how did cells come to have chloroplasts?

Question

According to the endosymbiotic theory, how did cells develop from mitochondria to chloroplasts?

Answer 1

It is important to note that only plant cells contain chloroplasts, not animal cells. The endosymbiotic theory suggests that cellular life that predated our current plant cells engulfed another smaller organism that was able to convert sunlight into energy. These primitive plant cells evolved to include these engulfed chloroplasts as they increased the cells' fitness & ability to reproduce -so they evolved to " live in harmony".

The chloroplasts are an organelle that allow plant cells to use light from the sun to produce ATP, NADPH, and O_2. This reaction is looped in with the Calvin cycle which use these products with atmospheric CO₂ to produce sugar and ultimately feed back into the initial reaction converting light energy. This is a perfect circle that produces energy for the plant and is a source of oxygen for the earth.