Question

1. if you were explaining to your classmate why protein channels are found in the cell membrane, you would say that

a. they allow some polarized, hydrophilic molecules to cross the cell membrane.
b. they decrease the permeability of the cell membrane to substances.
c. they allow some nonpolarized, hydrophobic molecules to cross the cell membrane.
d. they stabilize the cell membrane.

Explanation:

To determine the correct answer, we analyze each option:

• Option a: The cell membrane's lipid bilayer is hydrophobic, so polar (hydrophilic) molecules can't easily cross. Protein channels (like ion channels) facilitate the passage of these polar, hydrophilic molecules (e.g., ions, water - via aquaporins). This is correct.
• Option b: Protein channels increase the permeability of the membrane to specific substances (the ones they allow through), not decrease it. So this is incorrect.
• Option c: Non - polar, hydrophobic molecules can pass through the lipid bilayer directly without the need for protein channels. So this option is incorrect.
• Option d: The main structural components that stabilize the cell membrane are the lipid bilayer and cholesterol, not protein channels. So this option is incorrect.

Answer:

a. They allow some polarized, hydrophilic molecules to cross the cell membrane.