Biology / Unit 9 Bio 1987 short lesson, about 20 seconds
Secondary Endosymbiosis
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The idea
Secondary endosymbiosis occurs when a eukaryote engulfs and retains another eukaryote that had a chloroplast from primary endosymbiosis.
In practice
Euglenoids acquired their chloroplasts by engulfing a green alga, gaining a plastid surrounded by extra membranes marking its two-step origin.
Where people slip
A secondary plastid's extra surrounding membranes are the structural evidence of this two-step history— a primary plastid has only two membranes.
Your place on the trail
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