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Feversham College

AQA Biology Unit 4

Frihah Parvaiz

[Type the company address]

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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…

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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.

Energy flow through different levels of a food chain


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Food chain in a lake in the USA


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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.

Natural ecosystems Agricultural ecosystem
Solar energy only ­ no additional Solar energy plus energy from food
energy input (labour) and fossil fuels (machinery
and transport)
Lower productivity Higher…

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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…

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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…

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Intensive rearing of domestic livestock

Candidates should be able to
· apply their understanding of biological principles to present scientific arguments
that explain how these and other farming practices affect productivity


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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…


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