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The many relationships between the members of a community in an ecosystem can be described by food
chains and webs.
Each stage in a food chain is called a trophic level, and the arrows represent the flow of
energy and matter through the food chain.

Category
Producer Photosynthetic organisms that…

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The Sun is the source of energy for ecosystems.
However, as little as 1% of this light energy may be captured by green plants and so made available to
organisms in the food chain.
These organisms in turn pass only a small fraction of the energy that they receive to…

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Ecological pyramids show the mass or amount of energy stored by organisms at each trophic level.

Pyramids of Number

These show the numbers of organisms at each trophic level.
The number of organisms at lower trophic levels is greater than the number of organisms at higher
trophic levels.

Drawbacks:
·…

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Agricultural ecosystems are made up largely of domesticated animals and plants used to produce food.
There are considerable energy losses at each trophic level.
This means that the energy we receive from the food we eat is often only a tiny proportion of that
available from the sun at the…

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Productivity

In natural ecosystems productivity is relatively low.
The additional input to agricultural ecosystems is used to increase the productivity of a crop by reducing
the effect of limiting factors on its growth.

The energy used to exclude other species means that the crop has little competition for light, carbon…

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Pest An organism that competes with humans for food or space and can be a danger to health
Pesticide Poisonous chemicals that kill pests




Chemical Control

An effective pesticide should be:

Specific So that it is only toxic to the organisms at which it is
directed.
It should be harmless…

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Integrated Pest-Control Systems

Integrated pest-control systems aim to integrate all forms of pest control rather than being reliant on one
type.
The emphasis is on deciding an acceptable level of the pest rather than trying to eradicate it altogether.

Integrated control involves:

· Choosing animal or plant varieties that suit…

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Intensive rearing of livestock is designed to produce the maximum yield of meat, eggs and milk at the
lowest possible cost.
As energy passes along a food chain only a small percentage passes from one organism in the chain to
the next.
This is because much of the energy is…

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