Advanced Placement (AP) Biology Practice Exam

Which of the following substances would be considered hydrophilic?

1. Oil

2. Cellulose

3. Fat

4. Glycerol

The correct answer is: Cellulose

Cellulose is considered hydrophilic due to its structure and the presence of numerous hydroxyl (-OH) groups throughout its polymer chains. These hydroxyl groups are polar and can form hydrogen bonds with water molecules, facilitating interactions with water and thus making cellulose soluble in water to some extent. This property is critical in biological systems, particularly in plant cell walls, where cellulose provides structural support and interacts with the aqueous environment. In contrast, substances like oil and fat are nonpolar and hydrophobic, meaning they do not mix well with water. Glycerol, while it has some hydrophilic properties due to its hydroxyl groups, is often considered a more intermediate substance and may not be as distinctly hydrophilic as cellulose. The strong presence of hydroxyl groups makes cellulose a clear example of a hydrophilic substance, which can readily engage in interactions with water molecules.