The intense pressure found in the deep ocean can affect the structure of proteins in fish's cells, distorting the proteins'...

Let's begin by understanding the meaning of this sentence. We'll use our understanding of pause points and segment the sentence as shown - understanding and assimilating the meaning of each segment bit by bit!

Sentence Structure

• The intense pressure found in the deep ocean
  • can affect the structure of proteins in fish's cells,
    • distorting the proteins' shape.

• The chemical trimethylamine N-oxide (TMAO)
  • counters this effect,
    • ensuring that proteins retain their original configurations [?] TMAO
      • is found in high concentrations in the cells of the deepest-dwelling fish.

Understanding the Meaning

Let's start with the first sentence:

• 'The intense pressure found in the deep ocean can affect the structure of proteins in fish's cells, distorting the proteins' shape.'
  • This tells us that deep ocean pressure is a problem for fish - it messes up the shape of proteins in their cells.

Now the next part:

• 'The chemical trimethylamine N-oxide (TMAO) counters this effect'
  • So TMAO is the solution - it fights against that pressure problem.

• 'ensuring that proteins retain their original configurations'
  • This explains HOW it helps - TMAO makes sure the proteins keep their normal shape.

This is where we have the blank. Let's look at the choices:

• They all have "configurations" followed by different punctuation, then "TMAO"

To see what works here, let's read what comes after and understand what it's saying:

• 'TMAO is found in high concentrations in the cells of the deepest-dwelling fish.'
  • This is giving us additional information about where TMAO appears - it's especially concentrated in the fish that live deepest in the ocean.

Now, what do we notice about the structure here?

• After "configurations," we have: "TMAO is found in high concentrations..."
  • "TMAO is found" has a subject (TMAO) and a verb (is found)
  • This is a complete thought that can stand alone as its own sentence

• Before the blank, we have: "The chemical TMAO counters this effect, ensuring that proteins retain their original configurations"
  • "TMAO counters this effect" is also a complete thought with subject and verb
  • This can also stand alone as its own sentence

So we have two complete sentences - two separate, complete thoughts that each can stand on their own.

When we have two complete sentences, we need to separate them properly with a period (making them two distinct sentences).

The correct answer is A: configurations. TMAO

This creates two proper sentences:

1. "The chemical TMAO counters this effect, ensuring that proteins retain their original configurations."
2. "TMAO is found in high concentrations in the cells of the deepest-dwelling fish."

GRAMMAR CONCEPT APPLIED

Separating Complete Sentences

When you have two complete thoughts (called independent clauses in grammar terms) - each with its own subject and verb that can stand alone - you must separate them properly. You have several options:

Option 1: Use a period to create two sentences

• First complete thought. Second complete thought.
• Example: The pressure distorts proteins. TMAO counters this effect.

Option 2: Use a semicolon

• First complete thought; second complete thought.
• Example: The pressure distorts proteins; TMAO counters this effect.

Option 3: Use a comma + coordinating conjunction (and, but, or, nor, for, yet, so)

• First complete thought, and second complete thought.
• Example: The pressure distorts proteins, but TMAO counters this effect.

What you CANNOT do:

• Run them together with no punctuation (run-on sentence)
• Connect them with just a comma (comma splice)

In our question:

• "TMAO counters this effect, ensuring that proteins retain their original configurations" = complete sentence
• "TMAO is found in high concentrations in the cells of the deepest-dwelling fish" = complete sentence
• These need proper separation → period is the correct choice