The structure of cells has changed significantly over time. what concept explains the presence of mitochondria in cells?

Endosymbiosis explains the presence of mitochondria in cells.

Symbiogenesis, or endosymbiotic theory, is an evolutionary theory that explains the origin of eukaryotic cells from prokaryotes. It states that several key organelles of eukaryotes originated as a symbiosis between separate single-celled organisms.

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b a mature ovary of a plant.

where in your body is there an enzyme that does function at a high or low ph? what is the name of that enzyme and its function?