Question

When an oak tree is kept in a poisonous solution, the water rises to the top of the tree, although the tree is ready to take another supply of poisonous solution followed by the uptake of even pure water. This shows that
(a) Living cells are not involved in the ascent of sap
(b) Living cells play a major role in the ascent of sap
(c) Both xylem and phloem play a major role in the ascent of sap
(d) Living cells play $60\%$ role and vessels of xylem play $40\%$ roles in the ascent of sap

Answer 1

Hint: The transport of water across high distances such as up to the top of the tree is because of two forces known as the transpiration pull and root pressure. Transpiration is responsible for pulling the water up whereas root pressure pushes the water upwards.

Complete Answer:
The fact that the oak tree is taking in a poisonous solution and transporting it to the top tells us that the cells involved in this transportation cannot be living. This is because living cells would die or be damaged by the poison and the process of transportation would have stopped. It is also seen that the tree takes up another supply of the poisonous solution which is proof that the cells involved in the ascent of sap are non-living and thus were not damaged in the process.

 Additional information: Let us study the ascent of sap in detail.
- The process of the ascent of sap takes place in non- living cells of the xylem known as tracheids and xylem vessels.
- The root pressure which is developed by absorbing excess water and minerals causes water to be pushed upwards.
- The transpiration process that occurs in the stomata of leaves causes a deficit of water because of which water is pulled up molecule by molecule from the root to the tip of the leaves.
- Forces like cohesion, adhesion, and surface tension ensure that the long chain of water molecules do not break while being pulled upwards.
- Even if the chain breaks, the root pressure joins the chain again.
- In this way, water is transported to very high distances such as 15 meters against the force of gravity.
So, the correct option is ‘(a) Living cells are not involved in the ascent of sap’.

Note:
- Cohesion is the mutual force of attraction present between water molecules (same molecules)
- Adhesion is the attraction of water molecules to the surface of the tracheary elements.
- Surface tension is the attraction of water molecules being more in the liquid phase than in the gaseous phase.