11. What is root pressure? How it is useful to the plant?
Answers
Answer:
Root pressure is caused by active distribution of mineral nutrient ions into the root xylem. Without transpiration to carry the ions up the stem, they accumulate in the root xylem and lower the water potential. Water then diffuses from the soil into the root xylem due to osmosis.
NCERT based Answer for Class 11 Biology Students
Root Pressure:
Root pressure is the force that helps to drive fluids upward in the xylem. It is primarily generated by osmotic pressure in the cells of roots and can be demonstrated by exudation of fluid when a young stem is cut off just above the ground.
Effect of root pressure is observable at night and early morning when evaporation is low.
Excess water collects in the form of droplets around openings of vein near tip of grass blades. Such water loss in the liquid phase is known as guttation.
Mineral ions from soil are taken up by roots and get accumulated in xylem vessel by active transport.
Accumulation of ions leads to increased osmotic potential in root cells and low water potential in xylem vessels.
Low water potential of xylem sap compared to that of soil solution makes water move inside the roots. This increases pressure inside xylem; known as root pressure.
Usefulness of Root Pressure:
The greatest contribution of root pressure is to re-establish continuous column of water in xylem which often breaks under enormous tensions created by transpiration.
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