Photosynthesis photosystems. Illustration of Photosystem I (right) and Photosystem II (left), complexes of multiple proteins that react to transfer energy from sunlight to chemical molecules during photosynthesis. The proteins are embedded in the thykaloid membrane (blue) in a plant's chloroplasts. At left is a light-harvesting complex (yellow). At centre is a cytochrome b/f complex (orange and yellow). At right is an ATP synthase protein complex (red), which produces ATP (adenosine triphosphate). Electrons (e-) and protons (H+) are also shown. For this artwork with labels, see image C023/8815.