This phase occurs in the stroma of the chloroplast. Her reactions do not need the energy of light, so they occur not only in the light, but also in the dark. The reactions of the dark phase are a chain of successive conversions of carbon dioxide (coming from air), leading to the formation of glucose and other organic substances
The first reaction in this chain is carbon dioxide fixation; the carbon dioxide acceptor is the five-carbon sugar ribulozobi phosphate (RiBP); catalyzes the reaction of the enzyme ribulose bisphosphate carboxylase (RiBP-carboxylase). As a result of the carboxylation of ribulozobium phosphate, an unstable six-carbon compound is formed, which immediately decomposes into two phosphoglyceric acid (PHA) molecules.Then a cycle of reactions occurs in which phosphoglyceric acid is converted into glucose through a series of intermediate products. In these reactions, the energies of ATP and NADPH2 formed in the light phase are used; the cycle of these reactions is called the Calvin cycle:
6CO2 + 24H + + ATP -> С6Н12О6 + 6Н2О.
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