Practice question · Multiple choice
Why can oxygen cross a membrane unaided while a sodium ion cannot?
Hints
- The membrane interior is a hydrophobic layer of fatty-acid tails.
- A charged particle cannot pass through a hydrophobic core, whatever its size.
Show the answer
D. Oxygen is small and nonpolar, so it dissolves through the lipid core
Why
The bilayer’s core is hydrophobic, so small nonpolar molecules dissolve straight through. A sodium ion is actually smaller than an oxygen molecule but carries a charge, and a charged particle cannot enter a hydrophobic core, size is not the obstacle, charge is.
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