Which of the following statements about transportation of water, food and minerals in plants is NOT correct?

Question

Which of the following statements about transportation of water, food and minerals in plants is NOT correct?

1. A. The ascent of sap in tall trees primarily occurs due to transpiration pull, cohesion, and adhesion forces rather than root pressure alone.
2. B. Xylem transports water and dissolved minerals mainly in an upward direction, while phloem can transport food both upward and downward.
3. C. Phloem transport requires metabolic energy, whereas xylem transport is largely a passive process.
4. D. Minerals absorbed by roots move through phloem vessels to reach the leaves where they are utilized for photosynthesis. (Correct answer)

Correct Answer

Option D — Minerals absorbed by roots move through phloem vessels to reach the leaves where they are utilized for photosynthesis.

Detailed Solution & Explanation

The correct answer is Minerals absorbed by roots move through phloem vessels to reach the leaves where they are utilized for photosynthesis.

Key Points

• This statement is NOT correct. Minerals absorbed by the roots travel upward through the xylem, not the phloem. Water and dissolved minerals move exclusively in the xylem; the phloem carries the products of photosynthesis.
• The other three statements are correct:
  • Ascent of sap in tall trees is driven mainly by the transpiration pull, working together with the cohesion between water molecules and their adhesion to xylem walls — the cohesion–tension theory. Root pressure alone cannot lift water more than a few metres.
  • Xylem transports upward only, while phloem translocates both upward and downward depending on where the sinks are.
  • Phloem transport requires ATP, since sugars are actively loaded at the source; xylem transport is essentially passive, driven by evaporation from the leaves.

Additional Information

• Xylem versus phloem:

• Munch's pressure-flow hypothesis explains phloem translocation: sugar loaded at the source lowers water potential, water enters from the xylem, and the resulting turgor pressure drives the sap towards the sink, where sugar is unloaded.
• Transpiration additionally cools the leaf and maintains the mineral supply, which is why it is described as a "necessary evil" — the plant loses over 95% of the water it absorbs.