The First Complex Cells

What happened

Complex cells — eukaryotes, with a nucleus and internal compartments — evolved from simpler microbes. A key step was endosymbiosis: one cell engulfed a bacterium that became the mitochondrion, the powerhouse of the cell (and later, in plants, the chloroplast).

Why it matters

All plants, animals, fungi, and protists are built from eukaryotic cells; their origin made large, complex, multicellular life possible.

Sources

• Understanding Evolution, UC Berkeley. How important is endosymbiosis? · Reputable source