Question

In photosynthesis, what is an example of a light-independent reaction?

Answer 1

Hint: The main reaction that occurs in the Light Independent Phase is the carbon assimilation (also known as the Blackman reaction). The name through which Light independent reaction is known is the Calvin cycle. The stroma of the chloroplast is the site of the reaction. The reaction uses the assimilatory power (NADPH $ + $$H^+$ and ATP) produced by the Light Dependent Phase.

Complete answer:
The Calvin cycle is also known as the C3 cycle because the first stable compound formed is of the $3 - $C compound known as Phosphoglyceric acid (PGA). The Calvin Cycle occurs in three steps :
Carboxylation or Fixation of Carbon dioxide: Carbon dioxide enters into the stroma of chloroplast through the stomata. The $5$-C sugar Ribulose Bisphosphate (RuBP) present in the stroma reacts with Carbon dioxide in presence of the enzyme Ribulose bisphosphate carboxylase oxygenase (RUBISCO) and water to produce $6$-C compound Bisphospho Ribitol which splits to give two molecules of PGA.
Reduction: $3$ -Phosphoglyceric acid phosphorylated by ATP in the presence of enzyme Kinase produces Bisphosphoglyceric acid (BPGA). BPGA is reduced by NADPH $ + $ $H^+$ in presence of the enzyme Triose phosphate dehydrogenase to produce the first carbohydrate in the process of photosynthesis known as Phosphoglyceraldehyde (PGAld). $12$ molecules of PGAld are formed in this process, among them $2$ molecules are diverted for the production of glucose. Some molecules of $3$-PGAld isomerize into Dihydroxyacetone phosphate (DHAP). $2$ molecules of DHAP unite in presence of Aldose to form Fructose $1,6$- Bisphosphate.
Regeneration of RuBP: $10$ molecules of PGAld undergoes a series of complex reactions of various carbon numbers containing compounds, among them $5$-C sugar RuMP is important. $6$ molecules of RuMP are phosphorylated by $6$ molecules of ATP to form RuBP.

Note :
 RUBISCo is the most abundant protein present in the biological world. Previously the Light Independent Reaction was known as a Dark reaction that does not occur in dark as the essential components needed for the process are generated in the presence of sunlight but the direct involvement of light is not required as the process is carried through in the day time.