In sentence 1, most good is an incorrectly formed superlative. It should be best. Additionally fear is a noun, so it should be modified by the adjective incredible, not the adverb incredibly:

• Eva and Ellie, who had been best friends since their freshman year, both had an incredible fear of heights.

In sentence 3, the adjective real is used to modify the adjective freaked out. We should use the adverb really instead:

• The first time they went to a class, they were both really freaked out.

Sentence 4 misuses the adverb literally: it is being used as an intensifier. Replacing it with actually or possibly would be a good revision:

• Ellie’s hands shook so hard she couldn’t tie the rope to her harness, and the instructor said that Eva was actually the slowest climber he had ever seen.
• Ellie’s hands shook so hard she couldn’t tie the rope to her harness, and the instructor said that Eva was quite possibly the slowest climber he had ever seen.

Sentence 4 also uses the adverbial phrase “so hard” to modify the verb shook. Hard can either be an adjective or an adverb, so this is correct.

Sentence 2 has two improperly used conjunctions: while and and thus. With while, a subordinating conjunction, we just need to remove the comma beforehand since. The second conjunction (and thus) is a little more complicated. While this phrase is acceptable in speech, it’s not something that translate well to written text. The best solution is to revise the sentence to use a different part of speech entirely (in this case, we’ve used the preposition in order to):

• Some bacteria hide in host cells and evade detection as they feast on nutrients provided by the cells while others produce proteins that mimic the cell’s proteins in order to evade detection entirely.

The phrase “infection and survival in the host” is incorrect in sentence 3. Both infection and survival need to be connected to the host. Right now, the preposition in is doing that for both words. However, “infection in the host” doesn’t make sense in this case: “infection of the host” is the correct construction. We need to add another preposition:

• Others live extracellularly and use a variety of other mechanisms for infection of and survival in the host.

Sentence 4 uses the subordinating conjunction though where an adverbial conjunction (like however) should be used: “Some pathogens, however, do not survive in the host cell alone.”

In sentence 6, known by should be replaced with known as, or known by the name:

• Not only do these biofilms provide protection from the host, but they also allow the bacteria to communicate through a method known as quorum sensing.
• These biofilms not only provide protection from the host, but also allow the bacteria to communicate through a method known as quorum sensing.

In sentence 8, the preposition within should probably be changed to in since the host is not inside the community: “However, it also allows the host to eavesdrop on bacterial communication in the bacterial community.”

You may have noticed that this passage uses the when referring to bacteria and host cells (i.e., the bacteria and the host cell). In instances like this, you can decide if you want to use the definite the or the indefinite a and an—whichever you choose, make sure you are consistent.