Fig. 16.1 shows a food web in a woodland community that contains an oak tree, several insects, some small birds and a bird of prey. The arrows show the dire...
Question 1 Report
Fig. 16.1 shows a food web in a woodland community that contains an oak tree, several insects, some small birds and a bird of prey. The arrows show the direction in which energy flows between the organisms as one organism is eaten by another.
(a) State what the arrows in a food web represent. [1]
(b) State the name given to the oak tree in this food web. [1]
(c) Name one organism that is a secondary consumer in this food web. [1]
(d) Describe and explain what would happen to the number of caterpillars if all the blue tits were removed from the woodland. [3]
(e) Explain why a food web is a better model of feeding relationships than a single food chain. [2]
(f) Explain the role of the fungi in returning nutrients to the woodland. [3]
(g) Suggest one effect on the food web if a disease killed most of the oak trees. [2]
Answer Details
This question is about interpreting a food web (energy flow, trophic levels) and the effects of removing organisms. Note: the question text and mark scheme describe a woodland web (oak tree, caterpillars, blue tits, ladybirds, bird of prey); answer in those terms. If the displayed diagram shows different (marine) organisms, that appears to be a figure mismatch and should be checked by a reviewer.
(a) The arrows represent the direction of energy flow, that is the transfer of energy from one organism to the organism that eats it [1].
(b) The oak tree is a producer [1], because it makes its own food by photosynthesis and is the starting point of the food web.
(c) Any organism that eats a primary consumer is a secondary consumer, for example a blue tit or a ladybird [1] (it feeds on the caterpillars/aphids that ate the plant).
(d) If all the blue tits were removed, the number of caterpillars would increase [1]; because one of their predators has been removed [1]; so fewer caterpillars are eaten and more survive to reproduce [1] [3]. (Over time the increase may be limited as their food plants are eaten up.)
(e) A food web is a better model than a single food chain because it shows that an organism may have more than one food source and more than one predator [1]; so it represents the real, interconnected feeding relationships of the whole community more accurately [1] [2].
(f) The fungi are decomposers [1]; they break down dead organisms and waste material [1]; releasing mineral ions / nutrients back into the soil for plants to absorb [1] [3]. This recycles nutrients so producers can keep growing.
(g) If a disease killed most of the oak trees, any sensible linked effect (max 2): the caterpillars and aphids lose their food source, so their numbers decrease [1]; and this reduces the food available for their predators, so the numbers of blue tits / ladybirds also fall [1] [2].
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