Which organelle is responsible for photosynthesis?

Step 1: Analyze the question The question asks which cell organelle carries out photosynthesis, the process by which green plants make food using light energy.

Step 2: Explain the concept Photosynthesis is summarized by this equation:

6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂ (in the presence of light and chlorophyll)

It takes place in the chloroplast, a membrane-bound organelle found in plant cells and algae. Chloroplasts contain chlorophyll, the green pigment that traps light energy.

• Grana (stacks of thylakoids) are the site of the light-dependent reactions.
• Stroma is the fluid-filled part where the light-independent reactions (the Calvin cycle) happen.

Step 3: Check each option

• A. Cell wall: It gives the plant cell shape and support. It is made of cellulose and has no role in photosynthesis.
• B. Chloroplast: It contains chlorophyll and carries out photosynthesis. ✔
• C. Cell membrane: It controls the movement of substances into and out of the cell.
• D. Nucleus: It controls cell activities and contains the genetic material (DNA).
• E. Ribosomes: They are the site of protein synthesis.

Step 4: Answer The correct answer is B. chloroplast.

Exam tip: Link the words "Chloroplast = Chlorophyll = Photosynthesis". Also remember that the mitochondrion is the site of respiration, which is the usual follow-up question in the same topic.