Final answer:
The hydrophobic interior of protein-free lipid bilayers prevents the passage of hydrophilic molecules by repelling water-soluble substances, thereby acting as a barrier.Option 3 is the correct answer.
Step-by-step explanation:
The hydrophobic interior of protein-free lipid bilayers functions to prevent the passage of hydrophilic molecules. This is because the hydrophobic tails within the interior of the membrane repel water-soluble substances, thus inhibiting their passage through the bilayer. Conversely, small, nonpolar molecules can diffuse through the hydrophobic interior due to their compatibility with the lipid environment. The presence of membrane proteins facilitates the selective transport of ions and polar molecules through the membrane, but in the absence of proteins, the inherent hydrophobic nature of the lipid bilayer acts as a barrier.
The hydrophobic interior of protein-free lipid bilayers serves as a formidable barrier to hydrophilic molecules by leveraging the repulsion between water-soluble substances and the hydrophobic tails embedded within the membrane. This innate property prevents the passage of molecules that cannot seamlessly integrate into the lipid environment. In contrast, small, nonpolar molecules find easy passage through this hydrophobic milieu. Membrane proteins play a pivotal role in facilitating selective ion and polar molecule transport, emphasizing their significance in overcoming the inherent barrier posed by the lipid bilayer's hydrophobic core.