Question

multiple choice question
substances that cannot easily cross the lipid bilayer can still diffuse across the plasma membrane with the help of which of the following?
○ specific hydrophilic proteins or hydrophobic proteins
○ specific channel proteins or carrier proteins
○ specific transmembrane proteins or peripheral proteins
○ specific glycolipids or glycoproteins

Explanation:

To solve this, we analyze each option:

1. Hydrophilic/hydrophobic proteins: The key for aiding diffusion of non - lipid - soluble substances is the function of channel or carrier proteins, not just the hydrophilic/hydrophobic nature. So this option is incorrect.
2. Channel or carrier proteins: Channel proteins form pores for ions and small molecules to pass through, and carrier proteins change shape to transport substances. Both help in the facilitated diffusion of substances that can't cross the lipid bilayer easily. This option is correct.
3. Transmembrane/peripheral proteins: Peripheral proteins are on the membrane surface and don't aid in transporting substances across the lipid bilayer. So this option is incorrect.
4. Glycolipids/glycoproteins: These are mainly involved in cell - cell recognition and not in transporting substances across the lipid bilayer. So this option is incorrect.

Answer:

B. Specific channel proteins or carrier proteins