Aquatic ecology and Biodiversity

5.1.5. Dark rection

Unit 5- Productivity

5.1.5. Dark reaction
Carbon-fixing reactions are also known as the dark reactions. Carbon dioxide enters the cells of aquatic autotrophs through the process of diffusion. The Calvin cycle occurs in the stroma of chloroplasts. Carbon dioxide is captured by the chemical ribulose biphosphate (RuBP). RuBP is a 5-C chemical. Six molecules of carbon dioxide enter the Calvin cycle, eventually producing one molecule of glucose. The reactions in this process were worked out by Melvin- Calvin .
Dark Reaction (Calvin or Melvin reaction) and it is also called as Calvin cycle, CO₂ fixation cycle, carbon reduction cycle, reductive pentose path way etc. Dark reaction takes place in “stroma” . Dark reaction involves the reduction of CO₂ by ATP and NADPH₂ formed in the light reaction with the formation of organic matter (CHOs) - a new organic matter
CO₂+2NADPH₂+ n ATP -----------> (CH₂O) + H₂O +2NADP +n ADP +npi

Photosynthetic products
• Phosphoglyceric acid (PGA) - Stable product
• Sugar phosphate -Ribose diphosphate, pentosesugar, fructose diphosphte
• Non carbohydrate such as ammo acids
• Dissolved oxygen
• Energy