Which of the following best supports the endosymbiont theory that present-day eukaryotic cells are descendants of a successful symbiotic relationship between a host cell and an engulfed prokaryote? A. Chloroplasts and mitochondria replicate in a similar manner as some prokaryotes.
B. Chloroplasts are necessary for photosynthesis reactions in plant and bacteria cells.
C. Mitochondria and chloroplasts are able to produce ATP molecules to be used by the cell.
D. Mitochondria use proteins and nutrients produced in other regions of the eukaryotic cell.

A. Chloroplasts and mitochondria replicate in a similar manner as some prokaryotes

Explanation:

Endosymbiont theory deals with how eukaryotic organisms were formed from prokaryotic organisms. Prokaryotes such as Bacteria were documented as the first form of life on earth through fossil records before eukaryotes came into light.

Organelles such as Chloroplasts and mitochondria replicate in a similar manner as some prokaryotes. This supports the endosymbiont theory that present-day eukaryotic cells are descendants of a successful symbiotic relationship between a host cell and an engulfed prokaryote