Question

Of the following molecules, which would you predict diffuses most readily across membranes?

1) serine
2) glucose
3) oxygen
4) hydrogen ions
5) water

Answer 1

Oxygen is predicted to diffuse more readily across cell membranes than water because it is a small, nonpolar molecule that can easily move through the hydrophobic interior of the lipid bilayer.

Step-by-step explanation:

The student's question is about which molecule, oxygen (O₂) or water (H₂O), would diffuse most readily across cell membranes. According to the principles of simple diffusion, the structure of the lipid bilayer readily allows small, uncharged substances, such as oxygen, to pass through the cell membrane down their concentration gradient. Oxygen tends to diffuse quickly because it is nonpolar and very small, which allows it to move easily through the hydrophobic part of the phospholipid bilayer.

While water also can diffuse through the membrane to a certain extent due to its small size, its polar nature makes it less able to pass through the hydrophobic interior of the lipid bilayer without assistance. Therefore, oxygen is predicted to diffuse more readily across cell membranes than water due to its nonpolar characteristics and smaller molecular size.