What is the Most Probable Basis for the Evolution of Mitochondria

Question

What is the most probable basis for the evolution of mitochondria and chloroplasts?  
A) Bacteria can be taken up by host cells.
B) Light is an energy source.
C) ATP can carry energy.
D) Oxygen is a by-product of photosynthesis.
E) Energy can be transformed from one form to another.

Accepted Answer

The most probable basis for the evolution of mitochondria and chloroplasts is endosymbiosis, which suggests that these organelles were once free-living prokaryotic cells that were engulfed by a host cell. The engulfed cells then developed a symbiotic relationship with their host, eventually evolving into modern mitochondria and chloroplasts. This theory is supported by the fact that mitochondria and chloroplasts have their own genomes, replicate independently of the host cell, and have a similar size and structure to bacterial cells.