Affect of CO₂ on photosynthesis : Carbon dioxide acts as a major limitin factor for photosynhesis. The CO₂ is 0.03 % in atmosphere and increase in amount of CO₂ upto 0.05% in atmosphere increases the rate of photosynthesis. Beyond it the rate declines. It is due to the increase in the temperature.

The C₃ and C₄ plants responds differently o the CO₂ concentration. The C₃ plants respond to a higher concentration of CO₂ by showing increased rates of photosynthesis while the C₄ plants saturate at low level of CO₂ and do not show increase in the rate of photosynthesis.