Membrane fluidity is exclusively increased by

As the concentration of unsaturated fatty acids in the membrane is increased, fluidity increases. Among the options given, Linoleic acid is the only unsaturated fatty acid and the rest of then are saturated. According to the fluid mosaic model proposed by Singer and Nicolson, the cell membrane is like a sea of phospholipid bilayer with proteins floating in it like icebergs. This fluidity of the membrane is dependent largely on the lipid content of the membrane. The hydrophobic side chains of fatty acids can be aligned to provide a stiff structure to the membrane. As the temperature increases, these side chain transition from a ordered to a disordered fluid like state . The temperature at which this transition occurs from ordered to disordered state is called transition temperature(Tm). Higher the Tm, lower the fluidity of the membrane Longer and saturated fatty acids decrease the fluidity because their side chains interact more strongly with each other. conversely, unsaturated fatty acids increase the fluidity at lower Tm by decreasing the compactness of the side chains . Ref: Harper's illustrated Biochemistry 30th edition pgno: 483-484