(a) Experiments were carried out to determine the effect of light intensity on the rate of photosynthesis of a species of the unicellular protoctist, Chlorella. A cell suspension of Chlorella was used. Carbon dioxide uptake was used as a measure of the rate of photosynthesis. • The suspension of Chlorella was illuminated at a light intensity of 3 lux for 20 seconds. • The carbon dioxide uptake by Chlorella was measured at the end of the 20 second period of illumination. • The experiment was repeated at 6 lux, 9 lux, 12 lux and in a dark room. • The suspension was maintained at a temperature of 20 °C. Table 7.1 shows the results of the experiments. [Table 7.1]

1. (a)(i)Use Table 7.1 to calculate the rate of photosynthesis at a light intensity of 6 lux. Complete Table 7.1 by writing your calculated value in the space provided. [1]
2. (a)(ii)Plot a graph of the data in Table 7.1 on the grid in Fig. 7.1 to show the effect of light intensity on the rate of photosynthesis. Draw a curve and extend your curve to show what would happen to the rate of photosynthesis if the experiment is carried out at 18 lux. [Figure 7.1][3]
3. (a)(iii)Suggest an explanation for the shape of your curve from 12 lux to 18 lux.[2]
4. (b)In photophosphorylation, photoactivation of chlorophyll results in the synthesis of ATP. Describe how photoactivation of chlorophyll results in the synthesis of ATP in photophosphorylation.[4]

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