What does the thylakoid membrane house during photosynthesis?

What does the thylakoid membrane house during photosynthesis?

• A. Photosystems II and I, electron transport chain, and ATP synthase
• B. Rubisco and other Calvin cycle enzymes
• C. Water-splitting enzymes in the stroma
• D. NADPH synthase in the outer membrane

Answer: (A)

The thylakoid membrane is where the light-dependent reactions happen, so it houses the two photosystems (II and I), the electron transport chain that passes electrons between them, and ATP synthase that uses the proton gradient to make ATP. When light hits PSII, electrons are energized and move through the chain, pumping protons into the thylakoid lumen. This creates a proton motive force across the membrane, and ATP synthase uses that gradient to synthesize ATP as protons flow back across the membrane. After PSI, electrons are handed to NADP+ to form NADPH in the stroma, completing the light reactions and providing the energy and reducing power for the Calvin cycle in the stroma. Rubisco and other Calvin cycle enzymes sit in the stroma, not in the thylakoid membrane, so they aren’t part of this membrane’s machinery. The water-splitting complex is associated with PSII in the thylakoid membrane, not in the stroma, so the idea that it’s in the stroma isn’t accurate. NADPH production occurs via NADP+ reductase in the stroma after PSI, not from a separate NADPH synthase in the membrane.

The thylakoid membrane is where the light-dependent reactions happen, so it houses the two photosystems (II and I), the electron transport chain that passes electrons between them, and ATP synthase that uses the proton gradient to make ATP. When light hits PSII, electrons are energized and move through the chain, pumping protons into the thylakoid lumen. This creates a proton motive force across the membrane, and ATP synthase uses that gradient to synthesize ATP as protons flow back across the membrane. After PSI, electrons are handed to NADP+ to form NADPH in the stroma, completing the light reactions and providing the energy and reducing power for the Calvin cycle in the stroma.

Rubisco and other Calvin cycle enzymes sit in the stroma, not in the thylakoid membrane, so they aren’t part of this membrane’s machinery. The water-splitting complex is associated with PSII in the thylakoid membrane, not in the stroma, so the idea that it’s in the stroma isn’t accurate. NADPH production occurs via NADP+ reductase in the stroma after PSI, not from a separate NADPH synthase in the membrane.