Question

The cells of the roots contain cell sap at a ------concentration than that of surrounding soil water.
A. Higher
B. Lower
C. Equal
D. All of the following

Answer 1

Hint: In higher plants water is absorbed through root hairs from the soil. Walls of root hairs are permeable to water and roots take up the water from the soil.

Complete answer:
Root hairs are slender thin walled extensions of root, epidermal cells which increase the surface area for absorption. The water is taken by the roots from the soil and shifted to conducting tissue. It has to be transmitted to distinct parts of the plant. Root hair walls are permeable for water and are hydrophilic. Transpiration is more in the higher plants.
Root pressure is the pressure that is positive which occurs in the root by the means of active absorption of nutrients from the soil. A cell sap is found in the root hair and it has a greater concentration of salts as compared to surrounding soil water. Hence water starts coming outside to inside root hair.
The absorbed water reaches vascular tissue and from here it is supplied to all parts of the plant. So concentration of solute in cell sap is higher.
In xylem sap a negative water pressure occurs. The reason for that when a cut is given to shoot the water does not spill out. The absorption of water is the same as the transpiration rate. The cell sap has higher water concentration than the surrounding water which means that the cell sap has lesser water potential and soil has higher water potential. The absorption of water is affected by environmental conditions like available soil water, soil air and soil temperature.

Hence, the correct answer is option (A).

Note: Mineral ions are absorbed by the plant by the means of active transport and are not in favour of the concentration gradient. Minerals and nutrients are absorbed by osmosis and use the difference in concentration of nutrients between soil and the roots to move water.