All living organisms require energy. The ultimate source of all this energy is the sun. Solar energy is trapped by plants, and then transferred from organism to organism in a food chain. At each stage in this transfer much of the energy is lost to the environment.
Living organisms also require nutrient elements - in particular carbon and nitrogen - which they take from the environment. If this were just a one-way process, ecosystems would soon run out of these nutrients; but in fact they are returned to the environment, with the help of bacteria, via nutrient cycles
In every ecosystem, energy is transferred along food chains from one trophic level to the next. But not all the energy available to organisms at one trophic level can be absorbed by organisms at the next one: in fact the amount of available energy decreases dramatically at each level. Why?
Some of the available energy goes into growth in biomass and the production of offspring: this energy does become available to the next trophic level. However most of the available energy is used up in other ways:
Some is used up at the first trophic level as a result of photosynthesis, which uses up lots of solar energy in making glucose.
Some is used up in respiration, and given off as heat
Some is lost, in the form of biological material and heat, through excretion. (This energy is actually transferred to the decomposer food chain: more about this later!)
Some is used for movement and transport.
All the energy used in these ways returns to the environment, and is not available to the next trophic level. so much energy is lost at each level that however much you start off with it is almost all gone by the fourth trophic level
http://www.bbc.co.uk/schools/gcsebitesize/biology/livingthingsenvironment/2energyandnutrienttransferrev2.shtml
Living organisms also require nutrient elements - in particular carbon and nitrogen - which they take from the environment. If this were just a one-way process, ecosystems would soon run out of these nutrients; but in fact they are returned to the environment, with the help of bacteria, via nutrient cycles
In every ecosystem, energy is transferred along food chains from one trophic level to the next. But not all the energy available to organisms at one trophic level can be absorbed by organisms at the next one: in fact the amount of available energy decreases dramatically at each level. Why?
Some of the available energy goes into growth in biomass and the production of offspring: this energy does become available to the next trophic level. However most of the available energy is used up in other ways:
Some is used up at the first trophic level as a result of photosynthesis, which uses up lots of solar energy in making glucose.
Some is used up in respiration, and given off as heat
Some is lost, in the form of biological material and heat, through excretion. (This energy is actually transferred to the decomposer food chain: more about this later!)
Some is used for movement and transport.
All the energy used in these ways returns to the environment, and is not available to the next trophic level. so much energy is lost at each level that however much you start off with it is almost all gone by the fourth trophic level
http://www.bbc.co.uk/schools/gcsebitesize/biology/livingthingsenvironment/2energyandnutrienttransferrev2.shtml
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