Question

Assertion: Upward movement of water is called ascent of sap.
Reason: Upward movement of water occurs through xylem and phloem.
A. Both Assertion and Reason are correct and Reason is the correct explanation for Assertion.
B. Both Assertion and Reason are correct but Reason is not the correct explanation for Assertion.
C. Assertion is correct but Reason is incorrect.
D. Both Assertion and Reason are incorrect.

Answer 1

Hint: Plants absorb water from the roots and transpire through the leaves. Water travels from the root to other areas of the plant body against the force of gravity.

Complete Answer:
- The water and minerals absorbed by the roots are transported through xylem and the organic material synthesised in the leaves is transported by phloem to other areas of the plant. After the roots have been absorbed, the water is spread to all areas of the plant.
- In order to reach the uppermost areas of the plant, the water needs to pass upwards through the stem. The upward flow of water and minerals from the root to the other areas of the plant is referred to as the ascent of sap.
- Many hypotheses have been put forward to understand the mechanism of the growth of the sap, but the most commonly accepted explanation is Cohesive force or transpiration pull or cohesion-tension theory.
- Xylem is responsible for translocation of water, mineral salts, and hormones from the roots to the upper regions of the plant. The phloem translocates a number of organic and inorganic solutes, mostly from leaves to other parts of plants.
- Phloem is responsible for moving food mainly from the source of sucrose to the sink. The translocation of the phloem is bi-directional. This is in contrast with that of the xylem, where the flow is always one-way, i.e. upwards.

Thus the correct answer is option C i.e., Assertion is correct but Reason is incorrect.

Note: After the ions have entered xylem by active or passive uptake, or a mix of the two, the further upward transfer from the stem to other areas of the plant is by the transpiration stream.