Question

Which of the following factors affect the absorption of water by roots?
A) Soil temperature
B) Soil aeration
C) Relative humidity of the atmosphere
D) All of the above

Answer 1

Hint: In active absorption of water by roots, the root cells have an active role in the metabolic activities that produce energy. Passive absorption takes place when the rate of transpiration is high. Rapid transpiration from the leaves results in a pull which helps in absorption of water by the roots.

Complete answer:
There are various factors affecting water absorption. These factors include the following:
i) Availability of soil water: absorption of water is directly dependent on the amount of water present in the soil.
ii) Soil temperature: if the temperature is too low, the permeability of cell membrane will be decreased. At lower temperatures, the viscosity of capillary water is increased. In general, normal absorption of water takes place in the temperature range of twenty to thirty five degrees Celsius.
iii) Soil aeration: absorption of water takes place much faster in well aerated soil. Deficiency of oxygen in the soil is a cause of improper respiration in roots. This results in a decreased rate of absorption.
iv) Soil concentration: the rate of absorption of water is inversely proportional to the concentration of the minerals present in the soil.
v) Transpiration loss of water is dependent on vapour pressure gradient present between the leaf mesophyll tissue and the atmosphere. Hence, atmospheric humidity is also an important factor that determines the absorption of water from the soil.
vi) Active absorption is dependent on cellular respiration.

Hence the correct answer is option ‘D’.

Note: The gradient of water potential from the root hair to the xylem vessels is really need for the absorption of water by the roots. The root hair absorbs the water. Root hairs are permeable and hydrophilic, it absorbs water from the spaces between the soil particles. The cell wall of the root hair is thinly permeable with a semi-permeable plasma membrane.