If the thylakoid membrane were disrupted, which process would be most directly affected?

• A. ATP and NADPH production.
• B. Glycolysis in the cytoplasm.
• C. Oxygen consumption by mitochondria.
• D. CO2 fixation in the Calvin cycle.

Answer: (A)

The key idea is that the thylakoid membrane hosts the light-dependent reactions of photosynthesis, where light energy drives the electron transport chain, pumps protons to create a gradient, and powers ATP synthase to make ATP while also reducing NADP+ to NADPH. If the thylakoid membrane were disrupted, this electron transport chain would be compromised, stopping both the production of ATP and the formation of NADPH. Without these energy carriers, the plant cannot drive the reactions that depend on them.

Glycolysis occurs in the cytoplasm and does not rely on chloroplast thylakoids, so it wouldn’t be directly affected. Mitochondrial oxygen consumption is part of cellular respiration and uses oxygen and substrates produced in various parts of the cell, not the thylakoid membrane’s light reactions. CO2 fixation in the Calvin cycle happens in the chloroplast stroma and requires ATP and NADPH from the light reactions; it would be indirectly impacted due to the lack of energy carriers, but the immediate, direct effect of disrupting the thylakoid membrane is the loss of ATP and NADPH production.