Final answer:
The membrane with 40% cholesterol would have the least fluidity because the higher the proportion of cholesterol, the more rigid the membrane becomes, reducing its fluidity.
Step-by-step explanation:
The question is asking about the fluidity of cell membranes based on the percentage of cholesterol present in them. Cholesterol is an integral component of the plasma membrane and plays a significant role in determining membrane fluidity. It is located within the tail bilayer of the membrane, where it is interspersed between phospholipids. Higher cholesterol levels tend to reduce membrane fluidity because cholesterol makes the membrane more rigid. Therefore, among the choices provided, a membrane with the highest percentage of cholesterol would have the least amount of fluidity. Given the percentages, option (d) 40% would result in the membrane with the least fluidity because the proportion of cholesterol is the highest.