A Walk Through Time

Corporal Mergers

1300 Million Years Ago

Protoctists have co-evolved with photosynthetic bacteria for some time. Swallowed up but not digested, some bacteria provide the protoctist with a constant supply of food, which make them be self-sufficient algae. The engulfed bacteria receive a safe, comfortable home and rapid transport to sunlight. With their endosymbiotic (living inside) bacteria, the protoctists, now algae, are virtual living greenhouses.

These cross-species associations celebrate success with permanent mergers. The bacteria transform into new organelles called plastids. Eventually, splashes of green and red seaweed will decorate Earth's coasts.

(Photograph by Jeremy Pickett-Heaps, top, and Lois Brynes, bottom.)

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