What are the two main stages of photosynthesis?

The two main stages of photosynthesis are indeed the light-dependent reactions and the Calvin cycle.

During the light-dependent reactions, which occur in the thylakoid membranes of the chloroplasts, sunlight is captured by chlorophyll and other pigments. This energy is used to produce ATP and NADPH, which are energy carriers. Water molecules are split in this process, releasing oxygen as a byproduct.

In the Calvin cycle, which takes place in the stroma of the chloroplasts, the ATP and NADPH generated from the light-dependent reactions are utilized to convert carbon dioxide into glucose through a series of enzymatic reactions. This process does not require light, hence it is often referred to as the light-independent reactions.

Other options do not accurately describe the stages of photosynthesis. The light-independent reactions often refer to the Calvin cycle, but the Krebs cycle is a part of cellular respiration, not photosynthesis. Glycolysis is the process of breaking down glucose to produce energy, while Photosystem I and Photosystem II are components of the light-dependent reactions rather than distinct stages of photosynthesis.