Biology · Bioenergetics

The dark reactions of photosynthesis, also known as the Calvin cycle or light-independent reactions, occur in the stroma of the chloroplasts. This is because the stroma contains the necessary enzymes that facilitate the fixation of carbon dioxide into carbohydrates. In contrast, the light-dependent reactions occur in the thylakoids, specifically within the grana, where sunlight is captured and converted into chemical energy in the form of ATP and NADPH. Thus, options stating 'Grana', 'Thylakoid', and 'Both grana and stroma' are incorrect as they do not correctly identify the site of the dark reactions.

Grana are stacks of thylakoids where light-dependent reactions happen, not dark reactions.

The stroma is the fluid-filled space surrounding the grana within the chloroplast. It is where the dark reactions, also known as the Calvin cycle, occur.

Thylakoids contain chlorophyll and are the site of the light-dependent reactions, not the dark reactions.

The dark reactions do not occur in both grana and stroma; they exclusively take place in the stroma.