Where does the Calvin cycle take place in the chloroplast?

The Calvin cycle occurs in the stroma of the chloroplast. The stroma is the fluid-filled space surrounding the thylakoid membranes and is where key processes of photosynthesis, including the Calvin cycle, take place. In this region, carbon dioxide is fixed and reduced to produce glucose and other carbohydrates, with the help of ATP and NADPH generated in the light-dependent reactions that occur in the thylakoid membranes.

The other options do not serve as the location for the Calvin cycle. The thylakoid membranes are primarily involved in the light-dependent reactions, where light energy is converted into chemical energy. The outer membrane functions as a protective barrier for the chloroplast and does not play a direct role in photosynthesis. The granum, which is a stack of thylakoids, is also involved in the light-dependent reactions, not the Calvin cycle itself. Thus, the most accurate answer for the location of the Calvin cycle is indeed the stroma.