Energy Flows-Biology-AQA Additional Science

These revision cards contain information on pyramids of biomass, energy losses, energy in food production, decay and the carbon cycle.

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Pyramids of biomass and energy losses

Biomass is the mass of living material in plants and animals.

A pyramid of biomass represents the mass of the organisms at each stage in a food chain. It may be more accurate than a pyramid of numbers. For example, one bush may have many insects feeding on it but the mass of the bush is far greater than the mass of the insects.

Energy losses-Not all the food eaten can be digested, so energy is lost in faeces (waste materials). Some of the energy is used for respiration, which releases energy for living processes. This includes movement, so the more something moves the more energy it uses and the less is available for growth. In animals that need to keep a constant temperature, energy from the previous stage of the food chain is used simply to keep the animal at the correct temperature (e.g. 37°C in humans).

Energy is never really "lost". What it means here is that all of the energy in one stage of the food chain does not result in the growth of organisms in the next stage.

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Energy in food production

The shorter the food chain, the less energy will be lost. It is therefore more efficient for us to eat plants than it is to eat animals.

We can artificially produce meat more efficiently by:

  • Preventing the animal from moving so it doesn't waste energy on movement

This is seen as cruelty by many people and is controversial.

  • Keeping that animal at a warmer temperature so it doesn't use as much energy from food to keep itself at a constant temperature.

If we want to produce food from animals efficiently, then we have to limit the amount of energy they need while they are growing.

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Decay

Detritus feeders (such as some types of worms) may start the process of decay by eating dead animals or plants and producing waste materials. Decay organisms then break down the waste and dead plants and animals.

Decay organisms are micro-organisms (bacteria and fungi). Decay is faster if it is warm and wet.

All of the materials from the waste and dead organisms are recycled.

All organisms take up nutrients. If they didn't eventually release them the nutrients would run out.

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The Carbon Cycle

Photosynthesis removes CO2 from the atmosphere.

Green plants as well as animals respire. this returns CO2 to the atmosphere.

Animals eat green plants and build the carbon into their bodies. When plants or animals die (or produce waste) micro-organisms release the CO2 back into the atmosphere through respiration.

A stable community recycles all of the nutrients it takes up.

The recycling of carbon involves both photosynthesis and respiration.

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