Which organelle is primarily responsible for photosynthesis in plant cells?

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

Answer: (D)

Photosynthesis is the process by which plants convert light energy into chemical energy stored as glucose. The organelle that carries this out is the chloroplast. Chloroplasts contain chlorophyll, the pigment that captures light energy. Inside them, light-dependent reactions occur on the thylakoid membranes to make ATP and NADPH, while the Calvin cycle uses those energy carriers in the stroma to fix carbon dioxide into glucose. Chloroplasts are abundant in plant cells, especially in leaf tissues, which explains why plants can synthesize their own food. The other organelles have different roles: mitochondria generate ATP through respiration, the nucleus houses genetic material and controls cell activities, and ribosomes synthesize proteins. So chloroplasts are the site of photosynthesis.