Topic 2.4: Membrane Permeability

What gives the plasma membrane its selective permeability?

Its hydrophobic interior.

Which molecules can freely pass across the membrane?

Small nonpolar molecules (e.g., N2​, O2​, CO2​).

How do hydrophilic substances (large polar molecules/ions) cross the membrane?

Through embedded channels and transport proteins.

What specific part of the phospholipid prevents the movement of ions?

The nonpolar hydrocarbon tails.

Can small polar uncharged molecules (H2​O, NH3​) cross the membrane?

Yes, but only in small amounts.

What are the three roles of cell walls in plants, fungi, and bacteria?

Structural boundary, permeability barrier, and protection from osmotic lysis.

Selective permeability

The ability of a cell’s outer skin (the membrane) to act like a bouncer at a club

Osmotic lysis

The bursting of a cell due to excess water entering it, causing it to swell and break