What is the Difference Between Upper and Lower Epidermis?

The epidermis of a leaf is present on both sides of the leaf and is comprised of the upper and lower epidermis. The main difference between the upper and lower epidermis lies in their functions:

• Upper Epidermis: This layer is mainly involved in water conservation by eliminating excess sunlight. It consists of a single layer of cells containing few or no chloroplasts, making the cells quite transparent. The upper surface is covered with a waxy, waterproof cuticle, which helps reduce water loss from the leaf.
• Lower Epidermis: This layer is mainly involved in gas exchange. It is often where most of the stomata (thousands per square centimeter) are located. The stomata are guarded by two sausage-shaped cells called guard cells, which regulate the opening and closing of the stomata to control the exchange of gases between the leaf and the surrounding atmosphere.

In addition to their functional differences, the lower epidermis can be differentiated from the upper epidermis by the presence of stomatal crypts, which are pockets lined with trichomes that help capture evaporating moisture and maintain a relatively humid environment around the stomata. The lower epidermis also has a slightly thinner cuticle compared to the upper epidermis.

Comparative Table: Upper vs Lower Epidermis

The main difference between the upper and lower epidermis of a leaf is the presence of a cuticle layer in the upper epidermis and the location of stomata, which are typically found in the lower epidermis. Here is a table summarizing the differences:

The upper epidermis is a single layer of cells containing few or no chloroplasts, allowing light to pass through for photosynthesis in the underlying palisade and spongy layers. The lower epidermis is located on the underside of the leaf and has mainly a protective function, as well as allowing for gaseous exchange and regulation of water flow.