Fig. 5.1 shows the seaweed *Laminaria hyperborea*. This is a photosynthetic protoctist found in the coastal waters around Norway. The seaweed is grown commercially to obtain the glucose polysaccharide called alginate. This is used in certain food products. [Figure 5.1] An increase in carbon dioxide concentration in the atmosphere has resulted in higher concentrations of carbon dioxide in the ocean. This has caused a decrease in the pH of the ocean and has resulted in ocean acidification. Scientists are studying seaweeds such as *L. hyperborea* because they absorb a large quantity of carbon dioxide during photosynthesis. This may help to increase the pH of the ocean and reverse ocean acidification.

1. (a)(i)State where light absorption occurs in the chloroplasts of *L. hyperborea*.[1]
2. (a)(ii)Name one product of the light dependent stage of photosynthesis.[1]
3. (a)(iii)Outline the reactions occurring in the stroma that lead to the production of a polysaccharide, such as alginate. The first sentence has been completed for you. Carbon dioxide binds to RuBP.[4]
4. (b)(i)Laboratory experiments were carried out to investigate the effect of day length on the rate of photosynthesis in another marine autotroph, *Zostera marina*. • The temperature was controlled at 4°C. • A low concentration of carbon dioxide dissolved in the water was used. • The light exposure period (day length) was different for five groups of *Z. marina*. • This was maintained for 10 days to allow *Z. marina* to adapt to these conditions. • After 10 days, the rate of photosynthesis was measured for each group under the same controlled conditions. • The experiment was repeated using five groups of *Z. marina* with a high concentration of carbon dioxide dissolved in water. Table 5.1 shows the rate of photosynthesis for each group. [Table 5.1] With reference to Table 5.1, explain the difference in the rate of photosynthesis at high carbon dioxide concentration compared to low carbon dioxide concentration.[2]
5. (b)(ii)With reference to Table 5.1, describe and explain the effect of increasing day length on the rate of photosynthesis for the *Z. marina* in high carbon dioxide concentration.[3]
6. (c)(i)In the laboratory, a seaweed was grown in water with different pH values. All other variables, including temperature and light, were standardised. The mean rate of photosynthesis was calculated over a 24 hour period for each pH value. The results are shown in Fig 5.2. [Figure 5.2] With reference to Fig. 5.2, explain the effect on the rate of photosynthesis when the pH increases from 8.1 to 8.4.[2]
7. (c)(ii)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.[1]

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