Final answer:
The cuticle is a protective layer that covers the aerial parts of plants to prevent water loss, but it can also restrict gas exchange. Stomata regulate this exchange and certain adaptations like trichomes help reduce water loss in various environmental conditions.
Step-by-step explanation:
The cuticle on plants serves as a protective, waxy, waterproof layer that covers the aerial parts, such as leaves and stems, to prevent excessive water loss through transpiration. However, this layer also restricts the intake of carbon dioxide (CO₂) needed for photosynthesis. To regulate the exchange of gases and water vapor, plants have developed stomata (pores) that can open and close. In certain plants like liverworts, pores on the upper 'skin' or epidermis are formed by barrel-shaped clusters of cells capable of closing under dry conditions to conserve water, while still allowing CO₂ to reach photosynthesizing cells.
In environments with extreme temperatures, the epidermis of plants may be several layers thick, adding extra protection against water loss. Additionally, some plants have structures like trichomes, which deter herbivory and can further reduce transpiration. Trichomes do this by creating a layer of still air which slows down the movement of water vapor away from the leaf surface.