Question

Hygroscopic water is not available to plants because

• A. $\Psi$ is greatly increased
• B. DPD is greatly decreased
• C. $\Psi$ becomes strongly negative
• D. $\Psi$ is increased and DPD is decreased

Answer 1

Answer: (C)

$\Psi$ becomes strongly negative

Water potential (denoted by symbol psi) of pure water is maximum and its value is zero. Hence, water potential of all solutions is negative. Water flows from a region of higher water potential to a region of lower water potential, because a region having higher water potential has more number of water molecules as compared to the region having lesser water potential.

The hygroscopic water is present as a thin layer around soil particles, it is very tightly held and cannot be accessed by plant roots. Water potential of hygroscopic water is very high on negative side (i.e., very low water potential), hence this water is inaccessible to plants.