How does carbon dioxide concentration affect photosynthesis?

Carbon dioxide concentration directly affects the rate of photosynthesis because CO₂ is a primary raw material used in the Calvin cycle for glucose synthesis. As the concentration of carbon dioxide increases, the rate of photosynthesis generally rises because more substrate is available for carbon fixation.

At low CO₂ levels, photosynthesis is limited since RuBisCO, the key enzyme responsible for carbon fixation, does not have sufficient carbon dioxide to operate efficiently. This results in reduced glucose production even if light intensity and temperature are optimal.

As CO₂ concentration increases, the rate of photosynthesis improves until it reaches a saturation point. Beyond this level, the rate no longer increases because other factors, such as light intensity or enzyme activity, become limiting.

Higher CO₂ levels can also reduce photorespiration, a process in which RuBisCO binds oxygen instead of carbon dioxide, leading to energy loss. By increasing CO₂ concentration, plants can improve the efficiency of carbon fixation.

However, extremely high concentrations do not continuously enhance photosynthesis due to physiological limits and environmental constraints.

Overall, carbon dioxide concentration is a key limiting factor that significantly influences the efficiency and productivity of photosynthesis.