The structure that prevents water from escaping a leaf is called the cuticle.

Here's a breakdown:

* The Cuticle: This is a waxy, waterproof layer that covers the outer surface of the leaf. It acts as a barrier, preventing water loss through evaporation.

* Stomata: While the cuticle is generally impermeable to water, leaves also have tiny pores called stomata. These pores allow for gas exchange (taking in carbon dioxide and releasing oxygen) which is essential for photosynthesis. Stomata can open and close to regulate water loss, closing to minimize evaporation when water is scarce.

So, the cuticle is the primary barrier against water loss, but the stomata play a vital role in balancing the need for gas exchange with the need to conserve water.