Chloroplasts are of central importance to the plant cell. They contain chlorophyll which fundamentally converts sunlight into fuel that the mitochondria use for energy, known as photosynthesis. Chloroplasts and mitochondria are closely linked to one another, as well as very similar in structure to one another.
Chloroplasts have two membranes. The first external membrane is a porous membrane which is effective in keeping most cytoplasmic protein out of the chloroplast. The second inner membrane is much more selective being impermeable to even small ions. These two concentric membranes are similar to the cell membrane being that they are both composed of bilayer lipid construction. Inside of these two walls of madness lay stacks of pancake like structures which hold the chlorophyll and are called thylakoid. These stacks of thylakoids as a whole are called granum and the space between the grana is the stroma, the fluid inside the chloroplast. Links between the thylakoid are called lamella. Inside the grana is where the photosynthesis occurs.
Sunlight is described as packets of energy known as photons, and these photons are taken in by the chlorophyll, located in the grana. These photons give enough energy to start an electron-transport chain which in the end gives off O2 and carbohydrate known as glyceralderhyde 3-phosphate. The mitochondria receives this carbohydrate after it passes through the grana then the stroma and out the two membranes into the cytoplasm where it floats until found.
For the most part, the chloroplasts are located on the outside of the cell by the cell wall. The reason for this is that they can receive optimal sunlight on the outside oÕ the cell. The number of chloroplasts in a cell is encoded in the cells DNA. The chloroplasts themselves have DNA which encodes the lipids and proteins that it needs as well as produces them.
An interesting tibit about the mighty chloroplast is that according to the endosymbiont hypothesis, at one point chloroplasts were thought to be their own organism similar to bacteria, because of how alike their structures are to those of bacteria. Some bacteria uses chlorophyll to make thier own energy just like chloroplasts do, they have their own DNA, as well as protein-synthesizing structures just like bacteria do, leading scientists to believe that chloroplasts were once by themselves living as a bacteria does.