A Level Biology Practice Exam

What is the characteristic of hydrophobic molecules?

1. They attract water molecules

2. They are soluble in water

3. They repel water molecules

4. They cause water to evaporate

The correct answer is: They repel water molecules

Hydrophobic molecules are characterized by their aversion to water. This property stems from their nonpolar nature, meaning that they do not readily form hydrogen bonds with water molecules. As a result, hydrophobic substances tend to cluster together to minimize their exposure to water, effectively repelling water molecules. This behavior is significant in biological contexts, such as in the formation of cell membranes, where hydrophobic tails of phospholipids create a barrier that separates the internal environment of the cell from the aqueous surroundings. The incorrect options relate to properties that hydrophobic molecules do not exhibit. They do not attract water molecules or dissolve in water because of the lack of polar interactions. Similarly, while hydrophobic substances may affect the evaporation of water in some scenarios, they do not inherently cause water to evaporate. Thus, the core characteristic of hydrophobic molecules is their tendency to repel water.