The plant is invented
A cell swallows a cyanobacterium and keeps it
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Primary endosymbiosis with a cyanobacterium gave rise to the Archaeplastida: red algae, green algae and land plants. Chloroplasts still carry their own circular DNA and ribosomes, and divide by a bacterial mechanism. The event appears to have happened only once, which explains why all eukaryotic photosynthesis traces to a single origin. Later, green and red algae were themselves swallowed by other eukaryotes in secondary endosymbioses — hence diatoms and brown algae. Without this the planet would never have had forests, grasses or grain, and therefore no agriculture.
For children
The same trick happened a second time. A cell swallowed a bacterium that could use sunlight — and let it stay. The guest became the chloroplast, the green part that lets plants eat sunlight. All grass, all trees and all seaweed descend from that single meal.
Connects to
Part of Terra Saga — the story of Earth on a timeline. terrasaga.org