Question

A pressure that is responsible for pushing up water to small height in the stem is?
A. Positive root pressure
B. Turgor pressure
C. Pressure gradient
D. Negative root pressure

Answer 1

Water is a necessary component for the growth and development of plants. Water is absorbed from root hair and is carried up to the plant through the stem. This is observed through the phenomena of guttation. The phenomenon of guttation is the exudation of fluids from freshly watered plant stems after applying an incision to the stem.

Step by step answer: Transpiration can be defined as the phenomena of movement of water from the tips of the roots, through the stem and its evaporation from aerial parts of the plant. Leaf surfaces and foliage consist of tiny pores called stomata. These stomata are bordered with guard cells. Transpiration occurs through these pores, i.e., water evaporation occurs through stomata. Hydraulic conductivity of the soil and the pressure gradient magnitude through the soil are the two major factors influencing the water flow rate from the soil to the roots.
-Positive root pressure: Positive root pressure can be defined as the pressure required to push the water absorbed by the root hairs up to small heights in the stem through water-conducting vessels known as xylem. This can be observed experimentally by exudation of fluids on cutting the stem just above the ground. The flow of water molecules from the roots to the shoots is upheld by the transpirational pull.
-Turgor Pressure: Turgor pressure can be defined as the force within the cell that pushes the plasma membrane against the cell wall. Within the cell, turgor pressure is regulated by the osmotic flow of water. This causes cell wall expansion during growth. The rigidity of the cell is due to turgor. Loss of water from plant cells could lead to loss of turgor, causing wilting of flowers and leaves. Turgor plays a vital role in the opening and closing of the stomata in leaves. Turgor pressure can be managed by the semipermeable membrane that permits only some solutes to travel within the cell, maintaining minimum pressure.
-Pressure gradient: Pressure gradient can be termed as a physical quantity, which outlines in which direction and at what rate the pressure increases the most rapidly around a specific location.
-Negative root pressure: Transpiration is accounted to be maximum during the day time. A significant amount of water is lost during transpiration which causes guard cells present in stomata and other epidermal cells to become flaccid. Root pressure during transpiration tends to be the lowest. Due to this, the water is taken up from the xylem, causing a negative tension in xylem vessels.
Hence option A is correct.

Note: Around 6.87 meters is the measured maximum root pressure in some plants and the tallest trees are over 100 meters tall. Transpiration is regulated by the plants. They regulate it by controlling the sizes of the stomatal apertures.