Calvin Cycle in Photosynthesis

Calvin Cycle Definition

• The Calvin cycle, also known as the C3 cycle or light-independent or dark reaction of photosynthesis, is a set of chemical reactions that reduce carbon dioxide and other compounds into glucose.

Chemical Equation

• The Calvin cycle can be reduced to the following chemical equation: 3CO2 + 6 NADPH + 5H2O + 9ATP → G3P + 2H+ + 6 NADP+ + 9 ADP + 8 Pi
• G3P stands for glyceraldehyde-3-phosphate

Importance of Calvin Cycle

• The Calvin cycle is responsible for converting CO2 into glucose, which is then stored as carbohydrates (starch and sucrose) in plant cells
• The energy required for this process comes from ATP and NADPH produced during the light-dependent reactions of photosynthesis

Stages of Calvin Cycle

• Carbon fixation: CO2 binds to RuBP to form phosphoglycerate, catalyzed by the enzyme RuBisCO
• Reduction: 3-PGA molecules are converted into glucose using energy from ATP and NADPH
• Regeneration: G3P molecules are used to produce glucose, while others are recycled to regenerate RuBP

Key Points on C3 Cycle

• C3 cycle refers to the dark reaction of photosynthesis
• It is indirectly dependent on light and uses energy carriers produced during light-dependent reactions
• The cycle consists of three stages: carbon fixation, reduction, and regeneration

Difference between Cyclic and Non-Cyclic Photophosphorylation

• Cyclic photophosphorylation involves only Photosystem I, producing ATP
• Non-cyclic photophosphorylation involves both Photosystem I and II, producing ATP and NADPH

Dark Reaction of Photosynthesis

• Also known as carbon-fixing reaction or biochemical reaction
• A light-independent process that forms sugar molecules from water and carbon dioxide
• Occurs in the stroma of the chloroplast, utilizing NADPH and ATP products of the light reaction