Question

As CO₂ becomes source within air spaces of leaf, what is its effect on the rate of photosynthesis?

1) Increases the rate of photosynthesis
2) Decreases the rate of photosynthesis
3) Has no effect on the rate of photosynthesis
4) Cannot be determined

Answer 1

Increasing CO₂ concentration usually increases the rate of photosynthesis, while a loss of CO₂ leads to a decrease in photosynthesis rate due to less substrate available for the Calvin cycle and reduced activity of the enzyme rubisco.

Step-by-step explanation:

As CO₂ concentration increases within the air spaces of a leaf, it generally increases the rate of photosynthesis up to a certain point. This is because CO₂ is a crucial substrate for the Calvin cycle, where it is fixed and used to produce organic molecules like glucose. This process is light-dependent and assumes that other factors, such as water and light, are not limiting. However, if CO₂ is lost from the leaf, such as on hot, dry days when stomata close to conserve water, the concentration of CO₂ within the leaf can decrease. This leads to a decrease in the rate of photosynthesis, as there is less CO₂ available for the Calvin cycle. If the CO₂ level drops below a certain threshold, the enzyme rubisco, which catalyzes the fixation of CO₂, cannot function effectively, further inhibiting the rate of photosynthesis.