Question

Explain the fixation of carbon dioxide during the C₃ pathway

Answer 1

The photosynthetic reaction which does not require light (lightindependent) is called dark reaction. A dark reaction occurs in the stroma portion of chloroplast so it is called stroma reaction. It is also called Blackman’s reaction. Dark reaction is influenced by temperature. The different chemical reactions of dark reaction are enzymatic. Enzymes of stroma catalyze these reactions. Enzymatic reactions of dark reaction occur in the form of a Cycle and they were studied by Melvin Calvin, Benson and Bassham in 1949. So dark reaction is also called Calvin cycle or Calvin Benson cycle. They used tracer technique by using C₁₄O₂ in unicellular alga Chlorella and found a path of CO₂ in each step of a chemical reaction. The ATP and NADPH of light reaction are used for the fixation of CO₂ during the dark reaction. The main event of dark reaction is the fixation of CO₂. So dark reaction is also called CO₂ fixation cycle.