Editing Calvin cycle (section)

{{short description|Light-independent reactions in photosynthesis}}
<div class="skin-invert-image">{{plain image|File:Chloroplast structure.svg|The internal structure of a chloroplast|350px|right|bottom|#1abc31}}</div>
The '''Calvin cycle''', '''light-independent reactions''', '''bio synthetic phase''', '''dark reactions''', or '''photosynthetic carbon reduction''' ('''PCR''') '''cycle'''<ref>{{cite book|last1=Silverstein|first1=Alvin|title=Photosynthesis|date=2008|publisher=Twenty-First Century Books|isbn=9780822567981|page=21}}</ref> 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 (fluid)|stroma]], the fluid-filled region of a [[chloroplast]] outside the [[thylakoid membranes]]. These reactions take the products ([[Adenosine triphosphate|ATP]] and [[NADPH]]) of [[light-dependent reactions]] and perform further chemical processes on them. The Calvin cycle uses the chemical energy of ATP and the [[Reduction (chemistry)|reducing]] power of NADPH from the light-dependent reactions to produce [[Sugar|sugars]] for the plant to use. These substrates are used in a series of reduction-oxidation ([[redox]]) reactions to produce sugars in a step-wise process; there is no direct reaction that converts several molecules of {{CO2}} to 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 reaction]]s. In the dark, plants instead release [[sucrose]] into the [[phloem]] from their [[starch]] reserves to provide energy for the plant. The Calvin cycle thus happens when light is available independent of the kind of photosynthesis ([[C3 carbon fixation]], [[C4 carbon fixation]], and [[crassulacean acid metabolism|crassulacean acid metabolism (CAM)]]); CAM plants store [[malic acid]] in their vacuoles every night and release it by day to make this process work.<ref>{{cite journal | doi = 10.1104/pp.010818 | first = John C. | last = Cushman | title = A plastic photosynthetic adaptation to arid environments | journal = [[Plant Physiology (journal)|Plant Physiology]] | year = 2001 | volume = 127 | pages = 1439–1448 | pmid=11743087 | issue=4 | pmc=1540176}}</ref>