What is the term for the outer protective layer of a plant's leaves?

The outer protective layer of a plant's leaves is known as the cuticle. This is a waxy or sometimes fatty layer that provides several key functions for the plant. It helps to prevent water loss by minimizing evaporation from the leaf surface, which is essential for maintaining hydration in the plant and its overall health. In addition, the cuticle acts as a barrier against pathogens, pests, and environmental damage, allowing the plant to thrive in various conditions.

The other terms listed, such as bark, refer to the protective outer covering of stems and trunks of woody plants, and mesophyll denotes the inner tissue of the leaf that is involved in photosynthesis. Stoma refers to small openings on the leaf surface that facilitate gas exchange but is not a protective layer. The cuticle is specifically designed for protection, which is why it is the correct response to the question about the outer protective layer of a plant's leaves.