The fluidity of the plasma membrane is increased by

Cholesterol maintains the fluidity of the membrane. Cholesterol acts as a buffer to modify the fluidity of membranes. A lipid bilayer made up of only one type of phospholipid changes from a liquid state to a rigid crystalline state (gel state) at a characteristic freezing point. This change in state is known as a phase transition, and the temperature at which it occurs is called the phase transition temperature (Tm). The Tm is higher (fluidity is low) when the constituent fatty acid chains are long and mostly saturated (without double bonds). Long chains have greater interactions among themselves, making the membrane stiffer. Saturated fatty acids have straight tails, whereas unsaturated fatty acids have kinked tails. As more kinks are inseed in the tails, the membrane becomes less tightly packed, and therefore its fluidity increases. .