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Energy transfer
Photosynthesis is the main route by which energy enters an ecosystem.
The organisms in any ecosystem rely on sunlight which is converted into chemical
energy in photosynthesis and is passed on as food between other organisms.
Organisms can be divided into three groups: producers (photosynthetic organisms
that manufacture organic substances), consumers (obtain energy by consuming
other organisms) and decomposers. When organisms die, they contain energy that
is used by organisms that break down these materials into simple components.…read more

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Quantitative consideration of the efficiency of energy transfer between trophic levels.
Net productivity as defined by the expression
Net productivity = Gross productivity ­ Respiratory loss
gross production
net production.…read more

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Food chain in a lake in the USA
4…read more

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Energy and food production
Comparison of natural ecosystems and those based on modern
intensive farming in terms of energy input and productivity.…read more

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The ways in which productivity is affected by farming practices
that increase the efficiency of energy conversion. These include
· the use of natural and artificial fertilisers
Fertilisers are minerals that provide chemicals
needed for growth. Crops use up minerals
when growing, so their growth is limited by
lack of minerals. Adding fertilisers replaces
the minerals and this increases productivity
and the efficiency of energy conversion.…read more

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Comparison of biological and chemical control of organisms
Biological Control Chemical Pesticides
Very specific Always have some effect on non-
target species
Once introduced, the control Must be reapplied at intervals,
organism reproduces itself making them very expensive
Pests do not become resistant Pests develop genetic resistance,
and new pesticides have to be
How controlling pests affects productivity
Pests reduce productivity ;weeds compete with crop plants for resources.…read more

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Pyramids of numbers, biomass and energy and their relationship to their corresponding food chains and webs.
Pyramids of numbers show the number of organisms at each
trophic level. However they may not always be pyramid shaped
large tree's may distort the shape. However there are some
No account is taken of size of organism ­ one giant
tree is treated the same as one tiny aphid and each
parasite has the same numerical value as a larger host.…read more


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