Most changes in DNA, however, are too subtle to be detected by this technique and require molecular analysis. Mitochondria have two membranes, an inner and an outer, visible in this electron microscope photo of a mitochondrion. Note the reticulations, or many infoldings, of the inner membrane, This serves to increase the surface area of membrane on which membrane-bound reactions can take place. The existence of this double membrane has led many biologists to theorize that mitochondria are the descendants of some bacteria that was endocytosed by a larger cell billions of years ago, but not digested. This fascinating theory of symbiosis, which might lend an explanation to the development of eukaryotic cells, has additional supporting evidence.
Chloroplasts are the site of photosynthesis in eukaryotic cells.
They are disk-like structures composed of a single membrane surrounding a fluidcontaining stacks of membranous disks. Because of their geen color chloroplast are the only organelles that can be easily seen with a light microscope. There is a single membrane surrounding the chloroplast. This membrane surrounds a fluid called thestroma. Floating in the stroma are stacks of disks made up of membranes, these are the grana.