Biology – Transport mechanisms | e-Consult

Answer:

Xerophytic leaves exhibit several structural adaptations to minimize water loss via transpiration. These adaptations typically involve modifications to the epidermis, mesophyll, and stomata. Below is an annotated transverse section of a typical xerophytic leaf illustrating three key adaptations:

1. Thickened Epidermis with a Cuticle: The epidermis is often significantly thicker than in mesophytic plants. This thickness is due to a prominent cuticle, a waxy layer covering the outer surface. The cuticle is composed of cutin, a hydrophobic polymer, which is impermeable to water. This reduces water evaporation from the leaf surface.

[Annotated Drawing: A transverse section of a xerophytic leaf. Clearly label the epidermis, cuticle, and mesophyll. The cuticle should be depicted as a thick layer on the outer surface of the epidermis. Arrows should indicate the direction of water movement away from the mesophyll through the cuticle.]

2. Reduced Surface Area (e.g., Spines or Scale-like Leaves): Many xerophytes have reduced leaf surface area. This can take the form of spines (modified leaves) or scale-like leaves. Reducing the surface area exposed to the air directly minimizes the area from which water can evaporate. This is a highly effective adaptation.

[Annotated Drawing: A transverse section of a leaf with spines. The spines are clearly visible and labelled. The remaining leaf tissue is shown as a smaller area.]

3. Sunken Stomata or Stomatal Crypts: Stomata are pores through which water vapor escapes. In xerophytes, stomata are often sunken within pits or crypts on the leaf surface. These crypts create a humid microclimate around the stomata, reducing the water potential gradient between the leaf and the atmosphere. This lowers the rate of transpiration.

[Annotated Drawing: A transverse section of a leaf showing sunken stomata within a crypt. The crypt is clearly labelled, and arrows indicate the direction of water vapor movement from the leaf into the crypt, reducing the rate of transpiration.]

These three adaptations, among others, work synergistically to significantly reduce water loss in xerophytic plants, allowing them to thrive in arid environments.