Light-independent reaction overview

In photosynthesis, the light-independent reactions, also somewhat misleadingly called the dark reactions, are chemical reactions that convert carbon dioxide and other compounds into glucose. These reactions, unlike the light-dependent reactions, do not need light to occur; hence the term dark reactions. These reactions take the products of the light-dependent reactions and perform further chemical processes on them. The light-independent reactions are two: carbon fixation and the Calvin-Benson cycle.

In CAM plants, carbon fixation actually does take place at night.

Note that regeneration of the substrate for this reaction requires light. Thus it is not that correct to call this reaction as light-independent reaction.

Overview of the Calvin cycle and carbon fixation:

Phase I - Carbon Fixation:

Phase II: Reduction:

Phase III: Regeneration of Ribulose:

Carbon fixation

The carbon fixation reaction is the first step of the light-independent reactions. Carbon from carbon dioxide is "fixed" into a larger carbohydrate. Three pathways to occur: C3 carbon fixation (the most common), C4 carbon fixation, and CAM (Crassulacean Acid Metabolism). C3 fixation occurs as the first step of the Calvin-Benson cycle in all plants. C4 plants first fix carbon dioxide into malate, which is then used to supply carbon dioxide in the middle of the night to the Calvin-Benson cycle. CAM plants perform a similar process.

Calvin cycle

The Calvin-Benson cycle takes carbon dioxide and converts it to glucose, which the plant uses for energy.


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