Molecular evidence and comparisons of the biological mechanisms that algae use to harvest light have convinced scientists that both red and green algae are descendants of a single endosymbiotic event, with a eukaryotic cell swallowing a photosynthesizing phylum and gained the ability to make its own food.



A) have convinced scientists that both red and green algae are descendants of a single endosymbiotic event, with a eukaryotic cell swallowing 

The plural verb “have” is in agreement with the plural subject- Molecular evidence and comparisons of the biological mechanisms

“swallowing” is not parallel to “gained”

Eliminate


B) have convinced scientists that both red and green algae are descended from a single endosymbiotic event, in which a eukaryotic cell swallowed

The plural verb “have” is in agreement with the plural subject- Molecular evidence and comparisons of the biological mechanisms

In which correctly refers to endosymbiotic event

“swallowed” is parallel to “gained”

Correct.


C) have convinced scientists that both red and green algae having descended from a single endosymbiotic event, when a eukaryotic cell that swallowed


“having descended from a single endosymbiotic event” functions as a modifier. This makes it a sentence fragment. Incorrect. 

What is that the scientists are convinced about?

That both red and green algae are descended from a single endosymbiotic event.

“when” refers to a time. It cannot be use to refer to endosymbiotic event


D) has convinced scientists that both red and green algae are descended from a single endosymbiotic event, wherein a eukaryotic cell swallowed


The singular verb “has” is not in agreement with the plural subject “Molecular evidence and comparisons of the biological mechanisms”


E) has convinced scientists that both red and green algae are descendants of a single endosymbiotic event, and a eukaryotic cell swallowing


The use of “has” is incorrect for the same reason as D.