How is endosymbiosis related to eukaryotic evolution?

It is proposed that mitochondria and photosynthetic chloroplasts are primitive unicellular creatures with enough parts to have existed separately at some point in the past, which were engulfed by larger unicellular organisms that, instead of digesting them, benefited from their capacity to perform glycolosis (in the case of mitochondria) or photosynthesis (in the case of chloroplasts).

The engulfing cell became more complex as a result of the additional resources on board; over time, plasmids were passed down, enabling each new eukaryote to have both its own DNA and the DNA of its small mitochondria or chloroplast; eventually, the mitochondria or chloroplasts became organelles, no longer requiring their other components because they are protected in the host cell and still have membranes.

Endosymbiosis is related to eukaryotic evolution because it proposes that certain organelles within eukaryotic cells, such as mitochondria and chloroplasts, originated from free-living prokaryotic organisms that were engulfed by ancestral eukaryotic cells. Over time, these prokaryotic organisms established a symbiotic relationship with the host cell, eventually becoming integrated as organelles. This theory, proposed by Lynn Margulis, provides an explanation for the origin of some key organelles in eukaryotic cells and contributes to our understanding of the complexity and diversity of life.