Question

1. (a) What is the name of the theory that describes the process in which water moves up inside a plant?

(b) What are the forces that move water up through a plant?

(c) What is the energy source that drives this process?

Answer 1

Answer 1- a) The cohesion-tension theory describes how the water moves up through the xylem.

b) The water is carried upward through the xylem by the transpirational pull. Transpiration is controlled by the opening and closing of stomata. The water gets evaporated from the mesophyll cells in leaves. It creates a negative water potential gradient which results in the upward movement of water and minerals from the roots through the xylem to the leaf. Water is then lost through transpiration from the leaf.

c) The Energy source that causes upward flow of water is solar heat. The increase in solar heat increases the temperature. Due to this, the rate of transpiration is high. The water is lost from guard cell which leads to decreased water potential of guard cells. Then a cohesion pull in the xylem vessels is created to pull the water up to the guard cells.