In which part of the chloroplast does the Calvin cycle occur?

The Calvin cycle, which is essential for photosynthesis, takes place in the stroma of the chloroplast. The stroma is the fluid-filled space surrounding the thylakoid membranes and is rich in enzymes, necessary for the various biochemical reactions that make up the Calvin cycle. During this process, carbon dioxide is fixed into organic molecules through a series of reactions that ultimately produce glucose and other carbohydrates.

The thylakoid membranes, where the light-dependent reactions occur, do not participate in the Calvin cycle; instead, they are responsible for absorbing light energy and producing ATP and NADPH, which are then utilized in the Calvin cycle. The granum refers to the stack of thylakoids, thus also unrelated to the specific functions of the Calvin cycle. The outer membrane serves as a boundary for the chloroplast and does not play any role in the photosynthetic processes occurring inside. Therefore, the correct location for the Calvin cycle is indeed the stroma.