AP Biology / Unit 2: Cell Structure and Function
2.4 Membrane Permeability
Notes
The membrane is selectively permeable.
- Small nonpolar molecules ($\mathrm{O_2}$, $\mathrm{CO_2}$) pass easily.
- Ions and large polar molecules need transport proteins.
- Plant and bacterial cell walls add structure.
Practice
Which crosses the bilayer most easily?
Small and nonpolar.
Ions can't easily cross the lipid bilayer because:
Charged particles avoid the tails.
A cell wall made of cellulose is found in:
Bacteria use peptidoglycan.
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