What kinds of molecules pass through a cell membrane most easily?
A. large and hydrophobic
B.small and hydrophobic
C.large polar
D.ionic
E. monosaccharides such as glucose
The Correct Answer and Explanation is :
Correct Answer:
B. Small and hydrophobic
Explanation:
The cell membrane, also known as the plasma membrane, is a semi-permeable barrier that regulates what enters and exits a cell. It is primarily composed of a phospholipid bilayer, with embedded proteins and cholesterol molecules that influence membrane fluidity and permeability. The phospholipids have hydrophilic (water-attracting) heads and hydrophobic (water-repelling) tails, forming a hydrophobic core that significantly impacts molecule transport.
Factors Influencing Membrane Permeability:
- Size: Smaller molecules pass through more easily than larger ones.
- Polarity: Nonpolar (hydrophobic) molecules cross more easily than polar (hydrophilic) ones.
- Charge: Charged (ionic) molecules struggle to pass due to the hydrophobic interior of the membrane.
- Lipid Solubility: Lipid-soluble molecules can dissolve in the membrane and diffuse through.
Analysis of the Answer Choices:
- (A) Large and hydrophobic → While hydrophobicity helps, large molecules struggle to diffuse freely. Incorrect
- (B) Small and hydrophobic → These molecules (e.g., oxygen, carbon dioxide) easily pass through the membrane because they can dissolve in the lipid bilayer. Correct
- (C) Large polar → Large polar molecules (e.g., proteins) cannot pass without transport mechanisms. Incorrect
- (D) Ionic → Charged molecules (e.g., Na⁺, Cl⁻) require transport proteins or channels. Incorrect
- (E) Monosaccharides (e.g., glucose) → These require carrier proteins for facilitated diffusion. Incorrect
Thus, the best answer is B: Small and hydrophobic molecules, as they can dissolve in the lipid bilayer and passively diffuse across the membrane.
Now, I’ll generate an image representing how different molecules pass through the cell membrane.
Here is the generated scientific illustration of a cell membrane, depicting different types of molecules and their transport mechanisms. Let me know if you need any modifications or additional explanations!