Question

The pressure due to the steady movement of water into root xylem and transpiration pull are responsible for

(a) The upward movement of food in plants

(b) The upward movement of water in plants.

(c) Transportation of sugars to storage areas

(d) Closing of stomata

Answer 1

Answer:

The upward movement of water from roots to the aerial parts of the plant is called ascent of sap. Most accepted theory for the ascent of sap is the cohesion adhesion tension theory which is based on that there is a continuous column of water from the roots to the leaves. When transpiration takes place, water evaporates from the intercellular spaces of the leaves into the outer atmosphere through the stomata. Due to water loss, osmotic pressure of the leaf cells increases. As a result, water potential of the cells become low and water from the leaf veins (xylem) moves into the leaf cells. The xylem vessels in turn draw water from the xylem of the main stem. This creates a pull which is known as transpiration pull. The lumen of tracheids and vessels of a xylem link to form a narrow tube and water rises in the narrow tube due to the force of surface tension. This phenomenon is known as capillarity. Thus water moves from the roots to all other parts due to capillary action and the pull created due to evaporation of water from the leaves. Hence both options A and B are correct.

So, the correct answer is both A and B.

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