Final answer:
Phospholipid molecules orient their hydrophobic tails toward the center of the cell membrane to avoid water, while the hydrophilic heads face the watery environment outside and inside the cell. This amphipathic nature leads to the spontaneous formation of a bilayer, critical for plasma membrane structure.
Step-by-step explanation:
The tails of phospholipid molecules in the cell membrane are oriented toward the center because of the amphipathic nature of these molecules. Phospholipids have hydrophilic (water-attracting) heads and hydrophobic (water-repelling) tails. When phospholipids are in an aqueous environment, they arrange themselves in a bilayer with the hydrophobic tails facing inward, away from water, and the hydrophilic heads facing outward, towards the water.
Amphipathic Nature of Phospholipids
The amphipathic nature of phospholipids allows them to form a bilayer in water solutions, with the polar heads facing the surrounding water and the non-polar tails tucked away inside. This orientation occurs spontaneously and is driven by the energetically favorable interaction between the hydrophilic heads and water and the desire to shield the hydrophobic tails from water contact. This results in the characteristic double layer of the plasma membrane, providing the basis for a selectively permeable barrier between the cell and its environment.
Phospholipid Bilayer Formation
When many phospholipids align tail to tail, they form a phospholipid bilayer. This bilayer is crucial to plasma membrane structure, with hydrophilic heads pointing toward both the extracellular space and the intracellular space, creating a mosaic characteristic that contributes to the fluid nature of the membrane.