The plasma membrane:
A) is composed mostly of lipid molecules
B) is composed mostly of protein molecules
C) allows the ICF and ECF to easily exchange materials
D) is a barrier that prevents most molecules from passing through
E) is a very thick structure relative to the size of the cell

Question

Quizplus · Accepted Answer

The plasma membrane is composed mostly of lipid molecules, specifically phospholipids, which form a bilayer that surrounds the cell. This lipid bilayer also contains some proteins, but lipids make up the majority of the membrane.

Answer: D
 The plasma membrane is a barrier that prevents most molecules from passing through, which is necessary for maintaining the internal environment of the cell. Only small, nonpolar molecules (like oxygen and carbon dioxide) and small, uncharged polar molecules (like water) can easily pass through the membrane via simple diffusion. Other molecules require carrier proteins or specific channels to move across the membrane.

Answer: C and D
 While the plasma membrane is a barrier that prevents most molecules from passing through (as explained in choice D), it does allow for some materials to pass through via various mechanisms. Small, nonpolar molecules and small, uncharged polar molecules can pass through the membrane via simple diffusion (as explained in choice D). The membrane also contains specific channels and carrier proteins that allow for the controlled movement of certain molecules and ions in and out of the cell, which allows for the exchange of materials between the ICF and ECF (as explained in choice C).

Therefore, the best choices are A, D, and either C or D.

The Plasma Membrane