A Level Biology Practice Exam

How does an unsaturated fatty acid affect the structure of fats?

1. It makes them solid at room temperature

2. It allows them to stay liquid at room temperature

3. It creates uniform thickness

4. It increases the hydrogen content

The correct answer is: It allows them to stay liquid at room temperature

Selecting the option indicating that an unsaturated fatty acid allows fats to stay liquid at room temperature is accurate because of the structural characteristics of unsaturated fatty acids themselves. Unsaturated fatty acids contain one or more double bonds between carbon atoms in their hydrocarbon chains. These double bonds introduce kinks or bends in the fatty acid chains, preventing them from packing closely together. As a result, the intermolecular forces between the fatty acids are weaker compared to saturated fatty acids, which have no double bonds and can pack tightly, making them solid at room temperature. The presence of these kinks in unsaturated fatty acids contributes to a liquid state at room temperature, like that of oils. Other options do not align with the properties of unsaturated fatty acids. The solid state of fats at room temperature, for instance, relates more closely to saturated fatty acids that pack tightly together. Uniform thickness does not accurately represent the structural variability that unsaturated fats exhibit due to their kinks. Lastly, unsaturated fatty acids have fewer hydrogen atoms compared to their saturated counterparts due to the double bonds, meaning they do not increase hydrogen content, which is another reason this option is not valid.