Chloroplasts are organelles within plant cells and algae that are essential for photosynthesis. These green-colored plastids contain chlorophyll, which captures light energy to convert carbon dioxide into sugars, fueling plant growth and releasing oxygen. Chloroplasts also synthesize amino acids, fatty acids, and the lipid components of their own membranes. In addition to photosynthesis, chloroplasts are involved in various metabolic activities, including pigment synthesis, carbon fixation, starch storage, and antioxidant defense.
These oval or disc-shaped structures are complex, featuring a double membrane known as the chloroplast envelope and a third internal membrane system called the thylakoid membrane. The thylakoid membrane forms flattened discs called thylakoids, often arranged in stacks called grana. The space between the inner membrane and the thylakoid membrane is filled with a matrix called the stroma. Chloroplasts possess their own circular DNA, separate from the plant cell's nucleus, and can replicate by division, supporting the theory that they evolved from engulfed cyanobacteria.
