Final answer:
The light reactions of photosynthesis happen in the thylakoid membranes inside chloroplasts.
Step-by-step explanation:
The light reactions of photosynthesis occur in the thylakoid membranes of the chloroplast. These membranes house chlorophyll, the green pigment essential for capturing light energy, and the apparatus for the light-dependent reactions of photosynthesis. Electron carrier molecules in the thylakoid membrane arrange into electron transport chains that produce ATP and NADPH. In contrast, the Calvin cycle, which is the light-independent part of photosynthesis, takes place in the stroma of the chloroplasts.