Question

Dark reaction of photosynthesis occur in
A.Grana
B.Stroma
C.Matrix
D.Cytoplasm

Answer 1

Dark reaction is part of photosynthesis reaction. The dark reaction does not mean that a dark reaction takes place in the dark. This reaction is named dark reaction because it is dependent on the products of light reaction.

Complete answer: Dark reaction is also known as a biosynthetic phase. This reaction does not depend on light directly but depends on the product of the light reaction. After light reaction thylakoid has high energy chemical intermediates ATP and NADPH. The dark reaction occurs through the Calvin cycle. In the Calvin cycle, Carbon dioxide is incorporated into the plant leading to the synthesized sugar, which in turn forms starch. Stroma has all the enzymes required for fixing carbon dioxide. The dark reaction occurs in the stroma.
Grana: A pile of thylakoids forms grana. Photosystem I and photosystem II are both present in grana.
Stroma: The fluid surrounding the thylakoid called the stroma. Stroma has only photosystem I.
Cytoplasm: It is a jelly-like fluid present between the cell membrane and nucleus.
So the correct answer is (B).

Additional Information:
Calvin cycle is also known as the C3 cycle describe under three stages.
Carboxylation: Carbon dioxide fixation takes place in this step. Carbon dioxide is utilized for the carboxylation of RuBP. This step results in the formation of two molecules of 3-Phosphoglyceric acid.
Reduction: This step involves the utilization of two ATP molecules for phosphorylation and two of NADPH for reduction per carbon dioxide molecule. This step results in the formation of glucose.
Regeneration: Regeneration of the carbon dioxide acceptor molecule(Ribose bisphosphate).

Note: Some plants that live in tropical regions have the C4 pathway. This is also known as the Hatch and Slack Pathway. Sugarcane, Maize, Sorghum, Amaranthus are some good examples of plants that undergo Hatch and Slack Pathway.