Question
Fig. 2.1 shows the flow of energy through a natural ecosystem that is not used by humans
at any of the trophic levels.
The unit of energy flow is kJ per m2 per year.
(a) The letters L to O represent the different trophic levels in the ecosystem.
(i) Name the first and third trophic levels, L and N.
(ii) Suggest what is shown by the relative sizes of the boxes, L to O, in the energy
flow diagram in Fig. 2.1.
(iii) There are no predators in the ecosystem feeding on the animals in trophic level O.
Suggest and explain why there are no predators in the ecosystem feeding on the
animals in trophic level O.
(iv) P in Fig. 2.1 does not represent any organisms.
Explain what P represents in the energy flow diagram.
(b) People who live near this ecosystem would like to use some of the organisms at
trophic level M for food.
Suggest and explain what might happen to the ecosystem if the people took too many
of the organisms at trophic level M.
Answer/Explanation
Ans:
Question
(a) (i) State the principle source of energy for this food web.
………………………………………………………………………………………………………………………
(ii) Explain what the arrows on Fig. 8.1 represent.
………………………………………………………………………………………………………………………….
…………………………………………………………………………………………………………………………
(iii) State the number of different secondary consumers in this food web.
……………………………………………………….. secondary consumers
(iv) Name the organism that is both a secondary and a tertiary consumer.
………………………………………………………………………………………………………………………
(v) State what would happen to the number of hawks if the snakes in this food web all died.
Explain your answer.
number of hawks …………………………………………………………………………………………………
explanation …………………………………………………………………………………………………………
………………………………………………………………………………………………………………………….
………………………………………………………………………………………………………………………….
(b) (i) The food web shown in Fig. 8.1 changed when eagles moved into the area.
Eagles eat snakes and lizards.
Add this information to Fig. 8.1. You do not need to draw an eagle.
(ii) State one factor that will increase the eagle population and one factor that will decrease
the eagle population.
increase ……………………………………………………………………………………………………………..
decrease ……………………………………………………………………………………………………………
(iii) Define the term population.
………………………………………………………………………………………………………………………….
………………………………………………………………………………………………………………………….
………………………………………………………………………………………………………………………….
Answer/Explanation
Ans:
(a) (i)the Sun ;
(ii) transfer of energy ;
(iii) three ;
(iv) snake ;
(v) number of hawks: would increase /AW ;
explanation:
lizards / grasshoppers / slugs, not eaten by snakes ;
so increase in number ;
more food for hawks ;
(b) (i) line drawn from snakes to eagles and line from lizards to eagles with arrows in correct direction ;
(ii) increase eagles more snakes /more lizards / other food source ;
decrease eagles fewer snakes /fewer lizards / disease / competition (with another species)/natural disaster ;
(iii) population:
organisms of same species /type ;
living in same area / at the same time ;