(i) Light : The intensity of light affects the rate of photosynthesis and thus controls the rate of production of ATP and NADPH2 . An increase in light intensity will increase the rate pf photosynthesis (if no other factor is limiting). Beyond the light saturation inten-sity, the increased intensity of light does not increase the rate of photosynthesis. That intensity of light at which the CO2 used in photosynthesis is equal to that of liberated during respiration is called the light compensation point. The rate of photosynthesis does not depends upon the duration of light but the amount of carbohydrate produced, depends upon the duration of light. The quality of light also affects the process as it occurs only in the visible part of spectrum i.e., 380 nm – 760 nm wavelengths. It usually does not take place in ultraviolet and infrared rays as these rays are injurious to proto-plasm. The highest rate of photosynthesis is in red light followed by blue light while green light is least effective in photosynthesis as most of it is reflected back.

(ii) Temperature : Temperature along with other environmental conditions affects photo-synthesis in a number of ways. At low temperature, the rate of photosynthesis is low because the enzymes are affected adversly. At high temperature also, the enzymes get denatured and the rate of photosynthesis declines. The optimum range of temperature for photosynthesis is 20°C – 35°C. Upto 35°C, the process shows a progressive increase with rise in temperature and this increase follow vant Hoff’s Law, according to which the rate of chemical reaction doubles for every 10°C rise of temperature of other factors are not limiting.