Final answer:
Chlorophyll molecules are located in the thylakoid membranes of a chloroplast. Therefore, the correct option is D.
Step-by-step explanation:
The primary location of chloroplasts' thylakoid membranes is where chlorophyll molecules are found. The flattened, sac-like thylakoid membranes are found inside the chloroplasts and are responsible for the light-dependent photosynthesis processes.
Chlorophyll and other pigments found in these membranes absorb light energy during photosynthesis. Chlorophyll absorbs light, which sets off a chain of events that eventually produce ATP and NADPH, two forms of chemical energy.
The stroma, a different component of the chloroplast, is involved in the light-independent processes (Calvin cycle) that transform carbon dioxide into glucose, even though chlorophyll molecules are essential for absorbing light energy. The Calvin cycle enzymes and other components are found in the stroma, which encircles the thylakoid membranes.
Therefore, the correct option is D.