The plasma membrane is composed of a lipid bilayer that exhibits temperature-dependent fluidity. As temperature decreases, the fatty acid chains in the phospholipids pack more tightly, resulting in a reduction of membrane fluidity. This decreased fluidity can impair membrane protein function and affect cell signaling and transport processes. Clinically, understanding this concept is crucial during hypothermia management in surgery, as low temperatures may rigidify membranes and impact cellular functions. Thus, membrane fluidity decreases as temperature decreases, affecting cell viability and function.

Reference: Molecular Biology of the Cell, Alberts et al., 6th Edition.