Where does the Calvin Cycle take place?

Where does the Calvin Cycle take place?

• A. In the chloroplast outer membrane
• B. In the thylakoid membrane
• C. In the stroma
• D. In the cytosol

Answer: (C)

The Calvin Cycle takes place in the stroma, the fluid inside chloroplasts that surrounds the stacked thylakoids. This is where the enzymes of the cycle reside, including RuBisCO, and where CO2 is fixed to build sugars using the ATP and NADPH produced by the light-dependent reactions. The thylakoid membranes house those light reactions themselves (photosystems and electron transport chain) and generate ATP and NADPH, but the actual carbon-fixing chemistry of the Calvin Cycle happens in the stroma. The outer membrane is just a boundary, and the cytosol is outside the chloroplast; neither is the proper site for the Calvin Cycle’s enzymatic steps.

The Calvin Cycle takes place in the stroma, the fluid inside chloroplasts that surrounds the stacked thylakoids. This is where the enzymes of the cycle reside, including RuBisCO, and where CO2 is fixed to build sugars using the ATP and NADPH produced by the light-dependent reactions. The thylakoid membranes house those light reactions themselves (photosystems and electron transport chain) and generate ATP and NADPH, but the actual carbon-fixing chemistry of the Calvin Cycle happens in the stroma. The outer membrane is just a boundary, and the cytosol is outside the chloroplast; neither is the proper site for the Calvin Cycle’s enzymatic steps.