ABSTRACT
Photosynthesis uses solar energy to synthesize carbohydrate from carbon dioxide and water. In the light reactions, the light energy drives the synthesis of NADPH and ATP. In the dark reactions, the NADPH and ATP are used to synthesize carbohydrate from CO2 and H2O. Photosynthesis occurs in green plants, algae and photosynthetic bacteria. In green plants and algae, photosynthesis takes place in chloroplasts. Similar to a mitochondrion, a chloroplast has a highly permeable outer membrane and an inner membrane that is impermeable to most molecules and ions. In photosynthetic bacteria the light reactions take place in the bacterial plasma membrane, or in invaginations of it called chromatophores. Cyanobacteria carry out photosynthesis using two photosystems as in green plants. However, other photosynthetic bacteria, such as the purple photosynthetic bacterium Rhodospirillum rubrum, have only a single photosystem reaction center.
