<P> This process occurs only when light is available . Plants do not carry out the Calvin cycle during nighttime . They instead release sucrose into the phloem from their starch reserves . This process happens when light is available independent of the kind of photosynthesis (C3 carbon fixation, C4 carbon fixation, and Crassulacean acid metabolism); CAM plants store malic acid in their vacuoles every night and release it by day to make this process work . They are also known as dark reactions . </P> <P> These reactions are closely coupled to the thylakoid electron transport chain as reducing power provided by NADPH produced in the photosystem I is actively needed . The process of photorespiration, also known as C2 cycle, is also coupled to the dark reactions, as it results from an alternative reaction of the RuBisCO enzyme, and its final byproduct is also another glyceraldehyde - 3 - P . </P> <P> The Calvin cycle, Calvin--Benson--Bassham (CBB) cycle, reductive pentose phosphate cycle or C3 cycle is a series of biochemical redox reactions that take place in the stroma of chloroplast in photosynthetic organisms . </P> <P> The cycle was discovered by Melvin Calvin, James Bassham, and Andrew Benson at the University of California, Berkeley by using the radioactive isotope carbon - 14 . </P>

Where in the plant cell does the calvin cycle take place