13 . Select : the parts of cholesterol (specify I one or more answers) aliphatic chain carboxyl group OH group phosphorus cyclopentane

The correct answer is: cyclopentane.<br /><br />Cholesterol is a type of lipid molecule that is a crucial component of cell membranes and is also a precursor for the synthesis of other important molecules in the body. It is a complex molecule that consists of several different functional groups and structural features. Among the options provided, the cyclopentane ring is a key structural component of cholesterol. Cyclopentane is a five-membered carbon ring that forms the core structure of the cholesterol molecule. The other options, such as the aliphatic chain, carboxyl group, OH group, and phosphorus, are not directly part of the cholesterol molecule.