Question

You add a chemical that blocks the Calvin Cycle. What happens to the rate of the light-dependent reactions and why – be specific.

Answer 1

• ATP and NADPH are produced during light reactions of photosynthesis and they are later used as rich sources of energy for Calvin cycle/dark reactions. Calvin cycle is involved in the fixation of carbon from carbon dioxide which later changes into 3-carbon sugars that form either glucose or are reused in this cycle.
• An inhibitor of Calvin-cycle like glycolaldehyde inhibits phosphoribulokinase. When Calvin cycle is inhibited by glycolaldehyde, there is decrease in the usage of NADPH along with conversion of O2 to H2O2 (Hydrogen peroxide) in PSI.
• H2O2 further causes inhibition of proteins of PSII and thus effects overall process of phbotosynthesis.