According to the Endosymbiotic theory, all the components of eukaryotic cells were once individual prokaryotic cells which were able to function on their own.

The mitochondria was independent enough to perform aerobic respiration and produce energy and the chloroplasts were able to independently convert the energy from the Sun to the chemical energy through the process of photosynthesis.

Later, these cells were engulfed by a single cell and these prokaryotes combined to form a eukaryote that was capable of performing all the functions that the independent cells could.

So, the mitochondria and chloroplasts were able to reproduce on their own, had their own ribosomes and had DNA resembling that of bacteria as they were prokaryotic in nature.

However, mitochondria and chloroplasts could not be larger than the prokaryotic cells to support the endosymbiotic theory.

This is because in order to establish a relationship between the bacteria and the mitochondria and chloroplasts, and for these organelles to have developed from bacteria as their ancestors, they must have sizes comparable to bacteria and other prokaryotes.

At the same time, size in itself is not enough evidence to support origin of these organelles from the bacteria.

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3 years ago