of a pair of folds of mucous membrane called the vocal folds (true vocal cords) in the larynx. The vocal folds produce sound as they vibrate.

Trachea

The trachea, or windpipe, is a straight tube located anterior to the oesophagus. It extends from the larynx up to the mid-thoracic cavity and divides at the level of the 5th thoracic vertebra (T5) into

Trachea

Fig. 2.11 Anatomical regions of pharynx

Epiglottis

Lar ynx

Oesophagus

Fig. 2.12 Epiglottis

the right and left primary bronchi. The wall of the trachea is composed of 'C' shaped incomplete rings of hyaline cartilage and smooth muscle and is lined with pseudostratified ciliated columnar epithelium. These cartilage rings prevent the collapse of the trachea.

Bronchi

The trachea divides into the left and right primary bronchi, each of which enters the lung on that side. On entering the lungs, the primary bronchi divides into smaller bronchi- the secondary (lobar) bronchi, one for each lobe of the lung. The secondary bronchi continue to branch, forming still smaller bronchi, called tertiary (segmental) bronchi, that divide into bronchioles.

Left primary bronchus

Tertiary bronchi

Bronchioles

Terminal bronchiole

Respiratory bronchiole

Alveoli in a pulmonary lobule

Trachea

Cartilage ring

Cartilage plates

Roots of lungs

Secondary bronchus

Fig. 2.13 Trachea and bronchial tree

Bronchioles and alveoli

Bronchioles, in turn, branch repeatedly, and the smallest ones branch into even smaller tubes called terminal bronchioles. This extensive branching from the trachea resembles an inverted tree and is commonly called the bronchial tree or tracheobronchial tree. The tracheae, bronchi, and initial bronchioles are supported by incomplete cartilaginous rings.

Terminal bronchioles are subdivided into microscopic respiratory bronchioles, which, in turn, subdivide into alveolar ducts. Each alveolar duct ends as two or three alveolar sacs. Each alveolar sac is a chamber connected to two or more alveoli. An alveolus is lined by simple squamous epithelium and supported by a thin elastic basement membrane.

Lungs

The lungs are paired cone-shaped organs in the thoracic cavity. They are separated from each other by the heart and other structures of the mediastinum. Each lung is enclosed and protected by a double-layered serous membrane called the pleural membrane. The outer parietal pleura lines the wall of the thoracic cavity. The deeper visceral pleura covers the lungs. A small pleural cavity containing pleural fluid lies between the visceral and parietal pleurae. The pleural fluid reduces friction between the pleurae. It also causes the two membranes to adhere to one another, just as a film of water causes two glass plates to stick together. The base of each lung rests on the diaphragm and their apex extends superiorly. The right lung is larger than the left and has three lobes (superior, middle and inferior) while the left lung has two lobes (superior and inferior). Each lobe is supplied by a secondary bronchus.

Deoxygenated blood from pulmonary artery

Oxygenated blood to pulmonary vein

Respiratory bronchiole

Alveolar sac

Smooth muscle Terminal bronchiole

Alveolar pores

Alveolar duct

Capillaries

Alveolus

Fig. 2.14 Alveoli of lungs

Right primary bronchus

Upper lobe

Middle lobe

Lower lobe

lobe

Left primary bronchus

Upper lobe bronchus

Lower lobe bronchus

Notch for the heart

Lower lobe

Left lobe

The respiratory membrane, through which the exchange of gases takes place, is a thin (0.5µm) membrane and is made up of 3 major layers, namely, the thin squamous epithelium of alveoli, the endothelium of alveolar capillaries and the basement substance in between them. The lungs contain approximately 300 million alveoli, providing a surface area of 70m2. The parts from the external nostrils to terminal bronchioles constitute the conducting part which transports gases, humidifies, and clears foreign particles. Whereas alveoli and alveolar ducts form the respiratory or exchange part.

Events of respiration

Respiration involves the following events:

Pulmonary ventilation (breathing): Drawing O2 rich atmospheric air into the lungs and releasing CO2 rich alveolar air out of the lungs.

External respiration: Exchange of gases between the air in the alveoli and the blood in the pulmonary capillaries.

Transport of gases: Transport of gases by the blood between the lungs and tissue cells.

Internal respiration: Exchange of gases between the blood in systemic capillaries and the tissue cells. It is also known as tissue respiration.

Cellular respiration: It involves the utilisation of O2 by the cells for the catabolism of food for the production of ATP and the resultant release of CO2

2.3.3 Mechanism of respiration

The lungs are situated in the thoracic chamber which is anatomically an air-tight chamber. The thoracic chamber is formed dorsally by the vertebral column, ventrally by the sternum, laterally by the ribs and on the lower side by the dome-shaped diaphragm. It is a dome-shaped skeletal muscle that forms the floor of the thoracic cavity.

Trachea

Fig. 2.15 Human lungs

The anatomical setup of the lungs in the thorax is such that any change in the volume of the thoracic cavity will be reflected in the lung (pulmonary) cavity. Such an arrangement is essential for breathing, as we cannot directly alter the pulmonary volume. The movement of air into and out of the lungs is carried out by creating a pressure gradient between the lungs and the atmosphere. Inspiration can occur if the pressure within the lungs (intrapulmonary pressure or alveolar pressure) is less than the atmospheric pressure, i.e., there is a negative pressure in the lungs with respect to atmospheric pressure. Similarly, expiration takes place when the intra-pulmonic pressure is higher than the atmospheric pressure. The diaphragm and a specialised set of muscles - external and internal intercostals between the ribs, help in the generation of such gradients. Breathing involves two stages: inhalation (inspiration), during which atmospheric air is drawn in, and exhalation (expiration), during which the alveolar air is released. On an average, a healthy human breathes 12 -16 times/minute.

Inhalation

Contraction of the diaphragm causes it to flatten. This increases the volume of the thoracic cavity in the vertical axis. Contraction of the diaphragm is responsible for about 75 % of the air that enters the lungs during quiet breathing. When external intercostal muscles contract, they elevate the ribs and the sternum. This increases the volume of the thoracic cavity in the dorsoventral axis and lateral axis.

As the thoracic cavity expands, the parietal pleura lining the cavity is pulled outward in all directions, and the visceral pleura and lungs are pulled along with it. As the pulmonary volume increases, the intra-pulmonic pressure decreases to less than the atmospheric pressure. Because air always flows from a region of higher pressure to a region of lower pressure, air from outside moves into the lungs.

As both normal inhalation and forceful inhalation involve muscular contraction, the process of inhalation is an active process.

Ribs move out

Ribs move in

Diaphragm move down Diaphragm move back

Fig. 2.16 (a) Inhalation (b) Exhalation

Exhalation

Relaxation of the diaphragm and the external intercostal muscles returns the diaphragm and sternum to their normal positions and reduces the thoracic volume and, thereby, the pulmonary volume. This leads to an increase in intra-pulmonic pressure slightly above the atmospheric pressure causing the expulsion of air from the lungs. Normal exhalation during quiet breathing is a passive process because no muscular contractions are involved. Exhalation results from elastic recoil of the chest wall and lungs, both of which have a natural tendency to spring back after they have been stretched. Two inwardly directed forces contribute to elastic recoil.

1. The recoil of elastic fibres that were stretched during inhalation.

2. The inward pull of surface tension due to the film of alveolar fluid.

We have the ability to increase the strength of inspiration and expiration with the help of additional muscles in the abdomen. During deep forceful inhalation, accessory muscles of inspiration (e.g. sternocleidomastoid and pectoralis minor) also participate in increasing the size of the thoracic cavity.

Exhalation becomes active only during forceful breathing. During these times, the abdominal and internal intercostal muscles contract, which increases pressure in the abdominal region and thorax.

2.3.4 Exchange of gases

Alveoli are the primary sites for gas exchange. The exchange of gases also occurs between blood and tissues. O2 and CO2 are exchanged in these sites by simple diffusion, mainly based on pressure/ concentration gradient. The rate of gas exchange depends on the partial pressure of the gases, solubility of the gases, surface area, and diffusion distance.

In a mixture of gases, the pressure exerted by an individual gas is termed its partial pressure. For example, atmospheric pressure is 760 mmHg. The atmosphere contains about 20.95% oxygen. Therefore, the partial pressure of oxygen (pO2) in the atmosphere is 20.95% of 760 mmHg =159 mmHg. A gas always diffuses from the region of its higher partial pressure to the region of its lower pressure.

The partial pressure of oxygen is represented as pO2, and the partial pressure of carbon dioxide is represented as pCO2. Partial pressures of these two gases in the atmospheric air and the two sites of diffusion are given in the table. The data clearly indicates a concentration gradient for oxygen from alveoli to blood and blood to tissues. Similarly, a gradient is present for CO2 in the opposite direction, i.e., from tissues to blood and blood to alveoli.

Table 2.1 Partial pressures of oxygen and carbon dioxide

2.3.5 Transport of gases

Blood carries oxygen from the lungs to the heart and from the heart to various body parts. The blood also brings carbon dioxide from the body parts to the heart and then to the lungs.

Transport of oxygen

i. As dissolved gas: About 3% of oxygen in the blood is dissolved in the plasma, which carries oxygen to the body's cells.

ii. As oxyhaemoglobin: About 97% of oxygen is carried in combination with haemoglobin of the erythrocytes. Oxygen and haemoglobin combine in an easily reversible reaction to form oxyhaemoglobin.

Transport of carbon dioxide

In the oxidation of food, carbon dioxide, water and energy are produced. Carbon dioxide in gaseous form diffuses out of the cells into the capillaries, where it is transported in three ways.

i. As dissolved gas: Because of its high solubility, about 7% carbon dioxide gets dissolved in the blood plasma and is carried in solution form to the lungs.

ii. As bicarbonate ions: 70% of CO2 is transported as bicarbonate ions. At the tissue site where the partial pressure of CO2 is high due to catabolism, CO2 diffuses into blood (RBCs and plasma) and reacts with water to form carbonic acid H2CO3. This reaction occurs about 5000 times faster in RBCs than in plasma, as RBCs contain a very high concentration of the enzyme carbonic anhydrase (minute quantities of the same are present in the plasma, too).

Carbonic acid dissociates into hydrogen ions H+ and bicarbonate ions HCO3 Almost as rapidly as formed, all carbonic acid of RBCs dissociates in hydrogen and bicarbonate ions. Most of the hydrogen ions then combine with the haemoglobin in the RBCs because haemoglobin is a powerful acid-base buffer. In turn, many of the bicarbonate ions diffuse into the blood plasma, while chloride ions diffuse into the RBCs. This is made possible by the presence of a special bicarbonate-chloride carrier protein in the RBC membrane that moves their two ions in opposite directions at rapid velocities. Thus, the chloride content of venous (deoxygenated) RBCs is greater than that of arterial (oxygenated) RBCs.

iii. As carbaminohemoglobin: In addition to reacting with water, carbon dioxide also reacts directly with amino radicals (NH2)of haemoglobin to form an unstable compound carbaminohemoglobin (HbCO2). This is a reversible reaction. A small amount of carbon dioxide also reacts in the same way with plasma proteins. About 23% of CO2 is haemoglobin and plasma proteins.

2.3.6 Control of respiration

Breathing movements are majorly under the control of the respiratory centre located in the medulla oblongata in the hindbrain. Medulla oblongata is stimulated by the amount of CO2 in the blood. Breathing is faster when CO2 content in blood is high. Breathing movements are involuntary, but at times, rate of breathing can be increased or decreased. One cannot hold his breath beyond a point.

2.4 TRANSPORTATION IN HUMANS

2.4.1 Introduction to transportation in humans

The digestive system facilitates food digestion and absorption, requiring the circulatory system to transport nutrients throughout the body. Energy conversion, aided by oxygen, occurs in the respiratory system. The circulatory system transports oxygenated blood from the lungs to various body parts and returns deoxygenated blood for purification. Additionally, the circulatory system plays a role in transporting metabolic waste, which is subsequently eliminated by the excretory system. The transport system or the circulatory system consists of:

• Circulatory medium – blood and lymph

• System of blood vessels – arteries and veins

• The pumping organ – heart

Blood is a type of liquid connective tissue. Blood vessels play a major role in circulating blood in the body. Blood is composed of two main components: plasma and blood cells. Blood cells are also called corpuscles and are generated by stem cells present in the bone marrow.

Composition of blood

The two main components of blood are plasma and blood cells (formed elements).

A. Plasma

It is a pale yellow-coloured liquid. It is alkaline and occupies 55% of the total blood volume. The content of water in plasma is 90-92%. The solid components of plasma include inorganic and organic substances. Inorganic substances are different positive and negative ions such as, etc. Organic substances are glucose, amino acids, lipids, etc. Plasma also contains a protein, called fibrinogen, that is responsible for blood coagulation.

White blood cells, platelets

Red blood cells

Fig. 2.17 Composition of Blood

B. Formed elements (blood cells)

Blood cells contain:

1. Red blood cells or erythrocytes (RBCs)

2. White blood cells or leucocytes (WBCs)

3. Platelets or thrombocytes

1. Red blood cells

Red blood cells RBC are also called erythrocytes. They are the most common type of blood cell and primary means of delivering oxygen to the body tissues. There are 5.5 million RBCs in one cubic millimetre of blood.

Structure

• They have biconcave and disc-like structures.

• They do not have any nucleus in them.

• A red pigment, haemoglobin, is present in their cytoplasm.

• Haemoglobin imparts a red colour to the blood.

• Haeme means iron, and globin means protein. Thus, haemoglobin is an iron-containing protein.

Functions

The main function of RBCs is to transport oxygen from the lungs to different parts of the body and carbon dioxide from different tissues to the lungs. Haemoglobin combines oxygen forming a compound called oxyhaemoglobin. When oxyhaemoglobin reaches the region where the concentration of oxygen is low, it readily liberates oxygen.

2. White blood cells

White blood cells (WBCs) are also called leucocytes. They form a major part of the immune system and are involved in protecting the body against foreign invaders. They are smaller in number than RBCs. In one cubic millimetre of blood, the number of WBCs is 5000-10,000.

White blood cells are larger than red blood cells and contain a nucleus. The number of white blood cells in blood is less than in red blood cells. WBCs can be broadly classified into two categories based on their structure and function, which are granulocytes and agranulocytes.

A. Granulocytes

Granulocytes have granular cytoplasm and lobed nucleus. Granulocytes can be further classified into three categories of cells based on their structure and function: eosinophils, basophils and neutrophils.

Eosinophils

Eosinophils have a bilobed nucleus, and both lobes are connected with a thin strand. They make up only about 2-5 % of WBC. One millilitre of blood contains about 60-300 eosinophils. Cytoplasmic granules of eosinophils turn orange-red in response to the acid dye (eosin). The main function of eosinophils is to destroy pathogens, particularly parasitic worms, and respond to allergic reactions. Eosinophilia is a condition in which the number of eosinophils per unit volume of blood increases due to some parasitic infection.

Basophils

The nucleus in basophils has two or more lobes. About 1% of the leucocytes are basophils. One millilitre of blood contains 35-100 basophils. They are mostly found in skin and mucosal tissues. It turns blue-black in response to basic dyes. It secretes chemicals such as histamine, heparin and serotonin. Histamine produces an allergic reaction when an unwanted substance tries to enter our body. It also makes the blood vessels permeable so that other leucocytes can act against the pathogens. Heparin prevents the clotting of blood. Serotonin is a chemical that transmits messages from one area of the brain to another.

Neutrophils

The nucleus of neutrophils has 3-5 lobes. Neutrophils get stained in response to neutral dyes. About 70% of the total WBC count is neutrophils. One millilitre of blood contains 4000-5000 neutrophils. Neutrophils engulf the pathogens that invade our body by the process of phagocytosis. They act as the body's natural antibiotics.

White Blood Cells

Granulocytes

1. Neutrophil Helps in phagocytosis Fights against parasitic infection Produces inflammatory and allergic reactions Produces specific immune responses Fights off bacteria, viruses and fungi

Agranulocytes

2. Eosinophil 3. Basophil 4. Lymphocyte

B Lymphocyte T Lymphocyte Natural Killer Cell

5. Monocyte

Fig. 2.18 Types of white blood cells

B. Agranulocytes

The cytoplasm of agranulocytes is not granular. 35% of the total WBC count is granulocytes. They can be classified into two categories based on their structure and function, which are lymphocytes and monocytes.

Lymphocytes

They have a large monolobed nucleus. One millilitre of blood contains 1800-3000 lymphocytes. About of the total WBC count is lymphocytes. The main function of lymphocytes is the production of antibodies, which provide immunity to our body.

Monocytes

They have a large cytoplasm and kidney-shaped nucleus. One millilitre of blood contains 200-700 monocytes. About 2-3 % of the total WBC count is monocytes. They ingest microorganisms that intrude on our bodies and act as scavengers by removing the dead cells. The total WBC count of a person who is suffering from a type of blood cancer, leukaemia, increases. This in turn results in a decrease in the production of RBCs and platelets.

Platelets

Platelets are also called thrombocytes (Greek thrombos: lump; cyte: cell). Platelets are not true cells; rather, they are fragments of cells. They are colourless and irregular in shape. The cell fragments do not contain a nucleus, and their cytoplasm does not have granules. Their lifespan is very short. They survive for 3-5 days and then disintegrate in the spleen. The main function of platelets is to facilitate blood clotting.

2.4.2 Blood grouping

Even though human blood groups have similar composition of blood, they differ in certain aspects with reference to the membrane antigens of RBC and antibodies in plasma. The major groupings include the ABO system and the Rh system.

ABO grouping

It was proposed by Karl Landsteiner. This is based on the presence or absence of two surface antigens (isoagglutinogen - a type of sugar polymers) on the RBC namely A and B, which can induce an immune response during blood transfusion. The plasma contains two natural antibodies (anti-A antibodies and anti-B antibodies).

Blood groups

• 'A' blood group: Person with this group has antigen ' A ' on RBC and anti-B antibody in plasma. Person with 'A' blood group can donate blood to A and AB. He can receive blood from A and O.

• 'B' blood group: Person with this group has ' B ' antigen on RBC and anti-A antibody in plasma. He can receive blood from B and O. He can donate blood to B and AB.

• 'AB' blood group: Person with this group has both ' A ' and ' B ' antigens on RBC but no blood group antibodies in plasma. They can receive blood from all other blood types. Hence, a person with 'AB' blood group is a 'universal recipient'. He can donate blood to ' AB ' only.

• 'O' blood group: Person with this group has no antigens on RBC. But he has both anti-A and anti-B antibodies in his plasma. He can donate blood to all other types. Hence, he is a 'universal donor' but, he can only receive blood from only 'O'.

Blood transfusion

Erythrocytes

Antibodies

Antigens

Fig. 2.19 Blood groups

During blood transfusion, the recipient's antibodies (isoagglutinin) react with the donor's antigens on RBC and cause clumping of RBC, which is called agglutination. As this is dangerous, blood transfusion has to be done carefully between two matching groups.

Table 2.2 Blood groups and donor compatibility

Rh antigen was discovered in Rhesus monkeys by Landsteiner. This antigen (antigen-D) also occurs on the surface of the RBC of humans. Most of the humans (80%) have this antigen. They are called Rh positive (Rh+ ), which is a dominant blood group. Persons without Rh antigen are Rh negative (Rh- ). There are no natural antibodies against the Rh antigen. If an Rh- person receives blood from

Rh+person, the immune system recognises this foreign antigen and produces antibodies against the Rh antigen. Therefore, the Rh group should also be matched along with the ABO grouping during a blood transfusion.

2.4.3

Blood vessels

Blood vessels are a system of channels through which blood flows. Blood vessels are of three kinds, namely arteries, veins, and capillaries.

Arteries

Arteries are the blood vessels which carry blood from the heart to various parts of the body. All arteries (except the pulmonary artery) carry oxygenated blood. Pulmonary arteries carry deoxygenated blood from the right ventricle to the lungs. Arteries have thick, elastic and muscular walls, and they are not provided with valves. In arteries, blood flows under pressure and with jerks.

Veins

Veins carry blood from body parts towards the heart. All veins (except the pulmonary veins) carry deoxygenated blood. Pulmonary veins carry oxygenated blood from the lungs to the left atrium. Veins have thin, less elastic, and muscular walls in comparison to arteries. The lumen of veins are provided with valves to prevent the backflow of blood.

Capillaries

Capillaries are fine microscopic vessels. Arteries branch out into smaller and smaller arterioles, which finally form capillaries. These capillaries join to form venules, veins and finally, vena cava. Valves of capillaries are one cell thick. Through these thin walls, oxygen and carbon dioxide dissolved food and excretory products are exchanged with tissues.

Parameter

Function

Type of Blood

Arteries

Carry blood away from the heart

Carry oxygenated blood; except pulmonary artery

Veins

Carry blood towards the heart

Carry deoxygenated blood; except pulmonary vein

Blood flow With jerks Continuous flow

Pressure

Blood flows under high pressure

Blood flows under light pressure

Wall Elastic Non-elastic

Branching Branch progressively Unite progressively

Lumen Narrow Wide

Table 2.3 Difference between arteries and vein

2.4.4 Heart

It is situated in the mediastinum, slightly tilted to the left. The mediastinum is a region in the thoracic cavity between the lungs that extends from the sternum to the vertebral column, from the first rib to the diaphragm.

Structure of Heart

Pericardium

The heart is protected by a double-walled membranous sac called pericardium. The pericardial cavity pericardium contains a thin film of pericardial fluid that reduces friction between the layers of the serous pericardium as the heart moves.

Layers of the heart wall

The wall of the heart consists of three layers: the outer epicardium, the middle myocardium, and the inner endocardium. The epicardium is composed of a visceral layer of the serous pericardium (mesothelium) and a layer of delicate fibroelastic tissue and adipose tissue beneath it. The middle myocardium (myo = muscle) is composed of cardiac muscle tissue and makes up approximately 95% of the heart wall. The innermost endocardium (endo = within) is a thin layer of endothelium overlying a thin layer of connective tissue.

Chambers of the heart

Adipose tissue

Visceral layer of serous pericardium

Parietal layer of serous pericardium

Fibrous pericardium

Pericardial cavity

Our heart has four chambers: two relatively smaller chambers called atria and two larger chambers called ventricles. The atria are thin-walled and deliver blood under less pressure into the adjacent ventricles. The ventricles have thicker walls and pump blood under higher pressure over greater distances.

1. Atria

The atria are the two superior receiving chambers of the heart. Between the right atrium and left atrium is a thin muscular wall called the interatrial septum.

The atrium and the ventricle of the same side are also separated by a thick fibrous partition called the atrioventricular septum. However, each of these septa is provided with an atrioventricular opening through which the two chambers on the same side are connected. Each atrioventricular opening is guarded by an atrioventricular valve. These valves allow the flow of blood only in one direction, i.e., from the atria to the ventricles.

Myocardium

Fig.2.20 Layers of heart wall

The right atrioventricular valve is called the tricuspid valve. It consists of three leaflets or cusps. The left atrioventricular valve is called bicuspid valve or mitral valve. It has two cusps.

Arteries

Aorta

Superior vena cava

Right pulmonary arteries

Right pulmonary veins

Right atrium

Tricuspid valve

Papillary muscles

Right ventricle

Interventricular septum

2. Ventricles

Pulmonary trunk

Left atrium

Left pulmonary arteries

Valve of pulmonary trunk

Aortic valve

Double-leaf mitral valve

Left ventricle

Top of the heart

The ventricles are the two inferior pumping chambers of the heart. Internally, the right ventricle is separated from the left ventricle by the interventricular septum. The inner wall of each ventricle contains a series of ridges called trabeculae carneae or columnae carneae. Some of these ridges are large and cone-shaped and are called papillary muscles. The cusps of the atrioventricular valves (AV valves) are connected to trabeculae carneae by tendon-like cords called chordae tendineae.

Semilunar valves are located between the ventricles and the opening of large blood vessels originating from the ventricles.

The valve between the left ventricle and the aorta is called aortic semilunar valve. These are three in number.

The valve between the right ventricle and the pulmonary artery is called the pulmonary semilunar valve. These are also three in number.

Blood Vessel Entering

The Heart

1. Superior vena cava or anterior vena cava or precaval vein carries deoxygenated blood from the upper part of the body (head, chest and arms) to the right atrium.

2. Inferior vena cava or posterior vena cava or postcaval vein carries deoxygenated blood from the lower part of the body (legs and abdomen) to the right atrium.

Blood Vessels Leaving

1. Pulmonary artery carries deoxygenated blood from the right ventricle to the lungs for purification.

2. Aorta carries oxygenated blood to all parts of the body.

3. There are two coronary arteries (left and right) that originate from the base of the aorta and supply blood to the heart muscle.

Table 2.4 Blood vessels entering and leaving the heart

Fig.2.21 Structure of heart

Working of heart

A contraction of the heart is called a systole, and its relaxation is called a diastole. The contraction of atria is initiated and activated by the sinoatrial node (SAN pacemaker), which spreads waves of contraction across the walls of the atria via muscle fibres at regular intervals. When the wave of contraction originating from the sinoatrial node reaches the atrioventricular node (AVN pacesetter), the latter is stimulated, and excitatory impulses are rapidly transmitted from it to all parts of the ventricles via the bundle of His and Purkinje's fibres. These impulses stimulate the ventricles to contract simultaneously. The ventricles force blood through a long system of arteries and, hence, must exert great pressure on the blood.

2.4.5 Blood circulation

Double circulation

The two main circulatory routes are the systemic and pulmonary circulations.

A. Pulmonary circulation

The blood pumped by the right ventricle enters the pulmonary artery, whereas the left ventricle pumps blood into the aorta. The deoxygenated blood pumped into the pulmonary artery is passed on to the lungs, from where the oxygenated blood is carried by the pulmonary veins into the left atrium. This pathway constitutes the pulmonary circulation.

B. Systemic circulation

The oxygenated blood entering the aorta from the left ventricle is carried by a network of arteries, arterioles and capillaries to the tissues. The deoxygenated blood from tissues is collected by a system of venules, veins and vena cava and emptied into the right atrium. This is the systemic circulation. The systemic circulation provides nutrients, O2 and other essential substances to the tissues and takes CO2 and other harmful substances away for elimination.

Capillaries of the body and organs

Fig. 2.22 Double circulation

Pulmonary vein

Pulmonary artery

Aorta

Vena cava

Systemic circuit

Pulmonary circuit Lung capillaries

2.4.6 Cardiac cycle

A single cardiac cycle includes all the events associated with one heartbeat, and it consists of 3 stages:

1. Joint diastole (relaxation)

2. Atrial systole (contraction)

3. Ventricular systole

The term systole means to contract, and diastole means to dilate. Atria and ventricles never contract simultaneously. When the heart rate is 75 beats/min, a cardiac cycle lasts 0.8 seconds.

DIASTOLE

Relaxation of the heart chambers

Filling the right atrium with blood

The pulmonary valve opens

The tricuspid valve closes

VENTRICULAR SYSTOLE

The contraction of the ventricles

The aortic valve opens

The mitral valve closes

A three-way valve opens

Filling the left atrium with blood

ATRIAL SYSTOLE

Reduction of the atrial

The right ventricle is filling up

The mitral valve opens

The left ventricle is filling up

Atrial systole

It lasts about 0.1 sec during this phase, and the atria contracts. The ventricles are relaxed. Depolarisation of the SA node causes atrial depolarisation (marked by the P wave in the ECG).

Atrial depolarization causes atrial systole. As the atria contract, they exert pressure on the blood within, which forces blood through the open AV valves into the ventricles (active ventricular filling). Then, atrial contraction usually causes an additional 20 per cent filling of the ventricles. The end of atrial systole is also the end of ventricular diastole (relaxation). Thus, each ventricle contains about 120 mL at the end of its diastole. This blood volume is called the end-diastolic volume (EDV).

Fig. 2.23 Cardiac cycle

Ventricular systole

This phase lasts about 0.3 sec. The ventricles contract. The atria relax. The action potentials from SAN are conducted to the ventricles by AVN through the bundle of His and Purkinje fibres. This causes contraction of the ventricular muscles. As a result, the ventricular pressure increases causing the closure of tricuspid and bicuspid valves due to attempted backflow of blood into atria. This causes the first heart sound 'lub'.

As the ventricular contraction continues, the pressure in the ventricles increases further, and the semi-lunar valves guarding the pulmonary and systemic aorta open. The blood from the ventricles is pumped into the aortic arches.

Joint diastole (relaxation period)

This period lasts about 0.4 sec. This phase is called joint diastole, as both ventricles and atria are in a relaxed state. Ventricular repolarisation causes ventricular diastole. As the ventricles relax, the pressure within the chambers falls, and blood in the aorta and pulmonary trunk begins to flow backwards toward the regions of lower pressure in the ventricles. It causes the closure of the SL valves, which is associated with the 'dub' sound. As the ventricles relax, blood pressure falls.

When ventricular pressure drops below atrial pressure, the AV valves are pushed open by the pressure in the atria exerted by the blood which is emptied into them by the veins. Ventricular filling begins as the AV valves open. After the end of the relaxation period, the SAN generates a new action potential, and the events described above are repeated in that sequence, and the process continues.

2.4.7 Blood pressure

Blood pressure is the hydrostatic pressure exerted by blood on the walls of a blood vessel. It is measured by the use of a sphygmomanometer. Systolic blood pressure (SBP) is the arterial blood pressure during ventricular contraction. Diastolic blood pressure (DBP) is the arterial blood pressure during ventricular relaxation. Normal blood pressure is less than 120/80 mmHg (systolic/ diastolic). Pulse pressure is the difference between systolic and diastolic blood pressure.

Pulse pressure = systolic pressure - diastolic pressure

It normally is about 40 mmHg. For example, a person with a blood pressure of 120/80 would have a pulse pressure of 40 mmHg.

2.4.8 Lymphatic system

The lymphatic system is also a part of the circulatory system since the lymph also takes part in the transportation of food material and waste substances. Some amount of plasma, proteins and blood cells are expelled through the pores of the wall of the capillaries, and they occupy the intercellular spaces in the tissues. This is called tissue fluid. The lymphatic system comprises lymph vessels and lymph nodes. Tissue fluid that drains into lymphatic vessels from the intercellular spaces is called lymph. Lymph contains 94 per cent of water. Other than water, it contains various substances such as proteins, nitrogenous substances such as urea, carbohydrates, creatinine, chloride and

enzymes. The only blood cells present in the lymph are lymphocytes. Unlike the circulatory system, the lymphatic system is not a totally closed system. Lymph vessels transport lymph towards the heart and enable the fluid to enter the vena cava, which opens into the right atrium. Lymph passes through the lymph vessels due to the skeletal muscular contraction. Lymph also helps maintain of the composition of tissue fluid.

2.4.9 Hepatic portal system

Liver is an organ that acts as a digestive gland and an excretory organ. Blood does not directly flow from the digestive tract to the inferior vena cava. It is transported to the heart via the liver through a system of veins called the hepatic portal system. Deoxygenated blood passes through the hepatic portal veins and transports blood from the digestive tract and spleen to the liver.

Digested food is absorbed from the intestine and transferred to the blood. This blood is transported to the liver through the hepatic portal veins and undergoes processing before it reaches the heart. The hepatic portal system starts from the capillaries in the gastrointestinal tract and ends at the capillaries in the liver. Since the blood flows in this system from one capillary to another capillary through veins, it is called the portal system

EXCRETION IN HUMANS

2.5.1

Waste products

Ammonotelism

The process of excreting ammonia is called ammonotelism. Due to its toxic nature, ammonia can be tolerated only at very low concentrations, which is why animals need a lot of water to excrete it. Therefore, ammonia excretion is most common in aquatic species. For example, sponges, coelenterates, and many bony fishes are ammonotelic.

Inferior vena cava

Aorta

Hepatic vein

Hepatic artery

Hepatic portal vein from digestive tract

Fig.2.24 Hepatic portal system

2.5

Ureotelism

The process of excreting urea is called ureotelism. Terrestrial animals cannot afford to spend more water for excretion, they excrete less toxic nitrogenous wastes like urea and uric acid. Since water intake is limited, mammals, many terrestrial amphibians and marine fishes mainly excrete urea and are called ureotelic animals.

Uricotelism

The process of excreting uric acid is called uricotelism. Reptiles, birds, land snails and insects are uricotelic. They excrete uric acid as the principal nitrogenous waste in the form of pellets or paste with a minimum loss of water.

2.5.2 Components of human excretory system

The urinary system of humans consists of a pair of kidneys, a pair of ureters, a urinary bladder, and a urethra. Nephrology is the study of the anatomy, physiology, and pathology of the kidneys. The branch of medicine that deals with the male and female excretory systems and the male reproductive system is called urology

Kidneys

The kidneys are reddish, bean-shaped paired organs located just above the waist between the peritoneum and the dorsal wall of the abdomen. Because their position is posterior to the peritoneum of the abdominal cavity, they are said to be retroperitoneal organs. The kidneys are located between the levels of the last thoracic and third lumbar vertebrae and are partially protected by the eleventh and twelfth pairs of ribs. The right kidney is slightly lower than the left because the liver occupies considerable space on the right side superior to the kidney.

Ureters

The ureters are two narrow tubes lined by transitional epithelium. The ureters extend from the renal pelvis and run inferiorly to reach the urinary bladder.

Aorta Right kidney

Ureter

Urethra

Bladder

Left kidney

Inferior vena cava

Fig.2.25 Human excretory system

Urinary bladder

The urinary bladder is a hollow, distensible muscular organ situated in the pelvic cavity. It opens into the urethra. This opening is surrounded by circular smooth muscle fibres that form an involuntary internal urethral sphincter.

Urethra

The urethra is a small tube leading from the urinary bladder to the exterior of the body. In both males and females, the urethra is the passageway for discharging urine from the body. In males, it discharges semen as well. The urethra is longer in males and passes through the prostate and penis. The opening of the urethra to the exterior is called the external urethral orifice.

2.5.3 Kidneys

External anatomy of the kidneys

Each kidney has concave and convex surfaces. The concave medial border of each kidney faces the vertebral column. Near the centre of the concave border is a notch called the renal hilum (hilum renale) or hilus, through which the ureter, blood vessels, and lymphatic vessels pass. Inner to the hilum is a broad funnel shaped space called the renal pelvis with projections called calyces.

Internal anatomy of kidneys

The outer layer of connective tissue covering the kidney is a renal capsule. Inside the kidney, there are two distinct regions: a superficial, light-red area called the renal cortex and a deep, darker, reddish-brown region called the renal medulla. The renal medulla consists of several cone-shaped renal pyramids. The base of each pyramid faces the renal cortex. The apex of each pyramid is called the renal papilla and projects into a calyx. The portions of the renal cortex that extend between renal pyramids are called renal columns or columns of Bertini. Minor calyces are funnel-shaped chambers into which the renal papillae extend. The minor calyces of several pyramids merge to form major calyces. Each kidney has 8-18 minor calyces and 2-3 major calyces. The major calyces converge to form an enlarged chamber called the renal pelvis, which leads into the ureter.

Renal columns

Base of renal pyramid

Renal capsule

Renal papillae

Renal cortex

Minor renal calyx

Renal pelvis

Left ureter

Major renal calyx

Renal medulla

Microanatomy (histology) of the kidneys

Each human kidney possesses about one million structural and functional units, the nephrons

Each nephron consists of two parts: a renal corpuscle and a renal tubule.

A. Renal corpuscle

The renal corpuscle, or Malpighian body, consists of the glomerulus and the Bowman's (glomerular) capsule.

i. Glomerulus

The glomerulus is a network of blood capillaries.

ii. Bowman's capsule

Bowman's capsule is a double-walled epithelial cup that surrounds the glomerular capillaries. It has specialised simple squamous epithelial cells called podocytes (podo = foot; cytes = cells). The footlike projections of these cells, called pedicels, wrap around the single layer of endothelial cells of the glomerular capillaries and form the inner wall of the capsule.

B. Renal tubule

The renal tubule has three main sections. In the order that fluid passes through them, the renal tubule consists of a (1) proximal convoluted tubule, (2) loop of Henle (nephron loop), and (3) distal convoluted tubule.

Glomerulus

Afferent arteriole

Proximal convoluted tubule (PCT)

Renal artery (carries oxygenated blood)

Renal vein (carries oxygen-depleted blood)

Efferent arteriole Bowman’s capsule

Distal convoluted tubule(DCT)

Loop of henle

Collecting tubule

Descending limb of loop of henle

Ascending limb of loop of henle

Fig. 2.27 Structure of a nephron

The renal corpuscle and both convoluted tubules lie within the renal cortex; the loop of Henle extends into the renal medulla, makes a hairpin turn, and then returns to the renal cortex.

i. Proximal convoluted tubule

The wall of the proximal convoluted tubule (PCT) is made of simple cuboidal epithelium. The epithelial cells have a brush border of microvilli on their apical surface (surface facing the lumen). These microvilli increase the surface area for reabsorption and secretion.

ii. Loop of Henle

The loop of Henle connects the proximal and distal convoluted tubules. The first part of the loop of Henle is called the descending limb of the loop of Henle. It dips into the renal medulla then makes a hairpin turn and returns to the renal cortex which is the ascending limb of the loop of Henle.

The descending limb of the loop of Henle and the thin ascending limb is composed of simple squamous epithelium. The thick ascending limb of the loop of Henle is composed of simple cuboidal to low columnar epithelium.

iii. Distal convoluted tubule

The epithelium of DCT (and collecting ducts) is simple cuboidal, but the cells are smaller than those in the PCT and do not have many microvilli. In the last part of the DCT and in the collecting ducts, two different types of cells are present. The collecting ducts drain into large papillary ducts, which are lined by simple columnar epithelium.

The early part of the distal convoluted tubule contacts the afferent arteriole. As the columnar tubule cells in this region are crowded together, they are known as the macula densa. Alongside the macula densa, the wall of the afferent arteriole (and sometimes the efferent arteriole) contains modified smooth muscle fibres called juxtaglomerular (JG) cells. Together with the macula densa, they constitute the juxtaglomerular apparatus (JGA).

The DCTs of many nephrons open into a straight tube called a collecting duct. The collecting ducts unite and open into the renal pelvis through medullary pyramids in the calyces.

2.5.4

Urine

Formation of urine

The primary function of nephrons is to form urine. Urine is a liquid byproduct of metabolism in our body. Urine flows from the kidneys through the ureters to the urinary bladder. The formation of urine can be described in three stages listed as follows.

1. Ultrafiltration: Occurs in glomerulus

2. Selective reabsorption: Occurs in proximal convoluted tube

3. Tubular secretion: Occurs in distal convoluted tube

Ultrafiltration

The process of ultrafiltration involves the filtration of body solutes and fluids from the blood. This stage can described in the following points.

• The diameter of the efferent arteriole is smaller than that of the afferent arteriole, and hence, the bloodstream inside the glomerulus is under pressure.

• Due to this pressure, water and solutes pass through a membrane and enter Bowman's capsule.

• Blood cells, protein and fat molecules remain in the bloodstream.

• These are carried forward into the blood circulation through the efferent arteriole.

• Thus, the blood passing through efferent arteriole is more concentrated.

• The fluid that comes out of Bowman's capsule and enters the renal tubule is called glomerular filtrate.

• Glomerular filtrate is an extremely dilute solution containing a lot of useful materials such as glucose, amino acids, etc., along with urea which is a waste material.

Selective reabsorption

The process of selective reabsorption involves the absorption of certain components of the glomerular filtrate back into the blood as the filtrate flows through the nephrons of the kidney.

This stage can be described in the following points.

• Selective reabsorption takes place when filtrate generated from the glomerulus passes through the proximal convoluted tubule.

• This filtrate contains many useful materials like different ions, glucose, and amino acids along with waste material.

• Reabsorption of the useful material takes place from the filtrate in the proximal tubule to the bloodstream in the surrounding blood vessels.

• A major part of the water is reabsorbed by the process of osmosis.

• Some ions like sodium and chloride, glucose and amino acids required by our body are reabsorbed by an active transport system. Energy is required for such types of transportation.

• The next step of urine formation takes place in the distal convoluted tubule.

Tubular secretion

The process of tubular secretion involves the addition of certain materials to the tubular fluid by removing excessive quantities of certain dissolved substances from the body. This stage can described in the following points.

• The unwanted ions and nitrogenous waste materials like uric acid, ammonia, urea, creatinine, etc., are passed from the blood vessels to the renal tubule.

• Some substances like potassium ions and any foreign chemicals, such as medicines, are passed into the urine.

• These substances involve the activity of the cells of the tubular wall. Hence, this process is called tubular secretion.

• Then the urine so formed passes through the distal convoluted tube and reaches the collecting duct.

• In normal adults, the volume of urine formed every minute is approximately 120 ml.

Expulsion of urine

Renal pelvis, the innermost region of the kidney, receives urine from the collecting duct. From the renal pelvis, the urine enters the urinary bladder through the ureter. The urine gets stored in the urinary bladder temporarily and is passed through the urethra at certain intervals. The expulsion of urine from the urinary bladder through the urethra takes place by the relaxation of the sphincter muscle under the impulse from the brain. This process of regulated expulsion of urine from the urinary bladder through the urethra is known as micturition

Composition of urine

About 95% of the volume of urine is water, other substances are only about 5%. Organic substances include nitrogen, urea, creatine, creatinine, ammonia, uric acid, hippuric acid, oxalic acid, amino acids, allantoin, vitamins, hormones and enzymes. The inorganic substances include chloride, phosphate, sulphate, potassium, sodium, calcium, magnesium, iodine, arsenic and lead. It is important to note that no glucose is normally found in the urine.

Osmoregulation

Apart from the function of excretion, kidneys also perform the major function of osmoregulation. Osmoregulation is the process by which water and salt balance are maintained in the body through osmosis. By the process of osmoregulation, the water content and concentration of ions in the cells are maintained. The transfer of water from the body cells to the bloodstream and vice versa is governed by the process of osmosis. If the percentage of water as a solvent is higher in body cells than that in the bloodstream, water molecules move from the body cells to the bloodstream. When the percentage of water is in reverse order, the movement of water molecules takes place in reverse direction. Reabsorption is the process that occurs in the proximal convoluted tubule of the nephron which helps in osmoregulation.

Haemodialysis

Any abruption in the normal functioning of the kidney that does not result in the excretion of waste products and maintenance of salt and water balance may lead to renal or kidney failure. It can happen either due to an infection or injury to the kidneys.

In such conditions, the urea level in the blood rises. If the level of urea is increased to an alarming level, it might lead to death. Hence, the patient is required to get rid of the nitrogenous waste

substances using an artificial kidney. The process by which the blood of a kidney patient is purified is called dialysis. Haemodialysis is the type of dialysis in which needles are used to take the blood out in tubes.

Semipermeable membrane

QUICK REVIEW

Blood with waste products Dialysate

Line from artery to apparatus

Pump

Line from apparatus to vein

Fresh dialysing solution

Waste products pass through membrane

Tubing permeable(selectivelymembrane)

• The process of conversion of complex food substances to simple absorbable forms is called digestion. The components of our food are carbohydrates, proteins, fats, vitamins, minerals, water and roughage.

• The human digestive system consists of the alimentary canal and accessory organs.

• The gastrointestinal (GI) tract, or alimentary canal, is about 5-7 metres long and consists of many specialised regions.

• Chemical digestion is initiated in the oral cavity by the hydrolytic action of the salivary amylase.

• Pepsin converts proteins into proteoses and peptones. Rennin helps in the coagulation of milk proteins.

• Pancreatic juice has inactive enzymes: procarboxypeptidases, trypsinogen chymotrypsinogen, amylase, lipase and nucleases.

• The intestinal juice or succus entericus contains enzymes like disaccharidases, peptidases, phosphatase, nucleosidase, and a small amount of enteric lipase.

• Some water and salts, alcohol, some drugs such as aspirin, and moderate amounts of simple sugars are absorbed in the stomach.

Fig. 2.28 Haemodialysis

• Anaerobic respiration is the incomplete breakdown of organic molecules in the absence of oxygen with less yield of energy.

• Aerobic respiration yields more energy; cells must be supplied with oxygen for the oxidation of food material to obtain energy.

• The skin is a respiratory organ in some animals, including earthworms and amphibians.

• Most water-breathing animals use specialised respiratory structures called gills.

• The tracheal system of insects is made up of air tubes that branch throughout the body.

• Spiders and scorpions have book lungs for aerial respiration.

• The lungs are vascularised bags that serve as the respiration organs in many air-breathing tetrapods.

• The anterior portion of the nasal cavity, just inside the nostrils, is called the vestibule.

• Exchange of gases between the blood in systemic capillaries and the tissue cells. It is also known as tissue respiration.

• Cellular Respiration involves the utilisation of O2 by the cells for the catabolism of food for the production of ATP and the resultant release of CO2

• Expiration takes place when the intra-pulmonic pressure is higher than the atmospheric pressure.

• On average, a healthy human breathes 12-16 times/minute.

• The larynx is a passageway that connects the pharynx with the trachea.

• The glottis consists of a pair of folds of mucous membrane called the vocal folds in the larynx. The space between the vocal folds is called the rima glottidis.

• The wall of the trachea is composed of C-shaped incomplete rings of hyaline cartilage and smooth muscle and is lined with pseudostratified ciliated columnar epithelium.

• The trachea divides into bronchi, on entering the lungs, the primary bronchi divide into secondary bronchi, and tertiary (segmental) bronchi, which divide into bronchioles.

• Our heart has four chambers: two small chambers called atria and two larger chambers called ventricles.

• The opening of the inferior vena cava into the right atrium is guarded by a rudimentary Eustachian valve. The opening of the coronary sinus into right atrium is guarded by a valve of Thebesius.

• The right atrioventricular valve is called the tricuspid valve. The left atrioventricular valve is called bicuspid valve or mitral valve.

• The inner wall of each ventricle contains a series of ridges called trabeculae carneae or columnae carneae.

• The cusps of the atrioventricular valves are connected to trabeculae carneae by tendon-like cords called chordae tendineae

• Autorhythmic fibres form the pacemaker and the cardiac conduction system.

• Sinoatrial node (SAN) is the natural pacemaker of the heart. Located in the right upper corner of the right atrium. The atrioventricular node (AVN) is located in the lower left corner of the right atrium close to the A-V septum.

• The AV node gives rise to an atrioventricular (AV) bundle, or bundle of His. It divides to form the right and left bundle branches are called Purkinje fibres.

• Waste products generated by the human body are carbon dioxide, nitrogenous wastes, bile pigments, excess salts and vitamins.

• The main excretory organs in human beings are: lungs, skin, kidneys and liver.

• Excretion and osmoregulation are the two major functions of the excretory system.

• The process of expelling the toxic and unwanted waste from the body of an organism is called excretion.

• The major function of the pair of kidneys is the separation of waste from the bloodstream in the form of urine.

• A nephron is the microscopic structural and functional unit of the kidney.

• Each nephron consists of four regions: Bowman's capsule, proximal convoluted tubule, Loop of Henle and distal convoluted tubule.

• Osmoregulation is the process in which water and salt balance is maintained in the body by means of osmosis.

• The process by which the blood of a kidney patient is purified is called dialysis.

WORKSHEET - 1

MULTIPLE CHOICE QUESTIONS WITH SINGLE CORRECT ANSWER

I. Nutrition in humans

1. Freely movable tongue is attached to the oral cavity by

a. Chordae tendinea

c. Frenulum

2. Common passage for food and air is

a. Nasal cavity

c. Pharynx

b. Tendons

d. Papillae

b. Oesophagus

d. Oral cavity

3. Entry of food into the trachea is prevented by

a. Epiglottis

c. Sphincter of Oddi

b. Bicuspid valve

d. Epimysium

4. Opening of the stomach into the small intestine is guarded by

a. Cardiac sphincter

c. Pyloric sphincter

b. Anterior oesophageal sphincter

d. Sphincter of Oddi

5. Which of the following parts is divided into ascending, transverse, and descending parts?

a. Ileum

c. Rectum

6. The correct sequence of the following is

a. Duodenum, ileum, jejunum

c. Ileum, duodenum, jejunum

7. Number of salivary glands in humans is

a. 4 pairs

c. 3 pairs

8. The largest gland of the body is

a. Pancreas

c. Pituitary

b. Colon

d. Caecum

b. Jejunum, duodenum, ileum

d. Duodenum, jejunum, ileum

b. 2 pairs

d. 1 pair

b. Thyroid

d. Liver

9. In humans, the sphincter of Oddi guards the opening of

a. Pancreatic duct

c. Hepato-pancreatic duct

b. Hepatic duct

d. Wolfian duct

10. Hepato-pancreatic duct opens into the duodenum and carries

a. Bile

c. Both (a) and (b)

b. Pancreatic juice

d. Saliva

11. This gland is not associated with the digestive system

a. Liver

c. Pancreas

b. Adrenal

d. Salivary glands

12. If the pancreas is removed, the compound that remains undigested, is

a. Carbohydrate

c. Protein

b. Fat

d. All of these

13. Read the following statements thoroughly and identify whether they are true or false. Choose the right options accordingly.

Statement I: Bile is produced and stored in the liver and gall bladder, respectively.

Statement II: Common bile duct is the fusion of all the right and left hepatic ducts.

Statement III: Pancreas consists of two parts, exocrine and endocrine, which secretes insulin and glucagon hormone and pancreatic juices containing enzymes, respectively.

a. All statements are true

b. All statements are false

c. Statements I and II are true, while II is false

d. Statements I and II are true, while III is false

14. Trypsin digests proteins in

a. Stomach in acidic medium

c. Intestine in alkaline medium

b. Stomach in alkaline medium

d. Intestine in acidic medium

15. The enzyme that is not present in succus entericus is

a. Maltase

c. Nucleosidase

16. Emulsified fats are digested by

a. Gastric juice and pancreatic juice

b. Bile juice and intestinal juice

c. Pancreatic juice and bile juice

d. Pancreatic juice and intestinal juice

17. Mark the right statement among the following.

a. Trypsinogen is an inactive enzyme

b. Trypsinogen is secreted by intestinal mucosa

c. Enterokinase is secreted by pancreas

d. Bile contains trypsin

18. Food bolus forms in

a. Oesophagus

c. Buccal cavity

b. Nucleases

d. Lipase

b. Stomach

d. Nasopharynx

19. Passage of food into the stomach is controlled by

a. Pyloric sphincter

c. Gastro-oesophageal sphincter

20. Chyme is that food which is ready

a. For absorption in ileum

c. To enter into duodenum

b. Anterior oesophageal sphincter

d. Sphincter of Oddi

b. To enter into oesophagus

d. For defaecation

21. An enzyme in the gastric juice of infants that helps in the digestion of milk proteins is

a. Rennin

c. Lipase

22. In the intestine, trypsinogen is activated by

a. Rennin

c. Enterokinase

23. What do you mean by the absorption of food?

b. Amylase

d. Nuclease

b. Creatine kinase

d. Chymotrypsinogen

a. It is a process by which the end products of digestion pass through the intestinal mucosa into blood or lymph

b. It is a process of transportation of digestive food from the human alimentary canal to blood and lymph

c. It is a process of utilizing the absorbed food substances

d. Absorption is a process by which nutrients are absorbed from the large intestine into the blood and lymph through its mucous membrane

II. Respiration in humans

1. Nasopharynx opens into trachea through

a. Gullet

c. Syrinx

2. Trachea divides into bronchi at the level of

a. Atlas

c. 3rd cervical vertebra

b. Glottis

d. Alveoli

b. Axis

d. 5th thoracic vertebra

3. Which of the following is a part of both the digestive tract and the respiratory tract?

a. Trachea

c. Nose

b. Larynx

d. Pharynx

4. Vertebrate larynx arises from

a. Pharynx

c. Skin

5. Nasal cavity and oral cavity are separated by

a. Nasal septum

c. Hard palate

b. Alveoli

d. Ribs

b. Diaphragm

d. Mediastinum

6. Which of the following prevents the collapsing of Trachea

a. Muscles

c. Ribs

b. Diaphragm

d. Cartilaginous rings

7. Which one of the following is a possibility for most of us in regard to breathing by making a conscious effort?

a. One can breathe out air totally without oxygen

b. One can breathe out air through the eustachian tube by closing both nose and mouth

c. One can consciously breathe in and breathe out by moving the diaphragm alone, without moving ribs at all

d. The lungs can be made fully empty by forcefully breathing out all air from them

8. The majority of carbon dioxide produced by our body cells is transported to the lungs

a. Attached to haemoglobin

c. As bicarbonates

b. Dissolved in the blood

d. As carbonates

9. When CO2 concentration in the blood increases, breathing becomes:

a. Shallower and slow

c. Slow and deep

10. Respiration is controlled by

a. Cerebellum

c. Olfactory lobes

11. The covering of the lungs is called

a. Peritoneum

c. Pleural membrane

b. There is no effect on breathing

d. Faster and deeper

b. Medulla oblongata

d. Hypothalamus

b. Pericardium

d. Perichondrium

12. The exchange of gases in the alveoli of the lungs takes place through

a. Osmosis

c. Active transport

b. Simple diffusion

d. Passive transport

13. The partial pressure of oxygen in the alveoli of the lungs is

a. Equal to that in the blood

c. Less than that in the blood

b. More than that in the blood

d. Less than that of carbon dioxide

14. Lungs do not collapse between breaths, and some air always remains in the lungs, which can never be expelled because

a. There is a negative thoracic pressure pulling at the lung walls

b. There is a negative intrapleural pressure pulling at the lung walls

c. There is a positive intrapleural pressure

d. Pressure in the lungs is higher than the atmospheric pressure

15. Select the correct events that occur during inhalation [NEET-2020]

1. Contraction of diaphragm

2. Contraction of external intercostal muscles

3. Pulmonary volume decreases

4. Intra-pulmonary pressure increases

a. (3) and (4)

c. Only (4)

III. Transportation in humans

b. (1), (2) and (4)

d. (1) and (2)

1. Given below are four statements (i-iv) regarding the human blood circulatory system

i. Arteries are thick-walled and have narrow lumens compared to veins..

ii. Angina is acute chest pain when the blood circulation to the brain is reduced.

iii. Persons with blood group' AB can donate blood to any person with any blood group under ABO system.

iv. Calcium ions play a very important role in blood clotting. Which of the above statements is correct?

a. (i) and (iv)

c. (ii) and (iii)

b. (i) and (ii)

d. (iii) and (iv)

2. Globulins contained in human blood plasma are primarily involved in

a. Osmotic balance of body fluids

c. Clotting of blood

b. Oxygen transport in the blood

d. Defence mechanisms of the body

3. There is no DNA in

a. Mature RBC

c. A hair root

b. A mature spermatozoan

d. An enucleated ovum

4. In humans, blood passes from the post-caval to the diastolic right atrium of the heart due to

a. Stimulation of the sino auricular node

b. Pressure difference between the post-caval and atrium

c. Pushing open of the venous valves

d. Suction pull

5. Systemic heart refers to

a. The heart that contracts under stimulation from the nervous system

b. Left auricle and left ventricle in higher vertebrates

c. Entire heart in lower vertebrates

d. The two ventricles together in humans

6. Bundle of His is a network of

a. Muscle fibres distributed throughout the heart walls

b. Muscle fibres are found only in the ventricle wall

c. Nerve fibres distributed in ventricles

d. Nerve fibres found throughout the heart

7. Impulse of the heartbeat originates from

a. SA node

c. Vagus nerve

b. AV node

d. Cardiac nerve

8. At which point is the pulmonary artery different from a pulmonary vein?

a. Its lumen is broad

c. It has valves

b. Its wall is thick

d. It does not possess endothelium

9. The opening between the right atrium and the right ventricle is guarded by the valve named

a. Bicuspid valve

c. Mitral valve

10. All veins carry deoxygenated blood except

a. Pulmonary vein

c. Hepatic portal vein

b. Tricuspid valve

d. Semilunar valve

b. Hepatic vein

d. Renal vein

11. Blood pressure is measured by

a. Sphygmomanometer

c. Electrocardiogram

b. Stethoscope

d. Phonocardiogram

12. Thickening of arteries due to cholesterol deposition is

a. Arteriosclerosis

c. Blood pressure

13. Pulmonary vein carries

a. Deoxygenated blood

c. Mixed blood

14. Mitral valve is present between

a. Right atrium and ventricle

c. Right and left ventricle

15. Carotid artery supplies

a. Oxygenated blood to lungs

c. Oxygenated blood to brain

16. Pulmonary artery carries

a. Pure blood from lungs

c. Impure blood to lungs

17. 'Bundle of His' are

a. Nervous tissue supplied to ventricles

c. Muscular tissue supplied to ventricle

18. At high altitudes, RBCs of human blood will

a. Increase in number

c. Decrease in size

IV. Excretion in humans

b. Rheumatic heart

d. Cardiac arrest

b. Oxygenated blood

d. None of these

b. Left atrium and ventricle

d. Left ventricle and aorta

b. Oxygenated blood to intestine

d. None of the above

b. Impure blood from lungs

d. Pure blood to lungs

b. Nervous tissue supplied to heart

d. Muscular tissue supplied to heart

b. Decrease in number

d. Increase in size

1. What will happen if the stretch receptors of the urinary bladder wall are totally removed?

a. Micturition will continue

b. Urine will continue to collect normally in the bladder

c. There will be no micturition

d. Urine will not collect in the bladder

2. A person who is on a long hunger strike and is surviving only on water will have

a. Less amino acids in his urine

c. Less urea in his urine

b. More glucose in his blood

d. More sodium in his urine

3. Angiotensinogen is a protein produced and secreted by

a. Juxtaglomerular (JG) cells

c. Endothelial cells (cells lining the blood vessels)

b. Macula densa cells

d. Liver cells

4. The net pressure gradient that causes the fluid to filter out of the glomeruli into the capsule is

a. 50 mmHg

c. 10 mmHg

b. 75 mmHg

d. 20 mmHg

5. A person is undergoing prolonged fasting. His urine will be found to contain abnormal quantities of

a. Fats

c. Glucose

b. Aminoacids

d. Ketones

6. If Henle's loop were absent from mammalian nephron, which one of the following would be expected?

a. There will be no urine formation

b. There will be hardly any change in the quality and quantity of urine formed

c. The urine will be more concentrated

d. The urine will be more dilute

7. In the kidney, ultrafiltration occurs due to:

a. Osmotic concentration

c. Deoxygenated blood

8. The conversion of ammonia to urea is done by

a. Ornithine cycle

c. Fumaric cycle

9. Concentration of urine depends upon

a. Bowman's capsule

c. P.C.T

b. Glomerular hydrostatic pressure

d. Exocytosis

b. Arginine cycle

d. Citrulline cycle

b. Length of Henle's loop

d. Network of capillaries arising from glomerulus

10. There is an increase in blood urea when there is insufficient filtration in

a. Loop of Henle

c. Bowman's capsule

b. Distal tubule

d. Collecting tubule

11. Which one of the following is correct regarding the excretion?

a. A large amount of water from renal filtrate is reabsorbed in DCT, and a smaller amount is reabsorbed in PCT

b. The descending limb of the loop of Henle is completely impermeable to salts

c. Malpighian corpuscle is found in the medulla region of kidney

d. The colour of urine is pale yellow and is slightly alkaline in nature

12. Urea is transported by

a. Macrophages

c. Blood plasma

13. Enzyme released from the kidney is

a. Renin

c. Pepsin

14. Excretory product of birds and insects is

a. Uric acid

c. Ammonia

15. Colour of urine is yellow due to the pigment

a. Urochromogen

c. Carotene

b. RBC

d. WBC

b. Uricase

d. None of these

b. Urea

d. TMO

b. Urochrome

d. None of these

16. Which of the following is involved in the reabsorption of water in the kidney?

a. ADH

c. LH

b. MSH

d. GnRH

WORKSHEET - 2

MULTIPLE CHOICE QUESTIONS WITH SINGLE CORRECT ANSWER

1. Which one of the following pairs of food components in humans reaches the stomach totally undigested?

a. Starch and fats

c. Starch and cellulose

2. 'Digestion' word means

a. Burning of food

c. Hydrolysis of food

3. Maximum absorption of water occurs in

a. Colon

c. Stomach

4. Pepsin is inactivated at ph

a. Below 3

c. Above 5

b. Fats and cellulose

d. Proteins and starch

b. Oxidation of food

d. Breakdown of food

b. Rectum

d. Small intestine

b. Below 2

d. Above 3

5. A child took a sugar cane and sucked its juice. Regarding this, which of the following matches is correct?

Substrate Enzyme secretion Site of formation Products of enzyme

a. Proteins Pepsin

b. Starch Amylase

c. Lipids Lipase

d. Sucrose Invertase

Duodenum Polypeptides

Salivary Glands Glucose

Pancreas Fat Globules

Duodenum Glucose + Fructose

6. Identify the correct statement with reference to the human digestive system. [NEET 2020]

a. Serosa is the innermost layer of the alimentary canal

b. Ileum is a highly coiled part

c. Vermiform appendix arises from duodenum

d. Ileum opens into the small intestine

7. Which of the following options best represents the enzyme composition of pancreatic juice?

a. Amylase, peptidase, trypsinogen, rennin

b. Amylase, pepsin, trypsinogen, maltase

c. Peptidase, amylase, pepsin, rennin

d. Lipase, amylase, trypsinogen, procarboxypeptidase

8. Which of the following terms describe human dentition?

a. Pleurodont, Monophyodont, Homodont

b. Thecodont, Diphyodont, Heterodont

c. Thecodont, Diphyodont, Homodont

d. Pleurodont, Diphyodont, Heterodont

9. Statement I: Chymotrypsinogen and trypsinogen are released from gastric glands. Statement II: They help in the digestion of fats.

a. Both Statement I and II are true, and Statement II is supported by the explanation of Statement

b. Both Statement I and II are true, but Statement II is not supported by the explanation of Statement

c. Statement I is true, but Statement II is false

d. Statement I and Statement II are false

10. A baby boy aged two years is admitted to play school and passes through a dental check-up. The dentist observed that the boy had twenty teeth. Which teeth were absent?

a. Incisors b. Canines

c. Pre-molars d. Molars

11. Statement I: Larynx is a cartilaginous box which helps in sound production. Statement II: Epiglottis flap covers the glottis during swallowing and prevents the entry of food into the larynx.

a. Both statements are true

b. Both statements are false

c. Statement I is true, and Statement II is false

d. Statement I is false, and Statement II is true

12. The division of mammalian lungs into a very large number of tiny alveoli around alveolar ducts opening into bronchioles is

a. An inefficient system of ventilation of alveoli with very little residual air in the lungs

b. An inefficient system of ventilation of alveoli results in a very high percentage of residual air in the lungs

c. A very efficient system of ventilation of alveoli with no residual air in the lungs

d. An efficient system of ventilation of alveoli with little or no residual air in the lungs

13. Match the following columns

Column – I

A. Bronchial tree

B. Larynx

C. Trachea

D. Pharynx

a. 2 2 4 3

b. 1 3 2 3

c. 1 4 2 4

d. 1 1 3 4

Column – I

1. Passageway for air from the nasal cavity to larynx and for food from the mouth cavity to oesophagus

2. Conducts air from the larynx to the bronchi to its mucous lining and continues to filter air

3. Passageway for air, prevents foreign objects from entering the trachea and houses vocal cords

4. Flexible tube, which connects larynx with bronchial tree bronchial tree

14. In which part of the lungs does the gaseous exchange take place in humans

a. Trachea & alveolar duct

c. Alveolar duct & alveoli

b. Trachea & bronchi

d. Alveoli & trachea

15. For the occurrence of inspiration intra-pulmonary pressure should be

a. Equal to atmospheric pressure

c. Less than atmospheric pressure

b. More than atmospheric pressure

d. All of these

16. Volume of the thoracic chamber increases in the vertical axis due to

a. Contraction of external intercostal muscles

b. Relaxation of external intercostal muscles

c. Relaxation of diaphragm

d. Contraction of diaphragm

17. The expulsion of air during expiration is caused by the

1. Contraction of external intercostal muscles

2. Relaxation of external intercostal muscles

3. Contraction of internal intercostal muscles

4. Relaxation of the diaphragm

A B C D

a. 1 and 4

c. 2 and 4

18. What is true about diffusion capacity

b. 1 and 3

d. 1, 3, and 4

a. Diffusion capacity of CO2 is much higher than O2

b. Diffusion capacity of O2 is much higher than CO2

c. Diffusion capacity of O2 and CO2 is same

d. None of these

19. Expiratory muscles contract at the time of

a. Deep inspiration

c. Normal inspiration and expiration

b. Forceful expiration

d. Normal expiration

20. The function of the conducting part of the respiratory system is

a. Clearing dust particles from inhaled air

b. Humidifying inhaled air

c. Bringing inhaled air to body temperature

d. All of these

21. Which of the following statement(s) is/are correct?

Statement I: Bundle of His originates from the SA node

Statement II: The SA node is situated in the wall of right auricle.

Statement III: Auricular contraction stimulates the AV node.

Statement IV: The AV node sets up the cardiac impulses 72 times per minute.

Choose the correct answer

a. Only II

c. I and III

b. II and IV

d. I, II and III

22. Statement I: Systemic blood circulation occurs in human beings.

Statement II: The main purpose of this circulation is to carry oxygen and nutrients to the body tissues and to remove carbon dioxide and other wastes from the tissues.

a. Both statements are true

b. Both statements are false

c. Statement I is true, and Statement II is false

d. Statement I is false, and Statement II is true

23. During ventricular systole

a. Semilunar valves are closed

b. About 30 per cent of blood is pumped into the aorta from ventricles

c. Tricuspid and bicuspid valves are closed

d. Ventricular pressure declines

24. Which of the following statement is correct during each cardiac cycle?

a. The volume of blood pumped out by the Rt and Lt ventricles is same.

b. The volume of blood pumped out by the Rt and Lt ventricles is different.

c. The volume of the blood received by each atrium is different

d. The volume of the blood received by the aorta and pulmonary artery is different

25. Identify the correct statement for humans.

a. Arteries always carry oxygenated blood, while veins always carry deoxygenated blood

b. Venous blood is returned to the left auricle

c. Arteries are provided with valves, while veins are devoid of valves

d. Arteries always carry blood away from the heart, while veins always carry blood towards the heart

26. Systolic pressure is higher than diastolic pressure due to

a. Volume of blood in the heart is greater during systole

b. Arteries contract during systole

c. Blood vessels offer resistance to flowing blood during systole

d. Blood is forced into arteries during systole

27. Name the blood cells whose reduction in number can cause clotting disorders, leading to excessive loss of blood from the body.

a. Erythrocytes

c. Neutrophils

b. Leucocytes

d. Thrombocytes

28. The hepatic portal vein drains blood to the liver from

a. Heart

c. Kidneys

b. Stomach

d. Intestine

29. Which of the following events do not occur during joint diastole?

Statement I: All four-chambers are in a relaxed state

Statement II: Tricuspid and bicuspid are open

Statement III: Semilunar valves are closed

Statement IV: Blood from the pulmonary veins and vena cava flows into the left and right ventricles, respectively, through the left and right atria

The correct option containing the correct choice is

a. Only I

c. II and IV

b. Only III

d. None of these

30. Statement I: Though the AV node generates impulses, it is still not called the pacemaker of the heart.

Statement II: The rhythmicity of impulse production is not highest in the AV node in the neuromuscular conduction pathway.

a. Both statements are true

b. Both statements are false

c. Statement I is true, and Statement II is false

d. Statement I is false, and Statement II is true

31. Nitrogenous waste products are eliminated mainly as

a. Urea in tadpoles and ammonia in adult frogs

b. Ammonia in tadpoles and urea in adult frogs

c. Urea in both tadpoles and adult frogs

d. Urea in tadpoles and uric acid in adult frogs

32. Which one of the following statements is incorrect?

a. Birds and land snails are uricotelic animals

b. Mammals and frogs are ureotelic animals

c. Aquatic amphibians and aquatic insects are ammonotelic animals

d. Birds and reptiles are ureotelic

33. In Bowman's capsule

a. The afferent arteriole is narrower, whereas the efferent arteriole is wider

b. Afferent arteriole is wider, whereas efferent arteriole is narrower

c. Afferent capillary is wider, and efferent capillary is narrow

d. Afferent capillary is narrow, and efferent capillary is wide

34. Which of the following is incorrect?

a. A blood vessel leading to the glomerulus is called an efferent arteriole

b. Cortical nephron has no or highly reduced vasa recta

c. Vasa recta runs parallel to the Henle's loop in juxtamedullary nephrons

d. In the glomerulus, the afferent arteriole is wider than the efferent arteriole

35. The main function of the pyramids of the kidney is to

a. Contain collecting tubules of the kidney

b. Direct the urine to flow in the ureter

c. Support the openings of collecting canals

d. Store fat and protein

36. The processes involved in urine formation are

I. Tubular secretion

II. Glomerular filtration

III. Tubular reabsorption

IV. Tubular filtration

a. Only III

c. III and IV

37. Tubular reabsorption occurs in

I. Proximal convoluted tubule

II. Major part in collecting ducts

III. Loop of Henle

IV. Bowman's capsule

Choose the correct answer:

a. I and IV

c. I and II

38. Which of the following statements are true?

I. Glomerular filtrate is isotonic to plasma

b. I and II

d. I, II and III

b. II and III

d. All of these

II. When the urine passes into the collecting tubule, it becomes hypotonic

III. Filtrate is isotonic in the proximal convoluted tubule

IV. Filtrate becomes more and more hypotonic as it passes through the descending limb of Henle's loop

a. II and III

c. I and III

b. I, II and III

d. Only II

39. Use of an artificial kidney during hemodialysis may result in:

a. Nitrogenous waste build-up in the body

b. Non-elimination of excess potassium ions

c. Reduced absorption of calcium ions from the gastrointestinal tract

d. Reduced RBC production

40. The part of the nephron involved in the active reabsorption of sodium is

a. Distal convoluted tubule

c. Bowman's capsule

b. Proximal convoluted tubule

d. Descending limb of Henle's loop

NEURAL CONTROL AND COORDINATION

3.1 INTRODUCTION

Control and coordination are the regulation and integration of physiological processes to maintain homeostasis to internal and external stimuli in the body.

The neural (nervous) and endocrine systems are the two integrative systems that help in coordinating various body parts. The nervous system establishes a well-organised network of direct connections for rapid coordination, while the endocrine system achieves integration using chemical messengers known as hormones.

3.2 NERVOUS SYSTEM OF ANIMALS

The nervous system of animals comprises highly specialised cells called neurons that can detect, receive, integrate, and transmit different stimuli.

Except for sponges, all multicellular animals have a nervous system. The neural organisation is very simple in lower invertebrates.

The simplest nervous system is the nerve net of the radially symmetrical cnidarians (jellyfish, hydras, and anemones).

The axons of many nerve cells are frequently bundled together to form nerves in complex animals. These nerves form nerve channels to organise information flow along specific routes through the nervous system. Some animals, like echinoderms (e.g. sea stars), have a set of radial nerves connecting to a central nerve ring.

There are some bilaterally symmetrical animals that exhibit cephalisation, an evolutionary trend toward the concentration of neurons at the anterior (front) end of the body. In unsegmented worms, such as the planarian, a small brain and longitudinal nerve cords constitute the simplest central nervous system (CNS). More complex invertebrates, such as segmented worms (annelids) and arthropods, have more complex brains and double ventral nerve cords with segmentally arranged ganglia and segmental nerves.

Nerve net

Radial nerve Nerve Ring

Eyespot

Brain

Nerve cords

Transverse nerve

Brain

Ventral nerve cord

Segmental ganglia

(b) Sea star (echinoderm) (c) Planaria (flatworm) (d) Leech (annelid)

(a) Hydra (cnidarian)

Brain

Ventral nerve cords

Segmental ganglia

Anterior nerve ring

Longitudinal nerve cords

(e) Insect(arthropod)

Ganglia

(f) Chiton (mollusc)

Brain

Ganglia

Brain

Spinal cord (dorsal nerve cord)

Sensory ganglia

(h) Salamander (vertebrate)

(g) Squid (mollusc)

Fig. 3.1 Nervous system in animals

Nervous system organisation often correlates with lifestyle within an animal group. For example, the sessile and slow-moving molluscs, such as chitons, have relatively simple sense organs and little or no cephalisation. Active predatory molluscs, such as squids, have the most complex nervous system among invertebrates.

The vertebrates have a more developed nervous system. These animals have a single dorsal nerve cord differentiated from the brain and the spinal cord that constitute the central nervous system (CNS). Nerves and ganglia form the peripheral nervous system (PNS).

3.3 HUMAN NERVOUS SYSTEM

The human nervous system is categorised into two main parts: central nervous system (CNS) and peripheral nervous system (PNS)

The PNS encompasses all the body's nerves associated with the CNS, consisting of afferent fibres and efferent fibres. The PNS is further divided into two divisions known as the somatic nervous system and the autonomic nervous system. The autonomic nervous system is further classified into the sympathetic nervous system and the parasympathetic nervous system.

3.4 CENTRAL NERVOUS SYSTEM

The central nervous system (CNS) is made up of the brain and the spinal cord. It is the site of information processing and control.

3.4.1

The brain

The brain serves both as body's command and control centre and its primary organ for processing information. It controls our body's voluntary movements, equilibrium, functioning of vital involuntary organs (like, the heart, lungs, and kidneys), thermoregulation, hunger, thirst, circadian (24 hour) cycles, activity of several endocrine glands, and human behaviour. In addition, vision, hearing, speech, memory, intelligence, emotions, and thoughts are also processed by the brain.

Cranium: The brain is situated in the cranial cavity, i.e., the cranium of the skull. The brain box or cranium protects the brain from mechanical shocks and injury.

Meninges: The human brain is covered by tough tissue known as meninges. The cranial meninges are continuous with spinal meninges. The three meninges are:

1. Dura mater - The outer layer is called the dura mater. It is a thick layer of fibrous tissue.

2. Arachnoid - The middle layer is called the arachnoid. It is a very thin sheet of delicate connective tissue.

3. Pia mater - The inner layer, which is in contact with the brain, is called the pia mater. It is a moderately tough membrane of connective tissue fibres.

Cerebrospinal Fluid (CSF): The space present between the arachnoid and the pia mater contains cerebrospinal fluid. This extracellular fluid circulates through the subarachnoid space around the brain and spinal cord and through the cavities within the brain. It provides mechanical protection to the delicate brain and spinal cord by acting as a shock-absorbing medium. It is also a medium for minor exchange of nutrients and waste products between the blood and nervous tissue.

Ventricles: Four cavities are present within the brain called cerebral ventricles.

Subarachnoid space (contains cerebrospinal fluid)

Cerebellum

Spinal cord

Subarachnoid space of spinal cord

Fig. 3.2 Meninges and cerebrospinal fluid

Skull bone

Dura mater

Arachnoid mater Cranial meninges

Pia mater

Blood vessel

Cerebrum }

Cerebrum

Skull bone

The brain can be divided into three main regions: forebrain, midbrain, and hindbrain.

Forebrain

The forebrain consists of the cerebrum and diencephalon.

Cerebrum: The cerebrum is the largest and most complex of all the parts of the human brain. A deep longitudinal fissure divides the cerebrum longitudinally into two halves, which are termed the left and right cerebral hemispheres. The hemispheres are connected by a flat bundle of commissural nerve fibres called the corpus callosum. The left half of the brain controls the right side of the body and vice versa.

Cerebral cortex: The outer portion of the cerebrum is called the cerebral cortex, which makes up the grey matter of the cerebrum. The surface of the cortex is greatly folded. The upward folds, or gyri, alternate with the downward grooves, or sulci. Beneath the grey matter, there are millions of medullated nerve fibres connecting the neurons of the cerebral cortex with those located elsewhere in the brain. The large concentration of medullated nerve fibres gives this tissue an opaque white appearance. Hence, they are collectively called white matter.

The cerebrum has motor areas, sensory areas, and large regions called association areas, which are neither sensory nor motor. They are centres for memory, inter-sensory association, and communication.

Diencephalon: It is located between the cerebral hemispheres and superior to the brainstem. It includes the thalamus, hypothalamus, and epithalamus.

1. Thalamus: The cerebrum envelops a structure known as the thalamus, which is a major coordinating centre for sensory and motor signalling.

2. Hypothalamus: The hypothalamus lies at the base of the thalamus. The pituitary gland is attached to the hypothalamus by a stalk-like infundibulum. It contains several centres that control body temperature, regulate circadian rhythms and consciousness, clocks, urge to eat and drink, and regulation of emotions. It also contains several groups of neurosecretory cells that secrete hormones.

Frontal pole

Occipital pole

Longitudinal cerebral fissure

Right cerebral hemisphere Right cerebral hemisphere Left cerebral hemisphere

cerebral hemisphere

Fig. 3.3 Left and right cerebral hemispheres

3. Epithalamus: The epithalamus lies posterior to the thalamus and comprises the pineal gland.

Frontal lobe

Corpus callosum

Optic chiasma

Hypothalamus

Pituitary gland

Mammillary body

Midbrain

Pineal gland

Occipital lobe

Hindbrain

Medulla oblongata

Spinal cord Pons

The midbrain is situated between the thalamus/hypothalamus of the forebrain and the pons of the hindbrain. A canal known as the cerebral aqueduct passes through the midbrain. The dorsal part of the midbrain consists mainly of four round swellings (optic lobes) called corpora quadrigemina. They contain the centres for certain visual reflexes, such as those responsible for moving the eyes to view something as the head turns. They also contain the auditory reflex centres. The midbrain acts as the coordinating centre between the forebrain and hindbrain and controls certain involuntary movements.

The hindbrain comprises pons, cerebellum and medulla oblongata.

1. Pons: The pons appear as a rounded bulge on the underside of the brainstem, where it separates the midbrain from the medulla oblongata. It helps in the regulation of respiration.

2. Cerebellum: The cerebellum is a large mass of tissue located inferior to the cerebrum and posterior (dorsal) to the pons and medulla oblongata. It has a very convoluted appearance (cortex) to provide additional space for many more neurons. The cerebellum coordinates the contractions of skeletal muscles. It also maintains posture and balance.

3. Medulla oblongata: The medulla oblongata is continuous with the superior part of the spinal cord and contains both sensory tracts and motor tracts. It begins at the inferior border of the pons and extends up to the foramen magnum. The white matter of medulla oblongata consists of sensory (ascending) and motor (descending) tracts that extend between the spinal cord and other parts of the brain. The medulla contains centres that help to control respiration, gastric secretions, and cardiovascular reflexes.

Limbic lobe Thalamus Parietal lobe

Cerebellum

Fig. 3.4 Major parts of the brain

The midbrain, pons, and medulla oblongata of the hindbrain form the brain stem that connects the brain with the spinal cord.

3.4.2 The spinal cord

The spinal cord is in the vertebral canal (neural canal) of the vertebral column. It is protected by the vertebral arches and the spinal meninges. The three spinal meninges are dura mater, arachnoid mater, and pia mater. The spinal cord extends from the medulla oblongata to the superior border of the second lumbar vertebra in adults. The spinal cord has central grey matter surrounded by white matter. The grey matter of the spinal cord is H-shaped or butterfly-shaped. It is composed of cell bodies, neuroglia, dendrites, and unmyelinated axons. The grey matter surrounds a narrow longitudinal cavity called the central canal, or spinal neurocoele. The white matter consists of myelinated axons and is organised into four cord-like structures.

The spinal cord acts as a coordinating centre for simple spinal reflexes. The spinal cord conducts sensory and motor impulses to and from the brain and, therefore, acts as the 'middleman' between the receptors and the effectors.

Cerebellum

Spinal cord

Medulla

Pons

Fig. 3.5 The hindbrain

Brain

Spinal cord

Cervical

C1 - C7

Thoracic

T1 - T12

Lumbar

L1 - L5

Sacral

S1 - S5

Coccygeal

Fig. 3.6 Spinal cord

3.5 PERIPHERAL NERVOUS SYSTEM

The PNS encompasses all the body's nerves associated with the CNS, consisting of afferent fibres and efferent fibres. The PNS is further divided into two divisions:

1. Somatic nervous system

2. Autonomic nervous system

The somatic nervous system transmits signals from the central nervous system to skeletal muscles, whereas the autonomic nervous system transmits signals from the central nervous system to the involuntary organs and smooth muscles throughout the body.

The autonomic neural system or visceral nervous system is further divided into the sympathetic nervous system and the parasympathetic nervous system.

The PNS comprises all the nerves of the body associated with the CNS (brain and spinal cord). The nerve fibres of the PNS are of two types:

1. Afferent fibres (sensory)

2. Efferent fibres (motor)

The afferent nerve fibres transmit impulses from tissues/organs to the CNS and the efferent fibres transmit regulatory impulses from the CNS to the concerned peripheral tissues/organs.

3.6 PROTECTION OF THE BRAIN AND SPINAL CORD

Our body has protective barriers to take care of sensitive organs like the brain. The brain is protected by a hard bone called the skull. Inside the skull, the brain is surrounded by a fluidfilled cushion, the cerebrospinal fluid (CSF). This helps to keep it safe from any shocks. Another protective layer seen in the back side of the body is the vertebral column. It acts like a natural shield, protecting the spinal cord, which is like the brain's messenger, sending signals to different parts of the body.

3.7 HOW DOES NERVOUS TISSUE CAUSE ACTION?

In animals, the coordination between nervous tissue and muscle tissue plays an important role in movement. When a nerve impulse reaches the muscle, the muscle fibre undergoes a remarkable change at the cellular level. This change involves muscle cells altering their shape, ultimately becoming shorter to initiate movement.

The process of muscle movement involves cellular components, particularly certain proteins found within muscle cells. In response to electrical impulses from the nervous system, these proteins not

only change their shape but also undergo rearrangement. This rearrangement ultimately triggers the muscle cells to shorten, enabling the organism to move.

3.8 NEURON

A neuron, or nerve cell, is the basic structural and functional unit of the nervous system. Neurons are vital for transmitting information throughout the body, enabling processes like thinking, feeling, and movement.

3.8.1 Structure of a neuron

The neuron is the longest cell in the body. It carries messages in the form of electrical signals called nerve impulses. The neuron is an elongated branched cell having three components- cell body, dendrites, and axon. Another type of cells, known as the neuroglial cells, or glial cells, are nonneuronal cells that provide essential support and protection to neurons in the nervous system.

Cell Body

The cell body is like a typical cell, having a central nucleus and cytoplasm around it. Within the cytoplasm, there are tiny granules called Nissl's granules, which are rough endoplasmic reticulum with ribosomes. These ribosomes help in making proteins through a process known as protein synthesis. The cell body handles metabolic functions and growth and plays a role in receiving nerve impulses from dendrites, transmitting them to the axon.

Dendrites

Dendrites are short, branching processes extending from the cell body of a neuron. They receive sensations or stimuli from receptor cells, kick start electrical impulses, and carry these nerve impulses toward the cell body. The neuroplasm within dendrites contains both neurofibrils and Nissl's granules, contributing to the vital functions of the neuron.

Axon

The axon is the longest part of the neuron. It is a single, elongated fibre arising from the cyton. It conducts impulses away from the cell body. The axon endings are highly branched, and the terminal branches are called terminal arborisations. When terminal arborisation of the axon meets the dendrites of another neuron to form a synapse, they form a synaptic knob. At the synapse, the synaptic knob secretes a neurotransmitter chemical that initiates an electrical impulse on the dendron of the next neuron.

The cell membrane of the axon is called axolemma, and its cytoplasm is termed axoplasm. It lacks Nissl's granules. However, neurofibrils are present. The axon has an insulating and protective sheath of myelin around it. Nerve fibres (axons) having myelin sheath are termed myelinated nerve fibres, and those without this sheath are termed non-myelinated nerve fibres. In myelinated nerve fibres, Schwann cells form a myelin sheath around the axon. The gaps between two adjacent myelin sheaths are called nodes of Ranvier.

3.8.2

Classification of neurons

Based on their functions, the neurons are divided into the following types:

1. Sensory (receptor) neurons: These neurons are typically found in sense organs; these neurons receive impulses from receptors and carry them toward the central nervous system (comprising the brain and spinal cord).

2. Motor (effector) neurons: These neurons are responsible for transmitting impulses from the central nervous system (brain and spinal cord) to effectors, which are usually muscles or glands. The effectors respond to these stimuli.

3. Relaying (connector) neurons: These neurons are located in the central nervous system (brain and spinal cord). Their role is to act as bridges between sensory and motor neurons, facilitating the distant transmission of nerve impulses.

3.8.3

Nerves

Nerves are thread-like structures which emerge from the brain and spinal cord and branch out to almost all parts of the body. Nerves are composed of axons or nerve fibres bundled together like the strands of an electric cable.

3.9 NERVE IMPULSE

The nervous system runs in an organised fashion. It is stimulated using a receptor organ, such as the tongue, ear, or eye. Through sensory nerves, the stimulus is transmitted to the brain and spinal cord, where it is processed and translated into action. A reaction is generated by the motor neurons transmitting the action to the necessary organ (muscle or gland).

Now, what does an impulse mean? Let's use an example to grasp this better. Assume you have experienced a prick to your finger. Then, due to your brain's reaction to the prick, you remove your hand. Impulse refers to this message flow along the nerve. A nerve impulse only travels in one

Schwann cell Axon

Dendrite

Axon Soma

Node of ranvier Myelin

Fig. 3.7 Structure of a neuron

direction when it first emerges from a neuron. The neuron is attached to a sensory receptor, which interprets the input or message and transforms it into electrical waves. The neuron carries these waves. Dendrites receive the stimulus from the receptor organ, which is then transmitted to the neuron's cell body (cyton) and ultimately to the effector organ.

3.9.1 Synapse

The transmission of a nerve impulse from one neuron to another occurs at junctions known as synapses. A synapse is created by the membranes of a presynaptic neuron and a postsynaptic neuron, with the possibility of being separated by a gap known as the synaptic cleft. Synapses can be categorised into two types: electrical synapses and chemical synapses

Electrical synapses

Electrical synapses involve pre - and postsynaptic neuron membranes positioned closely with gap junction channels, enabling the direct flow of electrical current from one neuron to another. The transmission of impulses across electrical synapses closely resembles the conduction of impulses along a single axon. This impulse transmission across electrical synapses is faster as compared to that across chemical synapses. However, electrical synapses are found less in our system.

3.8 (A)

Chemical synapses

In a chemical synapse, the membranes of pre and postsynaptic neurons are divided by a fluid-filled region known as the synaptic cleft. The presynaptic neuron transmits an impulse (action potential) across the synaptic cleft to the postsynaptic neuron. The transmission of impulses at these synapses involves chemicals known as neurotransmitters. Within the axon terminals, there are synaptic vesicles containing neurotransmitters, facilitating the travel of impulses across the neurons.

3.9.2 Reflex Action

The process of response to a peripheral nervous stimulation that occurs involuntarily, i.e., without conscious effort or thought, and requires the involvement of a part of the central nervous system is called a reflex action.

Most body functions controlled by the nervous system involve reflexes. A spinal reflex is a reflex in which integration takes place in the spinal cord. A cranial reflex is a reflex in which integration takes place in the brain stem rather than the spinal cord, e.g., the tracking movements of your eyes as you read this sentence.

Reflex arc

The pathway followed by nerve impulses that produce a reflex is called a reflex arc. The response is called a reflex. The reflex arc is the basic functional unit of the nervous system. The reflex pathway comprises at least one afferent neuron (receptor) and one efferent (effector or exciter) neuron appropriately arranged in a series. E.g., knee-jerk reflex.

Knee-jerk reflex

Stretch reflexes can be elicited by tapping on tendons attached to muscles. The knee-jerk reflex operates as follows:

• Slight stretching of a muscle stimulates sensory receptors in the muscle called muscle spindles.

• In response to being stretched, a muscle spindle generates one or more nerve impulses that propagate along a somatic afferent (sensory) neuron through the dorsal root of the spinal nerve into the spinal cord.

• In the spinal cord (integrating centre), the sensory neuron makes an excitatory synapse with an interneuron that activates a motor neuron (efferent neuron).

• One or more nerve impulses arise in the motor neuron and propagate along its axon, which extends from the spinal cord to the muscle.

• Acetylcholine released by the motor nerve fibre stimulates the muscle (effector) to contract.

The sensory neuron synapses with a motor neuron in the spinal cord

Gray matter White matter Dorsal root (sensory neurons)

Sensory neuron Motor neuron

Spinal nerve

Quadriceps muscle

Stretch receptors fire action potentials

A hammer tap stretches the tendon in the knee, stretching receptors in the quadriceps.

The leg jerks forward.

Dorsal horn

Ventral horn

Ventral root (motor neurons) Spinal interneuron

The motor neuron conducts action potentials to the quadriceps, causing contraction.

Simultaneously, a spinal interneuron inhibits firing in the motor neuron for the antagonistic muscle.

Fig. 3.9 Knee-jerk reflex

Conditioned and unconditioned reflexes

A simple reflex is like an automatic response that happens without us thinking or learning. For example, pulling your hand away when it hurts or your leg jerking when someone taps your kneecap. Another type of reflex is the conditioned reflex, which is when our reflexes change based on what we learn or experience.

QUICK REVIEW

• Control and coordination are fundamental for the adaptive responses of living organisms to environmental changes.

• The nervous system, encompassing the central and peripheral components, is a key player in control and coordination.

• The brain, a vital organ in the central nervous system, consists of the cerebrum, cerebellum, and brainstem.

• The cerebrum is responsible for conscious thought and voluntary actions, while the cerebellum coordinates motor activities.

• The brainstem controls basic life functions like breathing and heartbeat

• Neurons, comprising a cell body, dendrites, and an axon, are the basic units of the nervous system.

• Synapses, communication points between neurons, use neurotransmitters for signal transmission.

• Reflex arcs offer rapid, automatic responses involving sensory, interneurons, and motor neurons.

WORKSHEET - 1

MULTIPLE CHOICE QUESTIONS WITH SINGLE CORRECT ANSWER

I. Nervous system in animals

1. The organisation of the nervous system generally correlates with the animal group's

a. Lifestyle

b. Behaviour

c. Body form d. Food habits

2. The neural system is better organised in the following

a. Freshwater polyp

c. Silverfish

b. Bath sponge

d. Sea anemone

3. In which animal can we observe that nerve cells are present, but the brain is absent?

a. Sponge

c. Cockroach

4. In earthworms, neurons are

a. Sensory only

c. Associated only

5. Identify the incorrect statement.

b. Earthworm

d. Hydra

b. Motor only

d. All of these

a. Brain and spinal cord form the central nervous system

b. Brain and spinal cord give rise to the peripheral nerves

c. Peripheral nerves and ganglia form the PNS

d. Nerves carry only messages towards the CNS

II. Central nervous system and peripheral nervous system

1. Which of the following is not related to cranial meninges?

a. Dura mater

c. White matter

b. Pia mater

d. Arachnoid

2. Which area of the brain is related to strong emotions?

a. Cerebral cortex

c. Limbic system

b. Cerebellum

d. Medulla

3. Association areas of the cerebral cortex are

a. Purely sensory

c. Neither sensory nor motor

4. The hypothalamus is not related to this function

a. Controlling body temperature

c. Urge to eat

5. The forebrain is divided into

a. Olfactory lobe, cerebrum, diencephalon

b. Olfactory lobe, thalamus, cerebrum, pons

c. Thalamus, hypothalamus, cerebrum, medulla

d. Pons, diencephalon, cerebellum

b. Purely motor

d. Absent

b. Urge to drink

d. Thinking, reasoning

6. For which of the following brain structures is the given autonomic function pairing incorrect?

a. Pons - Respiration

c. Medulla oblongata - Respiration

7. Medulla oblongata controls

i. Breathing and blood pressure

ii. Gut peristalsis and gland secretion

iii. Vasodilation and vasoconstriction

iv. Laughing and micturition

a. Only I

c. I, II, and III

8. Corpora quadrigemina acts as the center for

a. Audio and vision

c. Thermoregulation and chemical sense

b. Corpus callosum - Blood pressure

d. Thalamus - Intense pain

b. II and III

d. Only IV

b. Olfaction and gustation

d. None of the above

9. The activities of equilibrium, balancing, and coordination of muscles are governed by

a. Medulla oblongata

c. Cerebellum

10. Match the following.

Column I

A. Cerebrum

B. Cerebellum

b. Cerebrum

d. Pineal

Column II

i. Controls the pituitary

ii. Controls vision and hearing

C. Hypothalamus

D. Midbrain

a. A-v, B-iv, C-ii, D-i

c. A-iv, B-v, C-ii, D-i

11. The foramen of Monro is an aperture between

a. Third and fourth ventricle

c. Rhinocoel and diacoel

iii. Controls the rate of heartbeat

iv. Seat of intelligence

v. Maintains body posture

b. A-v, B-iv, C-i, D-ii

d. A-iv, B-v, C-i, D-ii

b. Lateral and third ventricle

d. Diacoel and metacoel

12. The centres for the control of voluntary activities are present in the

a. Thalamus and cerebral cortex of the brain

c. Cerebral cortex and medulla oblongata

13. The white matter of the spinal cord contains:

a. Nerve axons

c. Clusters of neurons and cell bodies

14. The spinal cord:

I. Is in the neural canal of the vertebral column

b. Thalamus and medulla oblongata

d. None of the above

b. Cell bodies

d. Motor neurons

II. Is composed of central grey matter, in which cell bodies of neurons are present

III. Does not conduct the reflex actions of the body

IV. Is composed of central white matter

a. Statement I and II are correct

c. Statement II is correct

b. Statement I and III are correct

d. All the statements are correct

15. Which part of the brain is more developed as compared to others?

a. Cerebellum

c. Optic nerves

b. Cerebrum

d. Medulla oblongata

16. Which part of the brain helps in the regulation of the body’s temperature?

a. Hypothalamus

c. Pituitary

17. Involuntary actions in the body are controlled by:

a. Medulla of forebrain

b. Thalamus

d. Medulla oblongata

b. Medulla of midbrain

c. Medulla of hindbrain

d. Medulla of spinal cord

18. Which of the following statements is correct among the following?

a. The opening at the base of the skull for the spinal cord is called the foramen of Monro.

b. The vertebra which bears the whole weight of the skull is the axis.

c. The axis vertebra in mammals differs from atlas in the presence of an odontoid process.

d. The cervical vertebrae are located in the thoracic region.

19. Which of the following protects the brain from shocks?

a. Pons

c. Dura mater

20. Cavities in the brain are called:

a. Auricles

c. Coelom

21. The PNS regulates:

a. Conscious thoughts and perceptions

c. Memory and learning

III. Neurons and nerve impulse

b. Cerebrospinal fluid

d. Arachnoid membrane

b. Ventricles

d. Lumen

b. Involuntary functions such as heartbeat and digestion

d. Sensory processing in the brain

1. In a neuron, conversion of the electrical signal to a chemical signal occurs at/in

a. Cell body b. Axonal end c. Dendritic end d. Axon

2. Among the following statements regarding the nodes of Ranvier in neurons, which one accurately describes their structural characteristics?

a. The neurilemma exhibits a discontinuity

b. The myelin sheath shows discontinuity

c. The nodes of Ranvier are covered by myelin sheath

d. Both the neurilemma and the myelin sheath display discontinuity

3. Which of the following statements is correct for chemical synapses?

i. Pre and postsynaptic neurons are separated by a fluid-filled synaptic cleft

ii. The membranes of the presynaptic and postsynaptic neurons are in close proximity

iii. Bidirectional movement of impulse

iv. Presence of neurotransmitter vesicles in the axon terminals

a. (i) and (ii)

b. (ii) and (iii)

c. (i) and (iv)

d. (ii) and (iv)

4. Which of the following statements regarding nervous tissue is incorrect?

i. Nervous tissue of the brain shows the least capacity for regeneration after injury due to limited neurogenesis

ii. Nissl's granules are composed of ribosomes and are strongly basophilic, exhibiting an affinity towards basic dyes

iii. Neuroglial cells are essential non-sensory cells responsible for supporting, protecting, and insulating neurons

iv. End plate junctions are specialised structures found at the neuron and neuron junction

a. (i) and (ii)

c. (iv) only

b. (i), (ii), and (iii)

d. (iii) and (iv)

5. Chemicals that are released at the synaptic junction are called ________.

a. Cerebrospinal fluid

c. Lymph

b. Hormones

d. Neurotransmitters

6. Which one of the following does not act as a neurotransmitter?

a. Acetylcholine

c. Norepinephrine

7. A synaptic cleft is

a. The space present inside the presynaptic neuron

c. The space separating the pre and postsynaptic neurons

IV. Reflex action

1. Which of the following is a reflex action?

a. Coughing

c. Knee-jerk

b. Epinephrine

d. Cortisol

b. The space present inside the postsynaptic neuron

d. The space present inside the synaptic vesicles

b. Blinking of eyes

d. All of the above

2. The somatic neural system, which is a part of the PNS, relays impulses from the CNS to

a. Involuntary organs

c. Skeletal muscles

3. Reflex action involves

a. Medulla oblongata

c. Optic lobe

b. Smooth muscles

d. Viscera

b. Cerebellum

d. Spinal cord

4. The interneurons that connect sensory and motor neurons are located in

a. Gray matter

c. Dorsal root ganglia

b. White matter

d. All of the above

5. The butterfly-like structure surrounding the centre of a human spinal cord is called

a. Funiculus

c. White matter

6. An example of a conditioned reflex is

a. Withdrawal of hand on touching a hot surface

c. Running indoors on the arrival of rain

b. Horn

d. Gray matter

b. Sneezing during cold

d. Salivation in dogs and seeing bread

7. Which of the following is not involved in knee-jerk reflex?

a. Muscle spindle

c. Brain

WORKSHEET - 2

b. Motor neuron

d. Interneurons

I. MULTIPLE CHOICE QUESTIONS WITH SINGLE CORRECT ANSWER

1. Which of the following is an integrative system?

a. Excretory system

c. Respiratory system

b. Nervous system

d. Digestive system

2. Identify the one with the simplest nervous system among the following:

a. Bath sponge

c. Planarian

b. Jellyfish

d. Polychaeta

3. Radial nerves are seen connecting to a central nerve ring in

a. Sea anemone

c. Sea star

b. Sea fan

d. Sea mouse

4. Which of the following has a relatively more complex nervous system?

a. First triploblastic animals

c. The largest group of animals

5. The brain stem does not include :

a. Mid-brain

b. First segmented worms

d. Pseudo coelomate animals

b. Medulla oblongata

c. Pons Varolii

6. Association areas of cerebral cortex are:

a. Purely sensory

c. Neither sensory nor motor

7. The hypothalamus is not related to this function.

a. Controlling body temperature

c. Urge for eating

d. Cerebellum

b. Purely motor

d. Absent

b. Urge for drinking

d. Thinking and reasoning

8. Not a part of the limbic lobe or limbic system of the brain is the

a. Amygdala

c. Cerebellum

9. Corpora quadrigemina is a part of

a. Cerebrum

c. Thalamencephalon

10. The centre for controlling respiration lies in

a. Cerebrum

c. Thalamencephalon

b. Hippocampus

d. Inner parts of the cerebrum

b. Medulla oblongata

d. Midbrain

b. Medulla oblongata

d. Mid brain

11. The thermoregulatory centre in the brain of a human being is

a. Pituitary

c. Hypothalamus

12. Primary visual area is located in

a. Diencephalon

c. Cerebellum

b. Diencephalon

d. None of these

b. Optic lobe

d. Cerebrum

13. The brain of a human being is distinguished by the presence of

a. Corpus albicans

c. Corpus spongiosum

b. Corpus callosum

d. Corpus luteum

14. Which among the following is unique to the human brain?

a. 3 meninges

c. Corpus callosum

b. 4 optic lobes

d. All the above

15. The part of the brain concerned with an urge to eat and drink has hormone-secreting cells and contains a centre for controlling body temperature is

a. Hypophysis

b. Hypothalamus

c. Cerebrum

d. Cerebellum

16. Match Column -I with Column -II and select the correct option from the codes given below.

Column I

A. Cerebrum

B. Cerebellum

C. Hypothalamus

D. Midbrain

a. A-v, B-iv,C-ii,D-i

c. A-iv, B-v, C-ii, D-i

Column II

i. Controls the pituitary

ii. Controls visual reflexes

iii. Controls the rate of heartbeat

iv. Seat of intelligence

v. Maintains body posture

b. A-v, B-iv, C-i, D-ii

d. A-iv, B-v, C-i, D-ii

17. The following transmit regulatory impulses from the CNS to concerned tissues

a. Efferent process

c. Afferent process

18. Nissl's granules are present in

a. Cyton

c. Both a & b

b. Reticular fibres

d. Afferent fibres

b. Dendron

d. Axon

19. Neurons of embryo, neurons of retina, and cerebral cortex of an adult differ from one another in

a. Number of axons

c. Number of dendrites

b. Nature of axons

d. Nature of dendrites

20. One of the following is related only to myelinated neurons. Identify it.

a. Dendrites

c. Telodendrites

21. 'Neuroglia' of the nervous system represents

a. Receptor cells

c. Supporting cells

22. Conduction speed of impulse is

a. More across an electrical synapse

c. Equal in both chemical and electrical synapses

b. Axon

d. Nodes of Ranvier

b. Gland cells

d. Nerve cells

b. More across a chemical synapse

d. Equal to that of action potentials

23. Chemicals that are released at the synaptic junction are called

a. Cerebrospinal fluids

c. Lymph

24. In a nerve cell, the potassium concentration is

a. Less on the outer side

c. Equal on both sides

b. Hormones

d. Neurotransmitters

b. Greater on the outer side

d. None of these

25. Which of the following is true about electrical synapses?

I. The membranes of pre and postsynaptic neurons are in very close proximity

II. These are rare in our neural system

III. The impulse transmission across this is always faster than that of a chemical synapse

a. I & III

c. I & II

b. II & III

d. I, II, & III

26. Arrange the following events of synaptic transmission in a proper sequence.

A. Binding of neurotransmitters to specific receptors on the postsynaptic membrane

B. Generation of a new potential in the postsynaptic neuron

C. Release of neurotransmitters into the synaptic cleft

D. Opening of ion channels in the postsynaptic membrane

a. (A), (C), (D), (B)

c. (C), (A), (D), (B)

27. Conduction speed of impulse is

a. More across an electrical synapse

c. Equal in both chemical and electrical synapses

b. (C), (A), (B), (D)

d. (D), (A), (C), (B)

b. More across a chemical synapse

d. Equal to that of action potentials

28. Identify the part having the receptors for neurotransmitters.

29. All sensory information to be registered consciously by the forebrain must pass via the

a. Thalamus

c. Cerebellum

b. Reticular formation

d. Pons

30. Observe the picture given below and identify the set of correctly labelled parts.

a. A- Cerebrum, B- Corpus callosum, C- Cerebellum, D- Pons, E- Pituitary

b. A- Cerebellum, B- Cerebrum, C- Corpus callosum, D- Pons, E- Pituitary

c. A- Cerebrum, B- Pituitary, C- Cerebellum, D- Pons, E- Corpus callosum

d. A- Cerebrum, B- Corpus callosum, C- Cerebellum, D- Pituitary, E- Pons

31. Which of the following is an example of a conditioned reflex?

a. Twitching of eyes

c. Watering of the mouth at the smell of food

32. Identify the reflex arc.

a. Brain - spinal cord - muscle

c. Receptor - spinal cord - muscle

33. Identify the one which is not a reflex action.

a. Salivation on the sight of food

c. Closing the eyelids when an object comes across suddenly

b. Withdrawal of hand on touching a hot plate

d. Flowing of tears while cutting onions

b. Muscle - receptor - spinal cord

d. Muscle - spinal cord - receptor

b. Weight-lifting

d. Typing by a professional

34. Select incorrect statement regarding synapses: [NEET-2021]

a. Electrical current can flow directly from one neuron into the other across the electrical synapse.

b. Chemical synapses use neurotransmitters

c. Impulse transmission across a chemical synapse is always faster than that across an electrical synapse.

d. The membranes of presynaptic and postsynaptic neurons are in close proximity to an electrical synapse.

35. Which part of the bran is responsible for thermoregulation? [NEET-2019]

a. Corpus callosum

c. Cerebrum

b. Medulla oblongata

d. Hypothalamus

CHEMICAL COORDINATION AND INTEGRATION

4.1 INTRODUCTION

Effective control of body functions requires continuous control and integration of the nervous and chemical control of the endocrine system.

Since nerve fibres do not innervate all cells in the body, cellular functions must be maintained, and therefore they require special coordination. These functions are performed by hormones. The nervous system and endocrine system work in coordination in many cases. Many important functions of the endocrine system are under the control of the nervous system. These two systems are often called the neuroendocrine system. However, there are some differences between the two systems.

Mediator molecules

Site of mediator action

Type of target cells

Time of onset of action

Duration of action

Close to the site of release (usually)

Muscle cells, gland cells, and other neurons

Typically within milliseconds

Generally briefer (milliseconds)

Far from the site of release

Cells throughout the body

Seconds to hours or days

Generally longer (seconds to days)

Table 4.1 Difference between the nervous system and endocrine system

Endocrine glands ( Gk. Endo = within, krinein = to secrete) secrete the chemicals, called hormones (= to excite), into the blood. It transports these to the target tissues located away from the site of secretion.

4.2 HUMAN ENDOCRINE SYSTEM

Fig. 4.1 Human endocrine system

The endocrine glands and their associated hormones constitute the endocrine system.

The pituitary gland, pineal gland, thyroid, adrenal gland, pancreas, parathyroid gland, thymus, and gonads (testes in men, ovaries in women) are the endocrine organs in our body. In addition, some other organs, such as the gastrointestinal tract, liver, kidney, and heart, also produce hormones.

4.2.1 Hypothalamus

The hypothalamus is an important part of the diencephalon and controls many functions of the body. It contains neurosecretory cells, called nuclei, that produce hormones. These hormones regulate the synthesis and release of hormones from the pituitary gland. The hormones produced by the hypothalamus are of two types:

1. Releasing hormones: These hormones stimulate the pituitary gland to release specific hormones.

2. Inhibiting hormones: These hormones prevent the pituitary gland from releasing certain hormones.

The hypothalamus is connected to the anterior lobe of the pituitary gland by hypophysial portal veins. However, it is connected to the posterior lobe of the pituitary gland mainly by axons of neurosecretory cells. The hormones of the hypothalamus influence the functioning of the pituitary gland. Hence, the hypothalamus is considered as the control centre of the endocrine system. It signals glands to turn on or off hormones as the body needs them. For instance, a hypothalamic hormone called gonadotropin-releasing hormone (GnRH) stimulates the pituitary gland to make

and release gonadotropins. On the other hand, somatostatin released from the hypothalamus stops the pituitary gland from releasing growth hormones.

The hormones originating in the hypothalamic neurons pass through axons and are released from their nerve endings. These hormones reach the pituitary gland through the hypophyseal portal system and regulate the functions of the anterior pituitary. The posterior pituitary however is under the direct neural regulation of the hypothalamus.

4.2.2 Pituitary gland

The pituitary gland was once called the 'master endocrine gland'. This is because it secretes several hormones that control other endocrine glands. The pituitary gland is located in sella tursica, a depression in the sphenoid bone, and is attached to the hypothalamus by a stalk. The pituitary gland in the human body is anatomically divided into two-

a. Anterior lobe or adenohypophysis

b. Posterior lobe or neurohypophysis

Hypophyseal artery

Hypophyseal portal veins

Anterior lobe of pituitary

Hypothalamus

Hypophyseal tract

Infundibulum

Posterior lobe of pituitary

Hypophyseal vein

4.2 Hypothalamus and pituitary gland

Anterior lobe or adenohypophysis

Adenohypophysis comprises two portions: pars distalis and pars intermedia. The pars distalis region of the pituitary is commonly called the anterior pituitary. Pars distalis produces growth hormone (GH), prolactin (PRL), thyroid-stimulating hormone (TSH), adrenocorticotrophic hormone (ACTH), luteinising hormone LH and follicle-stimulating hormone (FSH). Pars intermedia secretes only one hormone called melanocyte-stimulating hormone (MSH). In humans, the pars intermedia, is somewhat merged with pars distalis.

Human growth hormone (HGH) or somatotropin: The human growth hormone is a peptide hormone that helps in growth. Growth hormone promotes protein anabolism, the absorption of calcium from the bowel and the conversion of glycogen to glucose.

Fig.

Thyroid-stimulating hormone (TSH): TSH helps the thyroid gland synthesise and secrete thyroid hormones, thyroxine, triiodothyronine (T3) and thyroxine (T4).

Adrenocorticotropic hormone (ACTH): ACTH stimulates the synthesis and secretion of steroid hormones called glucocorticoids from the adrenal cortex.

Follicle-stimulating hormone (FSH): In females, the FSH stimulates the growth and development of the ovarian follicles. In males, FSH and androgens regulate spermatogenesis. FSH also induces Sertoli cells to secrete inhibin.

Luteinising hormone (LH): In females, the release of eggs from fully developed follicles (known as Graafian follicles) is induced by LH. It stimulates the corpus luteum (remains of the Graafian follicle after ovulation) of the ovary to secrete progesterone. In males, LH is referred to as interstitial cell-stimulating hormone (ICSH) because it stimulates the interstitial cells of Leydig in the testes to produce and release androgens.

Since, LH and FSH stimulate gonadal activity, they are called gonadotropins.

Prolactin (PRL): Prolactin in females regulates the growth of the mammary glands and the production of milk.

Melanocyte-stimulating hormone (MSH): MSH acts on the melanocytes (melanin-containing cells) and regulates the pigmentation of the skin. MSH increases skin pigmentation in lower vertebrates (fishes and amphibians) by stimulating the dispersion of melanin granules in melanocytes.

Posterior lobe or neurohypophysis

The posterior pituitary or neurohypophysis is also known as pars nervosa. It stores and releases two hormones called oxytocin and vasopressin. These hormones are synthesised by the hypothalamus and are transported to neurohypophysis through the axons of the hypothalamohypophyseal tract. From the posterior pituitary, they reach their target tissues through the blood.

Oxytocin (OT): In females, oxytocin stimulates strong contractions of the uterus during labour and the ejection of milk from the mammary gland after birth. Because of its role, oxytocin is called 'birth hormone' and 'milk ejecting hormone'.

Anti-diuretic hormone (vasopressin): ADH (anti-diuretic hormone) primarily acts on the kidneys, stimulating the reabsorption of water and electrolytes in the distal convoluted tubules, thereby reducing water loss through urine (diuresis). Its absence leads to a significant increase in urine output from the normal 1 to 2 litres to about 20 litres a day. ADH also induces arteriolar constriction, contributing to increased blood pressure.

Pituitary gland disorders

Pituitary dwarfism: The deficiency of growth hormone during childhood results in dwarfism which results in short stature, and slower growth of bones and other body organs.

Gigantism: Gigantism is caused by the hypersecretion of HGH during childhood. This results in an abnormal increase in the length of long bones. The person grows extremely tall, although their body proportions remain generally normal.

Acromegaly: Hypersecretion of HGH during adulthood causes disproportionate gigantism called acromegaly. Although HGH cannot produce further lengthening of the long bones because the epiphyseal plates are lost, the bones of the hands, feet, cheeks, jaws and other tissues enlarge.It may lead to serious complications and premature death if unchecked.

Diabetes insipidus: This disorder is due to defects in antidiuretic hormone (ADH) receptors or the inability to secrete ADH. A common symptom of diabetes insipidus is excretion of large volumes of urine, resulting in dehydration and thirst.

Fig. 4.3 Hormones of pituitary gland

Fig. 4.4 Acromegaly

4.2.3 Pineal gland

The pineal gland is situated on the dorsal side of the forebrain and is attached to the roof of the third ventricle at the midline. It secretes a hormone called melatonin governed by the diurnal dark-light cycle. More melatonin is produced during darkness. Melatonin contributes to the setting of the body's biological clock and plays a very important role in the regulation of a 24-hour rhythm (circadian rhythm). It helps in maintaining the normal rhythms of the sleep-wake cycle and body temperature. Additionally, melatonin also influences metabolism, pigmentation, menstrual cycle, and our defence capability.

4.2.4 Thyroid gland

The thyroid gland is a butterfly-shaped gland composed of two lobes located on either side of the trachea. Both the lobes are interconnected with isthmus, which is a thin flap of connective tissue. The thyroid gland is made up of follicles and stromal tissues. Each thyroid follicle consists of follicular cells surrounding a cavity. These follicular cells produce two hormones: thyroxine (T4), also known as tetra-iodothyronine, and tri-iodothyronine (T3). The synthesis of these thyroid hormones requires iodine and the amino acid tyrosine. Tetraiodothyronine contains four iodine atoms, while triiodothyronine contains three iodine atoms.

Epiglottis

Thyroid bone

Thyroid cartilage

Cricoid cartilage

Thyroid gland

Thyroid veins

Trachea

Fig. 4.5 Thyroid gland (anterior view)

Functions of thyroid hormones

• The thyroid hormones play an important role in the regulation of the basal metabolic rate (BMR). They increase BMR by stimulating cellular oxygen used to produce ATP. As cells produce and use more ATP, heat is given off, and body temperature rises. In this way, they maintain normal body temperature.

• Thyroid hormones also support the process of red blood cell formation.

• Thyroid hormones control the metabolism of carbohydrates, proteins, and fats.

• Thyroid hormones also influence the maintenance of water and electrolyte balance.

• Thyrocalcitonin (TCT), secreted by extrafollicular cells of thyroid gland regulates blood calcium levels.

• Thyroxine is essential for metamorphosis in amphibians.

Thyroid gland disorders

A. Hypothyroidism

Hyposecretion of thyroxine hormone causes hypothyroidism. It is characterised by sudden weight gain, decreased metabolism, slower heartbeat and lethargy.

• Cretinism: During pregnancy, if there is hypothyroidism, it can result in impaired development and maturation of the growing baby, leading to stunted growth (known as cretinism), mental retardation, low intelligence quotient, abnormal skin, deaf-mutism, and other complications. In adult women, hypothyroidism might cause irregularities in the menstrual cycle.

• Myxoedema (Gull's disease): Hypothyroidism during the adult years produces myxoedema. A hallmark of this disorder is oedema (accumulation of interstitial fluid), that causes the facial tissues to swell and look puffy. A person with myxoedema has a slow heart rate, low body temperature, sensitivity to cold, and a tendency to gain weight easily.

• Simple goitre, or endemic goitre: Iodine plays a crucial role in ensuring the normal synthesis of hormones in the thyroid. A deficiency of iodine in our diet leads to hypothyroidism and the enlargement of the thyroid gland, commonly known as goitre.

B. Hyperthyroidism

Hypersecretion of thyroxine hormone causes hyperthyroidism. It is characterised by increased heart rate or ventilation, increased metabolism, sudden loss of body weight and difficulty in sleeping. Sometimes, due to the development of thyroid cancer or thyroid nodules, the synthesis and rate of secretion of thyroid hormones may increase to abnormal levels, resulting in hyperthyroidism. This may negatively affect the body's physiology.

• Graves's disease: It is the most common form of hyperthyroidism. It is an autoimmune disorder in which the person produces antibodies for TSH receptors that bind to the receptors. They mimic the action of TSH and over-stimulate the thyroid gland to grow and produce thyroid hormones. Hence, normal negative feedback control is lost, leading to hyperthyroidism. A primary sign is an enlarged thyroid (goitre). Graves's patients often have peculiar oedema behind the eyes, called exophthalmos, which causes eyes to protrude.

(a)

(b)

Fig. 4.6 Thyroid disease (a) Simple goitre (b) Exophthalmos

4.2.5 Parathyroid gland

In humans, four parathyroid glands are present embedded on the back side (posterior surface) of the thyroid gland. These parathyroid glands produce a peptide hormone known as parathyroid hormone (PTH) or Collip's hormone. The secretion of PTH is regulated by the levels of circulating calcium ions.

Functions of parathyroid glands

• PTH enhances the activity of osteoclasts in the bone, which results in elevated bone resorption, which releases ionic calcium (Ca2+ ) into the blood.

• It increases the Ca2+ levels in the blood. It also stimulates the reabsorption of Ca2+ by the renal tubules.

• It promotes the formation of the hormone calcitriol, the active form of vitamin D. Calcitriol increases the rate of Ca2+ absorption from the gastrointestinal tract into the blood.

• The PTH is classified as a hypercalcemic hormone. Together with TCT, it plays a significant role in maintaining calcium balance in the body.

Parathyroid gland disorders

A. Hypoparathyroidism

Hypoparathyroidism leads to a deficiency of Ca2+, which causes neurons and muscle fibres to depolarise and produce action potentials spontaneously. This leads to tetany (sustained contraction) of skeletal muscle.

B. Hyperparathyroidism

Hyperparathyroidism is most often due to a tumour of one of the parathyroid glands. An elevated level of PTH causes excessive resorption of bone matrix, raising the blood levels of calcium and phosphate. The symptoms include kidney stones and bone-related complications like osteitis fibrosa cystica, osteoporosis, osteomalacia, and arthritis.

4.2.6 Thymus

The thymus gland is a lobular structure located on the heart's dorsal side and aorta. It is large in young children but shrinks with age.

The thymus plays a major role in the development of the immune system. This gland secretes the peptide hormones called thymosin

Thymosins help in the differentiation of T-lymphocyte, providing cell-mediated immunity. It also promotes the production of antibodies to provide humoral immunity in the body.

4.2.7

Adrenal gland

Our body has one pair of adrenal glands, one at the superior part of each kidney. The gland is composed of two types of tissues :

1. Adrenal cortex

2. Adrenal medulla

The adrenal medulla is centrally located, and outside this lies the adrenal cortex.

Right lobe

Left lobe

Septae

Lobule

Dendritic cell

Macrophage

Blood vessel

Thymocytes

Fig. 4.7 Thymus gland

Adrenal Gland

Left Kidney

Medulla

Cortex

Fig. 4.8 Adrenal gland

Adrenal cortex

The adrenal cortex secretes many steroid hormones, commonly called corticoids or corticosteroids. These steroid hormones are produced through the modifications of cholesterol. Some of the cortical hormones are:

Glucocorticoids

• These substances play a role in our body's carbohydrate metabolism, with cortisol being the primary glucocorticoid.

• Glucocorticoids promote processes such as gluconeogenesis, lipolysis, and proteolysis while inhibiting the cellular uptake and utilisation of amino acids.

• Cortisol is additionally engaged in sustaining the cardiovascular system and kidney functions.

• It induces anti-inflammatory responses and hinders the immune response.

• Cortisol also stimulates the production of red blood cells (RBCs).

Mineralocorticoids

• Corticoids that regulate the balance of water and electrolytes in our body are called mineralocorticoids.

• Aldosterone serves as the primary mineralocorticoid in our body, primarily impacting the renal tubules. It promotes the reabsorption of sodium (Na+) and water while facilitating the excretion of potassium (K+) and phosphate ions.

• Consequently, aldosterone plays a crucial role in sustaining electrolyte balance, body fluid volume, osmotic pressure, and blood pressure.

Androgens

• The adrenal cortex also produces minor quantities of androgenic steroids that contribute to the development of axial hair (chest hair), pubic hair, and facial hair during puberty.

Adrenal Medulla

• The adrenal medulla releases two primary hormones: epinephrine, also known as adrenaline, and norepinephrine (NE), commonly referred to as noradrenaline. These hormones are collectively termed catecholamines.

• Adrenaline and noradrenaline are swiftly released in response to any form of stress or emergencies. Hence, they are referred to as emergency hormones or hormones associated with the Fright-Fight-Flight response.

• They enhance alertness, cause pupillary dilation, induce piloerection (raising of hairs), and promote sweating, among other effects.

• Both hormones elevate the heartbeat, strengthen heart contractions, and increase the rate of respiration.

• Catecholamines also stimulate the breakdown of glycogen.

Adrenal gland disorders

Cushing syndrome: Hypersecretion of cortisol by the adrenal cortex causes Cushing's syndrome. This hypersecretion is due to a tumour in the adrenal gland that secretes cortisol or a tumour in the pituitary that secretes adrenocorticotropic hormone (ACTH). The elevated level of cortisol causes hyperglycaemia, osteoporosis, hypertension, and increased susceptibility to infection. People who need long-term glucocorticoid therapy, for instance, to prevent rejection of a transplanted organ may develop a cushioned appearance.

Fig. 4.9 Cushing syndrome

Addison's disease: Undersecretion of glucocorticoids and aldosterone causes Addison's disease. Most cases are autoimmune disorders in which antibodies cause adrenal cortex destruction. It alters carbohydrate metabolism causing acute weakness and fatigue. Loss of aldosterone leads to elevated potassium and decreased sodium in the blood, dehydration, low blood pressure, decreased cardiac output, arrhythmias, and even cardiac arrest.

4.2.8 Pancreas

The pancreas functions as a dual-purpose gland, serving as both an exocrine and endocrine gland. The endocrine portion comprises structures known as 'Islets of Langerhans,' with approximately 1 to 2 million of these islets present in normal human pancreas, constituting only 1 to 2 percent of the pancreatic tissue. The primary cells within the Islets of Langerhans are α-cells (17%) and β-cells (71%). α-cells secrete the hormone glucagon, while β-cells secrete insulin. Delta (δ) cells secrete somatostatin, and F-cells secrete pancreatic polypeptide.

Alpha cell (secretes glucagon)

Beta cell (secretes insulin) Delta cell (secretes somatostatin)

Fig. 4.10 T.S of pancreas

Exocrine pancreas (acinar cells and duct cells)

F cell (secretes pancreatic polypeptide)

Hormones of pancreas

Glucagon: Glucagon, a peptide hormone, plays a vital role in maintaining normal blood glucose levels. It acts on the liver cells, and stimulates the process of glycogenolysis and gluconeogenesis, which results in increased blood sugar. It also hinders cellular glucose uptake and utilisation, making it a hyperglycemic hormone.

Insulin: Insulin, also a peptide hormone, is crucial in regulating glucose homeostasis. It primarily acts on hepatocytes and adipocytes in adipose tissue, enhancing cellular glucose uptake and utilisation. This leads to a swift transfer of glucose from the blood to hepatocytes and adipocytes, resulting in decreased blood glucose levels (hypoglycemia). Insulin also stimulates the conversion of glucose to glycogen (glycogenesis) in target cells. Together, insulin and glucagon maintain glucose homeostasis in the blood.

Pancreatic disorders

Prolonged hyperglycemia can lead to diabetes mellitus, a complex disorder associated with glucose loss through urine and the formation of harmful compounds called ketone bodies. Diabetes mellitus is the most common endocrine disorder. As glucose is not transported into body cells, the utilisation of glucose falls increasingly lower, and the utilisation of fats and proteins increases. Blood glucose levels increase. Loss of glucose in the urine (glucosuria or glycosuria) occurs when the blood glucose concentration rises above 180mg/100ml. Other symptoms of diabetes mellitus are polyuria (excessive urine production due to an inability of the kidneys to reabsorb water), polydipsia (excessive thirst), and polyphagia (excessive eating/hunger). Diabetic patients are successfully treated with insulin therapy.

4.2.9 Gonads

Testis

A pair of testes is situated in the scrotal sac outside the abdomen of males. The testis serves a dual role as being the primary sex organ as well as an endocrine gland. It consists of seminiferous tubules and stromal or interstitial tissue.

Spermatozoa

Secondary spermatocyte

Primary spermatocyte

Spermatogonium

Fig. 4.11 Section of seminiferous tubule

Spermatid

Sertoli

The Leydig cells, or interstitial cells, which are present in the intertubular spaces, produce a group of hormones called androgens. The principal androgen is testosterone hormone. Androgens regulate the development, maturation, and functions of male accessory sex organs, including the epididymis, vas deferens, seminal vesicles, prostate gland, and urethra.

These hormones also stimulate muscular growth, the growth of facial and axillary hair, aggressiveness, and low pitch of voice, and play a major role in spermatogenesis (formation of spermatozoa).

Androgens influence male sexual behaviour (libido) by acting on the central nervous system and producing anabolic effects on protein and carbohydrate metabolism.

Ovary

Females have a pair of ovaries located in the abdomen. The ovary is the primary female sex organ, which produces one ovum (oocyte) during each menstrual cycle.

In addition, the ovary also produces two groups of steroid hormones called estrogen and progesterone

Estrogen: The ovary is composed of ovarian follicles and stromal tissues. The estrogen is synthesised and secreted mainly by the growing ovarian follicles. The principal estrogen is estradiol.

Estrogens produce wide-ranging actions such as stimulation of growth and activities of female secondary sex organs, development of growing ovarian follicles, the appearance of female secondary sex characters (e.g., high pitch of voice, etc.), and mammary gland development. Estrogens also regulate female sexual behaviour.

Progesterone: After ovulation, the ruptured follicle is converted to a structure called corpus luteum, which mainly secretes progesterone. Progesterone supports pregnancy and also acts on the mammary glands and stimulates the formation of alveoli (sac-like structures that store milk) and milk secretion.

Fig. 4.12 Transverse section of ovary showing ovarian follicles

Ovulation

Ovum

Mature Graafian follicle

Corpus luteum

Corpus albicans

Ovarian ligament

Endocrine Gland Hormone Hormonal Function

Posterior Pituitary Lobe

Anterior Pituitary Lobe

Antidiuretic hormone (ADH) Increases water reabsorption by the kidneys

Oxytocin (OT)

Stimulates uterine contractions

Growth hormone (GH) Stimulates cell division and growth

Prolactin (PRL) Initiates milk synthesis

Follicle stimulating hormone (FSH)

Luteinising hormone (LH)

Stimulates gamete production and sex hormone regulation

Stimulates secretion of sex hormones and ovulation

Thyroid stimulating hormone (TSH) Stimulates secretions of the thyroid gland

Adrenocorticotropic hormone (ACTH)

Pineal Gland Melatonin

Thymus Gland Thymosin

Triiodothyronine (T3)

Thyroid Gland

Thyroxine(T4)

Calcitonin

Parathyroid Gland

Parathyroid hormone (PTH)

Cortisol

Aldosterone

Adrenal Cortex

Adrenal Medulla

Epinephrine/Norepinephrine

Stimulates secretions of the adrenal cortex

Involved in the sleep/wake cycles

Stimulates increased production of T-cells

Increases metabolic rate

Increases metabolic rate

Stimulates osteoblast to remove calcium from the blood, lowering blood calcium levels

Stimulates osteoclast to release stored calcium into the blood, raising blood calcium levels

Maintains blood sugar levels between meals

Increases sodium and water reabsorption by the kidneys

Initiates a response similar to the sympathetic nervous system

Pancreas

Ovaries

Glucagon

Insulin

Estrogen

Progesterone

Testes Testosterone

Stimulates an increase in blood sugar levels

Stimulates a decrease in blood sugar levels

Stimulates the development of the female reproductive system

Stimulates the development of the female reproductive system

Stimulates the development of the male reproductive system

Table 4.2 Hormones secreted by endocrine glands and their functions.

4.3 REGULATION OF HORMONE SECRETION

Hormone secretion is regulated by neural mechanisms or by feedback mechanisms.

4.3.1 Neural mechanism

Nerve impulses to the adrenal medullae regulate the release of epinephrine. This is an example of a neural mechanism.

4.3.2 Feedback mechanisms

Feedback mechanisms are more common than neural mechanisms. Feedback can be either positive or negative, with negative feedback being the most common type and positive feedback being rare.

Negative feedback

In endocrine systems, negative feedback means that some feature of hormone action, directly or indirectly, inhibits further secretion of the hormone. For example, an increase in the blood levels of thyroid hormones inhibits the secretion of TRH and TSH.

Positive feedback

In positive feedback mechanisms, some features of hormone action cause more secretion of the hormone. For example, during childbirth, the hormone oxytocin stimulates contractions of the uterus, and uterine contractions, in turn, stimulate more oxytocin release.

QUICK REVIEW

• The endocrine system regulates various bodily functions through hormones.

• Major endocrine glands are the hypothalamus, pituitary, thyroid, adrenal, pancreas, parathyroid, thymus, gonads, and pineal gland

• The pituitary gland comprises three parts: pars distalis, pars intermedia, and pars nervosa

• Hormones from the pituitary regulate growth, peripheral endocrine gland activity, and somatic tissue development.

• The pineal gland produces melatonin, crucial for diurnal rhythms like sleep-wake cycles and body temperature regulation.

• Thyroid hormones control metabolic rate, neural system development, erythropoiesis, and metabolism of nutrients.

• The thyroid gland also regulates blood calcium levels by lowering them.

• Parathyroid hormone (PTH) from the parathyroid glands increases blood calcium levels, maintaining calcium homeostasis

• Thymosin from the thymus gland aids in T-lymphocyte differentiation for cellular immunity and antibody production for humoral immunity.

• Adrenal glands, comprising the medulla and cortex, secrete epinephrine, norepinephrine, glucocorticoids, and mineralocorticoids, regulating alertness, metabolism, and electrolyte balance.

• The endocrine pancreas secretes glucagon and insulin, managing blood glucose levels, with insulin deficiency leading to diabetes mellitus.

• Androgens from the testes regulate male reproductive system development and functions.

• Estrogen and progesterone from ovaries regulate the female reproductive system and pregnancy maintenance.

• Hormonal control often follows negative feedback mechanisms, maintaining internal balance.

WORKSHEET - 1

MULTIPLE CHOICE QUESTIONS WITH SINGLE CORRECT ANSWER

I. Human endocrine system

1. Identify A and B using the given information.

It regulates and coordinates cellular activities. It provides a point-to-point coordination among the organs.

The coordination is slow and long-lasting. It is fast but short-lived.

a. A - Enzyme coordination, B - Hormonal coordination

b. A -Neural coordination, B - Hormonal coordination

c. A - Hormonal coordination, B - Neural coordination

d. A - Hormonal coordination, B - Enzyme coordination

2. Which one of the following statements is correct?

a. Endocrine glands regulate neural activity, but not vice versa

b. Neurons regulate endocrine activity, but not vice versa

c. Endocrine glands regulate neural activity, and nervous system regulates endocrine glands

d. Neither hormones control neural activity, nor the neurons control endocrine activity

3. Which of the following hormones is derived from a single amino acid?

a. Thyroxine

c. Estradiol

b. Oxytocin

d. Epinephrine

4. Enzymes, vitamins, and hormones can be classified into a single category of biological chemicals because all of these

a. Help regulate metabolism

b. Are exclusively synthesised in the body of a living organism as at present

c. Are conjugated proteins

d. Enhance oxidative metabolism

5. 'Tropic hormones' means

a. Pituitary hormones

b. Local hormones

c. Hormones that affect another 'target' endocrine gland

d. Hormones that have receptors on almost all living cells of the body

6. Endocrine signalling is always

a. Electrical

c. Chemical

7. A hormone secreted by non-endocrine tissue is

a. Insulin-like growth factor (IGF)

c. Interferon

b. Mechanical

d. Physicochemical

b. Calcitriol

d. Enterokinase

8. Identify the following biomolecules, A and B based on their properties.

A

B

They are rarely synthesised in the body, mostly supplied through food. They are synthesised in the body itself.

In excess, they are excreted, but in deficiency they cause diseases. Their excess or deficiency may cause health disorders.

a. A - Hormones, B - Vitamins

c. A - Vitamins, B - Hormones

9. Match the following columns.

Column -I

b. A - Enzymes, B - Hormones

d. A - Vitamins, B - Cofactors

A. Protein hormones 1. Epinephrine

Column -II

B. Steroid hormones 2. Testosterone, progesterone

C. Iodothyronine hormones 3. Thyroid

D. Amino acid derivative hormones

a. A-1, B-2, C-3, D-4

c. A-4, B-2, C-3, D-1

4. Insulin and glucagon

b. A-4, B-3, C-2, D-1

d. A-4, B-2, C-1, D-3

II. Hypothalamus and pituitary gland

1. Which hormone of the hypothalamus reaches the target through portal circulation?

a. Somatostatin

c. Vasopressin

b. Oxytocin

d. All the three

2. The hypothalamus contains several groups of neurosecretory cells called:

a. Tract

c. Nuclei

3. The main function of the hypothalamus

a. Act as a biological cycle

b. Pituitary gland

d. Protoplasm

b. To act as an interface between nervous and endocrine systems

c. To form neurohypophysis

d. All the above

4. The pituitary gland is located

a. Above the epithalamus

c. Ventral to trachea

b. Anterior to the pineal body

d. In sella turcica

5. Oxytocin and vasopressin are transported to neurohypophysis through

a. Blood

c. Axons

b. Interstitial fluid

d. Lymph

6. Sertoli cells are regulated by the pituitary hormone known as

a. LH

c. GH

7. Match the following:

Column -I

b. FSH

d. Prolactin

Column -II

A. Hypothalamus 1. Lactation after childbirth

B. Anterior pituitary 2. Reabsorption of water by nephrons

C. ADH 3. FSH and LH

D. Prolactin 4. Gonadotropin-releasing hormone

a. A-2, B-4, C-3, D-1

c. A-4, B-3, C-2, D-1

b. A-1, B-3, C-2, D-4

d. A-2, B-3, C-1, D-4

8. Pigmentation of the skin is maintained by a. FSH b. LH c. MSH

9. Corpus luteum is maintained by

ACTH

a. LH b. GH c. ACTH d. Oxytocin

10. Autoimmune endocrine disorders are

a. Exophthalmos & simple goitre

b. Grave's disease & Addison's disease

c. Addison's disease & Cushing's syndrome

d. Grave’s disease & tetany

11. Which of the following hormones is not involved in sugar metabolism?

a. Aldosterone b. Cortisol c. Insulin d. Glucagon

12. Fright - Fight - Flight reaction causes activation of:

a. The parathyroid gland leads to an increased metabolic rate

b. The kidney, leading to suppression of renin angiotensin aldosterone pathway

c. The adrenal medulla, leads to increased secretion of epinephrine and norepinephrine

d. The pancreas leads to a reduction in blood sugar levels

III. Pineal, thyroid, parathyroid, and thymus glands

1. The function of the pineal body is to:

a. Regulate the calcium level

c. Regulate periods of puberty

2. The diurnal rhythm of our body is maintained by

a. Thyroid gland

c. Pituitary gland

3. Melanocyte-stimulating hormone is secreted by

a. Pars intermedia

c. Pars distalis

4. Basal metabolic rate is influenced by:

a. GH

b. Regulates sleep-wake cycle

d. Regulates growth

b. Pineal gland

d. Hypothalamus

b. Pars nervosa

d. Thymus

b. Glucagon c. Thyroxine d. ADH

5. Select the incorrect option.

a. Thyroid gland is the largest endocrine gland in humans

b. Thyroid secretes T3 and T4

c. Thyroid gland is composed of follicles and stromal tissues

d. Thyroid consists of four lobes

6. Which of the following conditions is not linked to a deficiency of thyroid hormones?

a. Cretinism

c. Myxoedema

7. PTH is

a. Hypercalcemic hormone

c. Endocalcemic hormone

8. Major roles of the thymus gland in humans is/are:

a. Differentiation of T-lymphocytes

c. Promote the production of antibodies

IV. Adrenal gland, pancreas and gonads

1. Adrenaline and noradrenaline do not promote

a. Breakdown of proteins

c. Glycogenesis

2. Main glucocorticoid is

a. Insulin

c. Cortisol

b. Goitre

d. Exophthalmos

b. Hypocalcemic hormone

d. Exocalcemic hormone

b. Differentiation of B-lymphocytes

d. Both (a) and (c)

b. Breakdown of lipids

d. Glycogenolysis

b. Glucagon

d. Aldosterone

3. Which hormone is primarily secreted by the adrenal cortex?

a. Adrenaline

c. Insulin

b. Cortisol

d. Glucagon

4. Which hormone is released by the adrenal medulla during stress situations?

a. Insulin

b. Cortisol

5. Addison's disease results from

a. Hyposecretion of adrenal

c. Hyperactivity of cells of Leydig

c. Adrenaline

d. Aldosterone

b. Hypertrophy of gonads

d. None of these

6. Diabetes mellitus is characterised by

a. Loss of appetite

c. Loss of glucose

7. Insulin is

a. Hypoglycemic hormone

c. Act on adipose tissue and hepatocytes

8. Androgens regulate

a. Development of accessory sex organs

c. Maturation of accessory sex organs

9. Progesterone is a hormone, which is

a. A protein useful for morphogenesis

b. Loss of growth

d. All of these

b. Decreases the blood sugar

d. All of the above

b. Muscular growth

d. All of the above

b. Helpful in relaxing the uterus during parturition

c. An enzyme helpful for growth

d. Responsible for growth and maintenance of decidua

10. The female hormone inhibin is secreted by

a. Zona pellucida

c. Corpus luteum

b. Ovary

d. Uterine epithelium

11. Fill up the blanks A to C with the correct combination of terms. Estrogens produce wideranging actions such as stimulation of growth and activities of _____A_____ secondary sex organs, development of growing _____B_____, the appearance of female secondary sex characters (e.g., the high pitch of voice, etc.), and _____C_____ gland development.

a. A - female, B - ovarian follicles, C - mammary

b. A - male, B - ovarian follicles, C - mammary

c. A - female, B - thyroid follicles, C - mammary

d. A - female, B - ovarian follicles, C - uterine

WORKSHEET - 2

I. MULTIPLE CHOICE QUESTIONS WITH SINGLE CORRECT ANSWER

1. Pick out the correct statement.

a. Hormones are nutrient chemicals that act as intercellular messengers.

b. Invertebrates possess very simple endocrine systems with few hormones.

c. The endocrine system alone coordinates and regulates the physiological functions in the human body.

d. The neural coordination is slow but long-lived.

2. Fill up the blanks A to C with the correct combination of terms. Hormones are ____A____ that act as _____B_____ messengers and are produced in _____C_____ amounts.

a. A - nutrient, B - intercellular, C - trace

b. A - non-nutrient, B - intracellular, C - trace

c. A - non-nutrient, B - intercellular, C - trace

d. A - non-nutrient, B - intercellular, C - large

3. Select the correct answer related to A and B based on their reactions.

They are consumed in the reaction. They act as catalysts and remain unchanged. They are effective only in low concentrations. They are more effective in relatively high concentrations.

The actions controlled by them are not reversible. The actions controlled by them are reversible.

a. A - Hormones, B - Vitamins

c. A - Vitamins, B - Hormones

4. Chemically hormones are

a. Biogenic amines only

c. Proteins only

5. Hormones are secreted by

a. Most metazoans

c. Invertebrates only

b. A - Enzymes, B - Hormones

d. A -Vitamins, B - Vitamins

b. Proteins, steroids, and biogenic amines

d. Steroids only

b. Vertebrates only

d. All living organisms

6. Select the incorrect statements.

a. Invertebrates possess a very simple endocrine system.

b. Vertebrates possess a large number of chemicals that act as hormones.

c. Arthropods are the first invertebrates with a well-organised endocrine system.

d. We get some hormones through food.

7. Largest endocrine gland in humans

a. Liver b. Thyroid c. Thymus d. Pituitary

8. Number of endocrine glands related to the brain:

a. One

b. Three

c. Two d. Five

9. Which of the following hormones is a derivative of amino acid?

a. Prostaglandin b. Progesterone c. Epinephrine d. Estrogen

10. Father of Endocrinology

a. Huxley

b. Thomas Addison

c. Abel d. Kimball and Murlin

11. A large number of hormones are secreted by

a. Pituitary

b. Thyroid

c. Hypothalamus d. Adrenal

12. The majority of endocrine secretions are released into

a. Arteries

b. Gut

c. Veins

d. All the above

13. Asha is about to face an interview. However, during the first five minutes before the interview, she experiences sweating, increased heart rate, respiration, etc. Which hormone is responsible for her restlessness?

a. Adrenaline and noradrenaline

b. Oxytocin and vasopressin

c. Estrogen and progesterone d. Insulin and glucagon

14. Which of the following hormones is not synthesised by the anterior pituitary?

a. Growth hormone

c. Oxytocin

b. Follicle stimulating hormone

d. Adrenocorticotrophic hormone

15. Mark the correct sequence of synthesis of hormones in human beings.

a. GnRH → FSH → Testosterone

c. GnRH → LH → Testosterone

b. GnRH → Progesterone → LH

d. TRH → TSH → Thyroxin

16. Which type of hormones control the menstrual cycle in human beings?

a. FSH b. LH c. FSH and LH d. Progesterone

17. Which set is similar?

a. Corpus luteum - Graafian follicles

c. Bundle of his - pacemaker

b. Sebum - sweat

d. Vitamin B7 - Niacin

18. In a pregnant woman having prolonged labour pains, if childbirth has to be hastened, i.e., to aid parturition, it is advisable to administer a hormone that can

a. Activate smooth muscles

c. Release glucose into the blood

19. Corpus luteum is maintained by

a. Luteinising hormone & lactogenic hormone

c. ICSH & progesterone

20. Pigmentation of the skin is influenced by

a. GH

b. ADH

b. Increase metabolic rate

d. Stimulate ovary

b. Luteotropic hormone & FSH

d. Gonadotropins & HCG

c. MSH d. Thyroxine

21. Sleep-wake cycle and menstrual cycle are influenced by

a. Thyroxine

b. Calcitonin c. FSH

d. Melatonin

22. A hormone responsible for normal sleep-wake cycle is [NCERT Exemplar]

a. Epinephrine

b. Gastrin

c. Melatonin d. Insulin

23. Cretinism, mental retardation, low intelligence quotient, abnormal skin, deaf-mutism, etc., are the results of

a. Hyperthyroidism

c. Hypothyroidism

24. Hypothyroidism during pregnancy leads to

a. Cretinism

b. Low IQ

25. Iodine is essential for the synthesis of

a. Thymosin

b. Goitre

d. Both (b) and (c)

c. Deaf-mutism d. All of these

b. Parathormone c. Thyroxine d. Adrenalin

26. Which of the following hormones correctly matched with its deficiency disease?

a. Relaxin - cretinism

c. Insulin - diabetes insipidus

b. Parathormone - tetany

d. Prolactin - astigmatism

27. Which of the following regulates the blood calcium and phosphate levels?

a. Glucagon

c. Parathyroid hormone

b. Growth hormone

d. Thyroxine

28. Hormone which promotes the production of antibodies is

a. Thymosin b. Thyroxine c. Parathormone d. Melatonin

29. Corticoids are the hormones which are secreted by

a. Renal cortex

c. Adrenal medulla

30. Glucocorticoids are the corticoids which

b. Adrenal cortex

d. Hypothalamus

a. Are involved in protein metabolism b. Are involved in fat metabolism

c. Are involved in glucose metabolism d. All of the above

31. Addison's disease is characterised by

a. Hypersecretion of PTH and aldosterone

b. Hyposecretion of cortisol and aldosterone

c. Hypersecretion of PTH and hypersecretion of cortisol

d. Hypersecretion of cortisol and PTH

32. Leydig cells secrete:

a. Insulin b. Inhibin c. Testosterone d. Fertilisin

33. Not a function related to androgen influence is

a. Libido

c. Spermatogenesis

b. Catabolism of proteins

d. Anabolism of proteins

34. Select the correct statement. [NEET-2020]

a. Glucagon is associated with hypoglycemia.

b. Insulin acts on pancreatic cells and adipocytes.

c. Insulin is associated with hyperglycemia.

d. Glucocorticoids stimulate gluconeogenesis.

35. Artificial light, extended work time and reduced sleep time disrupt the activity of [NEET-2019]

a. Thymus gland

c. Adrenal gland

b. Pineal gland

d. Posterior pituitary gland

CONTROL AND COORDINATION IN PLANTS

5.1 PLANT HORMONES

Hormones play an important role in the growth and differentiation of plants in addition to nutritional and genetic factors. The existence of hormones (chemical messengers) was suggested by Sachs. The term hormone was coined by Starling.

5.1.1 Introduction to plant hormones

Growth hormones (phytohormones) are defined as organic substances that are synthesised in minute quantities in one part of the plant body and are transported to another part. These hormones influence specific physiological processes. A group of plant hormones, including auxins, gibberellins, cytokinins, ethylene and abscisic acid regulate plant growth. Some hormones are growth promoters like auxins, gibberellins and cytokinins which can promote cell division, cell enlargement, pattern formation, tropic growth, flowering, fruiting, and seed formation, or growth inhibitors like abscisic acid, which can play an important role in plant responses to wounds and stresses of biotic and abiotic origin. These are also involved in various growth-inhibiting activities such as dormancy and abscission.

Ethylene is a gaseous hormone that helps in fruit ripening. Ethylene could fit either the growth promoters or inhibitors group, but it is largely an inhibitor of growth activities. The dual role of ethylene as both a growth promoter and inhibitor is due to its concentration-dependent effects and its involvement in different physiological processes at various stages of plant development.

Plant Hormone (Phytohormones)

Fig. 5.1 Plant hormones

5.1.2

Auxins

Auxins are the first discovered plant hormones. They promote the growth of plant organs. Indole3-acetic acid (IAA), also known as 3-IAA, is the predominant naturally occurring plant hormone belonging to the auxin class. Auxin was first isolated from human urine. Auxins are mostly synthesised in the shoot apex and also in the root apex.

There are two major categories of auxins, namely natural auxins and synthetic auxins

Functions of auxin

• Auxins promote the elongation of cells in the stem and coleoptile and longitudinal growth.

• Auxin is responsible for the initiation and promotion of cell division in cambium.

• Auxin helps in the initiation and promotion of cell division in tissue culture experiments and the formation of callus.

• Auxins promote root growth only at extremely low concentrations. At higher concentrations, they always inhibit root growth.

• Auxins induce apical dominance.

• Auxin is well known to induce parthenocarpy in several plants. External application of auxin on flowers causes the development of seedless fruits in orchids and tomatoes.

• The synthetic auxins such as 2, 4-D (2, 4-Dichlorophenoxy acetic acid), 2, 4, 5-T (2, 4, 5-trichlorophenoxyacetic acid) are used as selective herbicides.

• Auxins induce flowering in pineapples.

• They help to prevent premature leaf and fruit fall but promote the abscission of elder mature leaves and fruits.

5.1.3 Gibberellins

The gibberellins are plant growth hormones which enhance the longitudinal growth of stems when applied to intact plants. However, the gibberellins do not enhance the growth of isolated plant parts. The presence of meristematic cells is necessary for the elongation growth caused by gibberellins.

Acetyl-CoA is the precursor for gibberellins. Gibberellins have been reported to occur in various plant organs, such as roots, stems, leaves, buds, flower buds, root nodules, fruits, immature seeds and callus tissues of higher plants.

Functions of gibberellin

• Gibberellins help in the cell growth of stem, leaves and other aerial parts. Therefore, they increase the size of the stem, leaves, flowers and fruits. However, they do not show any such effect in the case of roots

• Gibberellins help in the removal of dwarfism in many genetically dwarf plants like peas and maize. The external supply of gibberellin to such plants causes rapid elongation.

Fig. 5.2 Effects of exogenous application of GA in shoot elongation of pea plant

• Certain plants like cabbage, beet, and cauliflower show a form of growth called rosette. It has been observed that such plants exhibit excessive internodal growth just before reproduction. Stimulation in the internodal growth just before reproduction is called bolting. If these plants are treated with gibberellins during conditions of rosette growth, the plants bolt and flower. Gibberellins also induce flowering in plants by substituting the cold treatment.

• Gibberellins overcome the natural dormancy of buds, tubers, seeds, etc. and allow them to grow.

• Formation of seedless fruits without fertilisation can also be induced by gibberellin treatment in many plants (e.g., tomatoes, apples, cucumbers, etc.).

• Some other effects of gibberellins are promoting flowering in long-day plants even under noninductive periods.

• Gibberellin treatment results in the elongation of the peduncle, thereby increasing the length of grapes stalks.

• They help in the stimulation of pollen germination and the growth of pollen tubes in some species.

• Gibberellin is used to speed up the malting process in the brewing industry. It elongates and improves the shape of fruits like apples. It also delays senescence.

5.1.4 Cytokinins

Miller and Letham isolated a naturally occurring cytokinin called zeatin from immature maize seeds. Since the discovery of zeatin, several naturally occurring cytokinins, and some synthetic compounds with cell division-promoting activity have been identified.

Natural cytokinin is an adenine derivative and is chemically isopentenyl adenine.

Dwarf plant Treated with GA

Cytokinins are mostly synthesised in the regions where rapid cell division occurs. For example, root apices, developing shoot buds, young fruits, etc.

Functions of cytokinins

• Induction of cell division is considered a major function of cytokinins in plants.

• Like auxin and gibberellins, cytokinins also cause cell elongation.

• Both auxin and cytokinins are essential for morphogenesis or differentiation of tissues or organs.

• The ageing process in plants is known as 'senescence'. Senescence in leaves is manifested by yellowing. Senescence is followed by the death of an organ or whole plant. Cytokinins delay the process of senescence by promoting nutrient mobilisation. The ability of cytokinins to delay the process of senescence is known as the Richmond-Lang effect.

• Cytokinins increase the potassium ion concentration guard cells and help in the opening of stomata.

• Cytokinins help to produce new leaves, chloroplasts in leaves, lateral shoot growth, adventitious shoot formation and to overcome apical dominance.

5.1.5

Abscisic acid (ABA)

Abscisic acid is an important growth-inhibiting hormone in plants. It is synthesised anabolically from acetyl Co-A units or catabolically from carotenoids. It has been detected in all major organs from root cap to apical buds.

Fig. 5.3 Isopentenyl adenine

Fig. 5.4 Structure of abscisic acid

Functions of abscisic acid

• The inability of the seeds to germinate or buds to grow (resting stage) is called dormancy. Abscisic acid induces dormancy of buds and seed dormancy.

• ABA promotes the abscission of flowers and fruits.

• When plants are subjected to water stress, abscisic acid synthesis in plants increases. The abscisic acid thus formed induces the closure of stomata and reduces the transpirational loss of water. Hence, it is called 'stress hormone'.

• In several plants, abscisic acid induces senescence or leaf ageing.

• ABA is also an important antitranspirant.

5.1.6 Ethylene

The distinctive features of ethylene, when compared to other hormones, are its simple structure and its gaseous nature. Ethylene is produced in almost all parts of the plants. It is synthesised from the amino acid methionine.

Functions of ethylene

• Ethylene accelerates the ripening of several fruits, e.g. apple, banana, and tomato. Due to this, ethylene is regarded as a fruit-ripening hormone.

• It enhances the respiration rate during the ripening of fruits, which is also known as climacteric fruit ripening.

• Ethylene causes triple response growth of pea seedlings. Inhibition of stem elongation, stimulation of lateral growth and induction of transverse geotropism is known as triple response growth.

• In several plants, ethylene suppresses or delays flowering.

• It inhibits longitudinal growth but stimulates transverse or horizontal growth.

• It induces flowering in mango and pineapple.

• Ethylene breaks seed and bud dormancy, initiates germination in peanut seeds, and sprouts of potato tubers.

• Ethylene promotes rapid internode/petiole elongation in deep-water rice plants.

• It promotes senescence and abscission of plant organs, especially leaves and flowers.

Hormone Auxin Gibberellins Cytokinins

Introduction

Substance that promotes elongation of coleoptile tissue.

Natural

Synthetic

Indole acetic acid (IAA), indole-3-acetonitrile (IAN), phenyl acetic acid

Indole-3-butyric acid (IBA), 2-napthoxyacetic acid, α-naphthyl acetic acid (NAA), 1-napthyl acetamide (NAD), 24-D, 245-T

Class of endogenous plant regulators. Discovered from Gibberella fujikuroi (fungus)

Gibberellin A (gibberellic acid)

Not yet synthesised

These are either natural or synthetic compounds with growth regulatory activity.

Zeatin, N6 dimethyl amino purine

Kinetin, adenine, diphenyl urea

Abscisic Acid

Simple organic molecule presents in the form of volatile gas and shows profound physiological effects. It is an accelerating substance for retaining or shredding of different organs.

Ethylene, ethephon, glyoxime

Ethylene, ethephon, glyoxime

Abscisin I and abscisin II

Function

Internode elongation, leaf growth, initiation of vascular tissues, cambial activity, fruit growth, apical dominance, inhibition of root growth and lateral buds, IBA induce rooting in cutting.

Rapid expansion of plant cells, stimulation of seed germination, breaking dormancy, increase stem elongation and size of leaves and induction of panthenocarpic fruit leading to seedless fruit sets.

Promote cell division, play a role in nucleic acid metabolism and protein synthesis. Promote lateral bud development and inhibition of senescence.

Ripening, leaf abscission, stem swelling, leaf bending, flower petal discolouration, and inhibition of stem and root growth. Breaking dormancy.

Table 5.1 Plant hormones, their derivatives and functions

Maleic hydrazide, daminozide, glyphosine, chlormequat chloride, morphactins

Helps in seed dormancy, enhanced in stress condition. Potential antitranspirant, inhibit GA actions. Inhibition of auxin.

5.2 PHOTOPERIODISM AND VERNALISATION

5.2.1

Photoperiodism

Photoperiodism is the response to the duration and timings of light and dark periods in terms of flowering. It was first studied by W. Garner and H.A. Allard in Maryland Mammoth (mutant variety of tobacco).

The hours of light that a plant has been exposed to is called a photoperiod. Depending on the length of photoperiod requirement for flowering, the plants are classified into short-day plants, long-day plants, day-neutral plants.

1. Short-day plants (SDP) or long-night plants: These are the plants where flowering takes place when they are exposed to shorter photoperiod, i.e., day length is less than the critical length, e.g. Maryland Mammoth tobacco (Nicotiana tabacum), Xanthium, Chrysanthemum, rice, sugarcane, potato, soybean (Glycine max), Aster, Dahlia, etc.

2. Long-day plants (LDP) or short-night plants: These are the plants where flowering takes place when they are exposed to a longer photoperiod, i.e., more than critical length, e.g. spring barley, sugar beet, henbane (Hyoscyamus niger), wheat, radish, oat, spinach, lettuce, etc.

3. Day-neutral plants: In these plants, flowering is unaffected by day length conditions, e.g. cucumber and maize. It is now also known that not only the duration of the light period but also the duration of the dark period is also of equal importance. Hence, flowering in certain plants depends on a combination of light and dark exposures and their relative durations. This response of plants to periods of day/night is termed photoperiodism.

5.2.2 Vernalisation

Vernalisation is a process in plants where exposure to a prolonged period of cold temperature induces or accelerates the transition from vegetative growth to flowering. Some important food plants such as wheat, barley, rye have two kinds of varieties: winter and spring varieties. The

Fig. 5.5 Flowering due to photoperiodism in plants

'spring' variety is normally planted in the spring and comes to flower and produce grain before the end of the growing season. Winter varieties, however, if planted in spring, would normally fail to flower or produce mature grain within a span of a flowering season. Hence, they are planted in autumn. They germinate, and over winter come out as small seedlings, resume growth in the spring, and are harvested usually around mid-summer. In vernalisation, by cold treatment, winter varieties are transferred into spring or summer varieties. The stimulus for vernalisation is perceived by buds, meristems, seeds, seedlings and even embryos.

Biennial plants exhibit vernalisation. These are monocarpic plants that normally flower and die in the second season. Sugarbeets, cabbages, carrots are some of the common biennials.

It is believed that the perception of the cold stimulus results in the formation of a floral hormone called vernalin, which is transmitted to other parts of the plant and is responsible for floral induction.

5.3 RESPONSE TO STIMULI IN PLANTS

Plants, like animals, need internal coordination to proceed with their growth and development in an orderly manner. In plants, control and coordination are not as highly developed as in animals. Plants cannot think, analyse, or memorise as human beings because they lack the brain and other parts of the nervous system. However, plants respond to external stimuli like light, touch, gravitational force and other stimuli through plant movements.

5.4 PLANT MOVEMENTS

Plant movement refers to the movement of the organs of the plants in response to external or internal stimuli. Plants exhibit various types of movements as part of their adaptive responses to environmental stimuli. In general, plants exhibit two distinct kinds of induced movements:

(i) Non-growth-dependent movements, or nastic motions

(ii) Growth-related motions (also known as tropical movements or tropism)

In tropisms, the direction of stimulation dictates the direction in which the plant component moves. In nastic movements, the direction of movement is not determined by the direction of the stimulus. Both these types of movement are affected by the action of plant hormones (phytohormones).

5.4.1

Tropic movements

Tropic movements, also known as tropisms, describe the growth response of a plant part to an external stimulus. In tropism, the direction of the stimulus dictates the direction of the plant's response. These are characterised by their slow pace. The plant part can exhibit either a positive

tropism, where it moves toward the stimulus, or a negative tropism, where it moves away from the stimulus. Plants respond to common environmental stimuli such as light, gravity, chemical substances, and water. These responses are categorised as follows:

Phototropism

Phototropism is the movement of a plant part in reaction to light. Shoots typically grow towards light, exhibiting positive phototropism. In contrast, roots grow away from light, showing negative phototropism. Auxins play a vital role in phototropism as they are synthesised at the tip of the shoot. When stimulated by light, the auxin hormone in the plant cells moves to the side of the shoot that is away from the light. Thus, the shady part of the shoot grows longer and the shoot of the plant bends towards the light.

Geotropism

Geotropism involves the upward and downward growth of shoots and roots, responding to the pull of gravity. Positive geotropism occurs when the plant part moves in the direction of gravity. Negative geotropism happens when the plant part moves against the direction of gravity. Shoots usually display negative geotropism, while roots typically exhibit positive geotropism.

Auxin spreads equally down both sides of the plant

Auxin collects on the shady side

Fig. 5.6 Phototropism

geotropism

geotropism

Fig. 5.7 Geotropism

Chemotropism

This is the plant's ability to move a portion of itself in response to a chemical stimulation. Positive chemotropism refers to plant parts that move or grow in the direction of the chemical, whereas negative chemotropism refers to plant parts that move or grow away from the chemical. Positive chemotropism is demonstrated, for instance, by the pollen tube's development in the direction of a chemical released by an ovule during the fertilisation process in a flower.

Hydrotropism

Hydrotropism is a type of tropic movement in which some parts of the plant like stem or roots grow towards or away from water. The bending of the roots of the plant towards the water shows positive hydrotropism.

Thigmotropism

Thigmotropism, also known as haptotropism, refers to movements in plants that result from contact with an external object. In twinners and woody vines, growth is reduced on the side where contact occurs, while there is increased growth on the side opposite the contact. Thigmotropic movements are evident in various plant structures, such as the tendrils of Cucurbitaceae, the petiole of Clematis, and the leaf apex of Gloriosa.

5.4.2 Nastic movements

Nastic movement in plants refers to the response of a plant part to an external stimulus, such as light, temperature, or contact, where the direction of the response is not influenced by the direction of the stimulus. Unlike tropic movements, nastic movements affect all parts of the plant organ uniformly, regardless of the direction of the applied stimulus. These rapid responses are immediate but don't involve growth. Various types of nastic movements include:

1. Seismonastic movements

2. Nyctinastic movements

Evenly moist soil

Water source

Dry soil

Fig. 5.8 Hydrotropism

Seismonastic movements

Seismonastic movements are triggered by touch or shock. These are rapid responses observed in the leaves of the 'touch-me-not' plant (Mimosa pudica), also known as 'Chhui-mui.' The compound leaves of this plant consist of four pinnae, each bearing numerous pinnules, with pulvini located at the base of the petiole, sub-petiole, and tertiary petioles. Pulvini are swollen regions comprising parenchymatous cells with thick-walled upper halves and thin-walled lower halves, separated by intercellular spaces and traversed by vascular strands.

Upon touch stimulus, the signal travels to the leaf base, causing a loss of turgor in the lower half of the pulvinus, resulting in leaf drooping. After a while, the cells in the lower half regain turgidity, allowing the leaf to return to its upright position. This touch-induced phenomenon is commonly referred to as thigmonasty.

Nyctinastic movements

Movements observed in the daily variation, responding to changes between day and night, in the positioning of flowers and leaves in numerous plants are referred to as nyctinastic or sleep movements. Depending upon stimulus, nyctinastic movements are of the following types:

i. Photonastic movements

Photonastic movements are plant responses to light stimuli where the direction of movement is not determined by the direction of the light source. An example of photonastic movement is observed in the flowers of the dayflower plant (Commelina communis). The petals of these flowers open in response to light, irrespective of the light source's direction. This adaptation enhances the flower's chances of attracting pollinators.

ii. Thermonastic movements

Thermonastic movements are responses in plants triggered by temperature changes. For instance, the petals of certain flowers, such as tulip (Tulipa), undergo thermonastic movements. These petals open or close based on temperature variations, influencing the flower's exposure to sunlight and affecting pollination. This adaptive behaviour allows the plant to optimise its reproductive processes in response to temperature fluctuations.

Fig. 5.9 Nastic movements in Mimosa pudica plant

Touch

Stimulus

Before touch

After touch

QUICK REVIEW

• Hormones are chemical messengers regulating growth and responses.

• Major classes of plant hormones are auxins, gibberellins, cytokinins, abscisic acid, and ethylene.

• Auxins promote cell elongation and apical dominance.

• Gibberellins stimulate stem elongation and cell division. It also induces seed germination.

• Cytokinins promote cell division and delay senescence.

• Abscisic acid induces dormancy and stress responses.

• Ethylene stimulates fruit ripening and promotes senescence.

• Plant movement refers to the movement of the organs of the plants in response to external or internal stimuli. Plants exhibit various types of movements as part of their adaptive responses to environmental stimuli.

• Phototropism is the growth response towards or away from light.

• Geotropism is the growth response towards or away from gravity.

• Chemotropism is the growth towards or away from a chemical stimulus.

• Hydrotropism is the growth response to water.

• Thigmotropism is the growth response to touch or physical contact.

• Nastic movements are rapid, reversible responses to stimuli, not dependent on the direction of the stimulus.

WORKSHEET - 1

MULTIPLE CHOICE QUESTIONS WITH SINGLE CORRECT ANSWER

I. Plant hormones

1. Bolting is associated with the physiological function of a. ABA b. Cytokinins c. IAA d. Gibberellic acid

2. 'Richmond-Lang effect' is related to a. Auxins b. Gibberellins c. Cytokinins d. ABA

3. Phytohormone which inhibits flowering in several plants but stimulates flowering in pineapple plants is

a. 2-4 D

b. IBA

c. GA3

d. Ethylene

4. Part of the plant body where Abscisic acid is not synthesised but Cytokinins are synthesised is

a. Leaves

b. Roots

c. Flowers d. Seeds

5. Which of the following phytohormones have similar effect on leaf senescence?

a. ABA and ethylene

c. GA and ABA

6. Cytokinins:

a. Promote abscission

c. Inhibit protoplasmic streaming

7. The first natural cytokinin of plants is

a. Zeatin

c. Dihydrooxyzeatin

8. Bakanae disease is caused by

a. Fungus

b. Alga

9. Gibberellins were first extracted from

a. Coleoptile tip

c. Fungus

10. Growth promoter hormones are

a. IAA, ABA and CK

c. IAA, GA and CK

11. Cytokinins are mostly produced in

a. Shoot apex

c. Young leaves

12. Cytokinins

a. Induce cell division and inhibit ageing

c. Induce abcission

b. ABA and zeatin

d. Ethylene and 2-4 D

b. Influence water movement

d. Help retain chlorophyll

b. Kinetin

d. Riboxylzeatin

c. Bacterium d. Virus

b. Root tip

d. Bacterium

b. IAA, GA and ABA

d. ABA, CK and GA

b. Root apex

d. Lateral buds

b. Maintain dormancy

d. Inhibit cell division

13. In germinating cereals, amylase synthesis is stimulated by

a. Cytokinins b. Abscisic acid c. Gibberellins d. Auxin

14. Cytokinins are generally

a. Acids b. Aminopurines c. Phenols d. Glucoside

15. Genetic dwarfness can be controlled by treating plants with

a. Cytokinins

b. Gibberellic acid

c. Auxin d. Antigibberellin

16. The hormone that breaks the dormancy of potato tuber is

a. IAA b. ABA c. Zeatin d. Gibberellin

17. The hormones which are found to be more effective in inducing parthenocarpy are

a. ABA

c. Ethylene

b. Gibberellin

d. Ethephon

18. A green plant bends towards the source of light when exposed to the light on only one side. Which of the following is the best explanation of this phenomenon?

a. The apices of the stems are attached by light.

b. The plant needs light for photosynthesis.

c. Auxin accumulates on the shaped side to induce great cell elongation on that side.

d. Light reduces length.

19. Gibberellins take part in

a. Bolting of rosette plants

c. Inducing genetic dwarfism

20. Which one is the test for gibberellin?

a. Bolting in cabbage

c. Rapid divisions in carrot cells

21. Which of the following is a cytokinin?

b. Replacing long-day requirement

d. Does not show bending movement

b. Morphogenesis in carrot cells

d. Elongation of oat coleoptile

a. Phytochrome b. Leucine c. Ethylene d. Zeatin

22. The compounds having a highly specific hydrophilic group or adenine and one non specific lipophilic group are named as

a. Auxins b. Cytokinins c. Gibberellins d. Ethylene

23. Cut or excised leaves remain green for long if induced to root or dipped in

a. Gibberellins b. Cytokinins c. Auxins d. Ethylene

24. The part of the plant body where cytokinins are synthesised is

a. Mature leaves

b. Flowers

c. Stems d. Root tips

25. To increase sugar production in sugarcanes, they are sprayed with

a. Gibberellin

b. Cytokinin

c. IAA d. Ethylene

26. Which of the following regulates most of the physiological processes and is one of the most widely used PGRS in agriculture?

a. Auxin

b. Ethylene c. ABA d. Cytokinin

27. How does ethephon increase the yield of cucumber?

a. Promotes senescence

c. Promotes male flowers

b. Promotes female flowers

d. Both (a) and (b)

28. ABA stimulates the _________ of stomata in the epidermis and _________ the tolerance of plants to various kinds of stresses:

a. Closure; decreases

c. Closure; increases

b. Opening; increases

d. Opening; decreases

29. Which one of the following statements concerning growth regulators is incorrect?

a. Gibberellins cause the formation of more male flowers in Cannabis.

b. Abscisic acid maintains seeds in a dormant state.

c. Cytokinins increase the K+ concentration in guard cells.

d. Some synthetic auxins control grass weeds in pulse crops.

II. Photoperiodism and vernalisation

1. Pick up the correct pair from the folllowing.

a. Xanthium - Long-day plant

b. Sunflower - short-day plant

c. Wheat - Short-day plant d. Tomato - Day-neutral plant

2. Flowering dependent on low-temperature exposure is

a. Vernalisation b. Thermotropy c. Cryoscopy d. Cryostat

3. The term 'vernalisation' was coined by

a. Garner and Allard

b. Darwin

c. Geoffery d. Lysenko

4. Which among the following is a day neutral plant (DNP)?

a. Cestrum b. Cucumber c. Potato d. Radish

5. The low temperature required for vernalisation is usually between

6. Vernalisation can often be replaced by

a. Auxin b. Cytokinin c. Gibberellins d. Ethylene

7. The stimulus responsible for vernalisation is

a. Phytochrome b. Vernalin c. Florigen d. None of these

8. Phytochrome is

a. Light receptor

b. Dark receptor

c. Photosynthetic pigment d. A light sensitive hormone

9. Phytochrome is involved in picking stimulus in

a. Phototropism

c. Photoperiodism

b. Photorespiration

d. Photosynthesis

10. For the production of flowering

a. Only a short exposure to appropriate photoperiod is required.

b. Exposure to appropriate photoperiod at any short intervals is required.

c. Short exposure to appropriate photoperiod at intervals of one hour is required.

d. Continuous exposure to appropriate photoperiods is required for flowering

11. The term photoperiodic after-effect means

a. Providing the plant with appropriate photoperiods after the blossoming.

b. Providing the plant with long exposures of appropriate photoperiods for flowering.

c. The effect of photoperiods after the flowering has occurred.

d. The production of flowers after a short exposure to appropriate photoperiods.

12. Long-day plants flower specially when the

a. Light period is lesser than some critical period.

b. Dark period is less than some critical length.

c. Light period is greater than some critical period.

d. Dark period is more than some critical length.

III. Tropic movements

1. The growth of the pollen tube towards the ovules is due to:

a. Phototropism

c. Geotropism

b. Chemotropism

d. Hydrotropism

2. The diurnal turgor changes in the leaves of Oxalis result in

a. Folding up at night

c. Folding up during the night and opening during the day

b. Folding up only during the day

d. Do not fold either at night or during the day

3. A vine growing up the wall producing creepers towards a light source outside your classroom is/are an example of a response to

a. Positive phototropism

b. Positive thigmotropism

c. Nastic movement

4. Some flowers open in the evening because of

a. Photonasty

c. Phototaxis

WORKSHEET - 2

d. Negative gravitropism

b. Phototropism

d. Nyctinasty

MULTIPLE CHOICE QUESTIONS WITH SINGLE CORRECT ANSWER

1. The hormones which regulate phloem transport are

a. Auxins

c. Gibberellins

b. Cytokinins

d. Ethylene

2. Which among the following is required for plant tissue culture?

a. Trypsin

c. Caffeine

3. Cytokinin synthesis is maximum in

a. Roots

c. Shoot tip

b. Kinetin

d. Coumarin

b. Leaves

d. Fruit

4. The plant substances which become inhibitory on accumulation are

a. Abscisic acid

c. Auxins

b. Phenolic inhibitors

d. Cytokinins

5. Which of the following is a natural growth regulator?

a. NAA

c. 2, 4-D

6. Closure of stomata is brought about by

a. Abscisic acid

c. Gibberellin

b. Ethylene

d. Benzaldehyde

b. Kinetin

d. IBA

7. Sprouting of potato can be prevented in storage by

a. Maleic hydrazide

c. Indole-acetic acid

b. Gibberellins

d. Cytokinins

8. The hormone capable of replacing the requirement of long photoperiods for flowering is

a. Ethylene

c. Gibberellin

9. Gibberellic acid induces flowering in

a. Some plants only

b. In long-day plants under short-day conditions

c. In short-day plants under long-day conditions

d. Day-neutral plants

10. Maximum concentration of cytokinins occurs in

a. Growing embryos and fruits

c. Lateral buds and fruits

b. Auxin

d. Cytokinin

b. Apical buds

d. Root tips

11. Morphogenesis is controlled by an interaction between

a. Auxins and gibberellins

c. Gibberellins and cytokinins

12. Which is not a physiological effect of auxins?

a. Cell elongation

b. Development of parthenocarpic fruits

c. Prevention of abscission of leaves and fruits

d. Reversal of genetic dwarfism

b. Auxins and cytokinins

d. None of the above

13. Consider the following statements regarding gibberellins. Which of the following are correct?

i. They cause fruits like apples to elongate and improve their shape.

ii. They promote bolting in beet and cabbages.

iii. They promote nutrient mobilisation.

iv. They are used to synchronise fruit-set in pineapples.

a. i, ii, iii and iv b. i, ii and iii

c. i and ii

d. ii, iii and iv

14. Cytokinins are said to be anti-ageing hormones because they delay senescence by

a. Controlling mobilisation of resources

c. Decreased morphogenesis and high respiration

b. Controlling protein synthesis

d. Both (a) and (b)

15. Name the gaseous hormone which stimulates transverse or isodiametric growth.

a. Ethylene

c. Sodium salt of NAA

16. The gaseous fruit ripening phytohormone is

a. Ethylene

17. Ethylene is a byproduct of

a. Developing seeds

c. Developing ovules

18. Abscisic acid promotes

a. Cell division

b. Kinetin

b. ABA

d. Ethephon

c. GA d. ABA

c. Leaf fall senescence and dormancy

b. Ripening in some fruits

d. Germinating seeds

b. Shoot elongation

d. Cell elongation and wall formation

19. Differentiation of callus requires a specific ratio of two hormones

a. Auxin and gibberellin

c. Gibberellin and abscisic acid

20. In autumn, leaf fall occurs because

a. Formation of abscission layer at the base of leaves

c. Leaf does not remain green

21. Consider the following statements about ethylene.

b. Auxin and abscisic acid

d. IAA and cytokinin

b. Leaf becomes heavy

d. Of low temperature

A. It breaks seed and bud dormancy, initiates germination in peanut seeds and sprouting of potato tubers.

B. Ethylene promotes rapid internode/petiole elongation in deep water rice plants.

C. Spraying juvenile conifers with ethylene hastens the maturity period, thus leading to early seed production.

D. It helps leaves/upper parts of the shoot to remain above water.

E. Ethylene controls xylem differentiation and helps in cell division.

F. Ethylene also promotes root growth and root hair formation, thus helping the plants to increase their absorption surface.

How many of the above statements are correct?

a. Two b. Three

22. Which is not true for abscisic acid?

a. Acts as antitranspirant

c. Increases stress tolerance in plants

23. Which is not affected by light?

a. Photosynthesis

c. Fertilisation

24. Short-day plants flower in

a. Spring

c. Autumn

c. Four d. Five

b. Synthesised in chloroplasts

d. Induces epinasty of leaves and flowers

b. Flowering

d. Transpiration

b. Summer

d. Both (a) and (b)

25. The effect of day length duration on plant development is

a. Chemotropism

c. Photoperiodism

26. Long-day plants blossom in

a. Rainy

c. Spring

27. Photoperiodism is probably due to the synthesis of

a. Cytokinins

c. Auxin

28. In short-day plants, flowering is induced by

a. Photoperiod less than 12 hours

c. Long night

b. Phototropism

d. Photonasty

b. Autumn

d. Both (b) and (c)

b. Gibberellins

d. Florigen

b. Photoperiod below a critical length and uninterrupted long night

d. Long-day

29. Which of the given events does not happen during seed germination?

a. Emergence of radical

c. Hydrolysis of stored polysaccharides and proteins

30. In short-day plants (SDP), flowering is induced by

a. Long night

b. Increase in rate of respiration

d. Photosynthesis by cotyledons

b. Photoperiod less than 12 hours

c. Photoperiod shorter than critical value d. Short photoperiod and interrupted

31. The phytohormone that helps in the germination of seeds, is [UP CPMT-2011]

a. ABA b. Auxin c. Gibberellin d. Cytokinin

32. Bolting may be induced by [J&K CET 2011]

a. Gibberellins b. ABA c. Auxin d. Cytokinin

33. The rosette habit of cabbage can be changed by application of [KCET 2011]

a. IAA b. GA c. ABA d. Ethaphon

34. Which one of the following pairs is not correctly matched? [Kerala CEE 2011]

a. Adenine derivative - Kinetin

b. Carotenoid derivative - ABA

c. Terpenes - IAA d. Indole compounds - IBA

35. Phototropic curvature is the result of uneven distribution of [CBSE AIPMT 2010]

a. Gibberellin b. Phytochrome c. Cytokinins d. Auxin

36. Apical dominance is caused by [OJEE 2010]

a. Auxin b. Cytokinin c. Ethylene d. Gibberellin

37. Fruit and leaf drop at early stages can be prevented by the application of [NEET-2017]

a. Cytokinins

b. Ethylene

c. Auxins d. Gibberellic acid

38. What is the characteristic feature of seismonastic movements?

a. Response to light

c. Response to temperature changes

b. Response to touch or shock

d. Response to gravity

39. What is the role of auxins in tropic movements?

a. Inhibition of growth

c. Induction of photoperiodism

b. Promotion of growth

d. Activation of thigmotropism

40. How do pulvini contribute to nastic movements in plants?

a. Transmit electrical signals

c. Act as flexible hinges

b. Facilitate gas exchange

d. Store energy for growth

HOW DO ORGANISMS REPRODUCE?

6.1 INTRODUCTION

Reproduction is the biological process through which organisms produce offspring, ensuring the continuation of their species. It is a fundamental aspect of life and can occur in various ways across different organisms. From asexual reproduction, where one parent produces genetically identical offspring, to sexual reproduction, which involves the fusion of gametes, the mechanisms by which organisms reproduce are diverse.

6.2 DO ORGANISMS CREATE EXACT COPIES OF THEMSELVES?

• Organisms appear similar because their body designs are alike.

• The blueprints for these designs must also be similar, which is reflected in the DNA.

• During reproduction, a fundamental event is the creation of a DNA copy.

• The DNA in the cell nucleus contains information for inheriting features from parents to the next generation.

• This DNA is used to make proteins, which determine the characteristics of an organism.

• Any changes in the DNA can lead to different proteins and ultimately result in altered body designs.

• When cells replicate their DNA, they create two copies that need to be separated.

• An additional cellular apparatus is created during DNA copying to ensure the two copies are properly separated.

• Variations in the copying can lead to differences between the resulting cells.

• These variations can be drastic enough that some cells cannot function properly and will die, while others, having less drastic effects, will survive.

• This inherent tendency for variation during reproduction is the basis for evolution.

6.2.1

Importance of variation

• Populations of organisms in an ecosystem have specific roles called niches.

• Reproduction allows organisms to occupy these niches and maintain their features.

• Consistent DNA copying during reproduction is crucial for retaining niche-utilising features.

• Reproduction plays a vital role in stabilising the population of species.

• Niches can change due to external factors beyond the control of an organism.

• Changes in temperature, water levels, or other impactful events can alter niches.

• If a population well adapted to a niche changes significantly, the population can be wiped out.

• Variations within populations provide a chance for survival in changing conditions.

• Individuals with advantageous variations can survive and thrive.

• Variation within populations is advantageous for long-term survival.

• It increases the chances of adaptation to new or changing environments.

• Variability contributes to the resilience and adaptability of populations.

6.3 MODES OF REPRODUCTION USED BY SINGLE ORGANISMS

Asexual reproduction is commonly observed in simpler organisms that are less structurally complex. The methods of asexual reproduction are:

• Fission

• Regeneration

• Budding

• Vegetative propagation

• Spore formation

6.3.1 Fission

Fission is divided into two types depending on how many offspring are produced.

Fig. 6.1 Types of fission

Binary fission

Binary fission is a reproductive process in which an organism splits into two parts, each of which then grows individually into two new organisms. The genetic material, known as DNA, is copied and distributed among the two daughter cells. The offspring will be exact copies of the parent organism. Examples are bacteria, archaea, Amoeba, and Paramecium

In some organisms like Leishmania that possess a whip-like structure at one end, the binary fission occurs in a particular orientation with respect to the whip-like structure.

Multiple fission

Multiple fission occurs when an organism divides into multiple parts that grow independently into new organisms. The nucleus of the cell undergoes repeated divisions, where each nucleus is surrounded by a small portion of cytoplasm and is enclosed by a plasma membrane. This results in the formation of many daughter cells within a protective casing called a cyst. When conditions are favourable, the cyst bursts and releases the daughter cells.

Mother cell

Bipartition

Daughter cells

Fig. 6.2 Binary fission in Amoeba

Fig. 6.3 Multiple fission in Plasmodium

6.3.2 Regeneration

Regeneration is a method of asexual reproduction where a new organism develops from a part of the parent organism. It is also the ability of an organism to grow back lost body parts. For instance, flatworms (Planaria) and Hydra demonstrate regeneration.

Regenerated parts

6.3.3 Budding

Budding is a way for organisms to reproduce asexually, where a new organism develops from a small bud on the parent's body. Yeast, a single-celled fungus, and Hydra, an organism from the Cnidaria phylum, both use budding for reproduction. However, the process of budding differs between fungi and Hydra.

Fig. 6.4 Regeneration in Planaria

Bud Developing bud Fully mature bud Young Hydra separates

Fig. 6.5 Budding in Hydra

Chain of buds

6.3.4 Vegetative propagation

This is the simplest method of reproduction and results in the multiplication of plants. The vegetative parts of some plants such as roots, stems, and leaves, detach and regenerate into new independent plant. The structures of vegetative propagation in plants capable of giving rise to new offspring are called vegetative propagules.

Vegetative propagation can be classified into two types.

Fig. 6.6 Budding in fungi

Cutting

Grafting

Layering

Tissue Culture 2. Propagation by stems

Propagation by leaves

1. Propagation by roots

Fig. 6.7 Types of vegetative propagation

Natural methods

Plants have different ways of growing new plants on their own without any help from humans. This is called natural vegetative propagation. The natural methods are of the following types.

Propagation by root

Certain plants have specialised roots, known as tuberous roots or root tubers, that serve two purposes: food storage and vegetative propagation. Root tubers develop from any part of the root or can be the entire root itself. Example: sweet potato.

Propagation by stem

Underground stems play a significant role in vegetative propagation. There are four main types of underground stems.

Enlarged underground stem for food storage

Solid, bulb-like stem with basal plate for nutrient storage Colocasia

Modified stem surrounded by fleshy scales for food storage Onion

Fig. 6.8 Tuberous root

Types of Underground Stem

Rhizome

Horizontal underground stem Ginger

Tuber

Potato

Corm

Bulb

Table. 6.1 Types of underground stem

Propagation by leaves

In certain plants, the edges of the leaves have notches or indentations. Adventitious buds, also known as epiphyllous buds, grow from these notches. When these buds separate from the parent plant and come in contact with soil, they develop adventitious roots and give rise to new plants. Example: Bryophyllum

Adventitious Buds

(a)

Fig. 6.9 Underground stems (a) Ginger (b) Onion (c) Colocasia (d) Potato

Fig. 6.10 Adventitious buds

Artificial propagation

Artificial vegetative propagation is a method used to reproduce economically important and useful plants. The goal is to create new plants with desired traits. There are three commonly used methods: cutting, grafting, layering and tissue culture.

• Cutting involves planting a part of the stem in the soil to grow a new plant.

• Grafting involves the joining of a part of the stem without roots to the rooted part of the stem of another plant.

• Layering involves bending a flexible stem and burying a portion in the soil to develop roots and grow a new plant.

Tissue culture

Tissue culture, also known as micropropagation, is a technique used to grow plants in a laboratory setting. It involves taking a small piece of plant tissue, such as a leaf or a bud, and placing it in a sterile nutrient-rich culture medium. Under carefully controlled conditions of light, temperature, and humidity, the tissue starts dividing and forming tiny plantlets. These plantlets are then transferred to another medium to encourage their growth and development. Tissue culture allows us to rapidly produce large numbers of plants with desirable traits, such as disease resistance or improved yield.

Fig. 6.11 Artificial propagation

Fig. 6.12 Tissue culture

6.3.5 Spore formation

Lower plants like mosses, ferns and fungi commonly reproduce asexually. They develop round structures called sporangia that contain spores. These sporangia, when mature, burst open to release spores. These spores are lightweight and have a tough protective covering.

6.4 SEXUAL REPRODUCTION

Sexual reproduction is the process where genetic information from two individuals of different sexes is combined to produce a new offspring. In sexual reproduction, gametes are merged to form these new offspring. There are specialised reproductive structures involved in this process, which produce male and female cells through a process called meiosis. Due to this, the chromosome number remains constant in generations.

6.5 SEXUAL REPRODUCTION IN FLOWERING PLANTS

Sexual reproduction in flowering plants happens in specialised reproductive structures called flowers.

Fig. 6.13 Spore formation

Fig. 6.14 Parts of a flower

Non essential parts

The non essential parts, such as the calyx and corolla of a flower, don't have a direct role in the reproduction process. They provide support and protection. The calyx is the outermost part and consists of leaf-like structures called sepals. It surrounds and protects the inner parts of the flower when it's in the bud stage. The corolla is the second part and has brightly coloured and scented structures called petals. Its function is to attract insects for pollination.

Essential parts

The essential parts of a flower are the ones directly involved in sexual reproduction. These parts are the male reproductive organ, called the stamen or androecium, and the female reproductive organ called the pistil or gynoecium.

Androecium

The androecium in flowers comprises stamens, the male reproductive units. A stamen consists of two parts: the filament and the anther. The filament is a long, slender stalk, and the anther is a small, bilobed structure at its top. The anther is responsible for producing and releasing pollen grains, which contain the male gametes for fertilisation.

Filament

Anther

Petal

Stigma

Pistil Style

Ovary

Sepal

Stamen

Fig.6.15 Structure of a flower

Filament

Anther

Pollen sacs

Stamen

Fig. 6.16 Androecium

Gynoecium

The gynoecium is the innermost part of a flower and is composed of the female reproductive units known as carpels. Each carpel is made up of three distinct parts: the ovary, style, and stigma.

• The stigma is a disc-like structure located at the top of the carpel that aids the process of pollination.

• The style is a long and narrow tubular structure that serves as a pathway for the male gamete to travel from the stigma to the ovary.

• The ovary, positioned at the base of the carpel, is a swollen part that contains one or more ovules which produce egg or ova.

Process of sexual reproduction

Sexual reproduction in plants involves the coming together of male and female gametes to form offspring, which is known as fertilisation. The process of sexual reproduction has three different phases as follows:

• Pre-fertilisation phase

• Fertilisation phase

• Post-fertilisation phase

Pre-fertilisation phase

During the pre-fertilisation phase, the first step is the formation of male and female gametes, followed by the transfer of the male gametes to the site of fertilisation. The process of forming gametes is called gametogenesis.

Formation of male gametes

• Male gametes are formed in a part of the flower called the anther.

• Inside the anther, there are special cells called microspore mother cells that eventually become the male gametes. These cells are initially diploid, which means they have two sets of chromosomes.

Stigma Style Ovule Ovary

Fig. 6.17 Gynoecium

• These cells undergo meiotic cell division, which results in the formation of haploid cells called microspores. These microspores are cells that have one set of chromosomes.

• The haploid microspores then go through another round of cell division called mitosis to become pollen grains.

• Each pollen grain is a small microscopic cell having a two-layered wall. The inner thin layer is called intine, while the outer thick layer is called exine. The exine has tiny openings called germ pores.

• Usually, the pollen grains are released when the anther wall bursts open. This release of pollen grains is called dehiscence

• The generative cell undergoes mitosis to produce two male gametes. This process is called male gametogenesis

• The tube cell elongates to form a pollen tube during fertilisation.

The formation of female gametes, or egg cells, takes place as follows:

• In plants, the formation of female gametes, or egg cells, begins within the ovary.

• The ovary contains small structures called ovules, connected to the ovary wall by a stalk called the funicle.

• These ovules are supported by the placenta, and within each ovule, there are protective coverings called integuments.

• The micropyle, a small opening, is located at the upper end of the ovule, while the opposite end is called the chalaza.

Fig. 6.18 Formation of male gamete Formation of female gametes

• Within the ovule, the nucellus provides nourishment, and a single cell from the nucellus differentiates into a diploid megaspore mother cell.

• Through meiotic cell division, haploid megaspores are formed. Typically, only one out of four megaspores survives and develops into an embryo sac, also known as the female gametophyte.

• The embryo sac contains eight haploid cells resulting from three rounds of mitotic division.

• Among these cells, two polar nuclei fuse to form a diploid secondary nucleus; three cells move towards the chalazal end and form antipodals, while the remaining three cells arrange at the micropylar end. Of these, the central cell is the egg cell (female gamete), and the adjacent two cells are synergids.

• The nucellus serves as a source of nourishment for the developing embryo after fertilisation takes place.

Pollination

Pollination is the process of transferring pollen grains from the anther (male reproductive organ) to the stigma (female reproductive organ) of the same flower or a different flower. There are two types of pollination:

Self-pollination

When the transfer of pollen from anther to the stigma occurs within the same flower, it is called selfpollination. It usually takes place in certain flowers that have both male and female reproductive organs.

Cross-pollination

Cross-pollination is when pollen grains are transferred from the anther of one flower to the stigma of another flower. This transfer happens between flowers of the same plant or different plants of the same species. Cross-pollination is common in flowers that have separate male and female reproductive organs. Even in flowers with both male and female reproductive organs, nature tends to prefer cross-pollination.

Fig. 6.19 Structure of an ovule

Fertilisation phase

This is the main phase of sexual reproduction. It involves the fusion of the male and female gametes. Fertilisation leads to the formation of a zygote, which is the first stage of the new offspring.

Post-fertilisation phase

After fertilisation, important changes take place. The zygote develops into an embryo, and the ovary of the flower grows into a fruit. The ovule inside the ovary develops into a seed. These changes are part of the post-fertilisation phase.

6.6 REPRODUCTION IN HUMAN BEINGS

Human beings are sexually reproducing organisms. The reproductive system, derived from the mesoderm, is responsible for the formation of gametes, fertilisation, and the development of immature offspring within the body. Sexual reproduction involves the processes of gametogenesis, insemination, internal fertilisation, cleavage, implantation, embryonic development, and parturition.

Human beings exhibit sexual dimorphism, with distinguishable differences in primary sex organs, secondary sex organs, and accessory sexual features.

Fig. 6.20 Cross-pollination

Primary sex organs

Male (Testis) Sperm

Female (Ovaries) Egg

Fig. 6.21 Primary sex organs

6.6.1

Male reproductive system

The male reproductive system is located in the pelvis region. It includes testes, accessory ducts, glands and external genitalia.

Testes

The testes are located in the scrotum, outside the abdominal cavity. They are oval-shaped and pinkish in colour. The scrotum maintains a lower temperature than the body, which is necessary for spermatogenesis. Each testis is connected to the dorsal abdominal wall by a spermatic cord. It consists of 200-300 lobules, and each lobule contains 1-3 seminiferous tubules. The seminiferous tubules are responsible for sperm production. The ends of the seminiferous tubules open into a network called the rete testis. The connective tissue of the testicular lobules contains Leydig cells, which secrete male sex hormones, including testosterone. Testosterone maintains secondary sexual characteristics and stimulates germinal cells for spermatogenesis.

Seminiferous tubules

Each seminiferous tubule is lined by germinal epithelium. The germinal epithelium consists of more cube-shaped male germ cells (spermatogonia) and a few large pyramid-shaped supporting cells, Sertoli cells.

To the apical surface of Sertoli cells, facing the lumen of the seminiferous tubule, many spermatocytes and spermatids are attached. Sertoli cells nourish developing spermatozoa. Hence, Sertoli cells are called nurse cells of the testis.

The testis is attached to the scrotal sac by a cord-like structure called gubernaculum. It is present in between the scrotal sac and epididymis. Testis is attached to the dorsal abdominal wall by spermatic cord. Spermatic cord consists of an artery, a vein, a lymph vessel, a nerve and vas deferens.

Fig. 6.22 Male reproductive system

Vas efferentia

Rete testis opens into nearly 10 - 20 convoluted tubules called vas efferentia. They leave the testis and open into a highly coiled, long, compact tubule (6m in length) called epididymis on the posterior surface of the testis.

Epididymis

Epididymis is lined by pseudostratified epithelium and secretes nutrients for the maturation of spermatozoa. The sperms attain motility in epididymis. Testis with epididymis is called testicle

Vas deferentia (sperm ducts)

A pair of thick-walled, muscular ducts arising from the epididymis is called vas deferentia. They enter the abdominal cavity through the inguinal canal.

Vas deferens loops over the urinary bladder and joins the duct of the seminal vesicle to form an ejaculatory duct. Sperms are temporarily stored in it.

Ejaculatory ducts

These are thin-walled muscular tubes. These are formed by the joining of the vas deferens and the duct of the seminal vesicle. Sperms are mixed up with the seminal vesicle secretions in ejaculatory ducts. They store and transport sperm from the testis to the outside through the urethra.

Urethra

It is a tubular structure that arises from the neck of the urinary bladder and opens at the tip of the penis through an external opening urethral meatus. It carries sperms, secretions of seminal vesicles, prostate gland, Cowper's glands and urine. It is the common duct (urinogenital duct) that carries urine and semen to the outside.

Penis

The penis is the male copulatory organ and hangs in front of the scrotum. It consists of corpora cavernosa dorsolaterally and corpus spongiosum on the midventral side around the urethra. The glans penis is the sensitive terminal part, covered by the foreskin called prepuce. The penis has blood sinuses, which fill with blood during erection, increasing its size and stiffness. It facilitates insemination.

Accessory glands

It includes a pair of seminal vesicles, a pair of Cowper’s glands and a prostate gland.

Seminal vesicles

These are paired elongated coiled musculoglandular sacs that occur between the male urinary bladder and rectum. Its glandular epithelium secretes seminal fluid. It consists of fructose, prostaglandins, calcium, ascorbic acid and other proteins. Fructose nourishes the sperm;

prostaglandins stimulate contractions in the female genital tract. Seminal fluid constitutes 60-70% of semen.

Cowper's glands

These are also called bulbourethral glands. These are a pair of glands that occur below the prostate gland. These glands secrete alkaline mucus. This alkaline mucus lines the urethra and protects the urethra from the acidic nature of urine.

Prostate gland

It surrounds the proximal part of the urethra. Its secretion is slightly acidic in nature and is used for nourishment and activation of sperm. Its secretion constitutes 20-30% of the semen. Prostate secretions nourish and activate the sperm.

Structure of sperm

Human sperm is a microscopic structure with plasma membrane all over its body. A typical sperm comprises a head, neck, middle piece and tail.

a sperm

The sperm head is flat and oval-shaped, consisting of an acrosome and a nucleus. The acrosome contains enzymes necessary for penetrating the egg. The neck is a short, narrow structure between the head and middle piece and contains two centrioles. The middle piece is cylindrical and contains mitochondria, providing energy for sperm movement. The tail is the longest part of the sperm, allowing it to swim. In humans, 200 to 300 million sperm are ejaculated during coitus.

6.6.2 Female reproductive system

The female reproductive system in human beings consists of ovaries (primary sex organ), oviducts, uterus, cervix, vagina, external genitalia and accessory glands. Associated with these organs, are a pair of mammary glands that secrete milk to nourish the baby. All these parts are structurally and functionally integrated to support ovulation, fertilisation, pregnancy, birth and child care.

Fig. 6.23 Structure of

Ovaries

The ovaries are almond-shaped, greyish-pink organs located on each side of the lower abdomen. They produce eggs and hormones like estrogen and progesterone. The ovaries are held in place by ligaments and have four regions: germinal epithelium, tunica albuginea, cortex, and medulla. The cortex and medulla together form the stroma

Fallopian tubes

The oviducts, also known as fallopian tubes, are muscular tubes about 10 to 12 cm long. They carry eggs from the ovaries to the uterus. The oviduct has three parts: infundibulum, ampulla, and isthmus.

The infundibulum is funnel-shaped, having finger-like processes called fimbriae at its end. The fimbriae have cilia that create a gentle current to guide the egg into the oviduct. The ampulla is the wider, curved part of the oviduct, while the isthmus is a straight, narrow segment that connects the ampulla to the uterus. Early embryonic development occurs in the oviduct

Uterus

The uterus is a muscular, pear-shaped organ that measures about 7.5 cm long and 5 cm wide. It serves as a sac-like structure to support and nourish the developing foetus. Ligaments keep the uterus in position, attaching it to the pelvic wall. The uterine wall has three layers:

• Outer perimetrium

• Middle myometrium (made of smooth muscles for strong contractions during childbirth)

• Inner endometrium (with ciliated and non-ciliated cells that undergo cyclical changes during the menstrual cycle)

Fig. 6.24 Female reproductive system

The lower part of uterus extends into the vagina and is called cervix. The cervix forms a cylindrical cavity called cervical canal. The cervical canal and the vagina together form the birth canal.

Vagina

The vagina is a muscular tube measuring about 8-10 cm in length. It serves as the female copulatory organ, menstrual flow pathway, and birth canal. The vagina has an opening called the vaginal orifice, which leads to the vestibule. The mucosa layer of the vagina is composed of nonkeratinised stratified squamous epithelium.

Vulva

The external genitalia in females is known as vulva. It is also referred to as pudendum. It includes the external structures associated with the passage of female genital tract that are located in the pelvis region. It contains a centrally located depression called vestibule and structures such as labia, clitoris, mons pubis and hymen.

Accessory glands

The accessory glands in female reproductive glands include:

1. The lesser vestibular glands are also called urethral glands. They are considered homologous to prostate glands in males.

2. The greater vestibular glands are also called Bartholin's glands. They are homologous to bulbourethral or Cowper's glands in males.

Mammary glands

A pair of mammary or milk-producing glands (breasts) is a characteristic of mammalian females. They are actually modified sweat glands. Each breast has a multi-porous median erectile nipple (for milk release) surrounded by a pigmented area called areola. Each breast consists of 15-20 glandular lobes separated from one another by fibrous tissue and adipose tissue. Each lobe contains a group of alveoli which secrete milk under hormonal stimulus. Alveoli open into mammary tubules which open into mammary ducts. These ducts form a broad mammary ampulla for storing milk. Each mammary ampulla then leads into a lactiferous duct, which opens by separate pores at the nipple.

6.25 Mammary gland

Fig.

6.6.3 Menstrual Cycle

Menstruation, also known as menses, occurs during the first 5 days of the menstrual cycle in human females. It happens regularly every 28 - 29 days, except during pregnancy, from the age of 10 - 14 years (menarche) until around 50 years (menopause)

The menstrual cycle includes three phases: menstrual phase, proliferative phase and secretory phase.

Menstrual phase

It is the first phase of the menstrual cycle in females characterised by menstrual bleeding which lasts for 3 - 5 days. It involves the shedding of the endometrial lining. The menstrual flow contains mucous, blood debris and degenerated unfertilised ovum. Hormone levels, such as progesterone and estrogen, decrease during this phase.

Fig.6.26 Menstrual cycle

Proliferative phase

Reduced ovarian hormone levels stimulate the hypothalamus to produce gonadotropin-releasing hormone (GnRH), which activates the anterior pituitary to release gonadotropins. Follicle stimulating hormone (FSH) influences the growth of primary follicles and the proliferation of granulosa cells, leading to the secretion of estrogen. Luteinising hormone (LH) and FSH levels peak in the middle of the cycle. High levels of LH and estrogen cause the rapid growth of the Graafian follicle. The maximum level of LH during mid-cycle triggers ovulation, resulting in the release of the ovum.

Ovulatory phase

This phase is characterised by the rupture of the Graafian follicle and the release of a mature ovum. This event is called ovulation. It occurs on the fourteenth day of the menstrual cycle when LH is at its peak. The released ovum is trapped by the fimbriae of the oviductal funnel and remains viable in the fallopian tube for 24 hours only.

Secretory phase

After ovulation, the secretory or luteal phase begins and lasts for 12 - 14 days. The empty Graafian follicle transforms into the corpus luteum under the influence of LH. The corpus luteum secretes progesterone and some estrogen. In the uterus, LH and progesterone contribute to the growth and thickening of the endometrium, which becomes secretory and prepares for implantation. Progesterone inhibits further ovulation if fertilisation occurs by suppressing GnRH production. In the absence of fertilisation, the corpus luteum regresses, resulting in reduced LH and progesterone levels. This leads to the degeneration of the corpus luteum and the shedding of the endometrium.

6.6.4 From fertilisation to birth

During coitus, male gametes in the form of semen are transferred into the female reproductive tract, that is, the vagina. Out of the 200 million sperms introduced into the vagina, less than 2 million (1%) reach the cervix of the uterus and only about 200 reach the secondary oocyte.

Fertilisation

The process of fusion of haploid male and haploid female gametes to form a diploid zygote is called fertilisation. The pronucleus of both the sperm cell and the mature egg cell combine to form a single diploid nucleus.

Fertilisation occurs within 12 to 24 hours after ovulation in the ampulla region of the fallopian tube. It occurs only when the ovum and sperm are transported simultaneously to the ampulla. This is a unique event, which leads to pregnancy.

Embryogenesis

Soon after its formation, the zygote undergoes several divisions to transform into an embryo. The developmental changes of a single-celled diploid zygote into a fully formed foetus till its birth is referred to as embryogenesis.

Cleavage

The zygote undergoes repeated mitotic divisions by a process called cleavage. Cleavage starts as the zygote moves through the isthmus of the oviduct.

The first mitotic division results in the formation of a 2-celled stage. The second and third mitotic divisions lead to 4-celled and 8-celled stages, respectively. The cells formed as a result of cleavage are called blastomeres. As the zygote undergoes complete division, this type of cleavage is called holoblastic cleavage.

Repeated mitotic divisions produce a solid ball of cells called morula, which has 16 cells. Morula is covered on the outside by a zona pellucida. The morula slowly descends towards the uterus in 4-6 days

Blastulation

As the morula descends down the fallopian tube towards the uterus, the cells in the morula rearrange to form an outer layer called trophoblast and an inner group of cells called inner cell mass. This hollow ball of cells is now called a blastocyst. The cavity inside the blastocyst is called the blastocoel cavity. Thus, the transformation of a morula into a blastula/blastocyst is called blastulation.

Implantation

After reaching the uterus, the blastocyst sheds the zona pellucida and embeds itself into the endometrial lining of the uterus. This process is called implantation. Implantation begins about the seventh day after fertilisation of the ovum. Blastocyst comes in contact with endometrium in the region of the embryonal knob or embryonic disc formed by the inner cell mass. Adherence of the blastocyst to the endometrium stimulates the uterine cells to undergo rapid division, which covers the blastocyst. Thus, implantation confirms pregnancy

Fig.6.27 Stages of fertilisation

Gastrulation

It is a process in embryonic development which is characterised by the movement of cells in small masses or sheets so as to form primary germinal layers. After implantation, the inner cell mass differentiates into an outer ectoderm, an inner endoderm and a mesoderm between them. The resultant stage of gastrulation is called gastrula. Inner cell mass or embryonal knob possesses stem cells which form all types of tissues and organs. The formation of different organs in the developing embryo is known as organogenesis.

Pregnancy

The condition of carrying a developing embryo or foetus inside the womb by the mother is called pregnancy or gestation. The period from conception till delivery of a fully formed child is called the gestation period. In humans, the gestation period lasts for nine months or 40 weeks

The trophoblast cells secrete a hormone called human chorionic gonadotropin (HCG). The hormone can be detected in the urine of a pregnant woman after implantation. HCG maintains the corpus luteum during pregnancy. It continues to secrete progesterone, which prevents menstruation and maintains the uterine lining in a nutrient-rich state.

Progesterone is also called pregnancy hormone, as it is essential for the maintenance of pregnancy. This hormone is also secreted by the placenta.

Development of foetal membranes and placenta

During organogenesis, the embryo develops membranous coverings and sacs called foetal membranes. Since these are extra embryonic, they are also called extra embryonic membranes. These are chorion, amnion, allantois and yolk sac. At this stage, the embryo is known as a foetus.

Fig.6.28 Foetal development

The foetal membranes provide protection to the growing foetus and facilitate vital functions like nutrition, respiration, excretion, etc.

Soon after implantation, the trophoblast develops chorionic villi and establishes a temporary association with the mother's tissues to carry out its vital biological functions.

The chorionic villi and uterine tissue become interdigitated with each other and jointly form a structural and functional unit between the foetus and mother, the placenta. The foetus is connected to the placenta by a long and flexible string called the umbilical cord, which helps in the transport of substances to and from the embryo.

Parturition and lactation

A fully formed foetus is expelled by the uterus of the mother at the end of the gestation period. This process of delivering or giving birth to a baby is known as parturition. The physical activities involved in parturition, like uterine and abdominal contractions, dilation of the cervix and passage of the baby through the birth canal, are collectively called labour.

Parturition is controlled by a complex neuroendocrine mechanism. Signals originate from fully formed foetus and placenta. They cause mild uterine contractions called foetal ejection reflex. This triggers the release of oxytocin from the maternal pituitary gland. Oxytocin induces uterine contractions, which in turn stimulates further secretion of oxytocin. Doctors inject oxytocin to induce delivery in certain cases.

6.6.5 Reproductive health

The term reproductive health refers to healthy reproductive organs with normal functions. The World Health Organisation (WHO), defines reproductive health as total well-being in all aspects of reproduction, i.e. physical, emotional, behavioural and social.

Therefore, a society with people having physically and functionally normal reproductive organs and normal emotional and behavioural interactions among them in all sex-related aspects can be called reproductively healthy.

Population control

Increased health facilities, along with better living conditions, have an explosive impact on the size of the population. The most important step to overcome this problem is to motivate people to have smaller families by using various contraceptive methods.

Contraception

The intentional prevention of conception by natural or artificial means is called contraception. An ideal contraceptive should be user-friendly, easily available, effective and reversible with no or least side-effects.

Contraceptive methods help to prevent unwanted pregnancies. These methods are grouped into the following categories.

6.29

A. Natural methods

Avoiding chances of ovum and sperm meeting. They include the following:

• Periodic abstinence: Couples avoid or abstain from coitus from day 10 to 17 (fertile period) of the menstrual cycle, as chances of fertilisation are very high during this period.

• Withdrawal or coitus interruptus: Male partner withdraws his penis from the vagina just before ejaculation to avoid insemination.

B. Barrier methods

The meeting of ovum and sperm is physically prevented with the help of barriers.

• Condoms: They are barriers made of thin rubber/latex sheaths that are used to cover the penis in males or the vagina and cervix in females. This prevents the semen from reaching the female reproductive tract. Nirodh is a popular brand of condom for males.

• Reusable barriers: They include diaphragms, cervical caps, and vaults made of rubber. These are inserted into the female reproductive tract to cover the cervix during intercourse. They block the entry of sperm through the cervix. Spermicidal creams, jellies and foams are used along with these barriers to increase their contraceptive efficiency.

C. Intrauterine devices (IUDs)

These devices are inserted by doctors or expert nurses in the uterus through the vagina. IUDs increase the phagocytosis of sperms within the uterus and suppress the fertilising capacity of sperms.

IUD is one of the most widely accepted methods of contraception for females in India. IUDs are ideal contraceptives for females who want to delay pregnancy or space children.

D. Oral contraceptive pills

Small doses of either progestogens or progestogen-estrogen combinations are used by females. They are used in the form of oral tablets and are popularly known as pills. Pills have to be taken daily for a period of 21 days, preferably starting within the first five days of the menstrual cycle. After a gap of 7 days (during which menstruation occurs), it has to be repeated in the same pattern till the female desires to prevent conception. Pills help avoid ovulation and implantation by inhibiting the secretion of the follicle stimulating hormone (FSH) and the luteinising hormone (LH) by the pituitary gland.

E. Surgical methods

(a) (b)

Fig. 6.30 Surgical methods (a) Vasectomy (b) Tubectomy

Surgical methods, also called sterilisation, are generally advised for the male/female partner as a terminal method to prevent any more pregnancies. Surgical intervention blocks gamete transport and thereby prevent the meeting of gametes.

1. Tubectomy: It is a sterilisation procedure done in females where a small part of the fallopian tube is removed or tied up through a small incision in the abdomen or through the vagina.

2. Vasectomy: It is a sterilisation procedure performed in males where a small part of the vas deferens is removed or tied up through a small incision on the scrotum.

Prevention of sexually transmitted diseases (STDs)

Diseases or infections that are transmitted through sexual intercourse are called sexually transmitted diseases (STDs), venereal diseases (VD) or reproductive tract infections (RTI). Common STDs include bacterial, viral and protozoan diseases.

i. The bacterial diseases include gonorrhoea, syphilis, chlamydiasis, etc.

ii. The viral diseases are hepatitis B, AIDS, genital herpes, and genital warts

Other diseases include trichomoniasis caused by a parasitic protozoan and vaginal candidiasis caused by fungal yeast.

Fallopian tube

Vas deferens

Incision & Stitches

Some of these infections, like hepatitis B and HIV, can also be transmitted by sharing injection needles, surgical instruments, etc., with infected persons, transfusion of blood, or from an infected mother to the foetus. Except for hepatitis B, genital herpes and HIV infections, other diseases are completely curable if detected early and treated.

Symptoms at the early stage are minor and include itching, fluid discharge, slight pain, swellings, etc., in the genital region. Infected females may be often asymptomatic and may remain undetected for long. The absence or less significant symptoms in the early stages of infection and the social stigma attached to STDs discourage the infected persons from going for timely detection and treatment. These at later stages often lead to complications like pelvic inflammatory diseases (PID), abortions, stillbirths, ectopic pregnancies, infertility or even cancer of the reproductive tract.

QUICK REVIEW

• Reproduction is vital for species survival; it enables continuity of generations and adaptation.

• DNA copying during reproduction leads to variations crucial for evolution and species survival.

• The types of reproduction are asexual and sexual modes of reproduction.

• Asexual reproduction includes fission, regeneration, budding, vegetative propagation and spore formation.

• Fission is of two types, binary and multiple fission, observed in simpler organisms.

• Regeneration is the ability to grow back lost body parts; it is seen in flatworms and Hydra.

• Budding is the process in which new organisms develop from parts of the parent body; it is observed in yeast and Hydra.

• Vegetative propagation occurs in plants via natural and artificial methods involving roots, stems, and leaves.

• Spore formation occurs in lower plants and organisms that produce spores for asexual reproduction (e.g., fungi, mosses, ferns).

• Sexual reproduction takes place in higher organisms like humans and higher plants.

• Flowering plants have non-essential (calyx, corolla) and essential (androecium, gynoecium) parts; the androecium produces pollen, while the gynoecium holds ovules.

• The sexual reproduction in flowering plants includes pre-fertilisation, fertilisation, and postfertilisation.

• Pre-fertilisation: Formation of male (pollen) and female (ovule) gametes.

• Pollination: Self-pollination within the same flower or cross-pollination between different flowers.

• Fertilisation: Fusion of male and female gametes leading to the formation of a zygote.

• Post-fertilisation: The Zygote develops into an embryo, the ovary into a fruit, and the ovule into a seed.

• In humans, there are specialised reproductive structures to carry out sexual reproduction.

• The male reproductive system has testes and its accessory structure that produces sperm to fertilise the egg.

• The sperm consists of a head (with acrosome containing enzymes for fertilisation), neck, middle piece (rich in mitochondria for energy), and tail for motility.

• The female reproductive system consists of ovaries, oviducts, uterus and vagina.

• The ovaries produce eggs in the females.

• The menstrual cycle includes menstrual, follicular, ovulatory and secretory phases that regulate ovulation, fertilisation, and preparation for implantation.

• Fertilisation occurs in the ampulla of the oviduct, resulting in the formation of a zygote.

• Stages include cleavage, formation of the morula, blastocyst, implantation into the endometrium, and embryonic development through gastrulation.

• Foetal membranes (chorion, amnion, allantois, yolk sac) and the placenta aid in foetal nourishment, gas exchange, and waste removal.

• Reproductive health involves physical, emotional, and social well-being, with a focus on ensuring healthy reproductive organs and interactions.

• Contraceptive methods include natural, barrier, hormonal, and surgical approaches for population control.

• Prevention of sexually transmitted diseases (STDs) involves awareness, early detection, and treatment to avoid complications and infertility. •

MULTIPLE CHOICE QUESTIONS WITH SINGLE CORRECT ANSWER

I. Introduction

1. Which is NOT a method of reproduction in organisms?

a. Sexual reproduction

c. Budding

b. Asexual reproduction

d. Photosynthesis

2. Which of the following best defines reproduction in organisms?

a. The process of growth and development in organisms

b. The process of cells dividing and multiplying in organisms

c. The process of organisms producing offspring of their own kind

d. The process of organisms obtaining energy and nutrients for survival

3. The purpose of reproduction in organisms is to:

a. Increase genetic variation within a population

b. Maintain the stability of species' populations

c. Adapt to changing environmental conditions

d. All of the above

4. Asexual reproduction involves:

a. Both maternal and paternal parents

b. Only maternal parents

c. Only paternal parents

d. Only one parent, either paternal or maternal

5. Which mode of reproduction do structurally less complex organisms undergo?

a. Asexual reproduction

c. Bacterial reproduction

b. Sexual reproduction

d. Fungal reproduction

II. Modes of reproduction used by single organisms

1. Which mode of reproduction is seen in prokaryotes?

a. Binary fission

c. Regeneration

b. Multiple fission

d. Fragmentation

2. Which of the following is the common mode of reproduction that takes place in protozoans?

a. Budding

c. Regeneration

b. Multiple fission

d. Fragmentation

3. Which is the most common mode of reproduction in Hydra?

a. Binary fission

c. Regeneration

b. Multiple fission

d. Budding

4. Which organisms are capable of reproducing through the method of regeneration?

a. Planaria

c. Algae

b. Sporangium

d. Amoeba

5. Which of the following methods is not a form of artificial vegetative propagation?

a. Cutting

c. Layering

6. Vegetative propagation in Bryophyllum is by

a. Stem

c. Leaf

b. Grafting

d. Growing from seeds

b. Roots

d. None of the above

7. In a tissue culture, pollen develops into a haploid plant. It is due to the property of

a. Totipotency

c. Parthenocarpy

8. The 'eyes' of the potato tuber are

a. Root buds

c. Shoot buds

9. In ginger, vegetative propagation occurs through

a. Bulbils

b. Runners

b. Organogenesis

d. Test tube fertilisation

b. Flower buds

d. Axillary buds

c. Rhizome d. Offsets

10. The part of the plant involved in sexual reproduction is

a. Shoot

b. Flower

III. Sexual reproduction in flowering plants

c. Stem d. Root

1. What is the reproductive process in flowering plants?

a. Photosynthesis

c. Fragmentation

2. Sexual reproduction involves the fertilisation of

a. Two gametes

c. Two ovaries

3. What is the male reproductive organ in the flower?

a. Stamen

b. Pistil

b. Binary fission

d. Sexual reproduction

b. Two sperms

d. Two eggs

c. Sepal d. Petal

4. What is the female reproductive organ in the flower?

a. Stamen b. Pistil

c. Sepal

d. Petal

5. Which is the most logical sequence with reference to the life cycle of angiosperms?

a. Germination, endosperm formation, seed dispersal, double fertilisation

b. Cleavage, fertilisation, grafting, fruit formation

c. Pollination, fertilisation seed formation, germination

d. Maturation, mitosis, differentiation, fertilisation

6. Pollen grain represents one of the following

a. Zygote

c. Female gametophyte

7. The pollen grain is

a. An immature male gametophyte

c. Partially developed female gametophyte

b. Microspore

d. Male gametophyte

b. A mature male gametophyte

d. The last stage of male gametophyte

8. Pollen-pistil dialogue is mediated by the chemical components of

a. Pollen only

c. Both pollen and pistil

b. Pistil only

d. External environment

9. Male gametes in angiosperms are formed by the division of

a. Generative cell

c. Microspore mother cell

IV. Reproduction in human beings

b. Vegetative cell

d. Microspore

1. The following are associated with the male reproductive system except

a. Seminal vesicle

c. Bulbourethral glands

b. Prostate gland

d. Bartholin's glands

2. Secretions of all these are required for the maturation and motility of sperms, except

a. Vas deferens

c. Vas efferens

3. Primary female sex organs are

a. Mammary glands

c. Ovarioles

b. Seminal vesicle

d. Prostate gland

b. Ovaries

d. Oviducts

4. Testosterone is synthesised inside the testes in

a. Interstitial cells

c. Follicles

5. The inner part of the stroma of an ovary is

a. Cortex

c. Medulla

6. 'Fimbriae' are

a. Finger-like projections of the uterus

b. Sertoli cells

d. Seminiferous tubules

b. Mesovarium

d. Germinal epithelium

b. Finger-like projections of edges of infundibulum

c. Finger-like projections of edges of ampulla

d. Finger-like projections of edges of the isthmus

7. Tubectomy prevents pregnancy by

a. Preventing fertilisation

b. Preventing ovulation

c. Altering FSH levels in the ovary

d. Altering LH levels in the ovary

8. Surgical removal of vas deferens is called

a. Tubectomy

c. Vasectolysis

b. Vasectomy

d. None of these

9. What is the function of progesterone present in oral contraceptive pills?

a. Inhibition of ovulation

b. Inhibition of oogenesis

c. Prevention of entry of sperm into cervix and make them inactive

d. Controls sexual behaviour

10. Which amongst the following is an accessory gland?

a. Epididymis

c. Prostate gland

b. Uterus

d. Testosterone

11. A mature Graafian follicle is generally present in the ovary of a healthy human female for around

a. 5 - 8 days of menstrual cycle

b. 11 - 17 days of menstrual cycle

c. 18 - 23 days of menstrual cycle

d. 24 - 28 days of menstrual cycle

12. Menstruation is a result of

a. Disintegration of epimetrium

c. Progression of endometrium

b. Disintegration of endometrium

d. Regression of myometrium

13. Which of the following is the correct sequence of hormonal increases beginning with menstruation?

a. Estrogen, progesterone, FSH

c. FSH, estrogen, progesterone

14. The longest phase in the menstrual cycle is

a. Proliferative phase

c. Menstrual phase

15. Menstruation occurs due to

a. Rising level of progesterone

c. Rising level of oestrogen

WORKSHEET - 2

b. FSH, progesterone, estrogen

d. Estrogen, FSH, progesterone

b. Secretory phase

d. Ovulatory phase

b. Rising level of LH

d. Declining level of progesterone

MULTIPLE CHOICE QUESTIONS WITH SINGLE CORRECT ANSWER

1. Analyse the following:

Assertion (A): Human beings do not involve asexual reproduction. Reason (R): Each cell of their body is diploid.

a. Both Assertion (A) and Reason(R) are true, and Reason (R) is the correct explanation of Assertion (A).

b. Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of Assertion (A).

c. Assertion (A) is true, but Reason (R) is false.

d. Both Assertion (A) and Reason (R) are false.

2. Analyse the following:

Assertion (A): Bacteria is divided by fission.

Reason (R): Meiosis occurs in Rhizobium.

a. Both Assertion (A) and Reason(R) are true, and Reason (R) is the correct explanation of Assertion (A).

b. Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of Assertion (A).

c. Assertion (A) is true, but Reason (R) is false.

d. Both Assertion (A) and Reason (R) are false.

3. Analyse the following:

Assertion (A): Gametes are formed in gonads.

Reason (R): Gonads are haploid in nature.

a. Both Assertion (A) and Reason(R) are true, and Reason (R) is the correct explanation of Assertion (A).

b. Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of Assertion (A).

c. Assertion (A) is true, but Reason (R) is false.

d. Both Assertion (A) and Reason (R) are false.

4. Which of the following unicellular organisms has a macronucleus for trophic function and one or more micronuclei for reproduction?

a. Euglena

c. Paramecium

5. Identify the incorrect statement.

b. Amoeba

d. Trypanosoma

a. In asexual reproduction, the offspring produced are morphologically and genetically identical to the parent.

b. Zoospores are sexual reproductive structures.

c. In asexual reproduction, a single parent produces offspring with or without the formation of gametes.

d. Conidia are asexual structures in Penicillium.

6. Find out the mismatch.

a. Binary fission - Amoeba

c. Conidia - Pencillium

b. Buds - Hydra

d. Gemmules - Paramecium

7. A clone is a group of individuals obtained through

a. Self-pollination

c. Vegetative propagation

b. Hybridisation

d. Cross-pollination

8. Many unicellular organisms reproduce by the process of

a. Fission

c. Ovulation

b. Regeneration

d. Non-disjunction

9. Which of the following statements best characterises asexual reproduction?

a. It allows animals that do not move around to produce offspring without finding mates.

b. It allows an animal to produce many offspring quickly.

c. It saves the time and energy required to produce gametes.

d. It produces genetically uniform populations.

10. Genetic recombination is possible only through

a. Budding

c. Sexual reproduction

11. The nourishing cells in the seminiferous tubules are

a. Spermatogonial cells

c. Leydig cells

12. Analyse the given statements:

b. Asexual reproduction

d. Fragmentation

b. Sertoli cells

d. Follicular cells

Assertion (A): In human males, testes are extra-abdominal and lie in scrotal sacs.

Reason (R): Scrotum acts as a thermoregulator and keeps the testicular temperature lower by 2°C for normal spermatogenesis.

a. Both Assertion (A) and Reason(R) are true, and Reason (R) is the correct explanation of Assertion (A).

b. Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of Assertion (A).

c. Assertion (A) is true, but Reason (R) is false.

d. Both Assertion (A) and Reason (R) are false.

13. Analyse the given statements:

Assertion (A): Urethra in human males acts as a urinogenital canal.

Reason (R): Urethra carries only urine, while sperms are carried by vas deferentia only.

a. Both Assertion (A) and Reason(R) are true, and Reason (R) is the correct explanation of Assertion (A).

b. Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of Assertion (A).

c. Assertion (A) is true, but Reason (R) is false.

d. Both Assertion (A) and Reason (R) are false.

14. Analyse the given statements:

Assertion (A): Penis of a male is homologous to the clitoris of a female.

Reason (R): Both are highly sensitive, and both are supported by corpora cavernosa.

a. Both Assertion (A) and Reason(R) are true, and Reason (R) is the correct explanation of Assertion (A).

b. Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of Assertion (A).

c. Assertion (A) is true, but Reason (R) is false.

d. Both Assertion (A) and Reason (R) are false.

15. Analyse the following:

Assertion (A): At puberty, the human male develops secondary sexual characteristics.

Reason (R): At puberty, there is decreased secretion of testosterone in males.

a. Both Assertion (A) and Reason(R) are true, and Reason (R) is the correct explanation of Assertion (A).

b. Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of Assertion (A).

c. Assertion (A) is true, but Reason (R) is false.

d. Both Assertion (A) and Reason (R) are false.

16. Analyse the following:

Assertion (A): The fallopian funnel of the oviduct has finger-like fimbriae.

Reason (R): The Graafian follicle of the ovary has a secondary oocyte hanging in the cavity called antrum.

a. Both Assertion (A) and Reason(R) are true, and Reason (R) is the correct explanation of Assertion (A).

b. Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of Assertion (A).

c. Assertion (A) is true, but Reason (R) is false.

d. Both Assertion (A) and Reason (R) are false.

17. Capacitation occurs in

a. Female reproductive tract

c. Epididymis

b. Rete testis

d. Vas deferens

18. Which of the following is correct regarding the consequences of overpopulation?

a. It increases the poverty of a country

b. It leads to a shortage of food supply

c. It results in unemployment

d. All of these

19. Causes for increased population growth in India is/are

a. Increase in birth rate

c. Lack of education

b. Decrease in death rate

d. All of these

20. Which of the following is incorrect regarding vasectomy?

a. Irreversible sterility

b. No sperm occurs in seminal fluid

c. No sperm occurs in epididymis

d. Vas deferntia is cut and tied

21. Contraceptive oral pills help birth control by

a. Preventing ovulation

b. Killing the sperms

c. Forming barriers between sperms-ova meeting

d. Killing the ova

22. Analyse the following:

Assertion (A): The duration from day 10 to 17 of the menstrual cycle is called the fertile period.

Reason (R): The chances of fertilisation are very high during this period.

a. Both A and R are true, and R is the correct explanation of A.

b. Both A and R are true, and R is not the correct explanation of A.

c. A is true, but R is false.

d. Both A and R are false.

23. STDs in females are generally undetected for a long time because

a. The symptoms are suppressed by estrogens

b. Immunity levels are higher in women

c. These diseases are often asymptomatic

d. None of the above

24. Analyse the following:

Assertion (A): The use of condoms has increased in recent years.

Reason (R): Besides contraception, they have the additional benefit of protecting the user from STDs and AIDS.

a. Both A and R are true, and R is the correct explanation of A.

b. Both A and R are true, and R is not the correct explanation of A.

c. A is true, but R is false.

d. Both A and R are false.

25. Analyse the following:

Assertion (A): The females infected by STDs may remain undetected for long.

Reason (R): Infected females may often be asymptomatic.

a. Both A and R are true, and R is the correct explanation of A.

b. Both A and R are true, and R is not the correct explanation of A.

c. A is true, but R is false.

d. Both A and R are false.

26. One of the following diseases is not a sexually transmitted disease

a. Trichomoniasis

c. Encephalitis

b. Chlamydiasis

d. Syphilis

27. Identify the most dangerous sexually transmitted disease among the following

a. Genital warts

c. Syphilis

28. Treponema pallidum causes

a. Genital warts

c. Candidiasis

b. HIV infection

d. Gonorrhoea

b. Gonorrhoea

d. Syphilis

29. Gonorrhoea is caused by

a. Treponema pallidum

c. Mycobacterium leprae

b. Entameboa histolytica

d. Neisseria gonorrhoea

30. Which of the following is not a sexually transmitted disease?

a. Trichomoniasis

b. Encephalitis

c. Syphilis

d. Acquired immunodeficiency syndrome

HEREDITY

7.1 INTRODUCTION

'Like begets like' means living organisms produce offspring that resemble them. For example, an elephant always gives birth to a baby elephant, and a mango seed always forms a mango plant. Sometimes, we may observe that a person's nose and hand clasping pattern are like his father's, and his eyes are like his mother's. How does a person share a character from his father and another from his mother? It is mainly due to inheritance or heredity.

Heredity is the transmission of characters from one generation to the next generation (offspring). Though children resemble their parents, they are not identical. Brothers and sisters vary greatly, and no two siblings closely resemble each other unless they are identical twins. This is due to variations. The differences shown by the individuals of a species and also by the progeny of the same parents are known as variations. Reproduction and changes in environmental factors are responsible for causing variations.

7.2 ACCUMULATION OF VARIATION DURING REPRODUCTION

Reproduction, in addition to inheriting variations from the first generation, maintains newly created differences in the second generation. Asexually reproducing organisms, like bacteria, give rise to individuals that closely resemble their parents, forming clones.

In sexual reproduction, greater variations arise due to the exchange of DNA segments during gamete formation through crossing over and the union of traits from two different parents during fertilisation. The accumulation or elimination of variations, influenced by both environmental factors and the reproductive process, serves as the basis for evolution.

Fig. 7.1 Difference in colour shows the accumulation of variation

Characteristics that are observed in an individual, such as eye colour, height, facial features, body colour, and more are called traits.

Traits are of two types:

1. Inherited traits

2. Acquired traits

7.3 INHERITED TRAITS

Inherited traits are passed from one generation to the next through genes and germplasm, and encompass features like skin and eye colour.

7.4 ACQUIRED TRAITS

Acquired traits are those gained during an individual's lifetime, such as the loss of an organ or life experiences. Unlike inherited traits, acquired traits do not affect genes and are not passed on to future generations.

For example, removing one leg of a mouse through surgery does not result in a leg-less future generation since the alteration does not impact the mouse's germ cells and, its genes.

7.5 MENDELIAN INHERITANCE

7.5.1 Introduction to Mendelian inheritance

The mechanism of inheritance was discovered long before DNA was identified. The way in which characters are transmitted from one generation to another was first demonstrated by Gregor Johann Mendel, hence he is known as the "Father of genetics".

Gregor Johann Mendel was an Austrian monk who worked at Altbrunn monastery near Brunn, now in Czechoslovakia.

He carried out breeding experiments on garden pea (Pisum sativum) plants for 7 years from 1856 to 1863, and proposed laws of inheritance in living organisms. During 1857-59, he selected true breeding varieties, or pure breeding strains of pea plant.

The variety in which the trait is under investigation remained unchanged from parent to offspring for many generations is called pure breeding strain or true breeding variety.

In 1866, he published his results and ideas in the fourth volume of 'Proceeding of natural history society of Brunn'. The title of the paper was 'Experiments on plant hybridisation'. During

Mendel's investigations into inheritance patterns, it was for the first time that statistical analysis and mathematical logic were applied to problems in biology.

Mendel's experiments had a large sampling size, which gave greater credibility to the data he collected. Also, the confirmation of his inferences from experiments on successive generations of his test plants proved that his results pointed to general rules of inheritance rather than being unsupported ideas.

Unfortunately, his work remained unnoticed and unappreciated. Mendel passed away due to kidney failure in 1884. In 1900, Mendel's results were rediscovered independently by three scientists: Hugo de Vries (Holland), Carl Correns (Germany), and Erich Tschermak (Austria).

7.5.2 Reasons for choosing pea plant

Mendel did all his significant genetic experiments with the garden pea (Pisum sativum). The garden pea was a good choice because it fits many of the criteria that make an organism suitable for use in genetic experiments.

• It is easy to cultivate and does not require much aftercare.

• It is an annual plant with a short life span, so it is easy to study different generations in a short period.

• Pea plants are both self-pollinated and cross-pollinated, which allows the geneticist to conduct desirable experiments.

• The hybrids produced are fertile.

• The pea plant shows a number of easily detectable contrasting characters.

• The stature of the plant is small with large flowers, which allows controlled breeding easily.

• A large number of seeds are produced by these plants. Therefore, experimental error is minimised.

7.5.3 Mendel’s experiments

Mendel worked with about 10,000 pea plants. Many scientists conducted hybridisation experiments before Mendel, but they were not successful in their experiments because they aimed to observe the inheritance of many characters in one experiment. The following are the reasons for the success of Mendel:

• His success was mainly due to the selection of pea plants as his experimental material.

• He restricted his experiments to one or a few pairs of contrasting traits in each experiment.

• He kept track of each character separately.

• He had a mathematical background, so he kept accurate quantitative data. The numerical data he obtained enabled him to do a rigorous analysis of the heredity transmission of characteristics. He verified his results through further experiments such as F3 and test cross, etc.

• Mendel selected 14 true-breeding pea plant varieties as pairs that were similar except for one character with contrasting traits.

Table 7.1 Seven pairs of contrasting traits

Fig. 7.2 Seven pairs of contrasting traits

Mendel conducted his experiments through three key stages:

• He chose parents that were either pure or true breeding to establish the first filial (F1) generation.

• The plants were self-pollinated to generate subsequent generations.

• Hybridization techniques were employed to create hybrid plants during the course of the study.

Monohybrid cross

Mendel initially conducted crosses between true-breeding strains of peas that differed in a single trait. Such crosses are called monohybrid crosses.

In pea plants, tall and dwarf represent contrasting traits of the character height of the stem. Mendel pollinated pea plants that gave rise only to tall plants (TT) with pollen from a true breeding variety that produced only dwarf plants (tt). He collected the seeds produced as a result of this cross and grew them to generate plants of the first hybrid generation. This generation is also called the Filial progeny or the F1. Mendel observed that all the F1 progeny plants were tall, like one of its parents; none were dwarf.

He made similar observations for the other pairs of traits- he found that the F1 always resembled either of the parents and that the trait of the other parent was not seen in them. Mendel selfpollinated F1 generation tall plants to produce F2 or second filial generation.

Fig. 7.3 Monohybrid cross

Mendel noted in the F2 generation that 75% of the plants were tall and 25% were dwarf, maintaining a consistent 3:1 ratio. Further, when the F2 plants were self-pollinated to generate the F3 generation, Mendel made the following observations:

• The 25% of dwarf plants from the F2 generation consistently produced only dwarf plants upon self-pollination.

• Among the 25% of tall plants in the F2 generation, self-pollination resulted in exclusively tall plants identified as pure tall or homozygous tall plants.

Selfing

(Tall) (Tall)

(Dwarf)

• The remaining 50% of tall plants in the F2 generation, when self-pollinated, produced tall and dwarf plants in a ratio of 3:1, referred to as hybrid tall plants. Homozygous dwarf

dwarf)

Fig. 7. 4 Second and third filial generation in monohybrid cross

In conclusion, it was determined that only one of the two parental traits becomes evident in hybrids. This trait is referred to as the dominant trait, while the other is called the recessive trait. Notably, the dominant trait (tallness) is observable in both homozygous and heterozygous conditions. On the contrary, the recessive trait (dwarfness) is only apparent in homozygous conditions, requiring inheritance from both parents.

Mendel conducted similar experiments with the other characters of Pisum sativum. The results were found to be similar with all the seven characters.

Dihybrid cross

Crosses that are performed between parents with differing traits in two pairs of characters are known as dihybrid crosses. In Mendel's experiment, he selected pure-breeding plants with

yellow and green seeds and round and wrinkled seed shapes. By cross-pollinating pure pea plants with round yellow seeds (RRYY) and wrinkled green seeds (rryy), he established the parent generation, referred to as the P generation. The seeds produced by the cross between the P generation resulted in the first filial generation (F1 generation), where all the seeds were round and yellow. Upon self-pollination of the F1 generation plants, the subsequent generation (F2 generation) exhibited a variety of seed types based on the dihybrid cross.

Findings of Mendel's dihybrid cross:

• F1 offspring always exhibited only one of the parental forms of a trait and not the other.

• Traits hidden in the F1 generation appeared in the F2 generation. In the F2 generation, both parental traits were evident. Mendel termed the trait form expressed in the F1 generation as the dominant trait.

• Furthermore, Mendel noted a difference in the behaviour of plants derived from F2 offspring with the dominant trait. One-third of them were true-breeding, while the remaining twothirds were not true-breeding and exhibited behaviour similar to F1 hybrid plants.

• Mendel noted a consistent absence of one parental form of a trait in the F1 hybrid generation, only to witness its reappearance unchanged in the F2 generation. This observation demonstrated that alternate forms of a trait could maintain their identity in hybrids and reappear unchanged in subsequent generations.

• In the dihybrid cross, Mendel identified four plant types in the F2 generation. He concluded that the factors governing each of the two characters assort independently of each other.

• The resulting phenotypes in the F2 generation were round yellow, round green, wrinkled yellow, and wrinkled green in the ratio of 9: 3: 3: 1, respectively.

Round and yellow seeded plants - (9/16)

9 in all are of the following four genotypes in the ratio of 1: 2 : 2: 4.

• One plant with RRYY genotypic constitution (homozygous) - 1/16

• Two plants with RRYy genotypic constitution (heterozygous) - 2/16

• Two plants with RrYY genotypic constitution (heterozygous) - 2/16

Four plants with RrYy genotypic constitution (heterozygous) - 4/16

Round and green seeded plants - (3/16)

3 in all are of the following two genotypes in the ratio of 1: 2.

• One plant with RRyy genotypic constitution (homozygous) - 1/16

• Two plants with Rryy genotypic constitution (heterozygous) - 2/16

Wrinkled and yellow seeded plants - (3/16)

3 in all are of the following two genotypes in the ratio of 1: 2.

• One plant with rrYY genotypic constitution (homozygous) - 1/16

• Two plants with rrYy genotypic constitution (heterozygous) - 2/16

Wrinkled and green seeded plants - (1/16)

Only one plant with rryy genotypic constitution (homozygous) - 1/16.

Thus, the genotypic ratio in a dihybrid cross will be 1: 2: 2 : 4: 1 : 2: 1:2:1

7.5.4 Mendel’s law of inheritance

Based on the results of monohybrid crosses, Mendel derived the following three postulates of inheritance.

Fig. 7.5 Dihybrid cross

1. Law of dominance

In a pair of contrasting traits of a character, one is a dominant trait, and the other is a recessive trait. The trait that is expressed in the F1 generation is called the dominant trait, and the factor for this trait is the dominant factor. The other trait that is not expressed in the F1 generation is called the recessive trait, and the factor for this trait is the recessive factor

In pea plants, tall (T) is the dominant trait and dwarf (t) is a recessive trait of the character height of the stem. A dominant trait is expressed when an individual has a pair of dominant factors or even a single dominant factor, but a recessive trait is expressed only with two recessive unit factors in an individual. This dominance was later considered the first law of inheritance or the law of dominance

2. Law of segregation

The two unit factors in a character segregate during gamete formation. Gametes formed are pure for the factors they possess. The paired condition of unit factors is restored by the random fusion of gametes during fertilisation. This segregation is later considered the second law of inheritance (or) law of purity of gametes (or) law of segregation. During the formation of gametes due to meiosis, the paired unit factors separate or segregate randomly with equal probability, so that each gamete receives only one of these factors. A pure tall pea plant produces gametes with the dominant factor (T), and a pure dwarf plant produces gametes with the recessive factor (t). A heterozygous tall pea plant produces two different types of gametes in equal proportions. Each gamete contains either 'T' or 't'.

3. Law of independent assortment

The principle or law of independent assortment asserts that the individual units (factors or genes) responsible for different characteristics are distributed into gametes independently of each other. These units undergo a random rearrangement in the offspring. For instance, in Mendel's dihybrid cross, the F1 generation, when self-bred, produced four types of offspring. Two of these types resembled the parents, while the other two exhibited a combination of traits. This variation occurred because the unit factors governing the two characteristics assort independently, allowing for diverse combinations in the offspring.

7.6 SEX DETERMINATION

Introduction to sex determination

Sexually reproducing organisms may be unisexual (gonochoric or dioecious) or bisexual (hermaphrodite or monoecious). Male and female gonads are present in different individuals in unisexual organisms but in the same individuals in bisexual organisms. The gonads, which produce gametes, form the primary sexual characters. The development of gonads in the body is sex determination, and the development of secondary sexual characters is sexual differentiation.

Chromosomal basis of sex determination

Chromosomes determine the sex of the individual. The chromosomes that have no role in sex determination are called autosomes. The chromosomes that are responsible for sex determination in unisexual or dioecious organisms are called allosomes or sex chromosomes. Allosomes may be similar (XX, ZZ) or dissimilar (XY, ZW) in a sex. The sex that produces only one kind of gametes concerning allosomes is homogametic (human female, cock), and the sex that produces two different types of gametes concerning allosomes is the heterogametic sex (human male, hen). The chromosomal basis of sex determination is of different kinds, like heterogametic sex determination, haplodiploidy method of sex determination, etc. The method of heterogametic sex determination was proposed by Carl Correns. This method is based on the number and nature of allosomes.

A. Sex determination based on the nature of allosomes: In this method of sex determination, both male and female sexes have the same number of allosomes, but the size of allosomes (nature) is different in one sex (heterogametic). This is of two kinds:

• XX - XY method

• ZW - ZZ method

XX-XY type of sex determination

XX-XY type of sex determination is seen in mammals, including human beings, some insects like Drosophila (fruit fly), etc. In this method, females are homogametic with the 'AAXX' karyotype (44 XX in human females), and males are heterogametic with the 'AAXY' karyotype (44 XY in human males). Y chromosome is shorter than the X chromosome. All the ova produced by females are similar to the AX complement, but 50% of the sperms produced by males are with the AX chromosome complement, and the remaining 50% of the sperms are with the AY chromosome complement. The sex of the offspring depends on the fertilising sperm. Sperm with a Y chromosome produces male offspring, while sperm with an X chromosome produces female offspring.

In the case of humans, the SRY gene located on the Y chromosome acts as a signal to set the developmental pathway toward maleness. It is the genetic makeup of the sperm that determines the sex of the baby. In each pregnancy, there is a 50% probability of either a male or a female baby

ZW-ZZ type of sex determination

This method of sex determination is seen in birds, moths, butterflies, etc.

In this type of sex determination, females are heterogametic with ZW. Males are homogametic with ZZ. Females produce two types of ova: 50% with AZ chromosome complement (producing males) and 50% with AW chromosome complement (producing females). All the sperms produced by males are with AZ chromosome complement. The sex of the offspring depends on the fertilising ovum.

B. Sex determination based on the number of allosomes: In this method, the difference in the number of allosomes determines the sex.

XX-XO type of sex determination

C. E. McClung first reported this method in grasshoppers. This method of sex determination occurs in a large number of insects, including grasshoppers and cockroaches.

Meiosis

Fig. 7.7 ZW-ZZ Type of sex determination

Fig. 7.8 XX-XO Type of sex determination

In this method, females are homogametic with the AAXX karyotype, and males are heterogametic with the AAXO karyotype. All the ova produced by the female are with 'AX'. But, 50% of sperms are with AX, and the remaining 50% with 'AO' chromosome complement. The sex of the offspring depends on the fertilising sperm.

7.7 GENETIC DISORDERS

7.7.1

Introduction to genetic disorders

Genetic disorders are defects that are caused by defective genes or chromosomal aberrations and anomalies. Genetic disorders are of two types : hereditary disorders and chromosomal disorders or syndromes. Genetic disorders caused by chromosomal aberrations or ploidy changes are called chromosomal disorders, which are nonhereditary. These are also called syndromes. Chromosomal disorders may be autosomal or allosomal. Genetic disorders due to defective genes that follow Mendelian inheritance are called Mendelian, hereditary, or gene disorders. Mendelian disorders may be due to autosomal or autosomal genes, either dominant or recessive. The following is the outline classification of genetic disorders.

Genetic Disorders

Chromosomal Disorders

Autosomal Disorders Allosomal Disorders

Mendelian Disorders

Autosomal Mendelian Disorders

disorders

Allosomal Mendelian Disorders

7.7.2

Chromosomal disorders

Chromosomal disorders are caused by the absence or excess or abnormal arrangement of one or more chromosomes. Failure of segregation of chromatids during cell division results in the gain or loss of chromosomes, which is called aneuploidy.

Euploidy

Monoploidy (n)

Diploidy (2n)

Polyploidy

Autopolyploidy

Allopolyploidy

Hypoploidy

Aneuploidy

Hyperploidy

Monosomy (2n-a)

Fig. 7.10 Chromosomal disorders

Nullisomy (2n-b)

Fig. 7.9 Genetic

Ploidy

1. Autosomal disorders

These are due to autosomal aneuploidy and aberrations. The following are some important autosomal syndromes.

A. Down's syndrome

This is an autosomal aneuploidy caused due to the presence of one extra chromosome (2n + a) also known as 21st trisomy. Due to the non-disjunction of the 21st pair of chromosomes, some ova receive a pair of 21st chromosomes (n + a). When these eggs are fertilised by normal spermatozoa, individuals with Down's syndrome are produced.

The affected individuals are characterised by short stature, small round head, broad flat face, flat back of head, many loops on fingertips, broad palm with characteristic palm crease, partially open mouth, big and furrowed (wrinkled) tongue, congenital heart disease, retarded physical, reproductive, psychomotor and mental development, etc. Broad flat face

Flat back of head

Many loops on fingertips

Palm crease

B. Cri-du-chat syndrome

and wrinkled tongue

This is due to the deletion of half of the short arm of chromosome 5. The cry of new babies is like the mewing of a cat, hence the name cat cry disease.

C. Patau's syndrome

This is due to trisomy of the 13th chromosome (2n + a).

D. Edward's syndrome

This is due to the trisomy of the 18th chromosome (2n + a).

2. Allosomal disorders

These are due to the aneuploidy of allosomes. The following syndromes are produced due to the nondisjunction of allosomes in human beings:

Big

Congenital heart disease

Fig. 7.11 Down's syndrome

A. Turner's syndrome

In Turner's syndrome, the affected individual has female external genitalia and internal genital ducts, but the ovaries are rudimentary. The karyotype is 45, 44X. It is due to the monosomy of the 23rd pair (2n - a). The symptoms are short stature, gonadal dysgenesis, an unusual face, webbing of the neck, and a broad shield-like chest with widely spaced nipples.

Webbed neck

Less developed breast

Less developed ovaries

B. Klinefelter's syndrome

They have male genitalia and internal genital ducts, but their testes are underdeveloped. Feminine sexual development is not completely suppressed. Karyotype is 47, 44XXY. It is due to the presence of one extra 'X' chromosome (trisomy) in the 23rd pair. The symptoms include hypogonadism, underdevelopment of secondary sexual characters, infertility, reduced I.Q., dyslexia (difficulty in learning), gynaecomastia (development of female characters like breasts), and the tall nature of the body.

No facial hair

Some breast developement

Very long arms

Less developed testes

Very long legs

Fig. 7.12 Turner's syndrome

Fig. 7.13 Klinefelter's syndrome

7.7.3 Mendelian disorders

1. Autosomal mendelian disorders

A. Myotonic dystrophy

It occurs when the dominant autosomal gene is located on the long arm of chromosome 19, which codes for myotonic dystrophy protein kinase (the predominant protein in skeletal muscle). In this, the muscles degenerate.

Affected parent

Unaffected parent

Unaffected Unaffected

Affected Affected

Fig. 7.14 Inheritance pattern of myotonic dystrophy

B. Sickle cell anaemia

This is an autosomal hereditary disorder due to mutation in the β cistron, which controls the synthesis of β polypeptide chains in the haemoglobin of RBCs. The gene is located on the 11th chromosome. As a result, glutamic acid at residue 6 in β-globin is substituted with valine (β6 Glu → Val). This causes the formation of deoxygenated haemoglobin. So, oxygen is not properly transported in the RBCs of the blood.

Fig. 7.15 Inheritance pattern of sickle cell anaemia

Sickle cell trait Sickle cell disease

Typical (No blood disorder)

7.16 Sickle cell and normal red blood cell

C. Phenylketonuria

This is an inborn error of metabolism due to a recessive autosomal gene located on chromosome 12. In the affected individuals, the phenylalanine hydroxylase enzyme that converts phenylalanine amino acid into tyrosine amino acid is not synthesised. As a result of this, phenylalanine accumulates and is converted into phenyl pyruvic acid, phenylacetic acid, etc.

Accumulation of these in the brain and cerebrospinal fluid leads to mental retardation. Due to poor absorption by the kidney, these substances are excreted through urine. Hypopigmentation of the skin and hair, etc., are the other symptoms.

7.17 Inheritance pattern of phenylketonuria

Fig.

Fig.

D. Thalassemia

Thalassemia is caused when the body does not make enough haemoglobin. It is of two types.

α-Thalassemia: In this the production of the α-globin chain is affected which is controlled by two closely linked genes, HBA1 and HBA2, on chromosome 17.

β-Thalassemia (Cooley's anaemia): In this the β-chain is affected which is controlled by a single gene, HBB, on chromosome 11.

Thalassemia (Major trait)

Unaffected (No thalassemia trait)

7.18 Inheritance pattern of thalassemia

E. Cystic fibrosis

This is due to a mutation in a gene present on chromosome 7. Fibrous cysts appear in the pancreas. It is characterised by abnormal transport of chlorine and sodium ions across the epithelium, leading to thick, viscous secretion.

Inheritance

Mother trait

Father trait

Fig.

Carrier father

Carrier mother Carrier

Unaffected Cystic fibrosis

Fig. 7.19

pattern of cystic fibrosis

Allosomal mendelian disorders

The genes located on the allosomes (sex chromosomes) are called sex-linked genes. The characters controlled by the sex-linked genes are sex-linked characters, and their inheritance is sex-linked.

A. Colour blindness

The cone cells present in the retina of the eye are sensitive to colour, and this trait is genetically controlled. People with recessive genes cannot detect certain colours and are called colourblind. The type of inheritance in which a parent passes the traits to the grandchild of the same sex but through the offspring of the opposite sex is called crisscross inheritance

Men are colour blind if they have recessive genes and have normal vision if they have a dominant gene on their X-chromosome. Women are colourblind if they have two recessive alleles and have normal vision if they have a dominant allele on both the X-chromosomes (homozygous) or on one X-chromosome (heterozygous, carrier).

B. Haemophilia

In this disease, a single protein, i.e., a part of a cascade of proteins that are involved in blood clotting, is affected. This is also called bleeder disease as in these patients, even due to minor injuries, blood oozes continuously, leading to the loss of blood and even death sometimes. Haemophilia was first observed in the Queen Victoria family. This is also called Royal disease because it is very common in the royal families of Europe. The gene for haemophilia developed as a recessive mutant in Queen Victoria. Carrier females appear normal. The possibility of haemophilic females is extremely rare because her mother must be a carrier, and her father should be haemophilic (unviable in the later age of life). Haemophilic males suffer from severe loss of blood through wounds and sometimes die because of this.

Fig. 7.20 Inheritance pattern of colour blindness

(Without haemophilia)

PARENTS

Father (Without haemophilia)

Mother (Carrier of haemophilia gene)

Daughter (Carrier of haemophilia gene)

7.8 PEDIGREE ANALYSIS

(Has haemophilia)

Daughter (Does not carry haemophilia gene)

Inheritance of traits in human populations is studied through the screening of family/analysis of family history (pedigree). The study of pedigree for a few generations to analyse the transmission of certain exceptional phenotypes/disorders and the possibility of their occurrence in a particular generation is known as pedigree analysis. Since desired crosses cannot be performed to study the inheritance of genetic disorders in humans, we study the pattern of inheritance of the traits by observing the family history. It is represented in the family tree over generations. The following are the various symbols used in the pedigree analysis:

7.22 Pedigree symbols

Fig. 7.21 Inheritance pattern of haemophilia

Fig.

QUICK REVIEW

• Heredity is the transmission of characters from one generation to the next generation (offspring).

• The differences shown by the individuals of a species and also by the progeny of the same parents are known as variations

• Gene is the determinant of a characteristic of an organism. It is the fundamental physical unit of heredity.

• A trait is a distinct, observable, and heritable characteristic or feature of an organism.

• Variations arise during the process of reproduction. There may be few in asexual reproduction, but many in the case of sexual reproduction.

• The offspring produced by sexual reproduction are not identical but show a great deal of variation from the parents.

• Sexually reproducing organisms like humans have two or more versions of genes for each trait, called alleles

• Mendel did all his significant genetic experiments with the garden pea (Pisum sativum).

• Mendel selected 14 true-breeding pea plant varieties as pairs that were similar except for one character with contrasting traits.

• A cross between two organisms with different traits of a character is called a monohybrid cross.

• The phenotypic ratio of the monohybrid cross is 3:1

• The genotypic ratio is 1:2:1.

• Mendel's principles of inheritance are the law of dominance, the law of segregation or purity of gametes, and the law of independent assortment.

• Different mechanisms are used for sex determination in different species.

• The sex of human offspring is genetically determined.

• Humans have 22 pairs of autosomes and one pair of sex chromosomes

• Females have similar sex chromosomes, XX, whereas males have an imperfect pair, i.e. XY. All eggs carry an X chromosome.

• The sex of the child depends on whether the egg fuses with the sperm carrying the X chromosome (resulting in a girl) or with the sperm carrying the Y chromosome (resulting in a boy).

• Variations beneficial to a species have a greater chance of flourishing in the species than harmful or neutral variations.

• Genetic disorders are caused by defective genes.

• Mendelian disorders are caused by defective genes that follow Mendelian inheritance.

• Genetic disorders due to chromosomal aberrations or ploidy changes are chromosomal disorders.

• Pedigree analysis studies the inheritance of traits in human populations through the screening of family/analysis of family history.

WORKSHEET - 1

MULTIPLE CHOICE QUESTIONS WITH SINGLE CORRECT ANSWER

I. Introduction to heredity and variation

1. The process of transmission of parental characteristics to the offspring is called ______.

a. Variations

c. Mendelism

b. Heredity

d. Hybridisation

2. During sexual reproduction, characters are transmitted through the _______.

a. Any vegetative cell

c. Propagules

b. Gametes

d. Clones

3. The difference in characters among the same progeny is due to __________.

a. Variations

c. Cloning of genes

4. Select the correct matching.

Column I

A. Locus

B. Gamete

C. Genome

D. Gene

a. A - II, B - III, C - IV, D - I

c. A - II, B - IV, C - III, D - I

b. Gene manipulation

d. Lack of alleles

Column II

I. A mature reproductive cell

II. Fundamental physical unit

III. A specific place on the chromosome

IV. One complete copy of all the genetic information

b. A - III, B - I, C - IV, D - II

d. A - I, B - III, C - IV, D - II

5. Select the incorrect match from the options given below.

a. Non allele - Alleles of different loci

c. Genotype - Genetic constitution of an organism

b. Gene pool - One complete copy of all the genetic information of an organism

d. Genetics - The study of heredity and variation

6. ____________ is the transmission of characters from ___________ to the next generation.

a. Variation, one generation

c. Heredity, one generation

II. Mendelian inheritance

b. Heredity, variation

d. Genetics, one generation

1. According to Mendel's experiments, how do both parents contribute to the DNA of progeny during sexual reproduction?

a. By sharing a single gene

c. By providing two copies of each gene

b. By contributing unequal gene sets

d. By transmitting hormones to offspring

2. What role do chromosomes play in the inheritance of traits?

a. They determine the number of hormones produced.

b. They regulate the enzyme activity.

c. They contain genes that control traits. d. They produce germ cells.

3. What is the pair of sex chromosomes present in human males?

a. XX

b. XY

4. Sex chromosomes are also called ________.

a. Autosomes

c. Allosomes

c. YY

d. XO

b. Homosomes

d. Diplosomes

5. The number of pairs of characters used by Mendel during his experiments was _____.

a. Ten b. Six

c. Seven d. Two

6. Which of the following characteristics of the pea plant was not studied by Mendel?

a. Length of stem

c. Shape of pod

b. Colour of plant

d. Colour of pod

7. The hereditary variations arise from ___________.

a. Asexual reproduction

c. Vegetative reproduction

b. Sexual reproduction

d. All of these

8. What was the main cause of the discovery of laws of heredity by Mendel?.

a. He analysed every trait independently

c. His plants were true-breeding

b. He was lucky that he did not come across linkage

d. All of the above

9. According to Mendel's experiment, which of the following traits is not seen in the F2 progeny?

a. Tall plant

c. Medium height plant

b. Short plant

d. Both tall and short plants

10. Analyse the following statements and choose the correct answer:

Statement A: Mendel's experiments involved the study of traits in pea plants to understand how they are inherited from one generation to the next.

Statement B: In Mendel's experiments, he observed that traits are always inherited from the mother only and not from the father.

a. Statement B is correct, and statement A is incorrect

c. Both statements A and B are incorrect

11. Which is correct about traits chosen by Mendel?

a. Green coloured pod is dominant

b. Terminal pod is dominant

c. Constricted pod is dominant

d. Tall plants are recessiv

b. Statement A is correct, and statement B is incorrect

d. Both statements A and B are correct

12. When a tall and red-flowered individual is crossed with a dwarf and white-flowered individual, the phenotype in the progeny is dwarf and white. What will be the genotype of the tall and flowered individual?

a. TTRR

c. TtRr

b. TtRR

d. TTRr

13. How is the equal genetic contribution of male and female parents ensured in the progeny?

a. Only the genetic material from the mother is passed on to the progeny.

b. The genetic contribution of the father is solely responsible for the progeny's traits.

c. Genetic material from both the mother and father combines during fertilization, ensuring equal genetic contribution.

d. The genetic contribution from the mother is dominant and overrides that of the father.

14. The genotype of a dominant phenotype is _________.

a. Only homozygous

c. Either homozygous or heterozygous

b. Only heterozygous

d. Neither homozygous nor heterozygous

15. The total number of chromosomes in a male grasshopper is __________.

a. Equal to female

c. Double than female

b. Less than female

d. More than female

16. When a tall pea plant is crossed with a dwarf pea plant in the progeny, all tall plants are produced, so the tall plant is

a. Only homozygous

c. May be heterozygous

b. May be homozygous

d. May be homozygous or heterozygous

17. In a dihybrid cross, the ratio of pure double dominants and pure double recessive individuals in F2 generation is ________.

a. 9:7 b. 1:4 c. 4:16 d. 1:1

18. If the gametes produced by an individual are different regarding allosomes, in that organism

a. The allosomes are different.

b. The two sex chromosomes are different.

c. Only one sex chromosome is present. d. 1 or 2

19. Fertilisation of abnormal gametes by normal gametes produces ________.

a. Euploid zygotes

c. Polyploid zygotes

b. Aneuploid zygotes

d. Triploid zygotes

20. Assertion (A): A study of the family history of inheritance of a particular trait provides an alternative for controlled crosses in human beings.

Reason (R): Control crosses that can be performed in other organisms are not possible in the case of human beings due to ethical and moral reasons.

a. Both Assertion (A) and Reason (R) are true, and Reason (R) is the correct explanation for Assertion (A).

b. Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation for Assertion (A).

c. Assertion (A) is true, but Reason (R) is false.

d. Assertion (A) is false, but Reason (R) is true.

21. Assertion (A): 21st trisomy is associated with late pregnancy, during which the female produces n+1 gametes.

Reason (R): With ageing in females, the incidence of non-disjunction of chromosomes during meiosis increases.

a. Both Assertion (A) and Reason (R) are true, and Reason (R) is the correct explanation for Assertion (A).

b. Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation for Assertion (A).

c. Assertion (A) is true, but Reason (R) is false.

d. Assertion (A) is false, but Reason (R) is true.

22. Read the following statements and find the incorrect statement.

i. Genetics deals with inheritance, as well as variation of characters from parents to offspring

ii. Variation is the process in which characters are passed on from parent to progeny.

iii. Inheritance is the basis of heredity.

iv. Inheritance is the degree to which progeny differ from their parents.

v. Humans knew from as early as 8000 -1000 B.C that one of the causes of variation was hidden in sexual reproduction.

a. ii, iv, v

c. ii, iv

b. i, iii, v

d. Only v

23. Statement I: In pea plants, experimental error is minimum. Statement II: Pea plants produce a large number of offspring.

a. Both the statements are true

c. Statement I is true, statement II is false

b. Both the statements are false

d. Statement I is false, statement II is true

24. Statement I: In a monohybrid test cross, the F1 parent produces genetically similar gametes. Statement II: A monohybrid test cross gives different offspring.

a. Both the statements are true

c. Statement I is true, statement II is false

b. Both the statements are false

d. Statement I is false, statement II is true

25. Statement I: The genotypic ratio of YYRR, YYRr, and YYrr is 1:2:1 in the F2 progeny of a dihybrid cross.

Statement II: The phenotype of all the above-shown individuals is yellow, round seeds.

a. Both statements are true

c. Statement I is true, statement II is false

b. Both statements are false

d. Statement I is false, statement II is true

26. Statement I: In human beings, the sex of the offspring depends on the fertilizing sperm. Statement II: In human beings, half of the sperms are with allosomes and the other half without allosomes.

a. Both statements are true

c. Both statements are false

27. The monohybrid test cross ratio is ______________.

a. 1:2:1

b. 3:1

b. Statement I is true, statement II is false

d. Statement I is false, statement II is true

c. 1:1

28. The characters that are expressed in the first generation are called _____.

a. Dominant characters

c. Both recessive and blend characters

29. The genotype of the F1 tall plants is _____.

a. Tt

c. TT

b. Recessive characters

d. None of the above

d. 2:1

b. tt

d. None of these

30. Mendel's principle of segregation was based on the separation of alleles in the garden pea during _____________.

a. Embryonic development

b. Seed formation

c. Gamete formation

d. Pollination

31. Progenies are phenotypically and genotypically similar in the ________.

a. F2 generation

c. F4 generation

b. F3 generation

d. F1 generation

32. Which of the following depicts the phenotypic ratio of a dihybrid cross?

a. 3:1

c. 3:4

b. 9:3:3:1

d. 9:4:4:2

33. Independent assortment of Mendel was under in framing ________.

a. Monohybrid cross

c. Incomplete dominance

b. Back cross

d. Dihybrid cross

34. Assertion (A): Mendel's experiments with pea plants laid the foundation for modern genetics.

Reason (R): Mendel's observations contradicted the blending theory of inheritance.

a. Both A and R are true, and R is the correct explanation of A.

c. A is true, but R is false.

III. Sex determination

b. Both A and R are true, but R is not the correct explanation of A.

d. A is false, but R is true.

1. If an individual contains only one sex chromosome, it is called _________.

a. Heterogametic

c. Heterogenous

b. Heterozygous

d. Heteronomous

2. The method of sex determination in human beings and Drosophila is _________.

a. XX-XO method

c. ZW-ZZ method

b. XX-XY method

d. ZO-ZZ method

3. In human beings, the sex of the offspring depends on ___________.

a. The fertilizing ova

c. The number of autosomes

b. The fertilizing spermatozoa

d. The number of allosomes

4. Which of the following accurately describes the chromosomal basis of sex determination in birds?

a. Females have two X chromosomes, while males have one X and one Y chromosome.

b. Females have two Y chromosomes, while males have one X and one Y chromosome.

c. Females have one Z and one W chromosome, while males have two Z chromosomes.

d. Females have one Y chromosome, while males have two X chromosomes.

5. In rare cases, the presence of male XX chromosomes or female XY chromosomes can be attributed to:

a. Genetic mutations in sex-determining genes.

b. Environmental factors influencing chromosomal development.

c. Incorrect labelling of chromosomal samples during testing.

d. Parental chromosomal exchange during meiosis.

IV. Genetic disorders

1. Identify the odd one among the following disorders:

a. Thalassemia

c. Sickle-cell anaemia

b. Phenylketonuria

d. Haemophilia

2. From the chromosomal complements given below, identify the one that shows female heterogamety.

a. ZZ-ZW

c. XX-XY

b. XX-XXY

d. XX-XO

3. What is the genetic disorder in which an individual has an overall masculine development, gynaecomastia, and is sterile?

a. Edward's syndrome

c. Turner's syndrome

b. Down's syndrome

d. Klinefelter's syndrome

4. An inborn error of metabolism that eventually affects mental development is called _______.

a. Albinism

c. Anaemia

b. Phenylketonuria

d. Bleeder's disease

5. Down's syndrome is due to trisomy of the 21st chromosome caused by

a. Nondisjunction during egg formation

b. Nondisjunction during sperm formation

c. Addition of extra chromosome during mitosis of the zygote

WORKSHEET - 2

d. Either a or b

MULTIPLE CHOICE QUESTIONS WITH SINGLE CORRECT ANSWER

1. Laws of inheritance are the basis for the scientific explanation of __________.

a. Heredity

c. Eugenics

b. Variations

d. Both a and b

2. Which term represents a pair of contrasting characters?

a. Homozygous

c. Complementary genes

b. Heterozygous

d. Allelomorphs

3. Which of the following is the base of the scientific explanation of the Law of Inheritance?

a. Mendelism

c. Eugenics

b. Variations

d. Heredity and variation

4. The determining pair responsible for each trait is called ____________.

a. Inherited factor

c. Generation

b. Character

d. Filial

5. A trait that 'overpowers' and conceals another trait is referred to as

a. Overpowering trait

c. Recessive trait

b. Dominant trait

d. Trait

6. What role do chromosomes play in the inheritance of traits?

a. They determine the number of hormones produced.

b. They regulate enzyme activity.

c. They contain genes that control traits.

d. They produce germ cells.

7. Which scientist is known as the 'Father of Genetics' due to his pioneering work on the inheritance of traits in pea plants?

a. Isaac Newton

c. Charles Darwin

b. Albert Einstein

d. Gregor Mendel

8. Which of the following mechanisms allows traits to be inherited from one generation to the next?

a. Growth

c. Differentiation

b. Respiration

d. Reproduction

9. How many pairs of contrasting characteristics did Mendel study in his experiments with the pea plants?

a. Eight b. Seven

c. Five d. Six

10. Identify the phenomenon that serves to preserve the parental characteristics in the next generation.

a. Crossing over

c. Linkage

b. Recombination

d. DNA replication

11. On crossing yellow-seeded plants with green-seeded plants, the F1 plants are ___________.

a. Homozygous yellow

c. Heterozygous yellow

b. Homozygous green

d. Heterozygous green

12. What shall be the genotypic ratio in the F2 generation of a monohybrid cross?

a. 3:1

b. 1:2:1

c. 1:1:1 d. None of these

13. How many different kinds of gametes are produced by the F1 offspring from a cross between a pure strain of plants with yellow peas and a pure strain of plants with green peas?

a. 1

b. 2

c. 3 d. 8

14. The law of dominance and recessiveness was a result of _____________.

a. Back cross

c. Dihybrid cross

b. Incomplete dominance

d. Monohybrid cross

15. How many types of combinations of gametes are possible in monohybrid F1 parents?

a. Two

b. Four

c. Six

16. Mendel's law of segregation is based upon the F2 ratio of:

a. 1:2

b. 3:1

c. 9:3:3:1

17. If the two sex chromosomes are similar, the individual is called a __________.

a. Homozygote

c. Homogenous

18. Mutation happens because of the _____________.

a. Loss of a segment of DNA

c. Change in a single base pair of DNA

19. Cystic fibrosis is a/an ________________.

a. Mendelian disorder

c. Chromosomal aberration disorder

b. Homogametic

d. Homonymous

d. Eight

d. 1:1

b. Gain of a segment of DNA

d. All these

b. Aneuploid disorder

d. Euploidy disorder

20. Individuals with which among the following syndromes have male genitalia and internal genital ducts, but underdeveloped testes?

a. Down's syndrome

c. Turner's syndrome

21. Karyotype is 44XXY in __________.

a. Turner's female

c. Patau's female

b. Patau's syndrome

d. Klinefelter's syndrome

b. Down's male

d. Klinefelter's male

22. Which of the following is the impossible outcome of Mendel's Experiment?

a. 3 tall and 1 short plant

c. 8 tall and 0 short plants

b. 24 tall and 8 short plants

d. 4 tall plants and 1 medium-height plant

23. Analyse the given statements.

Assertion (A): The type of chromosomes a child inherits from the father will determine the sex of that child in humans.

Reason (R): A father with the 'X' chromosome will have a daughter (XX), whereas a father with the 'Y' chromosome will have a boy (XY).

a. Both Assertion (A) and Reason (R) are true, and Reason (R) is the correct explanation for Assertion (A).

b. Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation for Assertion (A).

c. Assertion (A) is true, but Reason (R) is false.

d. Assertion (A) is false, but Reason (R) is true.

24. Identify the correct statement.

Statement 1: Gregor Mendel's experiments primarily involved the study of inheritance in plants, particularly pea plants.

Statement 2: Sickle cell anaemia is an autosomal hereditary disorder due to mutation.

a. Statement 1 is correct

c. Statements 1 and 2 are correct

25. Select the correct statements:

(i) Dominance is an autonomous feature of a gene.

(ii) Dominance depends on the gene product.

b. Statement 2 is correct

d. Statements 1 and 2 are incorrect

(iii) The product of a single gene always produces only one effect.

a. Only (ii)

c. (i) and (iii)

b. (ii) and (iii)

d. (i) and (ii)

26. It is said that Mendel proposed that the factor controlling any character is discrete and independent. His proposition was based on the _____________________.

a. Results of the F3 generation of a cross.

b. Observations that the offspring of a cross between plants having two contrasting characters show only the character without any blending.

c. Self-pollination of the F1 offspring.

d. Cross-pollination of the F1 generation with the recessive parent.

27. Which among the following cannot be explained on the basis of Mendel's Law of Dominance?

a. Factors occur in pairs.

b. The discrete unit controlling a particular character is called a factor.

c. Out of one pair of factors, one is dominant and the other is recessive.

d. Alleles do not show any blending, and both the characters appear as such in the F2 generation.

28. A child receives

a. 25% genes from his father

c. 75% genes from his father

b. 50% genes from his father

d. 100% genes from his father

29. A farmer has a strain of pea plants that consistently produce yellow peas when self-pollinated. However, when these yellow pea plants are cross-pollinated with another strain of pea plants that consistently produce green peas, all the offspring have yellow peas. Which inheritance pattern does this scenario best illustrate?

a. Dominant-recessive inheritance

c. Incomplete dominance

b. Codominance

d. Sex-linked inheritance

30. Read the following statements and select the correct answer.

Statement I : Heredity is the transmission of characters from one generation to the next generation.

Statement II: Variations are the differences in organisms within a very closely related group of organisms.

a. Both statements are true

b. Both statements are false.

c. Statement I is true, statement II is false.

d. Statement I is false, statement II is true.

31. If a plant is heterozygous and produced tall and dwarf in the F2 generation, it represents the law of ___________.

a. Dominance

b. Purity of gametes

c. Independent assortment

d. Free recombination

32. A true-breeding tall pea plant crossed with a true-breeding dwarf pea plant gave F1 and selfing of F1 plants, resulting in 787 tall and 277 dwarf plants in the F2 generation. The F1 plants are:

a. Homozygous

c. Azygous

b. Heterozygous

d. Polyzygous

33. The percentage of homozygous dominant individuals obtained from selfing Rr individuals is _______.

a. 25% b. 50% c. 75%

34. Which postulate of Mendel cannot be explained with a monohybrid cross?

a. Unit factors in pairs

c. Segregation of unit factors

0%

b. Dominance/recessive

d. Independent assortment of unit factors

35. When Mendel crossed a homozygous tall pea plant with a dwarf pea plant, the F1 generation consisted of _______________.

a. All pure tall plants

c. Some hybrid tall plants

b. All pure dwarf plants

d. All hybrid tall plants

36. The genes contributed by the mother to each of her progeny is called __________.

a. 1/2 b. 1/4 c. 1/8 d. 1/16

37. When a grey colour seed-producing pea plant is crossed with a white colour seed-producing pea plant, in the progeny, 164 grey seed-producing and 156 white seed-producing plants are obtained. This cross is called _____________.

a. Reciprocal cross

c. Incomplete dominance

b. Test cross

d. Codominance

38. The ratio of the total number of homozygotes to the total number of heterozygotes obtained in the F2 generation of a monohybrid cross is _________.

a. 1:1

2:1

1:2

3:1

39. The ratio of homozygous violet colour flower pea plants and heterozygous violet colour flower pea plants obtained in the F2 generation of a typical Mendelian monohybrid cross is _______. a. 3:1

1:1

2:1

40. When a green pod containing pea plant is crossed with a yellow pod containing pea plant, then in the progeny yellow pod containing plants are also produced. So, green pod containing plant is ________________.

a. Only heterozygous

b. Only homozygous

c. May be homozygous or heterozygous d. May be homozygous

41. Match the following and select the correct option.

List I

A. Colour of pod

B. Colour of flower

C. Colour of cotyledon

D. Colour of seed coat

a. A -I, B-IV, C-III, D - II

c. A-II, B-IV, C-I, D - III

42. Sickle cell anaemia is ___________.

a. Sex-linked inheritance

c. Infectious disease

43. Cystic fibrosis is caused by ______________.

a. Recessive autosomal allele

c. Recessive sex-linked allele

List II

I. Yellow

II. Green

III. White

IV. Violet

b. A-IV, B-I, C-II, D -III

d. A - III, B-IV, C-I, D - I

b. Autosomal heritable disease

d. Deficiency disease

b. Dominant autosomal allele

d. Dominant sex-linked allele

44. Short stature, a webbed neck, and a broad, shield-like chest are the abnormalities of _______.

a. Klinefelter's male

c. Turner's female

b. Down's female

d. Patau's female

45. Statement I: The law of segregation is one of the most important contributions to biology. Statement II: It introduced the concept of heredity factors as discrete physical entities that do not become blended.

a. Both statements are true

c. Statement I is true, statement II is false

b. Both statements are false

d. Statement I is false, statement II is true

46. Statement I: In his monohybrid cross with tall and dwarf pea plants, Mendel concluded that all tall plants in the F2 generation are not similar genotypically

Statement II: When Mendel self-pollinated the F2 plants, some of the tall plants produced only the tall plants, while other tall plants produced both tall and dwarf plants.

a. Both statements are true

c. Statement I is true, statement II is false

b. Both statements are false

d. Statement I is false, statement II is true

47. Statement I: Generally, the gametes are pure for the factors they possess.

Statement II: During the formation of gametes due to meiosis, the paired unit factors segregate randomly with equal probability.

a. Both statements are true

c. Statement I is true, statement II is false

b. Both statements are false

d. Statement I is false, statement II is true

48. Assertion (A): Male human beings are hemizygous for holandric genes. Reason (R): In male human beings, only one Y chromosome is present.

a. Both Assertion (A) and Reason (R) are true, and Reason (R) is the correct explanation for Assertion (A).

b. Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation for Assertion (A).

c. Assertion (A) is true, but Reason (R) is false.

d. Assertion (A) is false, but Reason (R) is true.

49. Assertion (A): XY-linked genes are incompletely sex-linked genes. Reason (R): XY-linked genes are also located on autosomes.

a. Both Assertion (A) and Reason (R) are true, and Reason (R) is the correct explanation for Assertion (A).

b. Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation for Assertion (A).

c. Assertion (A) is true, but Reason (R) is false.

d. Assertion (A) is false, but Reason (R) is true.

50. Assertion (A): In Klinefelter's male, feminine sexual development is not completely suppressed. Reason (R): In Klinefelter's male, one extra chromosome is present.

a. Both Assertion (A) and Reason (R) are true, and Reason (R) is the correct explanation for Assertion (A).

b. Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation for Assertion (A).

c. Assertion (A) is true, but Reason (R) is false.

d. Assertion (A) is false, but Reason (R) is true.

OUR ENVIRONMENT

8.1 INTRODUCTION TO OUR ENVIRONMENT

Everything around us forms our environment. It includes both living and non-living things. Living things comprise plants, animals, and microorganisms, while non-living things comprise all physical elements such as rainfall, wind, temperature, humidity, etc.

Living things are biotic elements and interact with the nonlivings things that form the abiotic elements of our environment. Nature's equilibrium is preserved by these interdependent relationships between organisms and abiotic elements. Thus, an environment has an impact on all living things.

8.2 ECOSYSTEM – WHAT ARE ITS COMPONENTS?

The term ecosystem was put forth by Sir Arthur Tansley in 1935. An ecosystem can be regarded as a functional unit of nature where living organisms interact among themselves and also with their surrounding physical environment. 'Eco' is the environment, and 'system' implies interacting and interdependent complex.

Ecology is the branch of science that deals with the study of the interaction between the living and non-living components of the environment.

Fig. 8.1 Ecosystem

Components of ecosystem

The ecosystem has two components - abiotic and biotic components. Ecosystem components

Fig. 8.2 Components of an ecosystem

Abiotic components

The non-living components of the ecosystem, such as the sun, air, temperature, rainfall, soil, wind, and minerals, are called abiotic components. The abiotic components affect not only the distribution and structure of organisms but also their behaviour and interrelationships.

These factors include:

i. Inorganic substances (water, carbon dioxide, nitrogen, oxygen, calcium, etc.)

ii. Organic compounds (carbohydrates, proteins, lipids, nucleic acid, etc.)

iii. Climatic factors (temperature, humidity, water, soil, minerals, pH, etc.)

Biotic components

Living organisms such as plants, animals, and microbes form the biotic components of the ecosystem. The biotic components interact with each other and with other abiotic factors to grow, reproduce and perform other physiological activities.

8.3

CLASSIFICATION OF ECOSYSTEM

In the biosphere, ecosystems can be classified based on their region, size, and formation.

A. On the basis of formation

Based on formation, ecosystems can be divided into natural and artificial ecosystems.

a. Natural ecosystem

An ecosystem that develops in nature without the involvement or interference of human beings is called a natural ecosystem. Terrestrial ecosystems like (forests, grasslands, deserts, etc.) formed on land, and aquatic ecosystems (like ponds, lakes, streams, estuaries, and sea) formed in water are natural ecosystems.

b. Artificial ecosystem

An ecosystem that is created and maintained by human beings is called an artificial or man-made or anthropogenic ecosystem. Agricultural lands, gardens, aquariums, and spacecraft are artificial ecosystems. A giant or the largest man-made ecosystem is an agroecosystem.

Fig. 8.3 Biotic and abiotic factors

B. On the basis of region

Another method of classification of ecosystems is based on the region they exist in, that is, on land or in water.

a. Terrestrial ecosystem

The ecosystems of land are known as terrestrial ecosystems. Some examples of terrestrial ecosystems are forests, grasslands, and deserts.

b. Aquatic ecosystem

The ecosystems that exist on the water are known as aquatic ecosystems. Based on the salinity of water, three types of aquatic ecosystems are identified: marine, freshwater, and estuarine.

C. On the basis of size

Ecosystem varies greatly in size. Based on size, the ecosystem can be divided into micro, meso, and macro.

a. Micro-ecosystem

A small ecosystem is called a micro-ecosystem (e.g., a pond, flowerpot, a site under a rock).

b. Meso-ecosystem

These are medium-scaled ecosystems (e.g., large lakes).

c. Macro-ecosystem

A large ecosystem is called a mega ecosystem (e.g., sea or ocean). Earth, which is a composite of all local ecosystems, is called biosphere or ecosphere. The entire biosphere (Earth) can be regarded as a global ecosystem or a 'giant ecosystem'.

8.4 CLASSIFICATION OF BIOTIC COMPONENTS OF ECOSYSTEM

Based on how dependent they are on one another for sustenance, the biotic elements of ecosystems can be divided into several groups. Depending on the mode of obtaining food, the biotic components can be classified into: producers, consumers, and decomposers.

8.4.1

Producers

Producers are autotrophs, i.e., those organisms that prepare their food using simple inorganic molecules. These include all green plants, blue-green algae (cyanobacteria), some bacteria, and phytoplanktons. Green plants contain the photosynthetic pigment chlorophyll that traps solar energy and forms glucose by using simple organic substances, namely water and carbon dioxide.

This process is called photosynthesis. The process of photosynthesis can be represented by the following equation:

Oxygen is released in this process. Plants then use the glucose to form complex compounds such as starch, proteins, and lipids.

8.4.2 Consumers

Consumers are unable to manufacture their food. Therefore they utilize materials and energy stored by the producers or consume other organisms. They are known as heterotrophs. The consumers are of the following categories.

a. Primary consumers

These are herbivores and depend completely on producers for their food. These organisms consume plants and plant products. For example, deer, goats, cows, rats, grasshoppers, tortoises, etc.

b. Secondary consumers

These include the animals that depend on a primary producer for their food. Secondary consumers can be carnivores and omnivores. They are known as primary carnivores or second-order consumers. For example, cats, dogs, foxes, frogs, water bugs, small fishes, etc.

c. Tertiary consumers

These are large carnivores that depend on primary and secondary consumers. They are known as secondary carnivores or third-order consumers. For example, sharks, crocodiles, wolves, lions, tigers, etc.

d. Quaternary consumers

These are even larger carnivores that feed on secondary carnivores. For example, tigers, lions, hawks, eagles, sharks, and crocodiles, etc.

In any food chain, the consumer present at the end of the chain is known as the top carnivore Humans can be primary, secondary, or tertiary consumers, depending on the food they eat.

8.4.3 Decomposers

Decomposers include bacteria and fungi. They obtain their food from the decomposition of dead producers (plants) and consumers (animals), as well as their waste products. The decomposers degrade the dead plants and animals into simple, small organic molecules that they utilize for themselves. Also, they release inorganic substances that are utilized by the plants into the environment. In this way, the decomposers help in the recycling of nutrients in the environment. Without decomposers, the Earth would be filled with piles of dead bodies. The decomposers are also called saprotrophs

Autotrophs

These organisms make their food by using water, CO2, sunlight, and chlorophyll.

Heterotrophs

They are organisms that cannot prepare their food and depend on others for it.

Green plants contain chloroplast. They do not contain chloroplast.

Derive it from inorganic sources after converting light energy into chemical energy.

Store chemical energy and sunlight.

Derive it directly or indirectly from other organisms.

They are not capable of storing energy.

They usually add O2 to the environment. They add CO2 to the environment.

They constitute the first trophic level.

They belong to second and, subsequently, higher trophic levels.

Table 8.1 Difference between autotrophs and heterotrophs

8.5 FLOW OF ENERGY IN THE ECOSYSTEM

Energy flow is the most essential requirement of all living things. Except for the deep sea hydrothermal ecosystem, where there is no light, the sun is the only source of energy for all the ecosystems on Earth. This is in the form of solar radiation or solar energy. Of the incident solar energy, less than 50% constitutes photosynthetically active radiation (PAR). Plants capture only 2 -10% of the PAR.

• Green plants, photosynthetic and chemosynthetic bacteria (producers/autotrophs) trap this solar energy and convert it into chemical form (food) from simpler inorganic materials. This chemical energy flows from one trophic level to another trophic level.

• Organisms at each trophic level depend on those at the lower trophic level for their energy demands. The amount of energy decreases at every successive level. The study of energy transfer between different trophic levels is called bioenergetics.

• All heterotrophs at various trophic levels in the ecosystems depend on producers for their food energy either directly or indirectly. So, the solar energy from the sun flows to producers and then to consumers in a stepwise manner.

• During this process, a good amount of energy is lost or dispersed, and some of it is also converted into other forms of energy. Thus, the flow of energy in any ecosystem is unidirectional.

• The energy that reaches the Earth is balanced by the energy that leaves the surface of the Earth as invisible heat radiation.

Incident solar radiation

Photosynthetically

Active radiation (PAR)

Captured in photosynthesis

gross primary productivity

Absorbed by gases/water vapour

Reflected by clouds

(2 to 10% of PAR) (50%)

Scattered by dust particles (100%) (50%) (1-5%)

Loss in respiration

Net primary productivity

Fig. 8.4 Fate of solar radiation incident on plant canopy

Living beings are the natural proliferations that depend on the continuous inflow of concentrated energy. The transfer of energy through a food chain is known as energy flow.

First trophic level producers (Plants)

Second trophic level primary consumers (Herbivores)

Third trophic level secondary consumers (Carnivores)

Fourth trophic level tertiary consumers (Top carnivores)

Fig. 8.5 Energy flows through different trophic levels

• Each trophic level has a certain mass of living material at a particular time, and it is called the standing crop. The standing crop is measured as the mass of living organisms (biomass) or the number of organisms per unit area. The biomass of a species is expressed in terms of fresh or dry weight (dry weight is more accurate than fresh weight).

• Energy flow between the trophic levels follows the 10% law as proposed by Lindeman (1942). According to this law, each trophic level gets 10% of its energy from its lower trophic level. The remaining is lost during the transfer or broken down in catabolic activities (respiration).

• For example, if the NPP (net primary production) in a plant is 100 kJ, the organic substance converted into the body mass of the herbivore that feeds on it is 10 kJ only. Similarly, the body mass of the primary carnivore is 1 kJ only.

8.5.1 Trophic levels

The environment includes several food levels called trophic levels. A trophic level is composed of those organisms that have the same source of energy and have the same number of steps away from the sun. The first trophic level in any ecosystem is producers, the second trophic level is primary consumers (herbivores), the third trophic level is secondary consumers, and the fourth trophic level is tertiary consumers, and so on.

Fig. 8.6 Generalized energy flow model of the ecosystem

Fig. 8.7 Different trophic levels in an ecosystem

8.5.2 Food chain

In any ecosystem, producers and different types of consumers are arranged in a linear sequence with respect to their food habits. Energy-rich food materials pass from producers to primary consumers (herbivores), from primary consumers to secondary consumers, and so on. The transfer of food energy from producers through a series of organisms in the ecosystem is called a food chain. Generally, a food chain ends with decomposers. The three major types of food chains in an ecosystem is the grazing food chain, parasitic food chain, and detritus food chain.

A. Grazing food chain (GFC)

This type of food chain starts from producers and passes through herbivores and carnivores. This can be represented as:

Grazing food chains are either terrestrial or aquatic. The food chains operating on land like a forest, grassland, desert, etc. are called terrestrial grazing food chains. These can be represented as follows:

Similarly, the grazing food chains operating in any water ecosystem like a pond, sea, etc. are called aquatic grazing food chains and can be represented as:

Grass (Producer)

Goat (Primary Consumer)

Man (Secondary Consumer)

B. Parasitic food chain

The food energy passes from larger organisms to small organisms in parasitic food chains. For instance, a tree that occupies the first trophic level provides shelter and food for many birds. These birds host many ectoparasites and endoparasites. The path of the flow of energy includes fewer large-sized organisms in the lower trophic levels and numerous small-sized organisms in the successive higher trophic levels.

C. Detritus food chain (DFC)

This food chain begins with dead organic matter (detritus). It is made up of heterotrophic organisms like bacteria and fungi. The energy and nutrient requirements of these organisms are obtained by degrading dead organic matter. These organisms are called decomposers or saprotrophs. Detritivores like earthworms are eaten by other animals. A detritus food chain can be represented as follows:

The nature of the energy flow may vary from one type of food chain to another.

Quaternary consumers

Tertiary consumers

8.5.3 Food web

In natural conditions, food chains never operate as isolated sequences. In an ecosystem, feeding relationships are much more complex. Omnivores in an ecosystem make the feeding relationships complex.

These omnivores, like man, birds, etc., have many interconnections with the animals of other food chains. They are interconnected, forming a sort of interlocking pattern. This is called the food web. A food web, unlike a food chain, shows several alternate pathways for the flow of energy. It allows an organism to obtain its food from two or more types of organisms of lower trophic levels.

The stability of an ecosystem in nature is maintained by the food web, then the food chain. This is because organisms at every trophic level are kept under a natural check so that an ecological balance is maintained.

It is a straight single pathway through which food energy travels in the ecosystem.

Members of higher trophic levels feed upon a single type of organism of lower trophic levels.

The presence of separate or isolated food chains adds to the instability of the ecosystem.

It consists of several interconnected food chains through which food energy passes in the ecosystem.

Members of higher trophic levels can feed upon several alternative organisms of the lower trophic levels.

The presence of food webs increases the stability of the ecosystem. It does not add to the adaptability and competitiveness of the organisms.

Food webs increase the adaptability and competitiveness of organisms.

Table 8.2 Difference between the food chain and food web

Goat

Kite Lion

Jackal

Wild cat

Snake Owl

Rabbit

Mouse

Green plant Producers

Fig. 8.9 Food web

Food Chain

Food Web

8.5.4 Ecological pyramids

The graphic representation of different trophic levels of the food chain in the form of a pyramid is called an ecological pyramid. The concept of ecological pyramids was introduced by Charles Elton. So they are called Eltonian pyramids.

The three ecological pyramids that are of usual importance are the pyramid of numbers, the pyramid of biomass, and the pyramid of energy. Pyramids of number and biomass may be upright or inverted. But the pyramid of energy in any ecosystem is always upright.

Pyramid of numbers

The pyramid of numbers is the graphic representation of several individuals per unit area of various trophic levels. In most ecosystems, the number of producers is at its maximum. The pyramid of numbers may be upright or inverted. Pyramids of numbers in a grassland and a pond ecosystem are upright.

• In a grassland ecosystem, only three consumer trophic levels are supported. In a pond ecosystem, four trophic levels, i.e. phytoplankton (producers), zooplankton (primary consumers and herbivores), small fishes (secondary consumers and primary carnivores), large fishes (tertiary consumers and secondary carnivores), are represented in descending order of their numbers.

• If the base and apex of the pyramid are narrow with the middle broad, it is spindle-form. In a forest ecosystem, a pyramid of numbers is in spindle form.

• The base of the pyramid is narrow, with large trees that are fewer in number. The middle part of the pyramid is broad with more herbivores (fruit-eating birds, elephants, deer, etc.). The top of the pyramid is narrow, with a lesser number of carnivores.

• The pyramid of numbers in the case of the parasitic food chain is inverted as the number of organisms at each trophic level progressively increases from bottom to top. In this pyramid, a large tree (a producer) supports many herbivores (squirrels and frugivorous birds) which support secondary consumers like ectoparasitic ticks, mites, and lice, which may support toporder consumers and hyperparasites.

Trophic Level

TC(Tertiary consumer)

SC(Secondary consumer)

PC(Primary consumer)

PP(Primary consumer)

Number of individuals

Fig. 8.10 Pyramid of numbers in a grassland ecosystem

Pyramid of biomass

The pyramid of biomass is the amount of biomass (dry wt kg/m2 ) present per unit area at different trophic levels. It is more accurate than the pyramid of numbers because the pyramid of numbers does not consider the size of the individual.

The pyramid of biomass is upright in grassland and forest ecosystems (terrestrial ecosystems). But in a pond ecosystem (aquatic ecosystem), it is inverted because the biomass of zooplankton or small fishes is far greater than that of phytoplankton.

Fig. 8.11 Pyramid of biomass shows a sharp decrease in biomass at higher trophic levels

Fig. 8.12 Inverted pyramid of biomass small-standing crop of phytoplankton supports large standing crop of zooplankton

Pyramid of energy

The pyramid of energy is the graphic representation of the amount of energy trapped per unit of time and area in different trophic levels. The pyramid of energy gives the best picture of the overall view of an ecosystem. As the energy is transferred from one trophic level to another, there is a gradual decrease of energy, and hence, it is always upright

Pyramids of energy are always upright as there is a progressive decrease of energy from the lower trophic level to the next higher trophic level. This is because when the energy flows from one trophic level to the next higher trophic level, some energy at each step is lost as heat. Each bar in the energy pyramid indicates the amount of energy present at each trophic level at a given time or annually per unit area.

J of

Fig. 8.13 Ideal pyramid of energy. Observe that primary producers convert only 1% of the energy in the sunlight available to them into NPP.

8.6 HOW DO OUR ACTIVITIES AFFECT THE ENVIRONMENT?

The basic concern of global environmental change is the ever-increasing human population that is putting an equally increasing demand for more food and resources.

The increasing use of resources by people, depletion of fossil fuel reserves, and large-scale changes in land use systems are impacting all components of the environment. The two environmental issues taht has major impact are: the depletion of the ozone layer and waste disposal.

8.6.1 Ozone depletion in the stratosphere

The atmosphere of the Earth contains a condensed layer of ozone gas known as the ozone layer. Living things are not harmed by this. It is necessary for the survival and sustenance of life on Earth. The atmosphere acts as a shield, absorbing most of the UV radiation and protecting the ecosystem. The ozone layer shields the Earth's inhabitants from harmful radiation.

• The ozone in the troposphere behaves like bad ozone and creates pollution problems. Ozone, hydrogen peroxide, and PAN form photochemical smog. An increase in ozone concentration near the Earth's surface reduces crop yields. It causes adverse effects on human and animal health by causing pulmonary oedema, fatigue, etc.

• The ozone O3 in the stratosphere acts as good ozone. It forms a shield and protects living beings on the Earth from UV radiation from the sun. Ozone in a column of air from the ground to the top of the atmosphere is measured in Dobson units (DU).

Formation of ozone

Molecular oxygen present in the stratosphere absorbs the short wavelength of ultraviolet radiation in the range of 1800Å - 2200 Å. This causes the splitting of molecular oxygen into its constituent atoms. The constituent atoms combine with molecular oxygen to produce ozone.

O2 → O + O

O2 + O → O3 (ozone)

In this way, ozone is a result of photochemical reactions in which the starting molecule is oxygen. In the stratosphere, along with the above reaction, another photochemical reaction also occurs. Ozone absorbs UV radiation in the range of 2000 - 2900 Å, which causes the breakdown of ozone molecules.O3 → O2 + O

O3 + O → 2O2

The photochemical reactions, which are the formation and destruction of ozone molecules, balance each other in normal times. This results in the effective absorption of ultraviolet radiation in the stratosphere and does not allow them to reach the Earth’s surface.

Reasons for ozone depletion in the stratosphere

• Major pollutants responsible for ozone depletion in the stratosphere are called ozone-depleting substances (ODS). Chloroflouro-carbons (CFCs), nitrogen oxides, and hydrocarbons like methane (CH4) are ozone-depleting substances.

• CFCs are widely used as coolants in air conditioners, refrigerators, aerosol propellants, etc. Jet engines, motor vehicles, and nitrogen fertilizers also cause CFC and nitrogen oxide pollution.

• Ozone depletion is a catalytic process. Although CFCs are inert in normal chemical and physical reactions, they release active chlorine radicals under the influence of UV radiation. They act as catalysts to convert ozone into oxygen. It results in a thinning of the ozone layer in the stratosphere, which is called an ozone hole. It is now regularly seen above Antarctica every year between late August and early October.

2. The free chlorine atom hits an ozone molecule.

1. UV causes a chlorine atom to break away from the CFC molecule.

Stratosphere

3. The chlorine atom pulls one oxygen atom away.

4. A free oxygen atom hits the chlorine monoxide molecule.

6.Free chlorine will continue to deplete ozone in the stratosphere.

Fig. 8.14 Effect of CFC on ozone

5. The result is another free chlorine atom.

CFC molecule

Effects of ozone depletion

Depletion of ozone in the stratosphere causes direct and indirect harmful effects. They are:

• UV radiation is shorter than UV-B and directly reaches the Earth’s surface. It causes mutations and impairs nucleic acids. It causes melanoma type of skin cancer.

• High concentrations of UV-B cause inflammation of the cornea (snow-blindness), cataracts, loss of immunity, etc.

• UV radiation affects crops, forests, animals, and materials such as paints and plastics.

• Decreased photosynthesis leads to an increase in the carbon dioxide concentration, resulting in global warming.

International efforts to check ozone depletion

Montreal protocol is a series of international agreements on the reduction and elimination of CFCs and other ozone-depleting substances, followed by the Vienna convention (1985) on protecting the ozone layer. Montreal Protocol is a landmark international agreement held in Montreal (Canada) in 1987. Around 150 countries signed this international agreement to limit the production and use of ozone-depleting substances, phasing out ozone-depleting substances, and implementing alternatives for CFCs. The UNO declared 16 September as Ozone Protection Day.

Another initiative was the Kyoto protocol, which is an international treaty aimed at addressing global climate change. It sets binding targets for industrialized nations to reduce their greenhouse gas emissions. Adopted in 1997, the protocol represents a collective effort to mitigate the impact of human activities on the environment.

8.6.2 Managing garbage we produce

In our everyday life, we use a lot of materials and throw them away. These useless leftover or discarded materials are called wastes. The waste materials can be gaseous (automobile exhausts, smoke from the chimneys of houses and industries), liquid (effluents from factories and industries, sewage or solid (food waste, cow dung, and human excreta, trash and rubbish, farm waste, industrial and chemical wastes). Mostly solid wastes are the main sources of soil pollution. The waste we generate may be biodegradable or non-biodegradable.

Fig. 8.15 The ozone hole is the area above Antarctica

When accumulated, these heaps of solid wastes make the surroundings dirty and pollute the soil. Earlier, the solid wastes generated due to human activities were easily degraded by decomposers present in nature and did not create a harmful effect on the environment.

Methods of waste disposal

Landfills: A landfill site is a location for the disposal of waste and is the oldest method of waste treatment. In this method, the solid waste is dumped into the low-lying areas. Each layer is about 1.5 meters covered with soil of about 20 cm thickness.

Composting: In this method, the waste is converted into humus and stable mineral compounds. This is of great use for the soil as it can be used as manure. The crop yield is improved, and there is less need for fertilizers and pesticides by microbial action.

Incineration: This process involves the aerobic burning of the combustible constituents of solid wastes like garbage, rubbish, and dead animals in the properly constructed hearth of furnaces at high temperatures(>670 °C). It can also be used to generate steam. It is an ideal method for medical waste management as it eliminates infectious organisms.

Pyrolysis: It involves anaerobic destructive distillation of the combustible constituents of the solid wastes at high temperatures (650 -1000 °C) to recover the chemical constituents and chemical energy of organic wastes.

QUICK REVIEW

• The biotic and the abiotic components of an ecosystem are interdependent.

• The producers use the energy from sunlight available to the rest of the ecosystem.

• There is a loss of energy as we move from one trophic level to the next; this limits the number of trophic levels in a food chain.

• The ecological pyramids of usual importance are the pyramid of numbers, the pyramid of biomass, and the pyramid of energy.

• The pyramid of numbers and biomass may be upright or inverted, but, the pyramid of energy is always upright.

• Human activities have an impact on the environment.

• The use of chemicals like CFCs has degraded the ozone layer. Since the ozone layer protects against the ultraviolet radiation from the Sun, this could damage the environment.

• The waste we generate may be biodegradable or non-biodegradable.

• The disposal of the waste we generate is causing severe environmental issues

• Some waste disposal methods include: landfills, composting, incineration and pyrolysis.

WORKSHEET - 1

MULTIPLE CHOICE QUESTIONS WITH SINGLE CORRECT ANSWER

I. Ecosystem and environment

1. The functional unit of nature is:

a. Organisms

c. Ecosystem

2. The two basic categories of the biosphere are:

a. Terrestrial

c. Both (a) and (b)

3. Forest, grassland, and desert are examples of:

a. Man-made ecosystems

c. Terrestrial ecosystems

4. An aquarium is a:

a. Terrestrial ecosystem

c. Man-made aquatic ecosystem

5. Aquaculture Pond is a:

a. Terrestrial ecosystem

c. Consumer

b. Environment

d. Ecology

b. Aquatic

d. None

b. Aquatic ecosystems

d. Both (a) and (b)

b. Natural aquatic ecosystem

d. Both (a) and (b)

b. Artificial ecosystem

d. Both (a) and (b)

6. According to many ecologists, the entire biosphere is regarded as:

a. Local ecosystem

c. Population

7. Artificial ecosystems are characterized by:

a. High productivity

c. High diversity

b. Global ecosystem

d. Community

b. Complex food chains

d. More cycling of nutrients

8. An ecosystem resists changes because it is in a state of:

a. Deficiency of light

c. Homeostasis

b. Shortage of components

d. Imbalance

9. Match the Column - I with Column - II:

Column - I

i. Cold desert ecosystem

ii. Grassland ecosystem

iii. Forest ecosystem

iv. Hot desert ecosystem

a. i - D, ii - A, iii - B, iv - C

c. i - E, ii - C, iii - B, iv - A

Column - II

A. Eastern Rajasthan

B. Prairies

C. Thar desert

D. Sunderbans

E. Ladakh

b. i -E, ii - A, iii - B, iv - C

d. i - E, ii - C, iii - B, iv - D

10. Which statement about a small pond ecosystem is incorrect?

a. This is a fairly self-sustainable unit.

b. All four basic components of an ecosystem are well exhibited.

c. The abiotic components of the water with all the dissolved organic and inorganic substances and the rich soil deposit at the bottom of the pond.

d. This ecosystem performs all the functions of any ecosystem except the unidirectional flow of energy.

II. Structure and function of the ecosystem

1. Primary producers of an aquatic ecosystem are:

a. Phytoplankton

c. Higher plants

2. An ecosystem contains:

a. Green plants and animals

b. Algae

d. All the above

b. Green plants, animals, decomposers, and abiotic environment

c. Producers and consumers

d. Green plants and decomposers

3. The following is a logical sequence:

a. Consumer - producer - decomposer

c. Producer - consumer - decomposer

b. Producer - decomposer - consumer

d. Decomposer - consumer - producer

4. Biological equilibrium is an equilibrium among the:

a. Decomposers and producers

c. Producers, consumers and decomposers

b. Producers and consumers

d. Producers

5. Which one of the following components of the ecosystem comes from outside?

a. Energy

c. Plants

b. Insects

d. Oxygen

6. The basic requirement for any ecosystem to function and sustain is:

a. Biotic components

c. Nutrient cycling

7. Which is not a structural aspect of the ecosystem?

a. Productivity

c. Diversity

b. Decomposers

d. Solar energy input

b. Species composition

d. Life cycle

8. The number of primary producers within a specified area would be maximum in:

a. Desert

c. Grassland

III. Energy flow

1. Food webs in the ecosystems are formed due to:

a. Independency

c. Both (a) and (b)

b. Forest ecosystem

d. Pond ecosystem

b. Interdependency

d. None

2. About how much of the chemical energy of producer tissues becomes the chemical energy of herbivore tissues?

a. 50%

c. 30%

3. The trophic level of a lion in a forest ecosystem is:

a. T4

c. T2

b. 10%

d. 1%

b. T3

d. Both (a) and (b)

4. What percentage of incident solar radiation is captured in photosynthesis by plants?

a. 0.8 - 4%

c. 100%

b. 2 - 10%

d. 50%

5. About how much of the solar energy that falls on the leaves of a plant is converted to chemical energy by photosynthesis:

a. 1%

c. 10%

6. A food chain starts with:

a. Nitrogen-fixing organisms

c. Respiration

7. A group of interconnected food chains is called a:

a. Pyramid of energy

c. Food cycle

8. The incorrect food chain among the following is:

b. 3.3%

d. 50%

b. Photosynthesising organisms

d. Decomposers

b. Food web

d. Complex food chain

a. Plants → Grasshopper → Frog → Snake → Hawk

b. Plants → Frog → Snake → Hawk

c. Plants → Caterpillar → Lizard → Snake

d. Zooplankton → Phytoplankton → Fish→ Bird

9. If the energy in the body mass of secondary carnivores is 0.1 kJ, the NPP of producers of that ecosystem:

a. 10,000 kJ

c. 100 kJ

b. 1,000 kJ

d. 10 kJ

10. The food chain that starts from plants and goes from smaller to larger animals is:

a. Detritus food chain

c. Parasitic food chain

11. Trophic levels in the ecosystem are formed by:

a. Only bacteria

c. Only herbivores

b. Saprophytic food chain

d. Predator food chain

b. Only plants

d. Organisms linked in the food chain

12. When a peacock eats snakes, which eat insects thriving on green plants, the peacock is:

a. A primary decomposer

c. A primary consumer

b. The apex of the food pyramid

d. Final decomposer

13. If 0.16 kJ is the NSP in tertiary carnivores, what is the NPP in that ecosystem? (Note: 0.01% of NPP is transferred to the tertiary carnivores.)

a. 80 J

c. 400 J

b. 1600 KJ

d. 8000 KJ

14. About how much of the net primary productivity of a terrestrial ecosystem is eaten and digested by herbivores?

a. 1%

c. 10%

IV. Ecological pyramids

b. 40%

d. 90%

1. Which of the following ecological pyramids is most representative of the functional characteristics of an ecosystem?

a. Pyramid of number

c. Pyramid of energy

b. Pyramid of biomass

d. All are equally representative

2. The organisms that are not represented in ecological pyramids are:

a. Producers

c. Herbivores

b. Saprophytes

d. Carnivores

3. The relationship in an ecosystem can be depicted by:

a. Pyramid of energy

c. Pyramid of numbers

4. The pyramid of numbers deals with the number of:

a. Species in an area

c. Individuals at a trophic level

b. Pyramid of biomass

d. All of the above

b. Individuals in a community

d. Subspecies in a community

5. The specific inverted pyramids of food chains from the following are:

a. Pyramid of energy

b. Pyramid of numbers in a parasitic food chain

c. Pyramid of number in pond ecosystem

d. Pyramid of energy, pyramid of numbers in a parasitic food chain, and pyramid of biomass in the sea

6. What type of ecological pyramid would be obtained with the following data?

Secondary consumer: 120 g

Primary consumer: 60 g

Primary producer: 10 g

a. Upright pyramid of biomass

c. Inverted pyramid of biomass

V. Ozone depletion and waste management

b. Pyramid of energy

d. Upright pyramid of numbers

1. Where is the ozone layer located in Earth's atmosphere?

a. Troposphere

c. Mesosphere

b. Stratosphere

d. Thermosphere

2. What is the main consequence of ozone layer depletion?

a. Increased global warming

c. Higher levels of air pollution

b. Enhanced photosynthesis

d. Increased skin cancer rates

3. Which of the following is a method for hazardous waste disposal?

a. Landfill

c. Incineration

4. Which is an example of biodegradable waste?

a. Plastic bottles

c. Banana peels

b. Recycling

d. Composting

b. Glass jars

d. Metal cans

5. Which international agreement aims to protect the ozone layer?

a. Kyoto protocol

c. Vienna convention

WORKSHEET - 2

b. Paris agreement

d. Basel convention

MULTIPLE CHOICE QUESTIONS WITH SINGLE CORRECT ANSWER

1. The unit of the biosphere is:

a. Ecosystem

c. Community

b. Biome

d. Population

2. Who proposed the term 'Ecosystem'?

a. Calvin

c. Tansley

3. All ecosystems have no boundaries because:

a. They require minerals for their functioning.

b. They cannot occur in isolation.

c. They are large.

d. They require light from all sources.

4. Biologists celebrate 5th June as:

a. World Population Day

c. World Hygiene Day

b. Odum

d. Gardner

b. World Environment Day

d. Malaria Day

5. Which of the following are artificial aquatic ecosystems?

a. Lakes and reservoirs

c. Fishery tanks and aquaria

6. An ecosystem is a:

b. Croplands and canals

d. All of these

a. Group of interacting species in one place at one time.

b. Biological community and components of physical environment with which the community interacts.

c. Group of interacting chemicals and their cycles.

d. Group of components that interact with one another.

7. The study of the relationship of organisms with their environment is called ecology, was defined by:

a. Odum

c. Ernst Haeckel

8. Which of the following is a giant ecosystem?

a. Biosphere

c. Ecosphere

9. The giant anthropogenic ecosystem is:

a. Garden

c. Agro ecosystem

b. Arthur Tansley

d. Nancy A. Moran

b. Earth

d. All of these

b. Aquarium

d. Pond ecosystem

10. The global ecosystem is too big and complex to be studied at one time, so it is convenient to divide it into two basic categories, namely:

a. Natural and man-made ecosystem

c. Terrestrial and aquatic ecosystems

b. Biotic and abiotic ecosystem

d. Both (b) and (c)

11. The organisms that thrive upon the remains of dead plants and animals are categorised as:

a. Carnivores

c. Scavengers

12. Artificial ecosystems are:

a. Cropland ecosystem

c. Aquarium

13. An abiotic component in an ecosystem is:

a. Bacteria

c. Water

14. Biotic components include:

a. Only consumers

c. Only producers and consumers

15. In a forest ecosystem, green plants are:

a. Decomposers

c. Primary producers

b. Omnivores

d. Predators

b. Aquaculture ponds

d. All of the above

b. Chlamydomonas

d. Chlorella

b. Only producers

d. Producers, consumers and decomposers

b. Primary consumers

d. Consumers

16. The two major functional components of an ecosystem are:

a. Food chain and decomposers

c. Mineral cycling and energy flow

b. Energy flow and food chain

d. Energy flow and decomposers

17. The energy available at the primary consumer level is:

a. Greater than that of the primary trophic level

b. Lesser than that of primary carnivore level

c. Greater than that of secondary carnivore level

d. Lesser than that of secondary carnivore level

18. In a food chain, initial organisms are:

a. Autotrophs

c. Primary consumers

b. Top consumers in the food chain

d. Secondary consumers

19. The sequence of species through which the organic molecules in the community pass is called a:

a. Food web

c. Nutrient cycle

20. In the ecological food chain, man is a:

a. Producer only

c. Both producer and consumer

b. Food chain

d. Pyramid of energy

b. Consumer and decomposer

d. Consumer

21. In a grazing food chain, the largest population is that of:

a. Producers

c. Decomposers

22. The organisms at the base of the food chain are:

a. Herbivores

c. Saprophytic plants

b. Secondary consumers

d. Primary consumers

b. Photosynthetic plants

d. Carnivores

23. A detritus food chain, in comparison to a grazing food chain, is:

a. Equal

c. Longer

24. We refer to the following as the food chain:

b. Broader

d. Shorter

a. Large number of human beings forming a human chain near a source of food

b. Large number of animals near a source of food

c. Transfer of food energy from the green plants through a series consumed by an organism

d. None of these

25. The correct path of energy flow in an ecosystem is:

a. Herbivores → carnivores → producers → decomposers

b. Herbivores → producers → carnivores → decomposers

c. Producers → herbivores → decomposers

d. Producers → herbivores → carnivores → decomposers

26. Mark the odd one (concerning the second trophic level):

a. Wolf

c. Cow

b. Eagle

d. Zooplanktons

27. Energy requirement for maintenance of the body with successively higher trophic level:

a. Decreases

c. Remains the same

28. In a food chain, herbivores are:

a. Primary consumers

c. Primary producers

29. In the detritus food chain, the primary consumer is:

a. Insect, larva, nematodes

c. Bacteria and fungi

b. Increases

d. Always 10%

b. Decomposers

d. Secondary consumers

b. Herbivores and nematodes

d. Both (a) and (c)

30. Which one of the following types of organisms occupies more than one trophic level in a pond ecosystem?

a. Fish

c. Frog

31. Ecological pyramids do not accommodate:

a. Food chain

c. Food web

b. Zooplankton

d. Phytoplankton

b. Trophic levels

d. None

32. The pyramid of numbers in a grassland ecosystem is:

a. Always inverted

c. Always upright

b. Inverted and upright

d. Spindle-shaped

33. For tree and grassland ecosystems, the pyramid of biomass is:

a. Upright

c. Spindle-shaped

b. Inverted

d. U-shaped

34. Which of the following ecological pyramids is most representative of the functional characteristics of an ecosystem?

a. Pyramid of number

c. Pyramid of energy

b. Pyramid of biomass

d. All are equally representative

35. The organisms which are not represented in ecological pyramids are:

a. Producers

c. Herbivores

b. Saprophytes

d. Carnivores

36. If a producer is a large tree that supports several herbivorous animals that are further attacked by ectoparasites, the pyramid of numbers shall be:

a. Inverted

c. Irregular

b. Upright

d. Spindle-shaped

37. World Ozone Day is celebrated in: [NEET 2018]

a. 5th June

c. 22nd April

b. 21st April

d. 16th September

38. In the stratosphere, which of the following elements acts as a catalyst in the degradation of ozone and release of molecular oxygen? [NEET 2018]

a. Carbon

c. Oxygen

b. Cl

d. Fe

39. The zone of the atmosphere in which the ozone layer is present is called: [NEET 2014]

a. Ionosphere

c. Stratosphere

b. Mesosphere

d. Troposphere

40. 'Good ozone' is found in the: [NEET 2011]

a. Mesosphere

c. Stratosphere

b. Troposphere

d. Ionosphere

41. Which of the following is a secondary pollutant? [NEET 2018]

a. CO

c. O3

b. CO2

d. SO2

1: LIFE PROCESSES IN PLANTS

Worksheet 1

I. Nutrition

1. b 2. d

II. Photosynthesis

III. Transportation in plants and transpiration

IV. Excretion in humans

Worksheet 2

IV. Respiration in plants 1.a 6. b

Worksheet 2

3: NEURAL CONTROL AND COORDINATION

Worksheet 1

I. Nervous system in animals 1. b 2. c 3. d 4.d 5.d

II. Central nervous system and peripheral nervous system

2: LIFE PROCESSES IN HUMAN BEINGS

Worksheet 1

I. Nutrition in humans

III. Neurons and nerve impulse

IV. Reflex action

II. Respiration in humans

III. Transportation in humans

Worksheet 2

21. c 26. c

4: CHEMICAL COORDINATION AND INTEGRATION

Worksheet 1

I. Human endocrine system

1. c 6. c 2. c 3.d 4.a 5. c 7.a 8. c 9. c

II. Hypothalamus and pituitary gland

1. a 6. b

III. Pineal, thyroid, parathyroid, and thymus glands

1. b 6. d 2. b 7. a 3. a 8. a 4. c 5. d

IV. Adrenal gland, pancreas and gonads

1. c 6. c 11. c 2. c 7. 3. b 8. d

Worksheet 2

1. c 6. d 11. a 16. c 21. d 26. b 31. b 2. c 7. b 12. c 17. a 22. c 27. c 32. c 3. a 8. c

5: CONTROL AND COORDINATION IN PLANTS

Worksheet 1

I. Plant Hormones

1.

b

II. Photoperiodism and vernalisation

III. Tropic Movements

Worksheet 2

6. HOW DO ORGANISMS REPRODUCE?

Worksheet 1

I. Introduction

II. Modes of reproduction used by single organisms

III. Sexual reproduction in flowering plants 1. d 6.d

IV. Reproduction in human beings

Worksheet 2

7: HEREDITY

Worksheet 1

I. Introduction to heredity and variation

1.b 6. c 2. b 3. a 4. b 5. a

II. Mendelian inheritance

1. c 6. b 11. a 16. a 21. a 26. b

III. Sex determination

1. a 2. b 3. b 4. c 5. a

IV. Genetic disorders

1.d 2. a 3. d 4. b 5. d

Worksheet 2 1. d 6. c 11. c 16. b 21. d 26. b 31. c 36. a 41. a 46. b 2.

8: OUR ENVIRONMENT

Worksheet 1

I. Ecosystem and environment

II. Structure and function of the ecosystem

1. d 6. d 2. c 7. d 3. c 8. d 4. c 5. a

III. Energy flow

b

b

IV. Ecological Pyramids

1. c 6. c 2. b 3. d 4. c 5. b

V. Ozone depletion and waste management 1. b 2. d 3. c 4. c 5. c

Worksheet 2