The outward-facing cell walls of epidermal cells contain which substance to reduce water loss?
options: pectin wax chitin suberin lignin
The correct answer and explanation is:
Correct Answer: Wax
The outward-facing cell walls of epidermal cells contain wax, specifically in the form of a waxy layer called the cuticle, which plays a crucial role in reducing water loss. This waxy cuticle covers the surface of the epidermis in most aerial parts of plants, such as leaves, stems, and fruits.
The wax is part of a hydrophobic layer made primarily of cutin and waxes. Cutin is a fatty acid polymer, and waxes are composed of long-chain hydrocarbons. These substances are secreted by epidermal cells and deposited on the surface, forming a continuous barrier that limits the evaporation of water from internal plant tissues.
The primary function of this waxy layer is to prevent desiccation, which is the drying out of plant tissues due to excessive water loss. This is especially important in environments where water availability is limited or when the air is dry. The cuticle helps maintain the plant’s internal water balance, which is essential for physiological processes like photosynthesis, nutrient transport, and cellular function.
Additionally, the wax layer provides protection against environmental stresses such as harmful ultraviolet radiation, pathogens, and mechanical injury. It also plays a role in reducing the adhesion of water and dirt on the leaf surface, which helps keep stomata, the pores responsible for gas exchange, clear and functional.
Other substances listed in the options have different functions. Pectin is found in the middle lamella and helps with cell adhesion. Chitin is found in fungal cell walls and insect exoskeletons, not plants. Suberin is found in the cork cells of roots and stems, acting as a barrier to water and solutes. Lignin strengthens cell walls, particularly in xylem vessels, but does not primarily reduce water loss.
Thus, the correct answer is wax.