Final answer:
A membrane with lipids containing octadecanoic acid (saturated fatty acid) and cholesterol is expected to have the highest transition temperature (Tm) because saturated fatty acids have straight chains that pack tightly and cholesterol further stiffens the membrane.
Step-by-step explanation:
The transition temperature (Tm) of a membrane is the temperature at which a membrane transitions from being fluid to being solid. Membranes containing lipids with saturated fatty acid tails, such as octadecanoic acid, have a higher Tm because the straight chains pack closely together and there is less molecular motion. In contrast, membranes that include lipids with unsaturated fatty acid tails, like 9-octadecenoic acid, have a lower Tm because the kink in the unsaturated fatty acid does not allow the lipids to pack as tightly, increasing fluidity. Cholesterol acts to stiffen membranes, but only to a certain extent; it fills in gaps between phospholipids, making the lipid bilayer less permeable and more ordered, which tends to increase the Tm compared to membranes without cholesterol.
Comparing the options provided, a membrane containing lipids with octadecanoic acid (saturated fatty acid) and cholesterol is expected to have the highest Tm because it will be the most rigid and least permeable due to the combined effects of saturated fatty acid tails, which pack closely together, and cholesterol, which fills in gaps between the lipids.