As a molecule moves through the plasma membrane it passes through
A) a hydrophobic layer of phospholipid heads, then a hydrophilic layer of phospholipid tails, and then another hydrophobic layer of phospholipid heads.
B) a hydrophobic layer of phospholipid tails, then a hydrophilic layer of phospholipid heads, and then another hydrophobic layer of phospholipid tails.
C) a hydrophilic layer of phospholipid heads, then a hydrophobic layer of phospholipid tails.
D) a hydrophilic layer of phospholipid heads, then a hydrophobic layer of phospholipid tails, and then another hydrophilic layer of phospholipid heads.
E) a hydrophobic layer of phospholipid tails, and then a hydrophilic layer of phospholipid heads.

Question

Quizplus · Accepted Answer

The plasma membrane is composed of a phospholipid bilayer, with hydrophilic (water-attracting) phospholipid heads facing outward towards the water inside and outside the cell, and hydrophobic (water-repelling) phospholipid tails facing inward away from the water. Thus, a molecule passing through the membrane encounters the hydrophilic heads first, then the hydrophobic tails, and finally the hydrophilic heads again.

As a Molecule Moves Through the Plasma Membrane It Passes