Which tissue forms the protective outer layer of a leaf and stem?

Which tissue forms the protective outer layer of a leaf and stem?

• A. Xylem
• B. Epidermis
• C. Phloem
• D. Cortex

Answer: (B)

The protective outer layer is the epidermis. This single, tightly packed layer covers leaves and stems, acting as a barrier against physical damage and pathogens and helping to reduce water loss with a waxy cuticle. In leaves, the epidermis is usually transparent to let light reach the photosynthetic cells beneath, and it often contains stomata—pore openings controlled by guard cells—to regulate gas exchange and transpiration. In stems, the epidermis provides the same protective cover, though in many woody parts it may be replaced by cork as plants mature. By contrast, xylem and phloem are internal vascular tissues for water and sugar transport, and cortex is a ground tissue located just inside the epidermis, not the outer surface.

The protective outer layer is the epidermis. This single, tightly packed layer covers leaves and stems, acting as a barrier against physical damage and pathogens and helping to reduce water loss with a waxy cuticle. In leaves, the epidermis is usually transparent to let light reach the photosynthetic cells beneath, and it often contains stomata—pore openings controlled by guard cells—to regulate gas exchange and transpiration. In stems, the epidermis provides the same protective cover, though in many woody parts it may be replaced by cork as plants mature. By contrast, xylem and phloem are internal vascular tissues for water and sugar transport, and cortex is a ground tissue located just inside the epidermis, not the outer surface.