Investigation of limiting factors — practice question

The unicellular green alga Chlorella, which is a photosynthetic protoctist, was first investigated as a possible food source. Large-scale cultivation turned out not to be economical, but because Chlorella provides many health benefits it is now produced on a mass scale and collected for use as a health food supplement. In a study of Chlorella productivity, the concentration of carbon dioxide was varied to see how this affected the light-independent stage of photosynthesis. A cell suspension of Chlorella was exposed to a bench lamp. For $200\ \text{s}$ the suspension received carbon dioxide at $1\%$. The carbon dioxide concentration was then lowered to $0.03\%$ for another $200\ \text{s}$. The concentrations of RuBP and GP (PGA) were recorded at regular intervals. The temperature of the suspension was kept at $25\,^{\circ}\text{C}$ throughout. The findings are shown in Fig. 1.2.