Q) Describe the dark reaction (Calvin cycle) of photosynthesis
Main points | |
Key idea: | Main stages of the Calvin cycle |
· 3 stages: (i) carbon fixation, (ii) reduction of glyceraldehyde-3-phosphate (G3P) and (iii) regeneration of ruBP | |
Key idea: | Stage 1 : Carbon fixation |
· Initially, 1 CO2 combines w 5C ribulose bisphosphate (RuBP), catalyzed by ribulose bisphosphate carboxylase · Product = unstable 6C compound, immediately breaks down to two 3C mol of phosphoglycerate (PGA) | |
Key idea: | Stage 2 : Reduction of PGA to G3P |
· PGA reduced to glyceraldehyde-3-phosphate (G3P) · Requires ATP + NADPH (fr light-dependent rx) · 12 G3P molecules made fr 6 CO2 that enter the cycle + ref to 2 of which are used to syn carbo (e.g. sucrose, starch or cellulose) | |
Key idea: | Stage 3 : Regeneration of RuBP |
· Remaining G3P mol undergo rx to form ribulose phosphate (RuP) which are then phosphorylated to regenerate RuBP required for cycle to repeat itself | |
Key idea: | Substrates for every one glucose synthesized |
· 6CO2 fixed, phosphates transferred fr ATP + e fr NADPH | |
Comments: (i) Visualize the answer with the aid of a labelled diagram. (ii) Verbalize the answer + write down the main points w/o referring to the answer (use abbreviations) (iii) Read again within the next 24h & once more within 72h (do not spend more than 10min) (iv) The Calvin cycle of photosynthesis is also known as the light independent stage or the dark reactions. (v) RuBP carboxylase is also known as rubisco or RuBP oxygenase. (vi) ATP and NADPH required for the reduction step are the products of the light dependent reactions of photosynthesis. | |
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