I need help with this question!
BS: Item 104 discrete:
When a biological membrane separates two fluid compartments apart with different solute concentrations, an osmotic pressure differential can arise between the compartments because the membrane:
A) dissolves only nonpolar substances
B) allows the passage of solute particles only
C) allows passage of most solvent particles but not solute particles
D) has electrical charges that attract some particles but not others
I chose A but the correct answer is C. I understand that A is incorrect because osmosis is the movement of SOLVENTS, not solutes, although the AAMC's explanation is that nonpolar substance dissolving in the membrane will not affect the concentration of soluble substance on both side of the membrane. However, I don't see how C is correct. Their explanation is that "the inability of most solute molecules to move across the membrane maintains the different solute concentration on both side of the membrane. However, the solute (water) does move across the membrane". First of all, isn't water the SOLVENT and not the solute? Even if I ignore that part, the osmotic pressure depend on the concentration of the substance, so since movement of the solute or the solvent across the membrane can both change the concentration, wouldn't that make C incorrect? Please enlighten me
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