Phospholipids form the main fabric of the plasma membrane. One feature of phospholipids is that when they are placed in an aqueous solution, they will self-assemble into a double layer (bilayer) that resembles the bilayer of the plasma membrane. This self-assembly occurs because phospholipids are hydrophilic at one end (the phospholipid head) and hydrophobic at the other end (the phospholipid tails).EF- A) hydrophilicCytoplasm- B) hydrophilicPM- C) grey on top, yellow on bottomPM- D) grey on bottom, yellow on topoutside MP- E) hydrophilicmiddle MP- F) hydrophobicoutside MP- G)hydrophilic

Lipids are composed of fatty acids which form the hydrophilic head and glycerol which forms the hydrophilic tail; their arrangement can give these non-polar macromolecules hydrophilic and hydrophobic properties.

Via diffusion, small water molecules can move across the phospholipid bilayer (C & D), acts as a semi-permeable membrane into the extracellular fluid or the cytoplasm (A & B) which are both hydrophilic and contain large concentrations of polar water molecules or other water-soluble compounds. ; the hydrophilic phosphate heads of the bilayer are attracted to water (grey spheres seen facing outwards) while their water-repellent hydrophobic tails (seen in yellow) face towards each other- allowing molecules of water to diffuse across the membrane along the concentration gradient.

The two ends of the transmembrane protein are within the extracellular fluid and cytoplasm, thus they are hydrophilic (E & G); however, the mid-section of the protein is embedded within the plasma membane, where most of its hydrophobic regions are located, and thus must be lipid-soluble and hydrophilic (F).