Question

Explain the root pressure theory.

Answer 1

1. This theory was proposed by J. Priestley.
2. According to this theory, the activity of living cells of the root is responsible for the translocation of water.
3. When a stem of a potted plant is cut a few inches above the soil by a sharp knife, xylem sap is seen flowing out/ oozing out through the cut end.
4. This exudation at the cut end of the stem is good proof of the existence of root pressure.
5. As water absorption by roots is a constant and continuous process, hydrostatic pressure is developed in the living cells of the cortex of the root. This is termed root pressure (coined by S. Hales).
6. Due to root pressure, water, along with dissolved minerals, is not only forced into the xylem but also conducted upwards against gravity.
7. Root pressure seems to be largely an osmotic phenomenon and its development is an active process.
8. The value of root pressure is +1 to +2 bars which is enough to pump water to a height of 10 to 20 meters.
9. Factors like oxygen, moisture, the temperature of the soil, salt contents, etc., influence root pressure.