Energy and ecosystems

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  • Created by: emma
  • Created on: 13-05-13 15:10
why is only around 3% of the suns energy available to plants converted into organic matter?
1) 90% reflected back into space or absorbed by the atmosphere 2)not all wavelengths can be absorbed/used 3)light might not fall on chlorophyll molecule 4)low co2 levels may limit rate
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what is the gross production?
the total quantity of energy that plants in a community convert to organic matter
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what is the net production?
the rate at which plants store energy.
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net production =
gross production - respiratory losses
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what percentage of energy is transferd from a primary to a secondary consumer?
about 20%
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why is such a low percentage of energy transferred from one trophic level to the next?
1) some of the organism is not eaten 2) some is lost in faeces (not digested) 3)some energy lost in excretory materials 4)energy lost as heat during resp. and from body to environment
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why do most food chains only have 4 or 5 trophic levels?
energy transfer between trophic levels is inefficient and there is insufficient energy to support breeding populations at trophic levels above this.
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what is the unit for the amount of energy available at each trophic level of a food chain?
kj m-1 y-1
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how can the efficiency of energy transfer between trophic levels be calculated?
energy available after / energy before X 100
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cons of using a pyramid of numbers?
no account of size is taken, so we don't always get a pyramid. numbers can also be so large that it is impossible to represent them on the same scale as everything else.
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what does a pyramid of biomass show?
the total mass of organisms at each trophic level.
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what is biomass measured in?
grams per cubic metre.
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what is the most accurate representation of energy flow through a food chain?
pyramid of energy.
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why are pyramids of energy more reliable than pyramids of biomass?
organisms with the same dry mass may store different amounts of energy.
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what is the unit of energy flow through pyramids of energy?
kjm-2 y-1
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what are the two main factors affecting the net productivity of an agricultural ecosystem are?
efficiency of crop at carrying out photosynthesis. the area of ground covered bu the leaves of the crop.
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what two additional forms of energy input energy in to farms compared with natural ecosystems?
food (for farmers) , fossil fules (to power machinery)
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how does intensive rearing improve energy-conversion rate?
feeding is controlled, so animals get optimum amount and type of food. less energy for muscle contraction as movement is restricted. environment is kept warm to reduce heat loss. predators are excluded so there is no loss to other organisms in web.
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how does selective breeding increase energy conversion?
varieties can be produced that are more efficient at converting food to body mass.
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Card 2

Front

what is the gross production?

Back

the total quantity of energy that plants in a community convert to organic matter

Card 3

Front

what is the net production?

Back

Preview of the front of card 3

Card 4

Front

net production =

Back

Preview of the front of card 4

Card 5

Front

what percentage of energy is transferd from a primary to a secondary consumer?

Back

Preview of the front of card 5
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