Question

It is ……………... that causes sap to rise through a plant stem to the leaves.

Answer 1

In plants, a force that helps to drive fluids upward into the water-conducting vessels (xylem). It is primarily generated by pressure within the cells of the roots and may be demonstrated by the exudation of fluid when the stem is stopped just above ground.

Complete answer:
Root pressure can also be called osmotic pressure that occurs within the cells of a root system. It causes the sap to rise through a plant stem to the leaves. It occurs when the moisture level of the soil is high in the xylem of some vascular plants.
The root pressure is partially liable for the increase of water in vascular plants, though it alone is insufficient for the movement of sap against the force of gravity, especially within the tallest trees. Moreover, the very truth that root pressures will in general be least when water loss from leaves (transpiration) is most noteworthy, which is carefully when plants most need water, shows that root pressure isn't driving sap development.
All things considered, the lifting power produced by evaporation and transpiration of water from the leaves and hence the cohesive and adhesive forces of particles inside the vessels, and perhaps different elements, assume generously more noteworthy functions inside the ascent of sap in plants.

So the correct answer to this question is “Root pressure”.

Note:
Root pressure can be easily observed when the trees are chopped down during the spring season. When a specific tree is chopped or saw down, we will generally see a stump that bleeds sap. From this observation, it is easy to conclude that here is the explanation for sap flow in maple, sap rising to the top of tall trees, and sap movement comes from a “pump” in the roots. The sap bleeding from stumps and other wounds in some tree species is the result of root pressure, a phenomenon that happens only under limited circumstances at certain times of the year.