A Level Biology Practice Exam

In what form do hydrophilic molecules typically interact with water?

1. They repel water

2. They dissolve in water

3. They form oil layers

4. They absorb water to grow

The correct answer is: They dissolve in water

Hydrophilic molecules interact with water primarily by dissolving in it. This characteristic arises from their ability to form hydrogen bonds and other polar interactions with water molecules. Hydrophilic substances, which include many ions and polar compounds, have partial positive and negative charges due to their molecular structure. When these molecules are introduced to water, the water molecules surround them, effectively integrating them into the solution through hydration. This process allows hydrophilic molecules to disperse evenly throughout the water, confirming that they readily mix with it. In contrast, other options represent different behaviors of molecules with water. For instance, hydrophobic molecules would repel water and therefore do not dissolve in it. The formation of oil layers pertains to hydrophobic compounds that do not mix with water but instead separate into distinct layers. While some substances may absorb water, this typically does not define the interaction of hydrophilic molecules with water, as their primary interaction is dissolution rather than absorption for growth purposes. Thus, the correct answer highlights the fundamental nature of hydrophilic molecules in their interaction with water.