Question

Root pressure develops due to
A. Increase in transpiration
B. Active absorption
C. Low osmotic potential in soil
D. Passive absorption

Answer 1

Hint: The spontaneous movement of solvent molecules through a selectively permeable membrane towards higher concentration.

Complete answer:
Root pressure is the transverse osmotic potential within the cells of a root system that causes sap to rise through a plant stem to the leaves. Due to the process of osmosis, the root pressure is formed inside the xylem. This is due to the high level of moisture in the soil during the night and during the day the transpiration becomes low.
Root pressure is caused by the active distribution of mineral nutrient ions into the root system. The ions accumulate in the root xylem since they are not carried up to the stem, this lowers the potential of the water. Due to the process of osmosis, water then diffuses from the soil and reaches to the root xylem.
Root pressure is caused by the accumulation of water in the xylem and pushing on the rigid cells. It provides a force, which pushes water towards the stem. The root pressure is positive pressure which is developed due to high osmotic pressure as it is high in the root in comparison to the water column above.
Active absorption is the process of water absorption through the plant roots which requires the energy in the form of ATP. This ATP is produced through the process of respiration of roots.
So, the correct answer is ‘Active absorption'.

Note: Osmosis may be described as a physical process in which any solvent moves across a semipermeable membrane separating two solutions of different concentrations. Transpiration is the exhalation of water vapor through the stomata. Passive absorption is the movement of minerals into the cell or tissue without the expenditure of energy.