(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]