Calvin cycle
light-independent reactions in photosynthesis
The Calvin cycle, bio synthetic phase, dark reactions, or photosynthetic carbon reduction (PCR) cycle of photosynthesis is a series of chemical reactions that convert carbon dioxide and hydrogen-carrier compounds into glucose. The Calvin cycle is present in all photosynthetic eukaryotes and also many photosynthetic bacteria. In plants, these reactions occur in the stroma, the fluid-filled region of a chloroplast outside the thylakoid membranes. These reactions use the products (ATP and NADPH) of the light-dependent reactions and carry out further chemical processes on them. The Calvin cycle uses the chemical energy of ATP and the reducing power of NADPH from the light-dependent reactions to produce sugars for the plant to use. These substrates undergo a series of oxidoreduction (redox) reactions to produce sugars in a stepwise process; there is no direct reaction that converts several molecules of CO2 into a sugar. There are three phases to the light-independent reactions, collectively called the Calvin cycle: carboxylation, reduction reactions, and ribulose 1,5-bisphosphate (RuBP) regeneration.
Though it is also called the "dark reaction", the Calvin cycle does not occur in the dark or during nighttime. This is because the process requires NADPH, which is short-lived and comes from light-dependent reactions. In the dark, plants instead release sucrose into the phloem from their starch reserves to provide energy for the plant.
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