AQA GSCE (9-1) Biology for Combined Science: Trilogy Student Book Look Inside

Biology

PHOTOSYNTHESIS

2

IDEAS YOU HAVE MET BEFORE:

IN THIS CHAPTER YOU WILL FIND OUT ABOUT:

PLANT CELLS ARE ADAPTED TO CARRY OUT THEIR FUNCTIONS.

HOW DO PLANTS' SPECIAL ADAPTATIONS HELP THEM SURVIVE AND GET ALL THEY NEED FROM THE ENVIRONMENT?

• Plants have adaptations that allow them to survive and grow, such as air pores in the leaves.

• Cells have specific adaptations so that they can carry out a specialised function in the plant.

• Photosynthesis happens in the mesophyll cells in leaves.

Water is absorbed through root hair cells.

• Green plants use water and minerals from the soil to grow. They use light, carbon dioxide and water to produce carbohydrates in their leaves by photosynthesis.

• The amount of photosynthesis can be affected by a range of different factors.

• The useful product of the photosynthesis reaction is glucose.

light from Sun

WHAT FACTORS AFFECT THE PHOTOSYNTHESIS REACTION? HOW DO THEY AFFECT IT?

PHOTOSYNTHESIS IN CELLS

oxygen released into the air via the stomata water from soil taken in through root hair cells on roots

carbon dioxide enters the leaf from the air via the stomata

PLANTS CAN MOVE NUTRIENTS AND WATER TO WHERE THEY ARE NEEDED.

HOW IS THE SUPPLY OF WATER TO A PLANT AFFECTED BY ENVIRONMENTAL CONDITIONS?

• Plants have a network of vessels that transport water and minerals to their leaves and flowers.

• All cells contain watery cytoplasm. Plants need water so that the chemical reactions needed to sustain life can occur.

THE STRUCTURE OF A LEAF ALLOWS MOLECULES TO BE TAKEN IN FROM THE ENVIRONMENT, AND TO BE PASSED OUT. • Diffusion is the movement of molecules from a higher concentration to a lower concentration until they are equally distributed.

• Substances that plants need diffuse into the plant.

Other substances pass out of plants by diffusion.

48

AQA GCSE Biology for Combined Science: Trilogy: Student Book

• The useful products of photosynthesis are simple carbohydrates, for example glucose and sucrose.

• Different environmental factors interact to limit the rate of photosynthesis in different habitats at different times.

• The environment in which plants are grown can be artificially manipulated.

film of water

lower epidermis

carbon dioxide enters leaf due to low wax cuticle concentration inside

spongy mesophyll cells

guard cell

• There are two transport systems in plants: xylem transports water up the plant and phloem transports substances up and down the plant.

• Water movement through the plant is affected by different environmental factors.

• Water loss in plants is a consequence of adaptations for photosynthesis.

DIFFUSION ALSO ALLOWS SUBSTANCES TO PASS IN AND OUT OF CELLS. WHICH SUBSTANCES DIFFUSE INTO PLANTS? • Different factors that affect the rate of diffusion in plant systems.

• Concentration gradients can affect the rate of photosynthesis.

• Substances move in and out of the leaf during different processes, for example, photosynthesis, respiration and transpiration.

cross-section of part of leaf

PLANTS MAKE THEIR FOOD WITH THE HELP OF SUNLIGHT.

• Adaptations of cells and tissues in leaves allow them to photosynthesise efficiently.

• Stomata are adapted to control the exchange of gases.

• Cells and tissues in leaves, stems and roots are designed for the maximum exchange of substances in and out of the plant.

carbon dioxide diffuses in through stomata

air spaces

high concentration of oxygen low concentration of carbon dioxide oxygen diffuses out through stomata

Photosynthesis

49

Biology

Exploring the heart

Key words

Learning objectives: • describe the structure and function of the heart • identify the functions and adaptations of the parts of the heart • explain the movement of blood around the heart.

aorta atrium (plural: atria) coronary artery pacemaker vena cava ventricle

Active or larger animals need a transport system with a pump. This is to maintain a constant supply of materials to meet the demand of all cells throughout the body, and to remove waste.

Ventricles have thicker walls than atria because they pump blood further. The left ventricle pumps blood around the body. It has a thicker wall than the right ventricle, which only pumps blood to the lungs.

Valves between the atria and the ventricles prevent the backflow of blood. They open to let blood through and then shut.

3 4

The heart

Describe the functions of the different chambers of the heart.

Describe how the atria and ventricles move blood through the heart.

Explaining blood flow

The heart is made of muscle. Heart muscle continually contracts and relaxes. It uses a lot of energy. Heart muscle receives oxygen and glucose for respiration from the blood brought by the coronary artery.

coronary arteries

The heart has two pumps (a double circulation) that beat together about 70 times every minute of every day.

Each pump has an upper chamber (atrium) that receives blood and a lower chamber (ventricle) that pumps blood out. Both atria fill and pump blood out at the same time, as do both ventricles. The natural resting heart rate is controlled by a group of cells located in the right atrium that act as a pacemaker.

• The vena cava (main vein) transports blood from the body to the right atrium.

• The pulmonary artery transports deoxygenated blood from the right ventricle to the lungs.

Describe how blood flows through the heart.

from body

from lungs

vena cava pulmonary vein right atrium left atrium right ventricle deoxygenated blood oxygenated blood

valve left ventricle

Key information Atria receive blood, ventricles pump it out.

oxygenated blood

right atrium

Figure 3.31 Why does the heart need an oxygen supply?

The parts of the heart

left atrium

valve open

• The pulmonary vein transports oxygenated blood from the lungs to the left atrium.

• The aorta (main artery) transports oxygenated blood from the left ventricle to the body.

AQA GCSE Biology for Combined Science: Trilogy: Student Book

valve open

A

Right atrium

Left atrium

Right ventricle

Did you know?

The complete cardiac cycle normally takes 0.8 seconds.

Heart relaxes and blood enters both atria.

The lungs

right ventricle C

Ventricles contract from the bottom upwards which forces blood into the pulmonary artery and aorta.

Left ventricle

B

left ventricle

Atria contract at the same time which forces blood into both ventricles.

Figure 3.34 The cardiac cycle

The heart has four main blood vessels:

106

aorta

Figure 3.33 Why does the heart need two pumps?

deoxygenated blood

valve shut

2

to body

valve closed

Blood from the body contains very little oxygen and enters the heart at the right atrium, passes into the right ventricle and is pumped to the lungs to be oxygenated.

What is the function of the heart?

to lungs

In the second century, Galen thought blood was made in the liver. He said it flowed round the body, but was used as fuel for the muscles. Galen also thought there were holes in the septum, which allowed blood to flow from one side of the heart to the other. In the seventeenth century, Galen’s ideas were disproved by William Harvey, who explained heart structure and described the blood vessels.

Blood from the lungs contains oxygen and enters the heart at the left atrium. It passes into the left ventricle and is pumped out to the body.

1

pulmonary artery

3.13

The body

Figure 3.32 Blood flow through the heart

5

Explain the sequence of contractions and valve openings as blood passes through the heart.

6

If a coronary artery supplying the left ventricle becomes blocked, what effect does this have on the functioning of the heart? Explain your answer.

Google search: 'heart structure'

107

Biology pituitary glandTIER ONLY HIGHER pituitary gland

KEY WORDS secondary sex characteristics testosterone

follicle FSH LH oestrogen progesterone

Learning objectives: • describe the roles of hormones in sexual reproduction • explain how hormones interact in the menstrual cycle.

Menstrual cycle hormones ovary

ovary These hormones interact with each other during the menstrual cycle. ovulation ovulation oestrogen progesterone oestrogen progesterone

Thickness FSH and of LHuterus in ng/cm3

The menstrual cycle is the reproductive cycle in women, which – by convention – starts with a period (menstruation), if the woman is not pregnant.

28th

26th

1st day

menstruation

3 4

176

Which four hormones control the menstrual cycle?

Which hormones maintain the lining of the uterus?

3rd

24th

uterus lining is shed

23rd

en

600 400

1

200

5th 6th 7th

ovulation

uterus lining starts to repair and grow again

20th continues to thicken

8th 9th

19th

10th

egg is released from ovary

18th 17th

11th

12th 16th

15th

14th

13th

Figure 5.28 The menstrual cycle lasts approximately 28 days, but this is highly variable.

AQA GCSE Biology for Combined Science: Trilogy: Student Book

4 2

Ovulation Ovulation

progesterone progesterone

8 8 6 6 4 4 2 2 0 18 20 22 24 26 280 18 20 22 24 26 28

COMMON MISCONCEPTION

LH

ovulation

ovary empty follicle 7 progesterone

oestrogen

22nd

uterus lining

stimulation

6

5 0 0 inhibition inhibition ovary 6 8 16 18 20 22 0 2 4 6 8 10 8 24 26 28 4 12 14

repair of wall of uterus

21st

pituitary gland

FSH

2 leads to eggs ovary maturing in tissues follicle 3

4th

egg dies if not fertilised

Four hormones control the menstrual cycle: • follicle stimulating hormone (FSH) causes eggs to mature in the ovaries • luteinising hormone (LH) stimulates the release of an egg from an ovary • oestrogen and progesterone maintain the lining of the uterus.

2nd

25th

The menstrual cycle

800 800 600 600 400 400 200 200 0 0 0 2 4 6 8 10 12 14 16 0 2 4 6 8 10 12 14 16

Figure 5.29 The menstrual cycle is ­controlled by four main hormones.

Last day 27th

menstruation

FSH

200

str og

What happens in males and females under the influence of these hormones?

menstruation 400

oe

2

LH

Ovulation

Oestrogen in pg/cm3

Give the main reproductive hormones in males and females.

600

0 0 2 04 26 48 610 812 10 14 12 16 14 18 16 2018 2220 2422 2624 28262 284 6 Time (days) progesterone 800 8

In the male, testosterone is the main reproductive hormone.

It is produced by the testes. It stimulates sperm production.

1

800

Progesterone in ng/cm3

Oestrogen is the main female reproductive hormone that is produced at this time. It is produced by the ovaries. Eggs start to mature in the ovaries and are released, at approximately one every 28 days. This process is called ovulation.

Oestrogen, progesterone and testosterone are steroid hormones. Steroid hormones also help to control glucose and protein metabolism, and water balance.

3 Progesterone inin ng/cm Progesterone ng/cm3

Secondary sex characteristics develop as our bodies produce reproductive hormones at puberty.

Ovulation

ovulation oestrogen progesterone

Did you know?

800 800 600 LH 600 LH 400 400 FSH 200 FSH 200 0 0 0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 0 2 4 6 8 10 12 14 16 18 20 22 24 26 28

oeoe strst ogrog enen

ovary

3 FSH and LHLH inin ng/cm FSH and ng/cm3

Our first exposure to sex hormones is not at puberty, but as a foetus. In the presence of male sex hormones (which needs a Y chromosome), male characteristics develop; in their absence, the foetus becomes female.

follicle stimulating luteinising hormone (FSH) hormone (LH)

3 Oestrogen inin pg/cm Oestrogen pg/cm3

pituitary gland

Reproductive hormones

5.10

luteinising follicle stimulating The menstrual cycle is concerned with the maturation of an egg every month and preparing luteinising follicle stimulating (LH) hormone (FSH) hormone the uterus to receive that egg if it is fertilised. This could result in (FSH) pregnancy. hormone (LH) hormone

Ovulation Ovulation

Human reproduction

9 development and maintenance of lining of uterus in preparation for pregnancy

Don’t confuse the pituitary hormones FSH and LH, which are regulatory, with the reproductive hormones produced by the ovaries (oestrogen and progesterone) and testes (testosterone).

Figure 5.30 The roles of the hormones as the cycle progresses are: 1 FSH is secreted by the pituitary gland.

2 FSH causes the eggs to mature in the ovaries.

3 FSH stimulates the ovaries to produce oestrogen.

4 & 5 Oestrogen inhibits further release of FSH and stimulates release of LH. 6 LH triggers ovulation – the release of the mature egg from the ovary – and …

7 … leads to the secretion of progesterone by the empty follicle that contained the egg.

8 Progesterone inhibits the release of LH and FSH. 9 Progesterone maintains the lining of the uterus during the second half of the menstrual cycle, in readiness for receiving a fertilised egg.

5

Which two hormones repair the uterus after menstruation and encourage its growth?

6

Suggest which hormones are involved in negative feedback.

Google search: 'FSH, LH and ICSH, oestrogen, progesterone'

177

Biology

Worked example

Check your progress

1

You should be able to:

■■ describe the structure of the

nervous system and location of the endocrine glands

➞

■■ i dentify fertility drugs and in-vitro fertilisation as possible solutions to infertility ■■ i dentify different methods of contraception

adapted to their role and the transmission of an impulse in reflex arc

➞

blood glucose concentration are controlled by the endocrine system

➞

➞ ➞

hormones in the menstrual cycle

■■ d escribe the techniques involved in fertility treatments ■■ d escribe how different methods of contraception work

are transmitted across synapses

■■ explain how negative

➞

■■ describe the role of

➞

Secretion of thyroxine is controlled by the release of the hormone thyroid-stimulating hormone (TSH) by the pituitary gland. It is secreted when levels fall. If levels increase to above normal levels, secretion of TSH is shut down.

of body control systems and compare nervous and hormonal control

■■ explain how nerve impulses

■■ describe how changes in

■■ identify the reproductive hormones and their role in the development of secondary sexual characteristics

➞

■■ describe how neurones are

■■ identify temperature, water and glucose concentrations as conditions requiring control

and endocrine systems are responsible for homeostasis

feedback is involved in homeostasis

■■ explain the roles and

➞

interactions of hormones in the menstrual cycle

2

The graph shows the effect of the hormone on her Basal Metabolic Rate (BMR).

■■ evaluate fertility treatments

➞ ➞

■■ e valuate the use of different methods of contraception

110

90 80 70 60 50

2 injection of 5mg of thyroxine

0 1

3

4

5

6

7

8

9

10

11

12

Time (days)

Discuss the effect of the hormone injections.

The injection of the hormone after 2 days produces a sharp increase in Priya’s metabolic rate. The next two injections only produce slight increases. After 8 days, her BMR starts to fall.

AQA GCSE Biology for Combined Science: Trilogy: Student Book

The student has, however, omitted a key term to describe the process – negative feedback. An annotated diagram could have been used to illustrate the principle (see section 5.9).

This is a part answer to the question.

The student has described the trend but could have illustrated the answer using data from the graph, e.g. after 2 days Priya’s BMR increases from 55 to 83, after 4 days, … etc.

100

40

190

This is a good answer. The student has been careful to say that TSH is released by the pituitary gland, as it is not produced there.

Priya is given several injections of thyroxine over six days of treatment.

injection of 5mg of thyroxine

➞

Describe how secretion of thyroxine is controlled.

■■ describe the components

injection of 5mg of thyroxine

homeostasis

■■ recall that the nervous

Basal Metabolic Rate (% of normal)

■■ recognise the need for

Priya has an underactive thyroid gland. She does not secrete enough of the hormone thyroxine.

The student should have made clear that Priya’s BMR attained its normal value after 6½ days, increased to slightly above normal (113%), and then, after eight days, decreased steadily.

The student’s answer is a description, but not really a discussion. It should have been stated that it is the role of thyroxine to act on the body’s cells to increase their metabolism.

On the basis of the fall in BMR after 8 days, the student could have suggested that the treatment would be unlikely to be effective without repeated injections.

Worked example

191

Biology

Variation

Key words

Learning objectives:

environmental variation evolution genetic variation

• recall that differences in the characteristics of individuals in a population is called variation • understand the genetic and environmental differences leading to variation.

Variation and survival

7.1

Variation is essential to survival. There is usually a large amount of genetic variation within a population. This is essential to survival. Scientists studying populations of organisms can see how variation has led to changes. Variation is crucial to evolution. Each species in a stable environment is there because it has adapted to survive in that habitat.

Harriett and Imogen are sisters. Their differences in appearance are the result of genetic and environmental variation.

Genetic and environmental variation The sisters inherited genes from their parents. They are similar to, but not identical to, their parents. They also resemble each other.

Figure 7.2 Brown bears are adapted to life in the forest; polar bears to life on Arctic ice. Polar bears evolved from brown bears more than 350 000 years ago.

Individuals of every organism that have been produced by sexual reproduction are different. With the exception of identical twins, we all have different genomes. Our genome gives us a unique set of characteristics.

Some of the sisters’ features have nothing to do with genetics.

Harriett wears non-prescription spectacles and has braided hair. Differences that arise during development are part of environmental variation. Some environmental causes of variation are under our control, but others are not.

Figure 7.1 The two sisters have features in common, but they also have differences.

Some human characteristics – the person’s phenotype – are the result of the interaction of the genome with the environment.

Some characteristics in humans affected by: Our genetics

The environment

A combination of both

blood group

hair colour and length

height

eye colour

language

skin colour

natural colour of hair

scars

weight

shape of earlobe

tattoos

sporting achievements

1

3

How is an organism able to live in a specific habitat?

4

Suggest two characteristics that enable polar bears to live on the Arctic ice.

The mechanism of genetic variation Genetic variation is the product of three processes that lead to differences in genomes: mutations, sexual reproduction and meiosis.

Mutations occur continuously. They happen spontaneously, by accident. Most mutations have no effect, but a few are harmful.

Rarely, mutations give rise to new phenotypes where the new characteristics are advantageous. When this occurs, the change in an organism can be quite rapid – over generations, rather than millions of years. Examples include the peppered moth and antibiotic resistance in bacteria.

Give two characteristics in humans that result from:

226

Give two characteristics in humans that result from a combination of genetic and environmental influences.

AQA GCSE Biology for Combined Science: Trilogy: Student Book

There are three processes that lead to genetic variation. Remember also that some mutations are not expressed in an organism, but where they are, most are harmful.

Did you know?

• genetic variation • environmental variation.

2

Remember!

Figure 7.3 A series of mutations in rats and mice have made some populations resistant to warfarin poison.

5

List three processes leading to genetic variation.

6

Give an example of where a mutation has been beneficial to an organism.

Warfarin disrupts the blood-clotting mechanism.

It is used as a drug to help control strokes and heart attacks. When used as a rat poison, the animals bleed to death. As a result of mutations, and the fact that rats reproduce rapidly, many rat populations are now resistant to the poison.

Google search: 'environmental variation, genetic variation'

227

Biology

End of chapter questions

13 The graph shows human population growth and the number of extinctions

over time.

60000

1 Mark

4

Why can badgers be primary and secondary consumers?

1 Mark

5

Why is good biodiversity important?

2 Marks

Explain why bluebells grow before the trees in a wood are in leaf.

7

Explain what an ’apex predator’ is.

8

Look at the data in the table to answer the questions.

Species

1 Mark 1 Mark

pH6.5

pH 6.0

pH5.5

pH5.0

pH4.5

Trout

✓

✓

✓

✓

Bass

✓

✓

Perch

✓

✓

✓

✓

✓

Frog

✓

✓

✓

✓

✓

Clam

✓

✓

Crayfish

✓

✓

✓

Snail

✓

✓

✓

Mayfly

✓

✓

✓

5000 4000 3000

20000

2000 10000

1000 0

0

year

pH 4.0

Describe what the graph shows.

2 Marks

More challenging 14 Give two functions of mangrove forests.

✓

2 Marks

15 Explain how destruction of rainforests without replanting has helped

increase the concentration of carbon dioxide in the atmosphere.

b Which organism can live in water between pH 5.0 and 4.5?

Explain how he should do this.

1 Mark

1 Mark

11 Lemmings are adapted to live very cold conditions. Explain two adaptations of

lemmings.

17 Explain the difference between natural and artificial ecosystems.

2 Marks

18 Jessica is carrying out an investigation into how many dandelions plants

10 Zoe has found sludge worms and bloodworms in the stream at the bottom of

her garden. What does this tell her?

6 Marks

Most demanding 2 Marks

Going further Why is it important to place quadrats in a random way rather than choose an area?

2 Marks

16 Alistair is going to investigate the population of dandelions in a field.

a Name two organisms that cannot live in water with a pH less than 6.0.

9

extinctions

30000

1800

6

6000

2010

Why are indicator species used to investigate an ecosystem?

human population

1980

3

40000

1950

1 Mark

1920

What are quadrats used for?

1890

2

7000

50000

1860

1 Mark

1830

What group of organisms break down dead organisms?

number of species becoming extinct

1

8000 human population/millions

Getting started

2 Marks

there are in her school playing field.

The field is 20 metres by 30 metres.

She selects 9 spots at random and samples each spot with a 1 m2 quadrat.

Jessica’s results are shown below.

Sample number

Number of dandelion plants

1

5

2

4

Jessica calculates the mean number of dandelions to be 3.1.

3

2

4

4

a Calculate the median and mode values for the number of dandelions across the areas sampled.

5

3

6

1

7

3

b Use the data to estimate the number of dandelion plants in the playing field.

8

2

9

4

1 Mark

1 Mark

19 Polar bears and killer whales live in the Arctic. They compete to feed on

seals. Explain the types of competition that will occur and which will have the most impact on polar bears.

12 Ken has lots of moss growing in his lawn. He wants to estimate what

percentage of his lawn is moss. Describe how Ken could do this, making sure the data he collects is random.

302

AQA GCSE Biology for Combined Science: Trilogy: Student Book

6 marks Total: 40 Marks

4 Marks

End of chapter questions

303