Energy and ecosystems
- Created by: olivia
- Created on: 06-01-13 14:37
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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