Chloroplasts are located in the cells of the leaves of green plants and in the cells of eukaryotic algae. They contain a green coloring pigment called chlorophyll that carries out the process of photosynthesis in the presence of sunlight, water vapor and carbon dioxide.
All green plants have special cell organelles called plastids, and chloroplasts are a kind of plastid. The chlorophyll in these chloroplasts is excited by sunlight and converts solar energy into usable chemical form. This is how sunlight enters the living ecosystem.
Chloroplasts have three membranes. The outer membrane is semipermeable and allows small molecules to pass through. The inner membrane is less permeable, while the third membrane is called the thylakoid membrane and appears as a series of flattened disks piled on top of each other. Chlorophyll is found in these thylakoids.