Difference Between Upper and Lower Epidermis

Main Difference – Upper Epidermis vs Lower Epidermis

Upper and lower epidermis are the two outermost layers of a leaf, which are found in the upper and the lower surfaces, respectively. Leaves are the major structure of plants involved in the production of food by photosynthesis. The cells of the leaves consist of photosynthetic pigments such as chlorophyll to capture energy from sunlight. Inorganic molecules are used to produce simple carbohydrates by this energy. Since leaves are the center of photosynthesis, the anatomy of the leaves is built in such a way to facilitate photosynthesis. The structure of upper and lower epidermis aid the process of photosynthesis. Moreover, both types of epidermis help to maintain the water balance of the plant. The main difference between upper epidermis and lower epidermis is that upper epidermis possesses a cuticle layer whereas lower epidermis possesses a large number of stomata.

Key Areas Covered

1. What is Upper Epidermis
      – Definition, Anatomy, Physiology
2. What is Lower Epidermis
      – Definition, Anatomy, Physiology
3. What are the Similarities Between Upper and Lower Epidermis
      – Outline of Common Features
4. What is the Difference Between Upper and Lower Epidermis
      – Comparison of Key Differences

Key Terms: Chloroplasts, Cuticle Layer, Gas Exchange, Guard Cells, Lower Epidermis, Stomata, Upper Epidermis, Water Conservation

What is Upper Epidermis

Upper epidermis refers to a single layer of cells on the upper surface of the leaf, which aids water conservation. It possesses a waxy and waterproof cuticle layer on top of the epidermal cells. The cuticle layer forms a shiny surface on the leaf, which expels the excess sunlight from the leaf. When the light intensity and heat are high, the cuticle layer prevents the water loss from the leaf. A cross-section of a leaf is shown in figure 1.

Difference Between Upper and Lower Epidermis

Figure 1: Cross Section of a Leaf

Upper epidermis is typically made up of a single layer of epidermal cells. Generally, epidermal cells lack chloroplasts. The transparency of the upper epidermis permits the passing of sunlight through the upper epidermis to the underlying cells. Beneath the upper epidermis, palisade layer, which contains cylindrical cells carrying out most of the photosynthesis, can be found. In floating plants, the stomata occur in the upper epidermis.

What is Lower Epidermis

Lower epidermis refers to a single layer of cells on the lower surface of the leaf that contains stomata and guard cells. It contains more stomata (thousands per square centimeter) than upper epidermis. A stoma is an opening on the epidermis, which allows the exchange of carbon dioxide and oxygen and transpiration. A pair of guard cells surrounds the stoma. The size of the stoma is controlled by the two guard cells based on the requirements of the plant. Typically in the day, stomata are kept opened. A lower epidermis is shown in figure 2.

Main Difference - Upper vs Lower Epidermis

Figure 2: Lower Epidermis

The guard cells also contain chloroplasts. They are the only photosynthesizing cells in the epidermis.

Similarities Between Upper and Lower Epidermis

Both upper and lower epidermis are the two outermost layers of the leaf.
The epidermal cells in both upper and lower epidermis do not contain chloroplasts.
Both upper and lower epidermis contain stomata.
The guard cells of both upper and lower epidermis contain chloroplasts.

Definition

Upper Epidermis: Upper epidermis refers to a single layer of cells on the upper surface of the leaf, which aids the water conservation.

Lower Epidermis: Lower epidermis refers to a single layer of cells on the lower surface of the leaf, which contains stomata and guard cells.

Outermost Layer

Upper Epidermis: Upper epidermis is the uppermost layer of the leaf.

Lower Epidermis: Lower epidermis is the lowermost layer of the leaf.

Number of Stomata

Upper Epidermis: Upper epidermis contains a few stomata.

Lower Epidermis: Lower epidermis contains a large number of stomata.

Chloroplast

Upper Epidermis: Upper epidermis contains less number of chloroplasts since it contains less number of guard cells.

Lower Epidermis: Lower epidermis contains more chloroplasts than the upper epidermis.

Cuticle Layer

Upper Epidermis: Upper epidermis possesses a cuticle layer to eliminate the excess sunlight.

Lower Epidermis: Lower epidermis possesses a thin cuticle layer.

Role

Upper Epidermis: Upper epidermis is mainly involved in water conservation by eliminating excess sunlight.

Lower Epidermis: Lower epidermis is mainly involved in the gas exchange.

Conclusion

Upper and lower epidermis are the two outermost layers of the leaf. The upper epidermis contains a thick cuticle in order to prevent the water loss. The lower epidermis contains more stomata than the upper epidermis, facilitating the gas exchange. The main difference between upper and lower epidermis is their anatomy and physiology.

Reference:

1.“ Upper Epidermis of a Leaf: Function & Definition.” Study.com, Available here.
2.“Lower Epidermis of a Leaf: Function & Concept.” Study.com, Available here.

Image Courtesy:

1. “Leaf anatomy” By H McKenna – (CC BY-SA 2.5) via Commons Wikimedia
2. “Plant leaf epidermis (251 16) Lower epidermis of lime tree (Tilia)” By Doc. RNDr. Josef Reischig, CSc. – Author’s archive (CC BY-SA 3.0) via Commons Wikimedia