Explain what the term limiting factor means in photosynthesis.
Suggest why the soil air and the air surrounding the leaves of the plants were kept separate.
Two sets of plants, A and B, were raised from seed in different concentrations of carbon dioxide: A - normal atmospheric concentration of carbon dioxide $(0.033\%)$; B - normal atmospheric concentration of carbon dioxide $\times 2$ $(0.066\%)$. Each set was kept at its own concentration of carbon dioxide, and their rates of photosynthesis were measured at different light intensities. The results are shown in Fig. 2.1 on page 5.
With reference to Fig. 2.1, describe and explain, in terms of limiting factors, the results obtained from the plants in set A.
Explain how the results of set A and set B differ at high light intensities.
In a second investigation, two sets of plants, C and D, were raised from seed, as before, in different carbon dioxide concentrations: • C - normal atmospheric concentration of carbon dioxide ($0.033\%$). • D - normal atmospheric concentration of carbon dioxide $\times 2$ ($0.066\%$). When the plants reached maturity, the growth-chamber conditions were changed to examine the rate of photosynthesis of each set in different carbon dioxide concentrations. The results are shown in Fig. 2.2.
Suggest explanations for why the plants in set D show a higher rate of photosynthesis per unit leaf area than those in set C.
Suggest explanations for the greater photosynthetic rate per unit leaf area shown by the plants in set D compared with set C.