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Module 4.3

The integration of respiration and photosynthesis into ecology; energy is transferred through
ecosystems and transfer efficiency can be measured.

Know photosynthesis is the main route by which energy enters ecosystems,
Appreciate energy is transferred through trophic levels in food chains and webs and is
dissipated as heat.

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Pyramids of numbers:

Length of bar is proportionate to the number of

BUT because it doesn't take the size of the individual into account ­ we get differing pyramids of

Therefore pyramids of biomass (gm-2)

Can weigh wet mass BUT it can vary due to the changes of…

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Energy transfer between trophic levels:

The sun is the source of energy for ecosystems.
It is lost in food chains
o Plants normally convert 1-3% of the suns available energy to them into organic
o Over 90% of the suns energy is reflected back into space by clouds and…

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Comparison of natural and agricultural ecosystems;

Natural ecosystems Agricultural ecosystems

Solar energy only ­ no additional energy Solar energy plus energy from food (labour)
input. and fossil fuels (machinery and transport)

Lower productivity Higher productivity

More species diversity Less species diversity

More genetic diversity within a species Less genetic diversity…

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Once introduced, the control organism Must be reapplied at intervals, making them
reproduces itself very expensive
Pests do not become resistant Pests develop genetic resistance, and new
pesticides have to be developed.

Integrated pest control systems

Choosing animal or plant varieties that suit the local area and are as pest-resistant…


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