Why Is There a Maximum Rate of Photosynthesis?
Photosynthesis uses light to synthesize organic compounds from carbon dioxide and water in a series of light-dependent reactions followed by a set of light-independent reactions. The rate of the reactions is principally limited by available light and carbon dioxide.
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Light-Dependent Reactions
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During the first stage of photosynthesis, pigments absorb light to be used in a process called photophosphorylation, which generates high-energy molecules for the light-independent reactions.
Light-Independent Reactions
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The light-independent reactions utilize the energy produced in photophosphorylation to synthesize sugar molecules through the Calvin-Benson Cycle (a series of reactions that take place inside the chloroplasts).
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Limiting Factor for Light-Dependent Reactions
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Available light is the major limitation in light-dependent reactions. As light levels increase, the rate of photosynthesis tends to increase until the photosynthesis rate plateaus because of limitations in the light-independent reactions.
Limiting Factor for Light-Independent Reactions
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The principle limitation for light-independent reactions is the energy provided by photophosphorylation. If light levels are sufficient to supply all needed energy, the limitation becomes available carbon dioxide for use in fixation.
Order of Limiting Factors
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The rate of photosynthesis is limited first by available light (wavelength and intensity), second by available carbon dioxide, and third by temperature (there is an optimum temperature for the enzymes involved in photosynthesis to operate).
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