Chloroplasts

Organelles of plant cells, which are mainly involved in photosynthesis.

As shown by the figure, chloroplasts are more or less ovate bodies within the cytosol of plant cells. Apart from photosynthesis, they are responsible for a number of other metabolic functions. They are not restricted to green plant organs, but can be found as non-green organelles (plastids) in all plant organs. The lower part of the figure shows the internal structure of chloroplasts. They are enclosed within two envelope membranes. Within these membranes, a complicated membrane system contains important enzymatic complexes of photosynthesis.

Chloroplasts contain some of the genes for their proteins, as well as the enzymatic apparatus to use these genes. This observation indicates that the organelles have developed by the endosymbiosis of formerly independent, photosynthetic bacteria.