Why the cuticle is thicker at the top than at the bottom of the leaf?

The cuticle is thicker at the top of the leaf to provide enhanced protection against environmental stressors such as UV radiation and water loss through transpiration. This upper layer, facing direct sunlight, helps to reduce evaporation and preserve moisture in the leaf. In contrast, the bottom side of the leaf typically has more stomata for gas exchange, requiring a thinner cuticle to facilitate this process. Thus, the thickness of the cuticle is adapted to the specific functions and exposures of each leaf surface.