Define root pressure.

Hint: The mechanism that helps plants transport water to smaller heights in the stem. It provides a modest push in the overall process of water transport. The great contribution it may provide is to re-establish the continuous change of water molecules in the xylem.

Complete answer:
We know that plants absorb water from the soil through their roots. This water is then transported to various parts of the plants through their vascular bundles. Various ions and minerals from the soil are actively transported into the vascular tissues of the roots. Subsequently, water also follows the ions and increases the pressure already building inside the xylem. Such positive pressure built up within the root is called root pressure. Thus, the transverse osmotic pressure within the cells of a root system that results in a rise of sap through the plant stem to the leaves is called ‘root pressure.’

Additional Information: -To demonstrate root pressure, we can make use of a soft-stemmed plant. Early in the morning, on a day with plenty of atmospheric moisture, cut the stem horizontally near the base with the sharp blade. You will witness drops of solution oozing out of the cut stem. This happens due to the positive root pressure.
-Root pressure does not play a major role in the water movement in tall trees.

Note: A natural example of root pressure can be observed at night and early morning when evaporation is low. The water that gets collected in the form of droplets around special openings of veins near the tip of grass blades and leaves, is all because of root pressure. Such loss of water in a liquid phase is known as ‘guttation.’