Biology 9700 · AS & A Level · Investigation of limiting factors

Investigation of limiting factors — practice question

Fig. 5.1 depicts the seaweed Laminaria hyperborea. This photosynthetic protoctist is found in coastal waters around Norway. It is commercially cultivated to obtain the glucose polysaccharide alginate, which is used in some food products. A rise in carbon dioxide concentration in the atmosphere has led to higher carbon dioxide levels in the ocean. This has reduced the pH of the ocean and caused ocean acidification. Scientists are investigating seaweeds such as L. hyperborea because they take in a large amount of carbon dioxide during photosynthesis. This could help to raise the pH of the ocean and reverse ocean acidification.
(a(i))[1]

State the site at which light is absorbed in the chloroplasts of L. hyperborea.

(a(ii))[1]

Name one product from the light dependent stage of photosynthesis.

(a(iii))[4]

Outline the reactions in the stroma that result in the formation of a polysaccharide such as alginate. The opening sentence has been completed for you: Carbon dioxide binds to RuBP.

(b(i))[2]

Using Table 5.1, explain how the photosynthesis rate at high carbon dioxide concentration differs from that at low carbon dioxide concentration.

(b(ii))[3]

Using Table 5.1, describe and explain how increasing day length affects the photosynthesis rate of the Z. mariana in high carbon dioxide concentration.

(c(i))[2]

Using Fig. 5.2, explain the effect on the rate of photosynthesis when pH increases from 8.1 to 8.4.

(c(ii))[1]

The lower pH values on Fig. 5.2 represent ocean acidification. Suggest why the results for the lower pH values do not fully support the idea that seaweeds can help to reduce ocean acidification.

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This 14-mark question has a full step-by-step worked solution and mark scheme. One marking point: “grana / thylakoid membranes / lamellae” …

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