Which organelle is the site of photosynthesis in plant cells?

• A. Nucleus
• B. Chloroplast
• C. Ribosome
• D. Mitochondrion

Answer: (B)

Photosynthesis in plant cells happens in chloroplasts, the organelles that capture light with the green pigment chlorophyll. Inside chloroplasts, the light-absorbing reactions occur on the thylakoid membranes to make ATP and NADPH, while the Calvin cycle in the stroma uses those molecules and carbon dioxide to build sugars. This combination of light capture and carbon-fixing steps is what lets plants convert light energy into chemical energy. Other organelles aren’t the sites of this process: the nucleus stores DNA, ribosomes make proteins, and mitochondria generate energy through respiration but don’t convert light into sugar.