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INSECTS THAT FLY - Part I The first insects with wings appeared many millions of years ago. Some people think that this happened as long as three hundred million years ago. Among the first flying insects were dragonflies. Some of them were not very different from the dragonflies of today. Dragonflies have two pairs of wings. These wings move up and down, but they cannot be folded away. The two wings beat together in flight and they do not touch each other. This system of flying works well when the dragonfly is moving in a straight line. However, this system does not work well when the dragonfly has to make a sharp turn. The two wings are then pushed against one another, which makes problems. If you observe dragonflies in flight, you will see that they do not make sharp turns but fly in wide, almost circular movements. Because of the difficulties caused by two pairs of wings working together, other insects have developed ways of joining their wings together to make one surface. Bees and wasps use a set of hooks that fasten their front and back wings together when they fly. Butterflies have wings that overlap so that they work as if they were one wing. Another way of solving the difficulties caused by having two pairs of wings is to reduce the size of the rear wing. Some moths still have a rear wing that hooks on to the front wing, but their rear wing is very small. Flies use only their front wings. Their rear wings have almost disappeared. And flies are great acrobats in the air, as we all know when we try to swat one which is annoying us. Their extraordinary agility is greatly aided by their vision. INSECTS THAT FLY - Part 2 This material has been discussed in detail in class with regard to the out-of-date information which it contains, in particular concerning the chemical Lindane. A newspaper article on the lethal effects of lindane was skim-read and oral questioning to elicit the main points took place. Aldrin, which is available as a dust or a spray, is used to control wireworm. It has to be used carefully as it is toxic to animals, and it should never be used on crops less than two weeks before they are harvested. BHC, which comes in dust, liquid or spray form, can be used on wheat bulb fly and some caterpillars. It must be used in small quantities as it affects the taste of the plants it is used on. DDT is a highly toxic liquid or powder which is capable of killing most known pests. Its use is now forbidden in many countries as it is poisonous to many animals and can harm humans if it becomes involved in our food chain. Derris is most commonly used as a powder but it is also available in liquid form. It is used to kill various pests but it should not be used near water as it is harmful to fish. Lindane, which is either a mild form of BHC, is used to control various pests. It comes either as a dust or as a liquid. (This information is completely incorrect, but has been included because this was commonly held to be true 20 years ago.)

INSECTS THAT FLY - Part 3 Look at the table in information (in note form) about insect pests which attack various crops. Look also at the paragaph about black fly. This was discussed in some detail in class, especially concerning pronunciation pest


crops affected



fly easily seen on crop



dust with derries

carrot fly

reddening of leaves


treat seeds with mild pesticide


onion fly

plants go rotten


treat with soil aldrin



holes eaten in crops

root crops

treat seeds with wireworm dust

treat crops with wireworm dust

wheat bulb fly

yellowing of centre of crop


treat seeds with BHC


black fly


Living organisms are divided into groups with similar characteristics, using the Linnean system of organisation, created in the 18th century by the Swedish botanist, Karl von Linne.


Living organisms are traditionally divided into the animal and plant kingdoms. Some biologists place the fungi, algae and many simple animals in a third kingdom called protista. Recently some biologists have placed the blue-green algae into a separate kingdom.


Each animal and plant belongs to a species and has a species name, which consists of two words in Latin. A species is a group of organisms that are similar to each other and can breed together. Each species belongs to a series of larger groups. A phylum is a main group and a class is a sub-group.




Protozoa Fungi Microscopic one-celled Mushrooms, toadstools & moulds creatures ANIMALS

Algae simple plant-like organisms seaweed


Animals WITHOUT backbones

Animals WITH backbones



Plants WITHOUT flowers Mosses & ferns

Plants WITH flowers Have flowers which produce seeds

Conifers Trees with needleshaped leaves & cones



One-celled animals, such as amoeba, belong to the protozoa phylum. Protozoa usually live in water - in the sea, in ponds or in damp places like puddles.

Coelenterates Coelenterates (pronounced see-elenterates) are animals with soft, hollow bodies and tentacles. Jellyfish, sea anemones and corals are all coelenterates. Annelids

Garden worms belong to a phylum called annelids. They have soft bodies, divided into rings or segments. Worms move by relaxing and contracting muscles in their bodies.


Arthropods have an exoskeleton, jointed legs and antennae. Their bodies are usually divided into three sections - head, thorax and abdomen. There are four main classes of arthropod. 1. Insects

Insects have six legs, two pairs of wings, two antennae and two compound eyes. 70% of all animals are insects.

2. Arachnids

Scorpions and spiders are arachnids. They have eight legs, no antennae, and simple rather than compound eyes.

3. Myriapods

These are arthropods with many legs, such as centipedes and millipedes.

4. Crustaceans

They have from 10 to 14 legs, two pairs of antennae and respire by means of gills. Shellfish such as crabs and prawns.


Soft-bodied animals with a single foot. Snails, slugs and mussels are all molluscs.


Spiny-skinned animals, such as starfish and sea urchins.


All animals with a backbone are vertebrates. FISH

Fish are cold-blooded vertebrates. They have scales and fins, they breathe with gills and live in water.

AMPHIBIANS Amphibians include frogs and newts. They are cold-blooded and can live both on

land and water. They lay eggs in water. Frogs eggs are called tadpoles. REPTILES

Reptiles include snakes, lizards and turtles. They have scaly skin and lay eggs with shells on land. Dinosaurs were reptiles.


Birds have feathers and wings and reproduce by laying eggs. They make nests in which they lay their eggs. When the baby birds hatch, they are called chicks. When the chicks are ready to fly, they are called fledglings.


Mammals are warm-blooded vertebrates with hair. They respire using lungs, they have two pairs of limbs and they feed their young with milk.


Algae are very simple plants with no stems, roots or leaves. They grow in very wet or damp places. Seaweed and pondweed are types of algae.


Fungi are unlike other plants as they are not green and cannot make their own food. Instead they feed off dead or decaying plants and animals. Many fungi are made up of tiny threads called hyphae. Mushrooms, mildews and moulds are all types of fungi.


Mosses are slightly more complex plants with very thin leaves and no proper roots. They reproduce by spores. They grow close to the ground in wet or damp areas. They are made up of hundreds of tiny separate plants.


Ferns are plants which have stems, leaves and roots, but no flowers. They grow in moist shady places, such as woods. At the backs of the leaves are dark spots called spores from which they reproduce.


Seed-bearing plants have roots, stems and leaves and reproduce by means of seeds. Unlike a spore, a seed is made up of many cells. There are two classes of seed-bearing plants.


Conifers are a class of seed-bearing plants. They have needle-shaped leaves and their seeds are produced in cones.

FLOWERING Flowering plants are also seed-bearing plants. They PLANTS include trees as well as flowers. Their seeds are

produced inside a fruit, which develops from a flower.

THE PLANT KINGDOM PART2 How do plants reproduce? Flowering plants reproduce themselves from seeds which form inside the ovary of the flower after fertilisation. Flowers produce a fine dust called pollen (known as pollen grains) in the anther. Pollination takes place when pollen is carried from an anther to a stigma. When the anther ripens, the pollen sacs split open and release the pollen grains. Pollen can be carried to a stigma in the same flower. This is called self-pollination. Insects such as bees, butterflies, wasps, dragonflies, carry pollen from flower to flower. The wind also often carries pollen from plant to plant. This process is known as cross-pollination. Insect-pollinated flowers have large, coloured scented petals and nectar, with which to attract insects. They have large pollen grains that stick to the insects body. They also have anthers and stigmas inside the flower, so that the insect can brush against them when it is drinking nectar. The presence of nectar, a sweet sugary substance, is also very attractive to insects and even small birds, in some areas of the world. In addition, flowers pollinated by night-flying insects often have a strong scent. Wind-pollinated flowers do not have large scented petals, or nectar, because they do not need to attract insects. Their anthers hang outside the flower, in order to catch the wind. They produce large amounts of very small light pollen grains which blow away easily in a slight breeze. They also have large feathery stigmas to catch pollen grains which are blown by the wind. Fertilisation Fertilisation takes place when a male sex cell joins up with a female sex cell, and this occurs in the following manner, after a pollen grain lands on a stigma. First a tube grows out of the pollen grain and grows towards the female sex cell. The male sex cell moves down the tube which then enters the female sex cell, the tip of the tube bursts open and the male sex cell joins up with the female sex cell. The ovule becomes a seed. The ovary becomes a fruit with the seed inside it. THE PLANT KINGDOM PART 3 How do plant diseases spread? Micro-organisms can cause diseases in plants as well as in humans and animals. Diseases are often infectious, which means that they can be passed on from plant to plant, usually by carriers such as insects, which may drink juices from a diseased plant and then inject them into a healthy one. What are parasites and how are they controlled? Plants are also attacked by parasites which can harm or even kill them. A parasite is an organism which lives on, or in, another organism. Parasites are never helpful, and are often harmful, to the host organism. Chemical sprays and disinfectants enable farmers to kill parasites and to control plant diseases. These substances can be sprayed over wide areas from aeroplanes and helicopters. Many farmers depend on this form of crop protection to save their harvest of grain, fruit or vegetables. Without it, many people all over the world would die of hunger.

CHARACTERISTICS OF LIVING THINGS PART1 Living things, or organisms, have certain characteristics in common which enable us to distinguish between living and non-living things:        

They move They grow They reproduce They are sensitive, i.e., they can sense and respond to changes in their surroundings Processes of Nutrition They feed They respire (breathe) i.e., they release energy from their food, often by combining it with oxygen They excrete

AND they are all made of cells. CHARACTERISTICS OF LIVING THINGS PART2 1. Only living organisms can move, ie, have the power of locomotion, or can move under their own power. Animals move when they are in search of food. Many simple plants live and can move in water. Many plants have reproductive cells that can swim. Many plants can move their leaves or other parts of their bodies. 2. All living organisms grow, that is, until they reach a certain size of a certain age. 3. All living organisms are capable of reproduction, which produces new organisms. 4. All living organisms respond to external stimuli. For instance, when animals are too hot or too cold, they will change their position and try to find either a cooler or a warmer place or position. Plants may react to changes in light intensity by opening or closing their flowers or their leaves. (*)These four activities or processes, movement, growth, reproduction and sensitivity use up a good deal of energy. It is this need for energy which explains why living organisms are also characterised by the three processes of nutrition, respiration and excretion. CHARACTERISTICS OF LIVING THINGS PART 3 Plant nutrition begins when carbon dioxide, water, and various inorganic substances are taken in or ingested. From these ingested materials, the plant makes, or synthesises, substances like sugars, starches and proteins. Sunlight is the source of energy for this synthesis. Animal nutrition is different, because animals cannot synthesise complex organic substances. Instead, animals must take in these substances as food. Although nutrition is very different in animals and plants, the results of the process are similar: the organism acquires energy-rich substances such as sugars. During respiration these substances are burnt, so that energy is released and becomes available for all the chemical activities that need energy. The waste materials that are formed as a result of the organism's chemical activities are removed from the body in the process of excretion. Energy is also required for this process.

CELLS - GENERAL PART 1 Every cell, plant or animal, has a cell membrane around it. Inside the cell is a jelly-like substance called cytoplasm, in which are many small structures called organelles. The most obvious of these organelles is usually called the nucleus. The whole content of the cell is called protoplasm. All plant cells are surrounded by a cell wall made of cellulose. Animal cells NEVER have cells walls made of cellulose. Cellulose belongs to a group of substances called polysaccharides. This substance forms fibres which give protection and support to the cell. The cell wall is a non-living layer of cellulose fibres. It is freely (fully) permeable to aqueous solutions and maintains the shape of the plant cell. All cells have a membrane surrounding the cell, called the cell or the plasma membrane. In a plant cell, it is very difficult to see because it is right against the cell wall. It is composed of a very thin layer of protein and fat. The cell membrane (plasmalemma) is selectively permeable and involved in osmosis and active uptake of ions and molecules. Cytoplasm is a clear jelly. It is nearly all water; about 70% is water in many cells. It contains many substances dissolved in it, especially proteins. CELLS - GENERAL PART2 A vacuole is a space in a cell, surrounded by a membrane and containing a solution. Plant cells have very large vacuoles, and contain a solution of sugars and other substances called cell sap. Animal cells have much smaller vacuoles, which may contain food or water. Endoplastic reticulum is a membrane network in the cytoplasm, which make fats and proteins out of smaller molecules in the cell. This substance is found in all cells. The nuclear membrane is a double unit membrane continuous with the endoplastic reticulum. Pores in the nuclear membrane allow exchanges of materials between nucleus and cytoplasm. Chloroplasts are NEVER found in animal cells, but most of the cells in the green parts of plants have them. They contain the green pigment called chlorophyll. Chlorophyll absorbs sunlight, and the energy of sunlight is then used for making food for the plant by photosynthesis. Chloroplasts often contain starch grains, made by photosynthesis. Animal cells NEVER contain starch grains. Every cell has mitochondria, which release energy from food. The energy is released by combining food with oxygen, in a process called respiration. The more active is a cell, the more mitochondria it has. Ribosomes are very tiny round objects, often attached to the endoplasmic reticulum. It is here that proteins are made, by joining together smaller molecules called aminoacids. The nucleus is where the information is stored in the chromosomes.

Chromosomes are very long and very thin. However, when the cell is dividing they become short and thick and can be seen with a good light microscope. CELLS – GENERAL PART 3 SUMMARY INFORMATION

Cell membrane: a thin skin around the cell, which lets some things pass through, but does not let other things pass through. Cytoplasm: a jelly containing hundreds of chemicals, which fills the cell. Nucleus: it controls what a cell does, and how it develops. Vacuole: a space within the cell containing air, liquids or food particles. Animal cells usually have several small vacuoles. The liquid is called cell sap. Choroplasts: tiny discs full of a green substance called chlorophyll. They trap the light energy that plants need for making food by photosynthesis. Red blood cells are disc-shaped. Their function is to carry oxygen around the body. White blood cells can change shape. They attack germs. CELLS – GENERAL PART 4 COMPARISIONS BETWEEN PLANT AND ANIMAL CELLS

Similarities Both have a cell membrane surrounding the cell. Both have cytoplasm Both contain a nucleus Both contain mitochondria Both contain endoplasmic reticulum Both contain ribosomes How plant cells are different from animal cells Plant cells

Animal cells

have cellulose walls have chloroplasts always have a vacuole, sometimes very large often have starch granules

do not have cellolose walls do not have chloroplasts only have small vacuoles

often regular in shape

never have starch granules; sometimes have glycogen granules often irregular in shape

Look at 3D cell models of a animal and plant cell. SUMMARY INFORMATION

Animal and plant cells obtain their food in different ways. Plants make their own food, so their cells contain chloroplasts. Starch granules store some of the food that they make. Animal often have to move to find their food, which is easier if their cells do not have a rigid wall

CELL DIVISION PART 1 The nucleus is the site of RNA synthesis. The nucleolus is the site of one type of RNA. A fertilised cell divides to make two daughter cells. which are identical. These divide to make four identical cells, which divide again and again to make a ball of cells. Some cells in the ball grow and change shape to do a particular job. These specialized cells group together to form tissues. Red and white blood cells form tissue which can carry oxygen and kill germs. This is called blood. Substances pass in and out of cells as tiny particles known as molecules. Molecules are the smallest particles of a substance. The movement of molecules is called diffusion. Osmosis is a special kind of diffusion which occurs when a molecule has tiny holes which allow water molecules to pass through, but which prevent larger molecules, like sugar, from passing through. Water moves from cell to cell in plants by osmosis. The cell membrane of a plant cell is semipermeable. CELL DIVISION PART 2 The cell membrane is also known as the plasma membrane or plasmalemma. It covers the entire cell and serves to hold it together. It also actively regulates what enters and what leaves the cell. It is only about 10 nanometers thick. In animal cells (as well as in plant, protist and fungus cells) the nucleus is separated from the rest of the cell by the nuclear envelope. Such cells are called eukaryotic cells (from the Greek eu (true) karyon (kernel). This is to show the difference between prokaryotic cells, which do not have a true membrane-enclosed nucleus and are more primitively organised. Prokaryotic cells are only found among the bacteria and their close relatives. The nuclear envelope is made up of two layers of membrane. These are very similar to the cell membrane but have many pores. Within the nucleus is a prominent structure called the nucleolus (sometimes there are two or more nucleoli) and a network of thin threads called chromatin. The chromatin contains the hereditary material of the cell. The fluid that fills the rest of the space in the nucleus is called the nuclear sap. The term "cytoplasm" is still used to designate all of the cell contents outside the nucleus but inside the cell membrane, although it is now known that cytoplasm is not the homogeneous substance it was once thought to be. One of the prominent organelles in the cytoplasm is the mitochondrion. 90% of the energy that eukaryotic cells get from oxidizing food molecules is developed there. The Golgi complex is a stack of membranous sacs in which various molecules are manufactured.

Centrioles are cylindrical bundles of microtubules that give rise to longer spindle microtubules that separate the two duplicate sets of chromatin at the time of cell division.

PHOTOSYNTHESIS PART 1 Photosynthesis is the process by which green plants produce food. The action of light on carbon dioxide and water syntheses carbohydrates. The process is complex but it can be simplified in the following equation. Light energy C6H12O6 + 6O2 chlorophyll (glucose) Chlorophyll is the substance which makes plants green. It is essential to the process. Glucose is a carbohydrate which plants need. The equation shows how the water molecule is split, and yields oxygen as a by-product. Sunlight provides the energy for the whole process, which takes place in the chlorophyll layer of leaves. Leaves have to be broad enough to catch and absorb the amount of sunlight needed by the plant. The carbon for the process is obtained from atmospheric carbon dioxide. This is absorbed through stomata which are small openings on the underside of leaves.

The hydrogen for the process comes from water which is drawn up from the soil through the plant’s roots. Plants give off the excess oxygen which is vital to the growth of living cells in other forms of life. Sugars, such as glucose, are used by plants as a source of energy. They are the foods which plants need in order to grow. Plants, in turn, provide food for all other forms of life. PHOTOSYNTHESIS PART 2 Differences in plant and animal nutrition Plants characteristically synthesize complex organic substances from simple organic raw materials. In green plants the energy for this process is sunlight. Plants can use this energy because they possess the green pigment chlorophyll. Photosynthesis, or "light-synthesis" is a "self-feeding" or autotrophic process. Animals, on the other hand, must obtain complex organic substances by eating plants or other animals. The reason for this is that they lack chlorophyll. Among these "other-feeders", or heterotrophs, we distinguish between "solid-feeders" or phagotrophs, and "liquid-feeders" or osmotrophs. Whereas phagotrophic organisms take in solid and often living food, osmotrophic ones absorb or suck up liquid food, usually from dead or rotting animals. Plants and animals, then have characteristically different feeding methods. However, we cannot define plants as autotrophs and animals as heterotrophs. The reason for this is that many plants lack chlorophyll and feed heterotrophically, and some animals do have chlorophyll and feed autotrophically.

OCEAN ANIMALS PART 1 The open ocean, the largest environment on earth, has twice the surface area of all the land and the fresh water put together, and its average depth is 4

km. The ancient environment has been remarkably stable until the last two decades of the 20th century. This is shown in some detail in the ONEDIN module "Introduction to the Marine Environment". Primary producers live in the epipelagic zone. They are plankton, tiny floating organisms. Plankton, that can perform photosynthesis, are called phytoplankton. Most are diatoms and dinoflagellates. OCEAN ANIMALS PART 2 DIATOMS

Tiny floating organisms called zooplankton prey on the diatoms and dinoflagellates. The most numerous and diverse zooplankton are the copepods. They include herbivores, carnivores, omnivores and parasites. Among the plankton are tiny larvae of crabs, starfish and molluscs. Many of these are sedentary as adults.


The planktonic larval stage enables the species to disperse widely. In the open ocean, there is nowhere to hide from predators. Many plankton are transparent, a good camouflage in the bright upper waters. Many fish have larvae that drift in the upper layers, where prey is abundant. Plankton often migrate to deeper waters by day and return to the surface to feed at night. The cooler water of the depths may help them to conserve energy by day, and the dimmer light may conceal them from predators. These plankton respond to light from above. If the light intensity is low, they stay closer

to the surface. If the water is clear and the light intensity higher, they sink deeper. Some of the plankton live right at the surface. They usually have a strong blue pigmentation. This may give them protection from strong ultra-violet light near the surface, or camouflage them against predators above them.


There are also large predators in the epipelagic zone. Tuna feed on squid and fish. They are streamlined and can swim powerfully for long distances. Marine mammals live in this zone. At first glance, fish and marine mammals look similar but they differ in very important ways. Fish are scaly; marine mammals such as the whale or dolphin are covered with soft skin. Fish breathe through gills; whales have lungs and respire through a blowhole in the top of the head. Fish fins are spiny; whale fins are solid and their flippers are bony. Whales evolved from land animals like the wolf, with long legs for walking. They may have gone through a seal-like stage with short limbs for walking or swimming. Now, they have only front limbs and a long, flexible backbone. Seals are highly streamlined, with a good deal of body fat which helps to keep them warm, and improves the smoothness of their streamlining. Seals and sea lions can spend days or weeks in the water, feeding at sea, making sea journeys of hundreds or thousands of kilometres, and returning to land to breed. The largest predators are whales. They are by far the most efficient of all the aquatic animals, hunting and catching all their food in the water. They sleep floating on the surface. Whales, like dolphins, mate in the sea and bear their calves in the water. The baby whale (calf) can swim as soon as it is born. A whale may eat 10.000 kg of plankton at one meal, though the main constituents of a whale's diet are shrimplike krill. OCEAN ANIMALS PART 5 MESOPELAGIC ZONE

In the mesopelagic zone, the temperature is more constant. Light intensity is low, decreasing to almost zero at the bottom of the zone, and blue light predominates. Many mesopelagic fish have mirror-like sides. These reflect only the available light, and if there is no light, they appear black. In this zone, prey is scarce. Deep sea fish are less streamlined than those of the upper waters. They have larger eyes, a darker, more shiny body and light organs along their sides and belly. Many of the fishes living in this zone have light-producing organs called photophores. Some of the small deep-sea sharks have tiny light organs all over the skin so that the whole fish glows with a greenish light. Lantern fish are very common in this zone. These small fish migrate hundreds of

metres to the surface every night. Most have light organs along their flanks. They have fewer photophores arranged in patterns specific to each species. They are thought to aid species recognition in deep waters. Luminous patches near the tail may be used to dazzle or surprise a predator. Not all of the deep-sea fishes are luminous. Generally species with large eyes have luminous organs while blind of small-eyed fish do not. Food is scarce in the deep sea, so the fishes are usually small. Predatory fishes inhabiting this zone often have very elastic stomachs which enable them to swallow prey several times bigger than themselves. In regions where there may be only one fish per cubic kilometre of water, the predators cannot afford to ignore any source of food. One fish that lights its own way in this zone is the deep-sea dragon. It has rows of photophores arranged on its cheeks and running along the side of its body. Underneath its mouth is a very long, thin barbel which is very sensitive to touch. Using its photophores and its barbel, the deep sea dragon is well equipped to detect the presence of enemies as well as attracting prey.


The bathypelagic zone is by far the largest zone. It is an ancient, almost changeless environment. Here it is constantly dark and cool and living organisms are sparsely distributed. Many fish are black. Emitting light would make them conspicuous here. Prawns are completely red at this depth, but appear black in the absence of light. Some predators use light organs to attract their prey. The deep sea angler fish has a luminous lure, and light organs inside its mouth, to bring prey closer. Many fish at this depth have enormous mouths and highly distendible stomachs. Some can take prey larger than themselves. This is extremely useful when meals may be few and far between. Very few animals of the bathypelagic zone migrate upwards to feed. The spem whale is known to descend to these depths to hunt giant squid which may be 43m long. In the deepest parts of the bathypelagic, where there are no luminous organisms, and where the pressure is very high, many fish are colourless and have small eyes. They locate their prey mainly by smell and by vibrations. Fast movement is not possible under high pressures and rigid skeletons would have difficulty in resisting these pressures. So deep sea fish have reduced skeletons and


PRODUCERS AND CONSUMERS PART 1 All living things need energy. They get their energy from food. Plants are called producers because they make their own food. They use sunlight to make food by photosynthesis. Without plants, humans and all other animals would starve to death. This is because they cannot make their own food. The only way animals can obtain energy is by eating, or consuming, plants or other animals. So animals are called consumers.


Food chains show how one living thing is the food for another. Energy passes along a food chain from producers to consumers as one member of the chain eats the next.

1. Seaweed is a producer. It produces food by photosynthesi s.

1. Periwinkles are called first consumers because they eat weed.

1. Herring gulls are called second consumers, because they eat periwinkles.

Seaweed --> periwinkle --> herring gull This is an example of a food chain. FOOD PYRAMIDS

On the right is a food pyramid. It shows how consumers can get larger in size, but smaller in number, as you go along the food chain.

When a moth caterpillar eats a leaf it uses up some of the energy from the leaf for itself. So there is less to pass on to a robin. That means the robin needs to eat several moth caterpillars to get enough energy. So there are fewer robins than caterpillars.


A plant or animal usually belongs to several food chains. For example, seaweed is eaten by limpets and winkles as well as by sea worms. In this way food chains are connected together to make food webs. This diagram shows a food web in the sea.



Many fungi and bacteria are decomposers. They feed on dead animals and plants. First they produce digestive juices which make the dead things rot, or decompose into liquid. Then they absorb the liquid.

Decomposers are important because: 1. they get rid of dead animals and plants 2. they release chemicals from dead things which soak into the soil and help to keep it fertile.


An ecosystem consist of a number of living organisms and their physical environment. The living organisms and their non-living environment are interrelated and interact with each other. There is a flow of energy from the non-living organisms to the living organisms. There are a number of materials cycles - that is, exchanges of materials between living and non-living parts. When we study an ecosystem we can therefore analyse its components (the structure of the ecosystem) and we can analyse its processes (the functions in the ecosystem). There are six major components in an ecosystem: 1. Inorganic substances such as carbon, nitrogen, oxygen, water, carbon dioxide etc. 2. Organic compounds such as proteins, carbohydrates etc. The organic and inorganic substances in an ecosystem regulate the work of the whole system. 3. Climate and other physical factors. Temperature, wind, light and rain are important physical factors. They affect all the processes in an ecosystem. 4. Producers. Only green plants are able to manufacture food from simple inorganic substances. In the process known as photosynthesis green plants in the light of sun combine carbon dioxide and water and produce carbohydrates.

5. Consumers. Consumers obtain their energy from green plants. Herbivores, such as cows and sheep, eat green plants but do not eat other animals. They are called primary consumers. Carnivores, such as dogs and cats, feed on other animals and are called secondary consumers. 6. Decomposer, such as bacteria and fungi. Decomposers break down the tissue and excretions of other organisms. Bacteria break down the flesh of dead animals. Fungi break down plant material. They enable chemical substances to return to the physical environment.


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THE GREENHOUSE EFFECT PART 1 Many people, including eminent scientists, accept that there is increasing evidence that the world is getting warmer. This is caused by what scientists call the Greenhouse Effect. Air behaves like the glass of a greenhouse; energy from sunlight passes through and is absorbed by the earth's surface. This warms up and emits heat, in the form of infra-red radiation. In clean air some heat is absorbed by carbon dioxide and water vapour, but most of it escapes back into space. Polluted air has far more carbon dioxide than clean air. In addition, polluted air has other pollutants such as methane, nitrous oxide and chlorofluorocarbons (CFCs). These are now all called "greenhouse gases". They absorb infra-red heat and radiate it back to the earth. In this way, heat is trapped and warms up the atmosphere. Carbon dioxide in the earth's atmosphere acts just like the glass in a greenhouse. It allows sunlight to pass through, but it stops infra-red radiation from the earth's surface from escaping back into space. Since 1850 world temperatures have risen by about 0.5 o C. It is agreed by almost all scientists that this rise is going to continue. Look at a graphic representation of the greenhouse effect, below (click on the thumbnail for larger view):

THE GREENHOUSE EFFECT: GLOBAL WARMING PART 2 The amount of carbon dioxide in the atmosphere should remain constant at about 0.003 percent, but in fact it is now rising all the time. This is because all the developed countries are highly industrialised and they produce carbon dioxide much faster than it can be absorbed by plants. (Look back at the English 1 course material). The effects of global warming: The rise in temperature could be particularly evident around the North Pole and the South Pole, causing the ice caps to melt at a much faster rate than is expected. This melting of the ice caps could cause a rise in sea level. In addition, on land, glaciers are also melting. If the ice caps continue to melt, then there could be a rise in sea level of up to 1.5 metres by the year 2050. This would cause disastrous flooding of cities and farmland in low-lying areas such as Holland, Florida and the Ganges Delta. Look at a graphic representation of the global warming due to the greenhouse effect:

THE GREENHOUSE EFFECT: CLIMATE CHANGE PART 3 Uneven heating of the world will cause regions that are already arid to become even drier. Central parts of North America, which produces much of the worldテ不 grain supply, may also become much drier. Creatures that are adapted to cold climates may have to spread northwards. Animals can do this relatively easily and quickly, but plants which cannot move could be killed by the effects of climate change. Some weeds, however, will thrive on the extra carbon dioxide, though grain, which we need for food, does not. This means that crops will be more difficult to grow and weeds which harm crops, will be far more abundant. Leaf tissue becomes less nutritious with increased carbon dioxide, so crop pests will eat far more. THE GREENHOUSE EFFECT: ACID RAIN AND POLLUTION PART 4 The earth's atmosphere is about 900 km thick but living things can exist only up to about 3.2 km above the earthテ不 surface. It is in this rather thin layer that most pollutants assemble. Sources of air pollution: By far the major source of air pollution comes from the burning of coal and oil in houses, factories, power stations and vehicle engines. When coal and oil are burned, they produce soot and smoke. They also give off a mixture of gases such as sulphur dioxide, carbon monoxide, carbon dioxide, oxides of nitrogen, and various hydrocarbons. These pollutants do not stay close to the source, but rise into the atmosphere, borne by warm air currents. Some remain airborne for quite a long time and can be carried hundreds of kilometres away from the source. Some of these pollutants therefore enter clouds and fall back to earth as rain (known as wet deposition or acid rain), and some fall back to earth as dry depositions. Sulphur dioxide is very harmful to plants, as it is taken into their leaves through their stomata. As a result, the leaf cells are destroyed and the leaves are damaged and may even drop off. In addition, when there is a lot of ozone in the atmosphere, some of the sulphur dioxide reacts with other substances in the atmosphere to form sulphuric acid. Other gases, such as nitrogen oxides, can also form acids. Because all this happens at a high level in the atmosphere, the acid is sometimes carried for hundreds of kilometres before it falls to the ground as acid rain or snow. Normal rain is in any case slightly acid, because some carbon dioxide dissolves in it. This forms a very weak acid called

carbonic acid. Normal rain has a pH of about 5.7. However, rain containing sulphuric acid may occasionally have a pH as low as 2.4. Look at a graphic representation of the pollution of the atmosphere and the acid rain, below (click on the thumbnail for larger view):

English for biology