Question

which of the following accurately describes why specific material uses a protein to cross the membrane?
○ the hydrophilic core of a membrane will only allow hydrophilic (i.e., polar) substances to cross without a membrane protein.
○ the membrane will allow any substance to cross it as long as it moves from a high concentration to a low concentration.
○ the membrane will allow any substance to cross it if the concentration of solute is high enough on one side of the membrane.
○ material can only cross the membrane via a protein.
○ the hydrophobic core of a membrane will only allow hydrophobic (i.e., non-polar) substances to cross without a membrane protein.

Explanation:

To solve this, we analyze each option based on cell membrane structure (phospholipid bilayer with hydrophobic core):

• Option 1: Membrane core is hydrophobic, not hydrophilic, so wrong.
• Option 2: Concentration gradient alone doesn’t allow all substances (e.g., polar can’t cross hydrophobic core freely), wrong.
• Option 3: Concentration level alone doesn’t override membrane permeability (hydrophobic core restricts polar), wrong.
• Option 4: Some substances (like small non - polar) can cross without proteins, wrong.
• Option 5: The cell membrane has a hydrophobic (non - polar) core. Hydrophobic substances can dissolve in this core and cross without proteins, while polar/hydrophilic substances need proteins. This matches membrane permeability principles.

Answer:

The hydrophobic core of a membrane will only allow hydrophobic (i.e., non - polar) substances to cross without a membrane protein.