Question

What is root pressure?

Answer 1

Hint: Root pressure is the force by which the plants conduct water from the soil. Water conducting vessels of plants like xylem helps to derive fluids upward by this force. The osmotic pressure in the root cells helps conduct this force. It is important for the plant but not a predominant conducting force.

Complete answer: The roots are the hair-like projections of plants located deep inside the soil. They function to provide anchorage to the plant, absorb nutrients and water from the soil, provide support to the plant and it is also involved in storing food. The root pressure is a force that acts against the force of gravity and transports water up into the plant. This force is generated in the water-conducting xylem vessels of plants. The osmotic pressure in the cells of the root generates the root pressure. This can be illustrated by oozing out fluid from the cut portions of the stem just above the ground. Although it is a major force that operates in xylem for water conduction, it is only partially responsible for rising of water in the vascular plants. It is insufficient for the sap movement against the gravitational force alone, especially in tall trees. It is a fact that root pressure is lowest when transpiration or water loss rate is highest in plants. But it is the condition when a plant needs more water. So, the root pressure is insufficient alone, therefore, it acts along with other sap driving forces like lifting force generated by evaporation and transpiration of water, cohesive and adhesive forces in vessels, etc. to transport water in tall trees.

Note: Low root pressure is observed during excessive transpiration. Root pressure is observed more commonly during spring season when leaves develop and transpiration rate is low. The major effects of root pressure come into play during nights and in the early morning when evaporation rates are comparatively very less.