Question

In the cohesion-tension theory, cohesion refers to the

• A. attraction between water molecules.
• B. attraction between the xylem vessels.
• C. attraction between water molecules and xylem vessels.
• D. attraction between water molecules and phloem.

Answer 1

The correct option is A

attraction between water molecules.

The correct option is A:

Explanation of the correct option

1. When water molecules are attracted to each other, this is called cohesion.
2. This is due to hydrogen bonds that develop between one molecule's partially negative oxygen and another molecule's partially positive hydrogen.
3. Intermolecular hydrogen bonding is a powerful force.

Explanation of the incorrect options

Option B:

1. Cohesion does not refer to the attraction between the xylem vessels in the cohesion-tension theory.

Option C:

1. Adhesion is the molecular attraction between molecules that are "unlike."
2. Adhesion occurs between water molecules and the molecules of the xylem cell walls in the case of xylem.
3. The molecular attraction between "like" molecules is known as cohesion. Hydrogen bonding between water molecules causes cohesion in water.

Option D:

1. The molecular attraction between molecules that are "unlike" is known as adhesion.
2. In the case of phloem, adhesion occurs between water molecules and the molecules of the xylem cell walls.

In the cohesion-tension theory, cohesion refers to the attraction between water molecules.