A researcher measures unaided crossing rates of various molecules through an artificial phospholipid bilayer (no proteins). Small nonpolar gases pass freely; small polar uncharged molecules pass slowly; large polar and ionic species are nearly excluded.
Why does Na+ have such low permeability in the bar chart?
- Acheck_circle
Charged ions cannot easily cross the hydrophobic core of the bilayer
- B
Na+ ions are the largest molecules in the chart
- C
Na+ ions react with cholesterol in the membrane
- D
Na+ binds covalently to phospholipid heads
Explanation
The hydrophobic interior of the bilayer is incompatible with charged species; ions require channels or pumps to cross.