Ancestors of which type of bacteria likely gave rise to chloroplasts?

Question

BlackTom AI · Accepted Answer

The question asks about the ancestral source of chloroplasts in plants and algae. 
Option 1: proteobacteria. While proteobacteria are the proposed ancestors of mitochondria in eukaryotes, they are not linked to chloroplast origin. Therefore this choice misattributes chloroplast ancestry to mitochondria-related lineages. 
Option 2: E. coli. This is a specific example of a proteobacterium and similarly misdirects the origin toward a common gut bacterium, not the plastid lineage. It reinforces the idea that not all bacteria contributed to chloroplasts. 
Option 3: streptococcus. This is a Gram-positive cocci genus and has no established role in endosymbiotic chloroplast origin, making it an incorrect source for chloroplast ancestry. 
Option 4: cyanobacteria. This option correctly identifies the lineage that gave rise to chloroplasts via endosymbiosis, as chloroplasts carry their own DNA and photosynthetic machinery closely related to cyanobacterial genes. 
Option 5: pseudomonas. Like E. coli, this is a member of the proteobacteria but is not implicated in the origin of chloroplasts; it does not align with the chloroplast endosymbiotic theory. 
Overall, only cyanobacteria fits the established endosymbiotic origin of chloroplasts, while the other options either point to mitochondria, unrelated bacteria, or incorrect lineages.

Ancestors of which type of bacteria likely gave rise to chloroplasts?单项选择题

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