A student wrote down information about an aquatic habitat. Fig. 4.1 contains the student’s notes: “Aquatic plants are food for freshwater shrimps and midges. Mayflies also eat aquatic plants. Mayflies are food for salmon. Stoneflies feed on midges and are eaten by salmon. Salmon also feed on freshwater shrimps. Herons feed on salmon.”
(a(i))[4]
Construct a food web to represent the feeding relationships shown in Fig. 4.1. Do not draw the organisms.
(a(ii))[3]
Complete Table 4.1 using the information in Fig. 4.1 by naming the missing trophic levels and giving one organism at each separate trophic level.
(a(iii))[3]
Outline how the energy in the primary consumers in this aquatic food web is used to make biomass in the secondary consumers.
(a(iv))[3]
Predict the impact on the feeding relationships shown in Fig. 4.1 of overharvesting of salmon.
(b)[1]
Describe what is meant by the term decomposer.
(c)[4]
Explain why it is more energy efficient for humans to eat crop plants than to eat livestock that have been fed on crop plants.
Worked solution & mark scheme
This 18-mark question has a full step-by-step worked solution and mark scheme. One marking point: “correct food web with arrows from food to feeder, e.g. aquatic plants → midges → stoneflies → salmon → herons” …