Question

which method is responsible for most of the absorption in higher plants?
A. Active absorption.
B. Passive absorption.
C. Osmotic absorption.
D. Non osmotic absorption.

Answer 1

Hint: In higher plants, root hair plays an important role in the mechanism of water absorption. Walls of root hairs are permeable to water and roots take up the water from the soil. Transpiration is more in the higher plants and the rate of water absorption is almost equal to that of transpiration.

Complete answer:
Methods of water absorption in plants are of two types:

(1) Active Absorption of Water: It is the process in which root cells play an active role in the absorption of water. It may be of two kinds:
Osmotic absorption - In this type of absorption water is absorbed from the soil and taken up by the xylem cells of the roots according to the osmotic difference between soil water and cell sap. The soil solution having less osmotic Pressure, has higher water potential than the cell sap; this negative water potential makes water continue to enter the root hair cell as long as the water potential of the root cell sap is more negative than that of the soil solution.
Non-osmotic absorption when absorption of water still occurs, if the concentration of the cell sap in the root hairs is lower than that of the soil water, or water is absorbed against the concentration gradient. This type of water absorption is non-osmotic in nature and against the gradient. Therefore, it requires energy that is obtained by the respiration.

 (2) Passive Absorption of Water: Passive absorption is the most common and rapid method of water absorption. This accounts for almost 98% of the total water absorbed by plants. The force for this type of water absorption originates in the arial parts of the plant due to transpiration and is called transpirational pull. Due to the presence of continuous columns of the water from leaves to the roots, water potential gradients develop between root hairs cell and soil solution and it is without osmotic forces of individual cells.
In higher plants there is more transpiration and more the transpirational pull, more the water is absorbed passively without energy consumption.

Hence, the correct answer is option (B).

Note: Mineral Ions is absorbed by the plant by active transport and thus it is against the concentration gradient.
Osmosis: Minerals and nutrients are absorbed by Osmosis and uses the difference in concentrations of nutrients between the soil and the root to move water (and nutrients) into the plant.