1. A bacterium engulfs a cyanobacterium by phagocytosis.

1. A vesicle forms in the cytoplasm of the bacteria and forms the outer membrane of the mitochondria. The cyanobacterium photosynthesis and provides energy for the bacterium whilst the bacterium provides protection for the cyanobacterium.

1. Some DNA moves from the cyanobacterial nuclear region to the bacterium nuclear region and a nuclear membrane forms and encloses the DNA to form a nucleus.

1. A cyanobacterium engulfs a bacterium by phagocytosis.

1. A vesicle forms in the cytoplasm of the cyanobacterium and forms the outer membrane of the mitochondria. The bacterium provides ATP whilst the cyanobacterium photosynthesises to produce glucose and provides protection for the bacterium.

1. Some DNA moves from the bacterial nuclear region to the cyanobacterium nuclear region and a nuclear membrane forms to enclose the DNA to form a nucleus.

1. A bacterium engulfs an Archaea by phagocytosis.

1. A vesicle forms in the cytoplasm of the bacterium and forms the outer membrane of the mitochondria. The Archaea provides nutrients for the bacterium and the bacterium provides protection for the archaea.

1. Some DNA moves from the Archaea nucleoid region to the nucleus of the host cell.

1. An Archaea engulfs a bacterium by phagocytosis.

1. A vesicle forms in the cytoplasm of the Archaea and forms the outer membrane of the mitochondria. The bacterium provides ATP to the Archaea and the Archaea provides nutrients and protection to the bacterium.

1. Some DNA moves from the bacterial nucleoid region to the nucleus of the host cell.

A cell must have an organelle to convert sugars to ATP before it develops an organelle to convert sunlight to sugars.

The mitochondria have been carbon dated to be older than chloroplasts.

Mitochondria are smaller than chloroplasts, so the engulfment of the prokaryotic ancestor of the mitrochondria would have occured more easily.

All eukaryotic cells contain mitochondria, whereas only plants and algae contain chloroplasts.