Question

Transpiration and root pressure cause water to rise in plants by
A Pushing it upward
B Pushing and pulling it respectively
C Pulling it upward
D Pulling and pushing it respectively

Answer 1

Hint: The process of water passing out from the surface of a plant or leaf 'Root Pressure'. It is the transverse osmotic pressure within the cells of a root system that causes sap to rise through a plant stem to the leaves.

Complete answer:The physiology of water uptake and transport is not so complicated. The main driving force of water uptake and transport into a plant is the transpiration of water from stomata that are present in the leaves. Transpiration is the process of water evaporation from within specialized openings in the leaves, called stomata. The evaporation creates a negative(-) water vapor pressure, which is developed in the surrounding cells of the leaf. Once this happens, water is pulled into the leaf from the vascular tissue, the xylem(transports water and nutrients), to replace the water that has been transpired from the leaf.
This pulling of water, or tension, that occurs in the xylem of the leaf, will extend all the way down through the rest of the xylem column of the tree and into the xylem of the roots due to the cohesive forces holding together the water molecules along the sides of the xylem tubing. (Remember, the xylem is a continuous water column that extends from the leaf to the roots.) Finally, the negative water pressure that occurs in the roots will result in a rise in water uptake from the soil. If transpiration from the leaf becomes less, as usually occurs at night or during cloudy weather, the drop in water pressure in the leaf will not be as great, and so there will be a lower demand for water (less tension) placed on the xylem.
The loss of water from a leaf (negative water pressure, or a vacuum) is comparable to placing suction to the end of a straw. If the vacuum or suction thus created is great enough, water will rise up through the straw. If you had a very large diameter straw, you would need more suction to lift the water. Likewise, if you had a very narrow straw, less suction would be required. This correlation occurs as a result of the cohesive nature of water along the sides of the straw (the sides of the xylem). Because of the narrow diameter of the xylem tubing, the degree of water tension, (vacuum) required to drive water up through the xylem can be easily attained through normal transpiration rates that often occur in leaves.
So, the correct option is D

Note: A leaf transpires about 90% of the water evaporated from a water surface of the same area. Root pressure occurs in the xylem of some vascular plants when the soil moisture level is high either at night or when transpiration is low during the day.