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Question Video: Describing the Role of Adhesion in the Xylem Biology

A student writes, “Adhesion in the xylem refers to the formation of hydrogen bonds between different water molecules, which results in the water forming a continuous column.” Are they correct? Why?

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Video Transcript

A student writes, “Adhesion in the xylem refers to the formation of hydrogen bonds between different water molecules, which results in the water forming a continuous column.” Are they correct? Why? (A) No, because adhesion results in the water molecules being spaced far apart, not forming a continuous column. (B) No, because the bonds formed in adhesion of water are ionic bonds, not hydrogen bonds. (C) No, because adhesion refers to the formation of hydrogen bonds between the water molecules and the molecules in the wall of the xylem. (D) Yes, because due to their polar nature, water molecules easily form hydrogen bonds with other water molecules.

Water is pulled up through a plant in the xylem vessels. There are intermolecular forces that allow this process to occur. So what are these forces? And does the student correctly describe one?

Water molecules in the xylem are attracted to each other by hydrogen bonds. This is known as cohesion. Cohesion helps the water be pulled up through the xylem. However, cohesion is not the only intermolecular force at work. It is complemented by the force that attracts the water molecules to the cells of the xylem wall. This force is called adhesion and is, again, the result of hydrogen bonds. Note that although the intermolecular forces at play in these two processes are the same, cohesion involves water molecules sticking to each other. And adhesion involves water molecules sticking to other cells.

So, the sentence written by the student is incorrect. Cohesion in the xylem refers to the formation of hydrogen bonds between different water molecules, which results in the water forming a continuous column, not adhesion. The correct answer is given by option (C). Adhesion refers to the formation of hydrogen bonds between the water molecules and the molecules in the wall of the xylem.

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