Question

Each of the following molecules move across membranes by simple diffusion except:

(A) oxygen
(B) fatty acid
(C) water
(D) glucose
(E) carbon dioxide

Answer 1

Glucose does not move across membranes by simple diffusion; it requires facilitated diffusion due to its polar nature.

Step-by-step explanation:

The molecules that move across membranes by simple diffusion are:

Oxygen (O2)

Fatty acid

Carbon dioxide (CO2)

These molecules are small, nonpolar, and can freely pass through the hydrophobic phospholipid bilayer of the cell membrane. Water (H2O) and glucose, on the other hand, cannot cross the membrane by simple diffusion. Water molecules rely on osmosis, which is the diffusion of water across the membrane, while glucose requires facilitated diffusion through specific protein channels in the membrane.

The molecule that does not move across membranes by simple diffusion is glucose. Oxygen (O2), fatty acids, water (H2O), and carbon dioxide (CO2) can pass through the cell membrane via simple diffusion due to their nonpolar, small, or uncharged nature. Glucose, on the other hand, is a polar molecule and too large to diffuse through the lipid bilayer without assistance. It requires facilitated diffusion, utilizing specific transport proteins to move across the membrane.