Final answer:
Low levels of CO2 in the leaf can hinder the Calvin cycle, leading to reduced photosynthesis and glucose production and may cause an increase in photorespiration, which is less efficient for the plant.
Step-by-step explanation:
When carbon dioxide (CO2) is low in the leaf, the efficiency of the Calvin cycle is compromised, leading to the inhibition of photosynthesis. If CO2 concentrations fall below a critical point, the enzyme rubisco, which catalyzes the carbon-fixing reactions of the Calvin cycle, cannot operate effectively. As a result, the production of glucose by the plant is reduced, impacting the plant's energy and growth processes. Additionally, photorespiration may occur, a process where O2 is used instead of CO2, which leads to the wasteful usage of energy and carbon compounds in plants.