In photosynthesis, the light-dependent reactions occur in which part of the chloroplast?

In photosynthesis, the light-dependent reactions occur in which part of the chloroplast?

• A. Stroma
• B. Chloroplast envelope
• C. Nucleus
• D. Thylakoid membrane

Answer: (D)

Light-dependent reactions take place in the thylakoid membranes inside the chloroplast. These membranes house the pigment–protein complexes (photosystems) and the electron transport chain that capture light energy to drive electron flow. As electrons move through the chain, protons are pumped into the thylakoid lumen, creating a proton gradient that powers ATP synthase to make ATP. NADP+ accepts electrons at the end of the chain to form NADPH. The Calvin cycle, which builds sugars, occurs in the stroma, not in the thylakoids. The chloroplast envelope is just the double membrane around the organelle, and the nucleus is a separate organelle. So, the light-dependent reactions happen in the thylakoid membrane.

Light-dependent reactions take place in the thylakoid membranes inside the chloroplast. These membranes house the pigment–protein complexes (photosystems) and the electron transport chain that capture light energy to drive electron flow. As electrons move through the chain, protons are pumped into the thylakoid lumen, creating a proton gradient that powers ATP synthase to make ATP. NADP+ accepts electrons at the end of the chain to form NADPH. The Calvin cycle, which builds sugars, occurs in the stroma, not in the thylakoids. The chloroplast envelope is just the double membrane around the organelle, and the nucleus is a separate organelle. So, the light-dependent reactions happen in the thylakoid membrane.