[Campbell Biology P.645] What is the key distinction between primary and secondary endosymbi... | Practice Question

What is the key distinction between primary and secondary endosymbiosis in the context of plastid evolution, as described in the text?

  • A: Primary endosymbiosis involves a heterotrophic eukaryote engulfing a prokaryote, while secondary endosymbiosis involves a heterotrophic eukaryote engulfing another eukaryote that already possesses a plastid.
  • B: Primary endosymbiosis always results in a plastid with four membranes, whereas secondary endosymbiosis results in two membranes.
  • C: Primary endosymbiosis led to mitochondria, and secondary endosymbiosis led to plastids.
  • D: Secondary endosymbiosis only occurs in marine environments, while primary endosymbiosis occurs universally.

Explanation

The text explicitly defines primary endosymbiosis as an ancestral heterotrophic eukaryote engulfing a photosynthetic cyanobacterium a prokaryote . It then describes secondary endosymbiosis as an event where "red algae and green algae underwent secondary endosymbiosis, meaning they were ingested in the food vacuoles of heterotrophic eukaryotes and became endosymbionts themselves." This clarifies that secondary endosymbiosis involves a heterotrophic eukaryote engulfing another eukaryote that already contained a plastid from a prior primary endosymbiosis event.