Root pressure develops due to

A. Increase in transpiration

B. Active absorption

C. Low osmotic potential in soil

D. Passive absorption

Root pressure refers to the osmotic potential within the root cells that causes sap to rise through the plant stem towards the leaves. This pressure is generated in the xylem due to the process of osmosis. Root pressure is most prominent during the night when soil moisture is high, and transpiration is low during the day.

The primary cause of root pressure is the active transport of mineral ions into the root system. These ions accumulate in the root xylem as they are not carried up to the stem, lowering the water potential in the roots. Consequently, water from the soil diffuses into the xylem through osmosis, building up the pressure.

Root pressure is a form of positive pressure created by the accumulation of water in the xylem, which exerts force on the rigid cell walls, pushing water upward through the stem. This pressure is a result of the higher osmotic pressure in the roots compared to the water column above.

Active absorption is the process by which water is absorbed by plant roots, requiring energy in the form of ATP. This ATP is produced through the process of root respiration.

Thus, the correct answer is "Active absorption."