Insects show impressive water conservation due to the wax coating on their cuticle. This wax layer helps prevent water loss by acting as a barrier to evaporation, making it particularly useful in conserving water in dry environments.

Here’s why the other options are incorrect:

A. The chitinous cuticle is impregnated with tanned protein – While chitin is an important component of the insect exoskeleton, it is the wax covering, not the protein, that contributes to water conservation.

B. Nitrogenous waste is eliminated as urea – Most insects eliminate nitrogenous waste in the form of uric acid, which is less water-soluble and helps conserve water. Some insects may excrete urea, but this is not the main factor for water conservation.

C. Chitin is impermeable to water – Chitin itself does not effectively prevent water loss; it is the wax covering the chitinous cuticle that provides this function.

D. The Malpighian tubules are impermeable to water – The Malpighian tubules play a role in excreting waste and conserving water, but it is the waxy cuticle that is primarily responsible for limiting water loss.