The leaf is the primary site of PHOTOSYNTHESIS in plants. There are three main factors affecting PHOTOSYNTHESIS and several corollary factors. The three main are: • Light irradiance and wavelength • Carbon dioxide concentration • Temperature. Light intensity (irradiance), wavelength and temperature In the early 20th century, Frederick Frost Blackman along with Albert Einstein investigated the effects of light intensity (irradiance) and temperature on the rate of carbon assimilation. • At constant temperature, the rate of carbon assimilation varies with irradiance, initially increasing as the irradiance increases. However, at higher irradiance, this relationship no longer holds and the rate of carbon assimilation reaches a plateau. • At constant irradiance, the rate of carbon assimilation increases as the temperature is increased over a limited range. This effect is seen only at high irradiance levels. At low irradiance, increasing the temperature has little influence on the rate of carbon assimilation. These two experiments illustrate vital points: First, from research it is known that, in general, photochemical reactions are not affected by temperature. However, these experiments clearly show that temperature affects the rate of carbon assimilation, so there must be two sets of reactions in the full process of carbon assimilation. These are, of course, the light dependent 'photochemical' stage and the light independent, temperature dependent stage. Second, Blackman's ...

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