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Section D: Ecology and the Environment

Chapter 14: Ecosystems 1 community all of the living organisms that share a habitat

habitat the place in an ecosystem where an organism lives

ecosystem a distinct self-supporting system of organisms interacting with each other and with their physical environment

population a group of organisms of the same species living in an area

2 Plants producers animals consumers primary consumers secondary consumers

3 energy photosynthesis animals food chains producer

4 a) primrose rabbit stoat

b) tiny water plants water fleas stickleback pike

c) grass zebra lion

d) tiny sea plants fish seal polar bear

e) rose bush aphid ladybird blue tit

5 a) A food web

b) Arctic moss and plants, because they use energy from the sun to make food

c) Insects, fish and tundra birds

d) Marine birds, seals, polar bears and arctic foxes

e) Any three appropriate food chains

f) Polar bears and arctic foxes would be in greater competition for food, but numbers of fish would be greater as there would be no seals to eat them. The fish would be eaten more by polar bears in the absence of the seals. Plant numbers might fall due to the increase in fish. The numbers of the organisms would fluctuate until a new balance is reached.

6 a)

b) The mass of biological material

c) A pyramid in which the blocks represent the mass of the organisms at each level in the food chain

d) The numbers dont always give a pyramid shape, e.g. one rosebush supports many aphids. Measuring biomass always gives a pyramid, as the mass always decreases along the chain.

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e) For numbers you simply have to count the organisms. To measure biomass, you have to uproot plants, or capture and possibly kill animals to find their dry mass, which is much more complicated and destructive.

7 a) It is released during respiration to be used in movement, warmth, growth of new cells and reproduction.

b) Much is lost as heat energy; some is passed out as waste.

8 a) i) 9.3%

ii) 9.3%

iii) 14.3%

b) 10.9%

c) The mass of the producers has to support the whole pyramid, and relatively little energy is transferred from producers to primary consumers, as they are difficult to digest.

d) Relatively little energy is passed up the chain, so there is not enough energy at the top of the chain to support many carnivores.

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10 a) Nitrogen is needed to make proteins.

b) These plants always have enough nitrates regardless of how well the soil is fertilised.

c)

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11 a) Three-quarters of the Earths surface is covered with water, so it is a very important habitat for living organisms. All living organisms rely on water as a major constituent of their cells.

b) Heat from the Sun evaporates water from the surface of the oceans, lakes and rivers. Plant transpiration and respiration from all living organisms release water vapour into the air. As air rises it cools, and water vapour forms tiny droplets of water as clouds. As clouds rise over mountains and high ground they cool more and water condenses further to form rain and/or snow. This precipitation falls on the Earth, where it joins the water or is taken into the bodies of living organisms to start the cycle again.

Chapter 15: Human influences on the environment 1 a) It provides exactly the right balance of mineral ions needed by plants for maximum growth, and

ensures plenty of nitrates for protein formation.

b) It ensures the best possible conditions for photosynthesis to be achieved plenty of light, warmth, high levels of carbon dioxide, etc.

2 Pests crops yield 30% stored pesticides biological

3 a) Type of pesticide What does it control?

herbicide plant pests/weeds

insecticide kills insect pests

fungicide kills fungi

b) Advantages: kill specific pests; increase yields and so increase income.

Disadvantages: pests may become resistant to a pesticide, so need to find substitutes; pesticides can be expensive and so reduce profits; can cause environmental damage.

4 a) A method of pest control that uses another organism to reduce the numbers of a pest organism.

b) Small numbers of pests do not have any noticeable effect on yields. Problems arise when pest numbers get too large. Biological pest control uses another organism for example a natural predator to reduce pest numbers to a level that does not have a negative impact on the crop. It does not completely eradicate the pest.

c) Any three methods chosen from: introducing a natural predator; introducing a herbivore; introducing a parasite; introducing a disease-causing micro- organism; introducing sterile males; using pheromones. For each method an appropriate description should be given of the general principle.

5 a) Any sensible suggestion, e.g. salmon, trout, tuna, sea bream, tilapia and (increasingly) cod.

b) Fish are kept in large tanks/enclosures so that water quality can be monitored. Their diet is carefully controlled, the fish are protected against predators, and pesticides are used to kill

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parasites. In some fish farms the water temperature and oxygen levels are controlled. Breeding is selective to encourage fast growth.

c) Disease may spread more easily than in the natural environment. There may be excessive use of antibiotics and pollution from fish waste. Pesticides used to control parasites can affect other fish. Farmed fish may escape and cross- breed with wild stock, and they are often fed on fish-meal made from wild fish.

6 organisms damaging human local population pollution

7 a) Burning petrol and diesel in car engines in low oxygen levels

b) It is poisonous. It joins with the haemoglobin in the blood and stops it carrying oxygen to the tissues. Breathing in too much carbon monoxide can kill you.

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9 a) Any three from carbon dioxide, methane, water vapour, nitrous oxide and CFCs

b) Short-wave radiation from the Sun strikes the surface of the Earth. Some is absorbed by the surface and some is re-emitted as longer-wave radiation. The greenhouse gases in the atmosphere absorb and then re-emit some of this longer-wave radiation towards the Earth, which warms the surface. This keeps the temperature at the surface of the Earth warm enough for life to exist.

c) Carbon dioxide and water vapour are increasing in the atmosphere as the burning of fossil fuels increases. Methane is also increasing as rubbish in landfill sites decomposes, as rice is grown and as cattle are farmed. Nitrous oxides are generated from soil management and the treatment of sewage and waste water. Fortunately CFCs, which are entirely man-made chemicals, are no longer used as refrigerants, etc., and their levels are falling. The more greenhouse gases there are in the atmosphere, the more heat is reflected back to the surface of the Earth and the warmer the temperature at the surface becomes.

d) Global warming is the gradual increase of the average temperature at the surface of the Earth. Serious effects include melting of the polar ice caps, rising sea levels, and changes in ocean currents, rainfall patterns, ecosystems (causing extinctions), farming practices and disease patterns; any other sensible points.

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10 a) Capable of being broken down and used as food by microorganisms

b) The human population is growing, making more waste to be dumped in the water.

c) There is plenty of organic matter in the water, which the microorganisms can use as food so they can grow and reproduce.

d) Reduction of the level of oxygen as it is used up. Increasing numbers of bacteria breaking down the sewage use up more oxygen from the water, so the level of oxygen dissolved in the water falls.

e) As the sewage pollution leads to oxygen depletion by microorganisms, the other organisms, such as fish, die from lack of oxygen in the water.

11 a) Plant roots bind the soil together and the tree canopy protects the soil from the worst of the wind and rain. Once the trees have gone, the soil is easily broken down and removed by erosion from wind and rain.

b) Once the soil is exposed, more water falls directly onto it and minerals are leached (washed) away into rivers and the sea. Also, leaves from the trees fall and rot, restoring minerals to the soil, but after deforestation this no longer happens.

c) Trees take up large amounts of water from the soil and release the water into the atmosphere in the transpiration stream as part of the water cycle. When the trees are lost, far less water returns to the atmosphere.

d) Trees in leaf remove carbon dioxide from the atmosphere for photosynthesis. They also produce oxygen as a waste product of photosynthesis. They dont use all they produce, so they add oxygen to the atmosphere and remove carbon dioxide as they make sugars. This carbon dioxide is then tied up in plant material for many years. Once the trees are cut down, less carbon dioxide is removed, so there is more in the atmosphere, and less oxygen is produced.