Question

Which of these molecules require a carrier protein to pass through the cell membrane?

(a) Small neutral solutes

(b) Water

(c) Polar molecules

(d) Non – polar molecules

This question was addressed to me during an interview.

My question is based upon Eukaryotic Cells and it’s Organelles topic in portion Cell : The Unit of Life of Biology – Class 11

Answer 1

The correct answer is:

(c) Polar molecules

Polar molecules, such as glucose or amino acids, generally require a carrier protein to pass through the cell membrane. This is because the cell membrane is composed of a hydrophobic lipid bilayer, which impedes the movement of polar molecules. Carrier proteins facilitate their transport by binding to the molecules and undergoing conformational changes to shuttle them across the membrane.

In contrast:

• Small neutral solutes (e.g., oxygen, carbon dioxide) can pass through the membrane by simple diffusion.
• Water can pass through the membrane via aquaporins, which are specific water channels.
• Non-polar molecules (e.g., lipids) can diffuse directly through the lipid bilayer without the need for a carrier protein.