Question

What are the four main forces which contribute to the ascent of sap (upward movement of water and minerals) ? Name them and explain in short.

Answer 1

1. Perhaps sufficient for herbaceous plants, root pressure accumulates enough force to push the sap in the xylem vessels up to a certain height.
2. The capillarity (narrow diameter) of xylem vessels permits the water from a lower level to rise to make up the vacuum produced by the loss of water owing to transpiration from the leaves.
3. Pull with transpiration. The tendency of water molecules to remain linked (cohesion) pulls more water molecules up when the water is lost from the leaf surface by transpiration, therefore producing a continuous column of water through the stem.
4. Attaching. It draws more water molecules from below when the leaf cells lose water during transpiration since it makes the water attach to the surface of the cells.