Cell Membranes: The Essence of Life

Cell membranes define life. They separate a cell's interior from its environment,

controlling what enters and exits. This selective permeability is key to life. Membranes are built

from lipids, especially phospholipids. These have a water-loving phosphate head and two water-fearing

fatty acid tails, making them amphipathic. In water, phospholipids spontaneously form a bilayer.

The heads face the water, and the tails hide inside. This bilayer seals

into spheres, creating a stable barrier. The oily core lets small,

non-polar molecules like oxygen cross easily. But it blocks large molecules and charged

ions. Cells use passive and active transport to move these across. The Fluid Mosaic