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The Theory of Endosymbiosis

The theory of endosymbiosis states that mitochondria and chloroplasts were once free-living prokaryotes. which were taken into other cells by endocytosis and this eventually led to the evolution of eukaryotes.

Mitochondria and chloroplasts have their own DNA and synthesise proteins in the matrix and stroma.Mitochondria and chloroplasts can also carry out chemiosmosis in their membranes to make ATP.

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Specification: OCR Biology A (H020), AS-level, 2.1.1 Cell structure. Topic: Cell Structure.

Key terms in this lesson

mitochondrion: An organelle with a double membrane, the inner one folded into cristae, that is the site of aerobic respiration and ATP production.
prokaryotic cell: A cell with no nucleus or membrane-bound organelles, found in bacteria.
eukaryotic cell: A cell with a nucleus and membrane-bound organelles, found in animals, plants, fungi and protoctists.
ATP: Adenosine triphosphate, a nucleotide that acts as the immediate energy source of a cell, releasing energy when hydrolysed to ADP and inorganic phosphate.

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