Question

1. Phospholipids are referred to as __________, meaning that they have a strongly hydrophilic region and a strongly hydrophobic region.

A. Amphipathic

B. Polypathic

C. Amphoteric

D. Neutral

2. In terms of the selective permeability of lipid bilayers, which is the correct order going from very low permeability to very high permeability?

		low - small ions - large uncharged polar molecules - small uncharged polar molecules - small nonpolar molecules - high
		low - small ions - large uncharged polar molecules - small uncharged polar molecules - small nonpolar molecules - high
		low - small nonpolar molecules - small uncharged molecules - large uncharged polar molecules - small ions - high
		low - small uncharged polar molecules - large uncharged polar molecules - small ions - small nonpolar molecules - high

Answer 1

1. Amphipathic

Phospholipids are amphipathic molecules. This means that they have a hydrophilic, polar phosphate head and two hydrophobic fatty acid tails. These components of the phospholipids cause them to orientate themselves, so that phosphate head can interact with water and the fatty acid tails can't, hence forming a bilayer.

2. Low small ions- larger uncharged polar molecules- small uncharged polar molecules- small nonpolar molecules - high

Small nonpolar molecules, such as O2 and CO2, are soluble in the lipid bilayer and therefore can readily cross cell membranes. Small uncharged polar molecules, such as H2O, also can diffuse through membrane , but larger uncharged polar molecules such as glucose cannot.