Food chains and energy transfer – Answer sheet
1.
What is the source of energy that almost all living things depend on?
[The Sun]
2. What is the name of the process in which plants absorb a small percentage of the Sun’s energy?
[Photosynthesis]
3. What happens to this absorbed energy?
[It is stored in the chemicals which make up the plant’s cells]
4. How does the energy stored in grass end up in a human that has just eaten a beefburger?
[It passes up the food chain when organisms (or parts of organisms) are eaten]
5. In the example above, not all of the energy in the grass makes it up the food chain to the human.
List three places where this energy could be transferred instead
[thermal energy (heat), waste products and uneaten parts]
6. Explain why this transfer of energy to other places limits the length of a food chain.
[Not enough energy available to sustain further predators]
7. What happens to the energy in organisms at the very top of a food chain when they die?
[Fed on by decay organisms (decomposers and detritivores)]
8. Estimate of %
[Herbivore = 10%, Carnivore = 10%, allow any answer between 5% and 15% for either;
this is calculated by measuring the energy stored in flesh and dividing it by the energy
intake. To convert to a %, this is them multiplied by 100.]
9. Describe and explain the differences between energy distribution for the herbivore and the carnivore.
[The carnivore has more respiration (looking for/chasing food), less waste in faeces (not
trying to digest large quantities of difficult to digest plant tissue)]
10. Use the estimates above to estimate the maximum energy that could be transferred from 100 MJ of energy
in grass to a fox that ate a rabbit that fed on the grass.
[1 MJ because 10% of 100MJ (i.e. 10MJ) is passed from grass to rabbit tissues and only
10% of this 10MJ (i.e. 1MJ) ends up as fox tissues - allow any answer that matches
estimates in question 8]
11. Explain why the energy transferred to the fox is likely to be less than this estimate.
[any one from: not all of the rabbit tissues can be digested by the fox; not all of the
grass tissues can be digested by the rabbit; not energy wasted in chasing rabbit/looking
for grass or energy wasted in faeces/digestion as these are accounted for by other
arrows]
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