Question

which statements correctly explain why different molecules cross the membrane at different rates?
large molecules pass more slowly because they cannot interact with the hydrophobic tails of the membrane lipids.
ions are very small so they can pass quickly through the membrane.
nonpolar molecules pass more quickly because they can interact with the hydrophobic tails of the membrane lipids.
both the size and polarity of a molecule influence the rate at which is can pass through the membrane in the absence of a protein transporter.
charged molecules pass more slowly than polar uncharged molecules because charged molecules are pushed away from the membrane by the charged headgroups of the phospholipids.

Explanation:

• Large molecules: Their slow passage is due to size - related steric hindrance, not inability to interact with hydrophobic tails.
• Ions: Despite being small, they are charged. The hydrophobic interior of the membrane repels them, so they do not pass quickly.
• Non - polar molecules: Can dissolve in the hydrophobic lipid bilayer (due to "like - dissolves - like" principle), so they pass more quickly.
• Size and polarity: Both factors (e.g., small non - polar molecules pass faster than large polar ones) influence membrane - crossing rate without transporters.
• Charged vs polar uncharged: Charged molecules are more strongly repelled by the membrane (due to charge - charge repulsion), so they pass more slowly than polar uncharged molecules.

Answer:

• Nonpolar molecules pass more quickly because they can interact with the hydrophobic tails of the membrane lipids.
• Both the size and polarity of a molecule influence the rate at which is can pass through the membrane in the absence of a protein transporter.
• Charged molecules pass more slowly than polar uncharged molecules because charged molecules are pushed away from the membrane by the charged headgroups of the phospholipids.