Final answer:
The waxy polymer on the leaves of vascular plants that protects them from pathogens is called cuticle. This waxy, waterproof cover prevents water loss and also limits the intake of carbon dioxide. To facilitate gas exchange, stomata or pores appear on the surface of the leaves.
Step-by-step explanation:
In land plants, a waxy, waterproof cover called a cuticle protects the leaves and stems from desiccation. However, the cuticle also prevents intake of carbon dioxide needed for the synthesis of carbohydrates through photosynthesis. To overcome this, stomata or pores that open and close to regulate traffic of gases and water vapor appeared in plants as they moved away from moist environments into drier habitats.