Energy Transfer in Ecosystems

Notes on energy transfer through food chains and the productivity of the transfer between trophic levels.

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Energy Transfer ­ Revision.
An ecosystem is all the organisms lining in a particular area, and all the abiotic factors. Energy can be
transferred through ecosystems. It can come in at photosynthesis, where sunlight energy is
converted by plants, and as plants are eaten by herbivores, and then herbivores are eaten by
carnivores, the energy is transferred through the food chain. Each of these stages (producers,
consumers...) are called trophic levels. Energy can be lost between levels in things that can't be
eaten, e.g. faeces or bones, but they are recycled back into the environment by decomposers, or is
lost to the environment when organisms use energy from respiration for movement or body heat.
Only about 10% actually becomes biomass, and this is what is available to the next trophic level.
Primary Productivity.
The energy that is taken in by the organism is called gross primary productivity. It is around 40% of
the available energy, as some parts of food are indigestible, so pass through organisms or are not
The energy which actually is available is what becomes biomass, it is stored or used for growth, is
called net primary productivity.
Net primary productivity = gross primary productivity (minus -) respiration
Calculating Energy Transfer
You can work out the efficiency of energy transfer between trophic levels, by getting the net
productivity of one level, divided by the net productivity of the previous level, and multiply by 100.
You get a percentage.


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