Question

The cohesion transpiration pull theory operates only in
A. Passive water absorption
B. Active water absorption
C. Conditions favouring transpiration
D. Conditions restricting transpiration

Answer 1

Hint: Cohesive and adhesive properties of water molecules from an unbreakable continuous water column in the xylem. Transpiration pull or tension exerted on the water column. Xylem vessels are tubular structures extending from roots to the top of the plants.

Complete step by step answer: The cohesion transpiration pull theory operates only in conditions favouring transpiration. Transpiration is the loss of water from the aerial parts of plants. The cohesion-tension theory is a theory of intermolecular attraction that explains the process of water flow upwards (against the force of gravity) through the xylem of plants. Transpiration pull, utilizing capillary action and the inherent surface tension of water, is the primary mechanism of water movement in plants. Active absorption is referred to as the absorption of water by roots with the help of adenosine triphosphate which is generated by the root respiration, as root cells actively take part in the process. Some conditions favouring transpiration are:
i. Light: Plants transpire more rapidly in the light than in the dark.
ii. Temperature: In plants, different temperatures result in different transpiration rates because water evaporates more rapidly as the temperature rises.
Hence, the correct answer is option C.

Note: Stomatal transpiration is the evaporation of water through the stomata in plants. Most of the water that is transpired from plants is done mostly this way, nearly 90% of the water transpired from the leaves of the plants exits through the stomata. Lenticular transpiration and cuticular transpiration are other examples of transpiration. Environmental factors like relative humidity, temperature, light, etc.