Notes

Energy is lost at each level in the food chain, as in the examples below.
 Energy lost through the process of respiration (as heat)
 Energy used up for movement (to search for food, find a mate,
escape from predators...).
 Warm-blood animals (birds and mammals) maintain a standard blood
temperature – they lose heat to the environment.
 Warm-blood animals lose heat energy in faeces and urine.
 Some of the material in the organism being eaten is not used by the
consumer, for example a locust does not eat the roots of maize, and
some of the parts eaten are not digestible.
Even plants do not make use of all the light energy available to them. This is
because some light:
 is reflected off shiny leaves
 is the wrong wavelength for chlorophyll to trap
 passes through the leaves without passing through any chloroplasts
 does not fall on the leaves.
On average, about 90% of the energy is lost at each level in a food chain.
This means that in long food chains, very little of the energy entering the
chain through the producer is available to the top carnivore. So there tend to
be small numbers of top carnivores. The food chain below shows how energy
reduces through the chain. It is based on maize obtaining 100 units of
energy.
1. a) Which form of the Sun’s energy is trapped by the producer? [1 mark]
b) Into which energy form is the Sun’s energy converted when it is
trapped by the producer? [1 mark]
2. a)The first consumer has received 6000 units of energy. How many units
of energy (X on the figure) have been passed to the second consumer? [1
mark]
b) How many units of energy (Y on the figure) are lost from the third
consumer to the decomposers. [1 marks]
3. a) Suggest why the proportion of the energy intake which a producer
loses to the environment (20%) is smaller than that lost to the environment
by a first consumer (30%). [2 marks]
b) Many countries have difficulty in producing enough food for their
population. How might it help to overcome this problem if humans were
always fed as first consumers, rather than second or third consumers?
[3 marks]
Answer
1. a) Light (or solar) energy
b) Chemical energy
2. a) 1200 units
b) 48 units
3. a) The consumer may be warm-blooded, so some energy is lost as heat.
Consumers usually move around to find food, a mate, or escape from
predators, which uses up energy, but producers do not move.
b) Feeding as a first consumer involves eating plants. Less energy is lost
to the environment when feeding at this level, so food production is more
efficient in terms of energy conservation.
the branch of biology that deals with the relations of organisms to one another and to their physical surroundings