Mitochondria and chloroplasts display similarities with bacteria that led to the endosymbiont theory. This theory states that an early ancestor of eukaryotic cells engulfed an oxygen-using non-photosynthetic prokaryotic cell. Eventually, the engulfed cell formed a relationship with the host cell in which it was enclosed, becoming an endosymbiont, a cell living within another cell. Indeed, over the course of evolution, the host cell and its endosymbiont merged into a single organism, a eukaryotic cell with a mitochondrion. At least one of these cells may have then taken up a photosynthetic prokaryote, becoming the ancestor of eukaryotic cells that contain chloroplasts.
—from Campbell Biology AP Edition, a book by Campbell
Active since October 7, 2017.
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| Universe | Races | Average WPM | First Race |
|---|---|---|---|
| Default (English) | 2,929 | 89.24 | October 7, 2017 |
| Instant Death Mode | 3 | 99.10 | January 10, 2019 |
| All TypeRacer Texts | 1 | 76.47 | February 24, 2022 |
| New English Texts | 1 | 108.31 | May 26, 2022 |