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13 Cards in this Set

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Agricultural ecosystems try to ensure...
...that as much of the available energy from the Sun as possible is transferred to humans.
Agricultural ecosystems channel the energy flowing through a food web into the human food chain and away from other food chains. This increases the...
...productivity of the human food chain
The rate at which plants assimilate (produce) chemical energy is called...
Gross productivity
What is productivity?
The rate at which something is produced
How is gross productivity normally measured and what are the units?
Usually measured for a given area over a given period of time, usually in units of kJm^-2year^-1
How much of the chemical energy produced by plants is used in respiration? What's the left over called?
About 20%. Net productivity
net productivity =
gross productivity - respiratory losses
What are the two main factors which affect net productivity?
The efficiency of the crop at carrying out photosynthesis. (Improved if all conditions are supplied for PS)

The area of ground covered by the leaves of the crop
How is an agricultural ecosystem prevented from reaching its climax community?
Most of the species in the community are excluded
In order to suppress unwanted species from an agricultural ecosystem, additional energy is required. What is this energy used for and where does it come from?
Plough fields, sow crops, remove weeds, suppress pests and diseases etc.

The energy comes from food and fossil fuels (from machinery. Energy from fossil fuels requires in an AE is IN ADDITION to solar energy, not instead)
In natural ecosystems productivity is relatively ___
low
Which type of ecosystem has greater species diversity?
Natural
Why is it bad to increase every factor necessary for PS to very high levels?
May damage the plant, e.g. high temp may denature the plant's enzymes. Also uneconomical