IGCSE Biology 2nd edition GCSE Biology 3rd edition

Here you will find the answers to the 'in-text' questions which occur in IGCSE Biology (2nd edition) and GCSE Biology (3rd edition) by D. G. Mackean, published by Hodder Education, London, UK.

Chapters: | Index | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 | 19 | 20 | 21 | 22 | 23 | 24 | 25 | 26 | 27 | 28 | 29 | 30 | 31 | 32 | 33 | 34 | 35 | 36 | 37 | 38 | 39 | 40 | 41 |

Chapter 25. The interdependence of living organisms

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food web
2. The tree and grass depend on the soil for anchorage, water and mineral nutrients.
The earthworm depends on the soil for making its burrows and for the humus it contains as a source of nutrients.
The soil depends upon the fall of leaves from the tree to renew its humus content and the earthworm uses leaves to pull into its tunnels. The soil also depends on the earthworms’ tunnels for drainage and aeration as well as the improvement and mixing of soil structure from passing through the earthworm’s alimentary canal.
The blackbird depends on the earthworms as a source of nutrition and the tree as a place to perch or hide from predators.
3. Photosynthesis in vine leaves - grapes - grape juice fermented to wine.
Photosynthesis in grass - eaten by cow - milk from cow - converted to butter.
Photosynthesis in wheat - production of wheat grains - eaten by chickens - eggs.
Photosynthesis in leaves of bean plant - seed production (beans).
4. Photosynthesis millions of years ago produced plants which became decomposed and fossilised to form petroleum or coal. Oil or coal burned to raise steam and drive generators.
Oil derived from fossilised plants (mainly algae or protista) becomes petroleum. When this is distilled, one of the products is petrol.
Photosynthesis in oat plants results in the production of oat grains which are eaten by racehorses and provide energy from respiration.
   Wind, waves and hydroelectric sources depend on energy from the sun but not specifically from sunlight. Tidal energy comes from the moon and the sun. Nuclear energy and geothermal energy (from the heat in the deep layers of the Earth) are independent of the sun. (not in text)
5. Long term observation will reveal what the fox and pigeon eat. This can be supported by evidence of their stomach contents at different times of the year.
Observation will also reveal which organisms eat the pigeons.
6. Domestic carnivores such as cats can catch and eat organisms to the point that the population is decimated. The animals above the victims in the food web will suffer or turn their attention to different prey.
Goats can eat the parts of plants that are usually unaffected by the indigenous herbivores. They may eat so much of the plants that they destroy the population altogether or reduce it so much that it cannot support its natural population of herbivores or insects.

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1. a Carbon atoms form the ‘backbone’ of the molecules needed by living organisms
 (e.g. C - C - C - C - C - C carbon ‘backbone’ of glucose molecule C6H12O6)
  for building all their body structures and supplying energy.
    b glucose, sucrose, cellulose, amino acids, lipids.
    c Animals get their carbon by eating plants or other animals.
chemical equations
3. In the leaf, the carbon atom would be incorporated into a molecule of glucose by the process of photosynthesis. The glucose molecule would be carried in the phloem to the potato tuber which would combine the glucose molecules into starch.
When eaten, the starch molecules are converted to glucose molecules by the process of digestion. The glucose molecules are then oxidised by respiration and the carbon atom in a molecule of carbon dioxide is released.

Page 230
1. The clover is a leguminous plant. These plants have root nodules which contain nitrogen-fixing bacteria. These bacteria can convert atmospheric nitrogen to nitrogenous compounds which are needed for healthy growth. Grass does not have root nodules and therefore suffers from nitrogen deficiency.

Page 231
1. To judge from the poor yield from plants deprived of nitrogen, this must be the mineral element which  produces the most profound effect.

A (Nitrate added) B (Nitrate removed)
nitrifying bacteria denitrifying bacteria
nitrogen-fixing bacteria leaching
manure uptake by plants
chemical fertilizers  
 (of plants and animals)

3. a Advantages.
      (i) Manure. Freely available on mixed farms.
           Contains organic material which improves soil structure.
           Slow release of nutrients.
      (ii) Chemical fertilizer. Composition can be adjusted to meet needs of different soils.
   b. Disadvantages
       (i) Manure. May not contain all essential elements e.g. trace elements, or the right balance of other minerals
           for a particular soil.
       (ii) Chemical fertilizers. Expensive. No organic matter to improve soil structure. More easily washed out.

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1. The energy for a muscle contraction in your arm comes from the respiration of glucose. The glucose is derived from carbohydrates in your food. These carbohydrates come from plants which have used the sun’s energy to build them by photosynthesis. Photosynthesis depends on; energy provided by sunlight.
2. The advantage would be that energy is not lost by the respiration of all the organisms in the food chain between the source and the final consumer e.g. eating plants instead of eating the animals which eat the plants. The disadvantage is that this would distort the food chain by depriving primary consumers of their food source, e.g. eating plankton would deprive fish of a food source.

Download the answers in PDF format below
Section 1, Chapters 1-5
Section 2, Chapters 6-9
Section 3, Chapters 10-12
Section 3, Chapters 13-17
Section 3, Chapters 18-20
Section 4, Chapters 21-24
Section 5, Chapters 25-27
Section 5, Chapters 28-29
Section 6, Chapters 30-34
Section 6, Chapters 35-37
Section 7, Chapters 38-39
Section 8, Chapters 40-41

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