Question

Root pressure can transport water and dissolved mineral nutrients from roots through the xylem, to the tops of relatively short plants when transpiration is low or zero. The above statement was supported by:

• A. Transpiration pull
• B. Root pressure theory
• C. Capillary force theory
• D. All of the above

Answer 1

Answer: (B)

Root pressure theory

The root pressure is the osmotic pressure within the cells of a root system that generates due to the difference in the pressure gradient. This difference results in the flow of water from high water potential to low water potential and water are absorbed by the root from the soil. According to root pressure theory, hydrostatic pressure is generated in the root system due to the accumulation of water absorbed by the roots, which is responsible for the ascent of sap. Root pressure is created due to the gain of water whereas, transpiration is the loss of water in the form of water vapour. Therefore, root pressure is inversely proportional to the rate of transpiration and that's why it occurs when the rate of transpiration is low during the day or when the soil moisture level is high at night. At night, the temperature is low and the humidity (moisture) level is comparatively high which would slow the rate of transpiration.

So, the correct option is B.