Rate of Photosynthesis: Limiting Factors

Topics: Carbon dioxide, Photosynthesis, Light Pages: 3 (624 words) Published: April 17, 2013
Rate of photosynthesis: limiting factors
Limiting factors The main factors affecting rate of photosynthesis are light intensity, carbon dioxide concentration and temperature. In any given situation any one of these may become a limiting factor, in other words the factors that directly affects the rate at which photosynthesis can take place masking the effects of the other factors. Light and rate of photosynthesis At low light intensities, as light intensity increases, the rate of the light-dependent reaction, and therefore photosynthesis generally, increases proportionately (straight line relationship). The more photons of light that fall on a leaf, the greater the number of chlorophyll molecules that are ionised and the more ATP and NADPH are generated. Light dependent reactions use light energy and so are not affected by changes in temperature.

Rate of photosynthesis

Intensity of light

As light intensity is increased further, however, the rate of photosynthesis is eventually limited by some other factor. So the rate plateaus. At very high light intensity, chlorophyll may be damaged and the rate drops steeply (not shown in the graph). Chlorophyll a is used in both photosystems. The wavelength of light is also important. PSI absorbs energy most efficiently at 700 nm and PSII at 680 nm. Light with a higher proportion of energy concentrated in these wavelengths will produce a higher rate of photosynthesis. Carbon dioxide and rate of photosynthesis An increase in the carbon dioxide concentration increases the rate at which carbon is incorporated into carbohydrate in the light-independent reaction, and so the rate of photosynthesis generally increases until limited by another factor. As it is normally present in the atmosphere at very low concentrations (about 0.04%), increasing carbon dioxide concentration causes a rapid rise in the rate of photosynthesis, which eventually plateaus when the maximum rate of fixation is reached.

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