Final answer:
Cholesterol helps maintain the fluidity of cell membranes by preventing them from becoming too rigid in cold temperatures and too fluid in high temperatures. The correct option is d) Makes the membrane more flexible at high temperatures.
Step-by-step explanation:
The function of cholesterol in membranes is essential for maintaining the membrane's fluidity across various temperatures. Specifically, the correct statement describing this function is that cholesterol enables the membrane to stay fluid more easily when cell temperature drops.
It acts as a buffer, making the membrane less fluid and more rigid when the temperature increases, which prevents it from becoming too permeable, and maintains fluidity when the temperature decreases, thus preventing the membrane from solidifying. Cholesterol achieves this by fitting in between the fatty acid tails within the phospholipid bilayer, and adjusting the membrane's fluidity as required by the temperature changes. The correct option is d) Makes the membrane more flexible at high temperatures.