CBSE Class 10 Answered

i) Temperature - The dark reactions of photosynthesis are enzymatic and hence temperature controlled. Though the light reactions are also temperature sensitive, they are affected to a much lesser extent. The C₄ plants respond to higher temperatures and show higher rate of photosynthesis while C₃ plants have a much lower temperature optimum.

The temperature optimum for photosynthesis of different plants also depends on the habitat that they are adapted to. Tropical plants have a higher temperature optimum than the plants adapted to temperate climates.

ii) Water - The effect of water as a factor is more through its effect on the plant, rather than directly on photosynthesis. Water stress causes stomata to close hence reducing CO₂ availability. Besides, water stress also makes leaves wilt, thus reducing the surface area of the leaves and their metabolic activity as well.

iii) CO₂ -