Answer:
option A
Question (In proper order):
According to the hypothesis of serial endosymbiosis, which of the following was a key initial step in the origin of mitochondria?
A. prokaryotic host cell engulfed an aerobic, heterotrophic bacterium.
B. eukaryotic host cell engulfed an aerobic, heterotrophic bacterium.
C. prokaryotic host cell engulfed an aerobic, photosynthetic bacterium.
D. eukaryotic host cell engulfed an aerobic, photosynthetic bacterium.
Explanation:
The serial endosymbiotic theory or SET describes the eukaryotic evolution process. The SET theory is based on the primary endosymbiosis mechanism, according to which, an aerobic bacterium was phagocytosed by another cell of prokaryotic origin.
Further, instead of dying, the ingested cell survived upon the chemical nutrients already present in the host cell. The two cells carried out regular metabolism and reproduced. The resulting offspring of the host cell had the engulfed bacterium, which was of heterotrophic origin. Â
In the course of evolution, the host cell became dependent on the phagocytosed bacterium for its survival in the presence of the atmospheric oxygen. Later on, the engulfed bacteria acquired the role of the mitochondria. Similarly, after some time there was serial ingestion of the photosynthetic bacterium, which formed the plastids (such as chloroplasts). Â
