it has been hypothesized that chloroplasts originated from photosynthetic cyanobacteria that became symbiotic inside a host cell. Which of the following observations provides the strongest evidence for this suggestion?
A) microscopically, chloroplast appear similar to cyanobacteria
B) chloroplast DNA shows clear similarities to cyanobacterial DNA
C) both chloroplast and cyanobacteria are green and perform photosynthesis
D) Photosynthetic cyanobacteria and fungi form a mutualistic association in lichen
Chloroplast DNA shows clear similarities to cyanbacterial DNA.
To evaluate which observation provides the strongest evidence for the suggestion that chloroplasts originated from photosynthetic cyanobacteria, let's examine each option:
A) Microscopically, chloroplasts appear similar to cyanobacteria:
While this observation suggests a similarity between chloroplasts and cyanobacteria, it alone is not strong evidence for their shared origin. There can be other reasons for the similarity, such as convergent evolution or functional requirements of photosynthesis.
B) Chloroplast DNA shows clear similarities to cyanobacterial DNA:
This observation provides stronger evidence, as it suggests a direct genetic relationship between chloroplasts and cyanobacteria. Similarities in DNA sequences indicate a common ancestry or a gene transfer from cyanobacteria to chloroplasts.
C) Both chloroplasts and cyanobacteria are green and perform photosynthesis:
While this observation is relevant, it is not the most definitive evidence because it could be possible for two organisms to independently evolve similar traits. Additionally, there are non-cyanobacterial organisms that are green and perform photosynthesis.
D) Photosynthetic cyanobacteria and fungi form a mutualistic association in lichen:
This observation is not directly related to the origin of chloroplasts, as it describes a different symbiotic relationship between cyanobacteria and fungi. Hence, it does not provide strong evidence for the suggestion.
Based on these evaluations, option B, "Chloroplast DNA shows clear similarities to cyanobacterial DNA," provides the strongest evidence for the suggestion that chloroplasts originated from photosynthetic cyanobacteria. DNA similarities indicate a shared genetic history and support the hypothesis of endosymbiotic origin.