Chloroplast

[Diagram of a plant chloroplast. Notice the bi-layer membrane and the thylakoids.]

The chloroplast, basically, is the organelle responsible for photosynthesis. Structurally it is very similar to the mitochondrion. It contains a permeable outer membrane, a less permeable inner membrane, a intermembrane space, and an inner section called the stroma. However, the chloroplast is larger than the mitochondria. It needs to have the larger size because its membrane is not folded into cristae. Also the inner membrane is not used for the electron transport chain. Instead it contains the light-absorbing system, the electron transport chain, and ATP synthetase in a third membrane that forms a series of flattened discs, called the thylakoids.