A photosystem is a complex of proteins and pigments found in the thylakoid membranes of chloroplasts in plant cells. It plays a crucial role in the process of photosynthesis, where light energy is converted into chemical energy. There are two main types of photosystems: Photosystem I and Photosystem II, each with distinct functions and absorption spectra. During photosynthesis, photosystems capture light energy using pigments like chlorophyll. This energy excites electrons, initiating a series of reactions that ultimately produce ATP and NADPH, which are essential for converting carbon dioxide into glucose.