Final answer:
The proteins of the electron-transport chain in photosynthesis are located in the thylakoid membrane of the chloroplasts.Therefore, the answer to the question is (d) thylakoid membrane.
Step-by-step explanation:
Photosynthesis is a vital process that occurs in the chloroplasts of autotrophic eukaryotes, particularly within the cells of the mesophyll in plants. The proteins of the electron-transport chain, which are critical for the light reactions of photosynthesis, are located in the thylakoid membrane. These proteins form part of the electron-transport chains that generate ATP and NADPH. The energy captured from sunlight by chlorophyll molecules embedded in the thylakoid membrane is transferred to ATP and NADPH, and ultimately used during the Calvin cycle to produce glucose.