What occurs first in the process of photosynthesis?

In photosynthesis, the first step that occurs is the light reactions. During these reactions, chlorophyll and other pigments in the thylakoid membranes of chloroplasts absorb light energy, which is then converted into chemical energy in the form of ATP and NADPH. This process also results in the splitting of water molecules (photolysis), which releases oxygen as a byproduct.

The light reactions are crucial because they provide the energy necessary for the subsequent Calvin cycle, where ATP and NADPH generated in the light reactions are used to convert carbon dioxide into glucose through a series of biochemical transformations. Therefore, understanding that the light reactions set the stage for the entire photosynthesis process is key to grasping how plants convert light energy into stored chemical energy.