Where do the light-dependent reactions take place?

Where do the light-dependent reactions take place?

• A. In the mitochondrion
• B. In the stroma
• C. In the nucleus
• D. In the thylakoid

Answer: (D)

Light-dependent reactions occur in the thylakoid membranes of chloroplasts. This is where the photosystems, the electron transport chain, and ATP synthase are located, allowing light energy to drive the transfer of electrons, create a proton gradient, and produce ATP and NADPH. The splitting of water at photosystem II releases oxygen and provides electrons to the chain. The proton gradient across the thylakoid membrane powers ATP synthase to generate ATP, while electrons eventually reduce NADP+ to NADPH. By contrast, the stroma is where the Calvin cycle uses ATP and NADPH to fix carbon, mitochondria handle cellular respiration, and the nucleus houses genetic material. So the thylakoid is the site of the light-dependent reactions.

Light-dependent reactions occur in the thylakoid membranes of chloroplasts. This is where the photosystems, the electron transport chain, and ATP synthase are located, allowing light energy to drive the transfer of electrons, create a proton gradient, and produce ATP and NADPH. The splitting of water at photosystem II releases oxygen and provides electrons to the chain. The proton gradient across the thylakoid membrane powers ATP synthase to generate ATP, while electrons eventually reduce NADP+ to NADPH. By contrast, the stroma is where the Calvin cycle uses ATP and NADPH to fix carbon, mitochondria handle cellular respiration, and the nucleus houses genetic material. So the thylakoid is the site of the light-dependent reactions.