Question

Passive absorption of water by root system is the result of-
A. Forces created in the cells of the root
B. Increased respiratory activity in root cells
C. Tension on the cell sap due to transpiration
D. Osmotic force in the root system

Answer 1

Passive absorption of water is similar to diffusion. It is the process by which an ion or molecule passes through a cell wall along a concentration gradient, i.e., from the region of higher concentration to the region of lower concentration. This type of movement requires no usage of energy which means it is ATP independent. It is the most prevalent method of water absorption.

Complete answer:
In the process of passive absorption the concerned force arises from the aerial parts of the plant, mainly from the leaves and thus causing tension in the xylem sap.
Some other features of passive absorption are-
a. It needs no energy.
b. This mode of water absorption is insensitive to inhibitors.
c. Faster method of water absorption when compared to active absorption.
d. It takes place through the apoplastic route.
e. 96 percent of the water absorption by plants takes place through passive absorption.
f. In the case of water absorption, the force lies in the shoot of the plant. In creating the force, the major role is played by the transpiration pull, and negative turgor pressure is developed.

Therefore, the correct answer here will option (C).

Note: Starting from the root tip to the apical portion of the plant there is a column of water in the xylary elements. This water column is continuous and is maintained by the root pressure. Root pressure is the positive hydrostatic pressure developed in root cells due to the active entry of solute from the pericycle to xylem vessels of the root. The most important of this root pressure is to recreate continuous water columns at high temperatures. This root pressure is responsible for creating the force called transpirational pull.