Energy and ecosystems

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Food chains and webs

Producers: photosynthesising organisms

Consumers: eat producers

Decomposers: break down the complex molecules in dead matter

Food chain: describes the feeding relationship between producers and consumers. 

Trophic level: a stage in a food chain

Food webs: shows how different food chains in a habitat link together

Energy transfer

Plants can not convert all of sun's energy into organic matter because:

- Most of the sun's energy is reflected back into space

- Not all wavelengths of light can be absorbed

- Not all of the sun's light will actually hit the chlorophyll

- Another factor may be limiting the rate of photosynthesis

How to calculate the amount of energy converted to organic matter:

the amount of energy converted to orgainc matter is called the gross production.

gross production = net production + respiratory losses

the net production is the rate at which a plant stores energy

Only a small amount of plant energy is used by consumers because:

- Not all of the plant can be eaten

- Not all of the plant can be digested

- Some of the energy can be lost in waste products. I.e urine

- Some of the energy is lost as heat

This poor efficiency explains why:

- Most food chains do not have many trophic levels

- The total biomass of the organism decrease at each trophic level

- The total amount of energy stored is less at each trophic level

Energy transfer = (energy available after the transfer / energy available before) x 100

Energy transfer is measured in kJ m-2 year-1

Ecological pyramids

Provide quantitative info

Pyramid of number: shows the number of organisms at each trophic level

Pyramid of biomass: shows total mass of organisms at each trophic level. The units used                      …


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