Additional biology- food chains and cycles

Additional biology- food chains and cycles


Efficiency of food production

The efficiency of food production can be improved by reducing the amount of energy lost to the surroundings. This can be done by:

  • preventing animals moving around too much
  • keeping their surroundings warm

Mammals and birds maintain a constant body temperature using energy released by respiration. As a result, their energy losses are high. Keeping pigs and chickens in warm sheds with little space to move around allows more efficient food production. But this raises moral concerns about the lives of such animals. In reality, a balance must be reached between the needs of farmers and consumers and the welfare of the animals.

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Calculating energy efficiency

Energy balance in a bullock. 100 kJ eaten, 63 kJ excreted, and 4 kJ transferred to body tissue (

This bullock has eaten 100 kJ of stored energy in the form of grass, and excreted 63 kJ in the form of faeces, urine and gas. The energy stored in its body tissues is 4 kJ. So how much has been used up in respiration?The energy released by respiration = 100 - 63 - 4 = 33 kJOnly 4 kJ of the original energy available to the bullock is available to the next stage, which might be humans. The efficiency of this energy transfer is efficiency = 4100 × 100 = 4%

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Shorter food chains

Food production is more efficient if the food chain is short, because a higher percentage of energy is available to us.

1 hectare of land can produce 0.3 tonnes of beef - or 7.5 tonnes of wheat grain (

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The carbon cycle

All cells - whether animal, plant or bacteria - contain carbon, because they all contain proteins, fats and carbohydrates. Plant cell walls, for example, are made of cellulose - a carbohydrate.

Carbon is passed from the atmosphere, as carbon dioxide, to living things, passed from one organism to the next in complex molecules, and returned to the atmosphere as carbon dioxide again. This is known as the carbon cycle.

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Carbon dioxide

Removing carbon dioxide from the atmosphere

Green plants remove carbon dioxide from the atmosphere by photosynthesis. The carbon becomes part of complex molecules such as proteins, fats and carbohydrates in the plants.

Returning carbon dioxide to the atmosphere

Organisms return carbon dioxide to the atmosphere by respiration. It is not just animals that respire. Plants and microorganisms do, too

Passing carbon from one organism to the next

When an animal eats a plant, carbon from the plant becomes part of the fats and proteins in the animal. Microorganisms and some animals feed on waste material from animals, and the remains of dead animals and plants. The carbon then becomes part of these microorganisms and detritus feeders.

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