Energy is stored in organisms as chemical energy.
When one organism eats another, this energy is passed on.
A food chain is a diagram which shows the flow of energy from one organism to another as they eat one another.
A trophic level is another name for 'energy level'
Not all the energy is passed on in a food chain. Some is lost in other ways.
Some is released in respiration to allow movement and keep the organism warm (if endothermic)
Lots is egested (undigested food in faeces)
There are fewer organisms as you go along a food chain because energy is lost at each stage.
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Pyramids
Pyramids of numbers show stages in a food chain.
Each level on a pyramid of numbers is called a trophic level.
Pyramids of biomass show the total dry mass of the organisms at each trophic level.
Pyramids of numbers are not always pyramid shape whereas pyramids of biomass are.
Data for pyramids of biomass must be obtained from dry mass, so the organisms have to be killed. Therefore only a small sample can be used which may not be representative.
Pyramids of energy are produced by sampling and burning the organisms from each trophic level in a calorimeter, to determine how much heat energy is produced per gram.
This is very time-consuming and very destructive to the environment.
They only take a snapshot of an ecosystem at one moment in time.
Pyramids of energy are always pyramid shaped because energy is lost at each level, so the size of each bar decreases at each successive trophic level.
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Conclusion
The amounts of biomass and energy contained in living things always gets less at each stage of a food chain, from producers onwards. Biomass is lost as waste products and used to release energy in respiration. This is used for movement and to control body temperature. Only a small amount is used for growth.
