Biology 9700/43 — May/June 2014

(a) The unicellular green alga, Chlorella, a photosynthetic protoctist, was originally studied for its potential as a food source. Although large-scale production proved to be uneconomic, the many health benefits provided by Chlorella mean that it is now mass produced and harvested for use as a health food supplement.

Fig. 1.1 shows cells of Chlorella.

In one study into the productivity of Chlorella, carbon dioxide concentration was altered to investigate its effects on the light-independent stage of photosynthesis.

• A cell suspension of Chlorella was illuminated using a bench lamp.
• The suspension was supplied with carbon dioxide at a concentration of $1\%$ for 200 seconds.
• The concentration of carbon dioxide was then reduced to $0.03\%$ for a further 200 seconds.
• The concentrations of RuBP and GP (PGA) were measured at regular intervals.
• Throughout the investigation the temperature of the suspension was maintained at $25\ ^{\circ}\text{C}$.

The results are shown in Fig. 1.2.