Final answer:
Increasing temperature or unsaturated fatty acid content in lipid bilayers is the least effective way to reduce lateral diffusion of membrane proteins, as both increase membrane fluidity.
Step-by-step explanation:
The least effective way to dampen the lateral diffusion of membrane proteins in lipid bilayers is to increase the temperature or to increase the number of unsaturated fatty acids. This is because both higher temperature and the presence of unsaturated fatty acids with more kinks or bends in their structure increase the fluidity of the membrane, hence allowing more free movement of the membrane components. On the contrary, the presence of cholesterol in the membrane would fill the space between fatty acids in the hydrophobic interior, thus dampening the lateral mobility of membrane components by reducing fluidity and membrane permeability to some ions.