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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.
Solution
- Perhaps sufficient for herbaceous plants, root pressure accumulates enough force to push the sap in the xylem vessels up to a certain height.
- 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.
- 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.
- 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.
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