Question

1. Draw an example of a photosynthetic eukaryotic cell that has chloroplasts that arose in an ancestral lineage via primary endosymbiosis.
2. Draw an example of a photosynthetic eukaryotic cell that has chloroplasts that arose in an ancestral lineage via secondary endosymbiosis.

Answer 1

Endosymbiosis is the concept of one cell engulfing another and both cells benefiting from the relationship.

Endosymbiosis was originally considered after the observation of the similarity between plant chloroplasts and free-living cyanobacteria.

Plastids in eukaryotes derive from primary endosymbiosis with ancient cyanobacteria.

Chlorarachniophytes are a type of algae that resulted from secondary endosymbiosis, when a eukaryote engulfed a green alga (which itself was a product of primary endosymbiosis with a cyanobacterium).

Figure:- Primary and secondary endosymbiosis: The hypothesized process of endosymbiotic events leading to the evolution of chlorarachniophytes is shown.

In a primary endosymbiotic event, a heterotrophic eukaryote consumed a cyanobacterium. In a secondary endosymbiotic event, the cell resulting from primary endosymbiosis was consumed by a second cell. The resulting organelle became a plastid in modern chlorarachniophytes.

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