Explain how the spiracles and tracheal system of insects are adapted to minimise water loss whilst still allowing adequate gas exchange.

Spiracles are equipped with sphincter or valve muscles that can close the opening when the insect is not actively breathing, thereby preventing water loss from the body surface. Insects also use a discontinuous or intermittent gas‑exchange cycle – the spiracles open only for short periods, so the tracheal system is exposed to the external atmosphere for a limited time. This reduces the total time available for evaporation. The tracheal system delivers oxygen directly to cells by diffusion along the thin‑walled tracheoles; because the gas is transported internally, there is no large moist surface exposed to the environment. The ends of the tracheoles remain fluid‑filled and the moist internal surface is deep within the body, maintaining a steep oxygen gradient while the humid air inside the tracheal system minimises the evaporation gradient and thus water loss.