4. how does a cell membrane retain its shape?
a. the forces of polar molecules pushing on one another
b. the force of water molecules pushing on the lipids of the bilayer
c. the attractive forces of the lipid tails
d. the repellant forces between the heads and tails of the bilayer
5. what molecules are embedded within a cell membrane that allow needed materials to pass through?
a. dna
b. rna
c. proteins
d. carbohydrates