Which component of the plasma membrane contains a hydrophobic region and acts as the primary barrier to most foreign substance

a) phospholipid

b) cholesterol

c) protein

d) carbohydrate chain

the correct answer is option A

Phospholipids structure consists of two parts –

a)Hydrophillic Head

b)Hydrophobic tail  

The phospholipids are arranged in two parallel layers thereby forming by the phospholipid bilayer. It is the part of cell membrane and arranges them in a way that their hydrophilic heads face towards the outwards direction and the hydrophobic tails face each other. The hydrophobic tails opposes the transfer of fluid movement specially the water and the fatty acid head containing negative phosphate group opposes the movement of charged ions. They allow transfer of material  under specific circumstances.

helicase, i think thats it