Which of the following would diffuse through a cell membrane the most easily?

Question

BlackTom AI · Accepted Answer

When considering what would diffuse through a cell membrane most easily, it's helpful to recall the properties of the phospholipid bilayer. It is hydrophobic in the interior, which favors the passage of nonpolar, uncharged substances.
Option 1: 'a small polar molecule' — Polar molecules interact with the hydrophobic core unfavorably, so they diffuse more slowly than nonpolar molecules. This option would diffuse, but not as readily as nonpolar substances.
Option 2: 'a positively charged ion' — Ions carry charge and are strongly repelled by the hydrophobic core of the membrane, making their passive diffusion extremely limited without transport proteins. This option is unlikely to diffuse easily.
Option 3: 'a large nonpolar molecule' — Nonpolar molecules can cross the membrane, but size matters: larger molecules diffuse more slowly due to higher obstruction and steric hindrance. While they can diffuse, they do so less readily than small ones.
Option 4: 'a small non-polar molecule' — This matches the membrane's preference: small, nonpolar molecules experience minimal energetic barrier and diffuse rapidly across the hydrophobic interior.
Option 5: 'a large polar molecule' — Polar and especially large polar molecules face significant barriers to passive diffusion and typically require channels or transporters; this would diffuse least easily among the options.
In summary, the combination of being small and nonpolar provides the least resistance to crossing the lipid bilayer, making diffusion across the membrane most favorable for small non-polar molecules.

Which of the following would diffuse through a cell membrane the most easily?单项选择题

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