Question

Pressure caused by water entering the root from the soil is known as
(a) Imbibition
(b) Root pressure
(c) Turgor pressure
(d) Wall pressure

Answer 1

Hint: Exchange of substances like water, gases, nutrients, and hormones in plant cells take place by diffusion and osmosis, which cause movement of water from root to all plant parts by xylem and movement of nutrients and hormone from leaves to all plant part by phloem.

Complete Answer:
The root consists of a tiny outgrowth called root hair which helps in water absorption from the soil, absorption of water in the root exert pressure which is known as root pressure. Root pressure was put forth by Atkin and Priestly in 1916, root pressure is a positive hydrostatic pressure developed in xylem which shows unidirectional movement. Movement of water takes place from root hair to endodermis via the apoplast pathway and then water gets accumulated in the cortical cell, root pressure pushes the cortical water toward xylem. Root pressure gets affected in the case of starvation, low temperature, drought, and unavailability of oxygen.

Additional information:
Imbibition is the process of absorption of water by dry adsorbents like cellulose, protein, and starch. The amount of water absorbed by imbibant is not equal to the volume of imbibant because some water molecule evaporates out due to compression of water.
Turgor pressure is the pressure exerted by the cell membrane toward the cell wall. It is also known as hydrostatic pressure which is positive in all cells except plasmolyzed cells. Hypotonic solution develops positive turgor pressure on cell wall which causes swelling of protoplast and vacuole whereas hypertonic solution develops negative turgor pressure on cell wall which causes shrinkage of protoplast and vacuole.
Wall pressure is inward pressure exerted by a cell wall over the turgid protoplast. It may be equal or opposite to turgor pressure.

So, the correct answer is ‘Root pressure’.

Note: Root pressure is absent in gymnosperm because gymnosperm consist of very tall plants and root pressure is not efficient to transport water up to height more than 100 ft. Transportation of water in gymnosperms takes place by tracheids.