Question

Describe one observation that supports the theory that mitochondria and chloroplasts originated as independent prokaryotic organisms. I need help for Biology.

Answer 1

Answer:

• Both organelles present their genetic material.
• Both organelles divide by binary fission
• Both organelles present a double membrane, the internal one looks identical to the bacterial membrane, while the external membrane looks like the eukaryotic one.
• In the internal membrane are placed the energy centers, just as it occurs in bacterias membrane.
• The sizes of the organelles are similar to the size of some procaryotes

Explanation:

The endosymbiotic theory essentially states that some organules of the eukaryotic cells, such as mitochondria and chloroplasts, were once free-living bacteria. Probably, these organisms must have been phagocytized but not digested by another cell. These bacteria were able to adapt to their host, establishing a bond of dependence among each other.

Both organelles have many similarities with other free-living bacteria. For this reason, the theory states that chloroplasts derivate from cyanobacteria (because they both absorb sunlight, store the energy in ATP, and produce organic molecules) and that mitochondria derivate from rickettsias (because they produce ATP in the same way, by using the Krebs Cycle and Oxidative Phosphorylation).

This theory is supported by a few characteristics of the chloroplasts and mitochondria that suggest that they once were free cells. For example,

• Both organelles present their genetic material. This DNI is independent of the cells´ DNA, is bi-catenary and circular, identical to the bacterial DNA, and very different from the one of the eukaryotic cells.
• Both organelles divide by binary fission, not by mitosis, and can synthesize their ribosomes and organelles.
• Both organelles present a double membrane, a characteristic that reinforces the idea of being phagocyted. The internal membrane looks identical to the bacterial membrane, while the external membrane looks like the eukaryotic one.
• In fact, in this internal membrane are placed the energy centers, just as it occurs in bacterias membrane.
• Finally, the sizes of the organelles are similar to the size of some procaryotes