The stroma is:

The stroma is:

• A. The double membrane that surrounds the chloroplast
• B. The fluid-filled interior of the chloroplast that stores lipids
• C. The fluid-filled interior of the chloroplast where the Calvin cycle occurs
• D. The stacked membranes of the thylakoids

Answer: (C)

The stroma is the fluid-filled interior of the chloroplast where the Calvin cycle occurs. This space surrounds the thylakoid membranes and contains the enzymes needed to fix carbon dioxide into sugars, powered by ATP and NADPH produced during the light-dependent reactions. It’s not the chloroplast’s outer double membrane, nor the interior of the thylakoids (the lumen), nor the stacked membranes themselves (the grana). So the stroma is the site of the Calvin cycle.

The stroma is the fluid-filled interior of the chloroplast where the Calvin cycle occurs. This space surrounds the thylakoid membranes and contains the enzymes needed to fix carbon dioxide into sugars, powered by ATP and NADPH produced during the light-dependent reactions. It’s not the chloroplast’s outer double membrane, nor the interior of the thylakoids (the lumen), nor the stacked membranes themselves (the grana). So the stroma is the site of the Calvin cycle.