Significance of transpiration:
1. Facilitating a cooling effect by absorbing plant heat and converting water into vapor during transpiration.
2. Ensuring optimal turgor pressure by absorbing excess water during transpiration, promoting healthy growth.
3. Assisting mineral transport by generating a transpiration pull, aiding the roots in absorbing and distributing soil minerals.
4. Supporting water transport through a transpiration pull, maintaining a steady water supply to the upper parts of the plant.
Root pressure theory:
1. J. Pristley proposed the Root Pressure Theory.
2. The translocation of water is facilitated by the active involvement of living cells within the root.
3. Absorption of water by root hairs is a consistent and ongoing process, resulting in the development of hydrostatic pressure in cortical cells.
4. This hydrostatic pressure, known as root pressure, compels water to move into the xylem, initiating its upward conduction.
5. Root pressure, as a phenomenon, is attributed to osmosis.
6. The continuous absorption of water by root hairs contributes to a constant hydrostatic force in the root system.
7. This force generated within the roots promotes the movement of water towards the xylem vessels.
8. The osmotic nature of root pressure underscores the significance of solute concentration in driving the movement of water.
9. Ultimately, the Root Pressure Theory elucidates the dynamic process by which osmotic forces within the root system facilitate the upward translocation of water in plants.
Limitations of root pressure theory:
1. Not relevant for plants exceeding 20 meters in height.
2. The upward movement of sap is observed even when root pressure is absent.
3. Plants with active transpiration lack the development of root pressure.
4. Root pressure is nonexistent in taller gymnosperms.
5. Xylem sap experiences tension, exhibiting negative hydrostatic pressure.