Advanced Placement (AP) Biology Practice Exam

Unsaturated fats are generally liquid at room temperature primarily due to their molecular structure. These fats contain one or more double bonds between carbon atoms, which introduce kinks into the fatty acid chains. These kinks prevent the fat molecules from packing closely together, resulting in a liquid state at room temperature.

In contrast, saturated fats have no double bonds between carbon atoms, allowing them to pack tightly together. This close packing contributes to their solid state at room temperature. Trans fats, which are a type of unsaturated fat that has been artificially hydrogenated to make them more solid, also do not remain liquid at room temperature. Hydrogenated fats can be created from unsaturated fats but are generally altered to be solid or semi-solid.

Thus, the structure of unsaturated fats, with their double bonds causing kinks in the fatty acid chains, is what allows them to remain liquid at room temperature, making this the correct response.