[Campbell Biology P.251] A specific poison inhibits the enzyme rubisco, preventing carbon fi... | Practice Question
A specific poison inhibits the enzyme rubisco, preventing carbon fixation in the Calvin cycle. What immediate and long-term effects would this have on the overall process of photosynthesis, including the light reactions?
A: The Calvin cycle would cease due to lack of carbon fixation. Consequently, the consumption of ATP and NADPH would stop, leading to their accumulation and a halt in the regeneration of ADP and NADP+, which would then inhibit the light reactions.
B: The Calvin cycle would stop, but the light reactions would continue to produce ATP and NADPH indefinitely as they are independent processes.
C: The light reactions would accelerate to compensate for the inhibited Calvin cycle, leading to an overproduction of ATP and NADPH.
D: Only the sugar production phase of photosynthesis would be affected; ATP and NADPH would still be consumed by other cellular processes.
Explanation
The Calvin cycle relies on ATP and NADPH produced by the light reactions. If rubisco is inhibited, carbon fixation stops, and the Calvin cycle can no longer proceed or consume ATP and NADPH. This accumulation of ATP and NADPH and lack of ADP and NADP+ regeneration would then create a feedback inhibition on the light reactions, effectively halting the entire photosynthesis process.