Question

The movement of water and dissolved minerals from the roots to the leaves is best explained by

• A. Translocation
• B. Cohesion-tension theory
• C. Pressure-flow hypothesis
• D. Tensile strength

Answer 1

The correct option is B

Cohesion-tension theory

The correct option is B.

Explanation for the correct option:

1. Cohesion-tension theory provides the most comprehensive explanation for how water and dissolved minerals flow from the roots to the leaves.
2. Dixon and Jolly proposed this theory in 1894.
3. According to this hypothesis, water flows continuously from the root through the stem and into the leaves.
4. The cohesion force, a potent attraction between water molecules, keeps them joined together.
5. Surface tension is created when water molecules are more attracted to one another than they are when they are in a gaseous state.
6. The transpirational pull is the term for the tension that results from perspiration.

Explanation for the incorrect options

Option A:

1. Translocation is the transfer of elements within a plant from leaves to other tissue.
2. The food that the plant produces cannot reach other areas of the plant without translocation.

Option C:

1. In plants, the mechanism explained for the translocation of sugars from source to sink is referred to as the pressure-flow hypothesis.
2. Osmosis is the process through which water enters the phloem from the nearby xylem.
3. The osmotic pressure rises as a result. It drives the phloem sap in that direction, which is toward the sink, where there is less pressure.
4. Hence, the osmotic pressure at the sink should be reduced.
5. Through active transport, sucrose is transported directly from the phloem sap into the cells in the sink.
6. Once the water has moved out of the phloem and the sugar has been removed, the osmotic pressure decreases.

Option D:

1. Tensile strength is the highest stress that a material can endure without failing as a result of the molecules or atoms holding together or remaining elastic when being pulled apart, whereas plant fiber strength is the highest stress that a material can endure while remaining the same without falling.

Final answer: The movement of water and dissolved minerals from the roots to the leaves is best explained by the Cohesion-tension theory.