Question

Put solutes in order according to a phospholipid bilayer's permeability to them, beginning with the lowest permeability at the top:

A) Ions, Water, Gases (e.g., O2, CO2)
B) Water, Gases (e.g., O2, CO2), Ions
C) Gases (e.g., O2, CO2), Ions, Water
D) Ions, Gases (e.g., O2, CO2), Water

Answer 1

In order of the phospholipid bilayer's permeability from lowest to highest, it is Ions, Water, and Gases (O₂, CO₂). Ions have the lowest permeability due to their charge, water requires assistance to cross, and gases can diffuse more freely due to being small and nonpolar.

Step-by-step explanation:

The question relates to the permeability of a phospholipid bilayer to different solutes. According to their permeability, solutes should be ordered as follows, starting with the lowest permeability:

1. Ions
2. Water
3. Gases (e.g., O₂, CO₂)

The phospholipid bilayer of a cell membrane is selectively permeable due to its hydrophobic interior, which allows small, nonpolar, uncharged molecules like gases (O₂ and CO₂) to easily pass through by simple diffusion. In contrast, polar molecules like water require some assistance, and ions, which are both polar and charged, are repelled by the hydrophobic interior and therefore have the lowest permeability—requiring specialized proteins to cross the membrane.