A Level Biology Practice Exam

What does adhesion in plants refer to?

1. The attraction between water molecules

2. The interaction of water molecules with soil

3. The attraction between water molecules and the walls of xylem vessels

4. The force pulling water up through plant roots

The correct answer is: The attraction between water molecules and the walls of xylem vessels

Adhesion in plants specifically refers to the attraction between water molecules and the walls of xylem vessels. This interaction is significant as it helps water climb against the force of gravity through the plant's vascular system. The properties of water, particularly its ability to form hydrogen bonds, enhance this adhesion, allowing water to "stick" to the cellulose in the xylem walls. This mechanism is crucial for the process of transpiration, where water is lost from leaves and creates a negative pressure that facilitates the upward movement of water from the roots. By adhering to the xylem walls, water not only supports this upward movement but also helps maintain column integrity, thus preventing cavitation, which can disrupt water transport within the plant. In short, the adhesion of water to the xylem vessels is a fundamental aspect of plant transport systems, enabling efficient hydration and nutrient transport throughout the organism.