Difference Between Guard Cell and Epidermal Cell

Main Difference – Guard Cell  and Epidermal cell

Guard cell and epidermal cell are two types of cells found in the epidermis of plants. The epidermis is originated from the dermal tissue of plants, bringing the contact of the plant with the external environment. It is the outer layer of leaves, stems, and roots of the plant. Guard cells contain chloroplasts and are capable of carrying out photosynthesis. But epidermal cells do not contain chloroplasts. The main difference between guard cell and epidermal cell is their role; two guard cells form a stoma, controlling the gas exchange of the plant by regulating the size of the stoma whereas epidermal cells provide a protection to the plant from the external environment.

This article explains,

1. What is a Guard Cell
     – Definition, Characteristics, Function
2. What is an Epidermal Cell
     – Definition, Characteristics, Function
3. What is the difference between Guard Cell and Epidermal Cell

What is a Guard Cell

Guard cells are specialized cells found in the epidermis of leaves and stems of plants. They promote the gas exchange of plants with the external environment, forming a stoma. Two guard cells are involved in the formation of the stoma. The opening and closing of the stomatal pore are regulated by the turgidity of the guard cells. When water is available, guard cells become turgid and the stomatal pore is opened. But, when water is not available, turgidity of guard cells is reduced, shrinking the cell, which leads to the closing of the stomatal pore. The opening of the stomatal pore allows the exchange of gasses like carbon dioxide, oxygen, and moisture. When water is available, the stomatal pore allows the carbon dioxide to enter the plant leaf. When carbon dioxide is available to photosynthesizing cells, they initiate photosynthesis and the produced oxygen and moisture are removed via stomal pores.

Since the opening and closing of stomal pores are regulated by the turgor pressure of guard cells, this turgor pressure should be regulated in order to regulate the pore size depending on the plant’s needs. The regulation of the turgor pressure of guard cells is achieved by the controlling movement of ions and sugars into and out of the cells. Potassium and chloride ions are mainly involved in the regulation of the turgor pressure of guard cells. Other than the gas exchange, guard cells are involved in the photosynthesis by bearing chloroplasts in the cells. Guard cells are the only cells involved in photosynthesis in the epidermis.

Figure 1: Opening and closing of stoma 

What is an Epidermal Cell

Epidermal cells are the cells found in the outermost layer of plants. Epidermal cells are irregular in shape and tightly bound to each other in order to provide the mechanical support to the plant. They are the least specialized cells found in large numbers. Most plants contain a single layer of epidermal cells in their epidermis. The cell walls of the epidermal cells consist of cutin, preventing the water loss from plant body. Epidermal cells are covered with a cuticle layer as well. Sometimes, the cuticle is covered with wax, giving a bluish or whitish color to the plants surface. The wax layer also protects plants from extreme sunlight and the wind. The cuticle layer is thinner on the underside of the leaf than the upper side. However, epidermal cells do not contain chloroplasts; thus, it cannot play any role in the photosynthesis. Epidermal cells in roots are involved in the absorption of water and ions from soil. These cells contain special structures like hairs and they do not have a cuticle layer. Plant leaf epidermis is shown in figure 2. Guard cells are shown in green color and the rectangular-shaped cells are the epidermal cells.

Figure 2: Plant leaf epidermis 

Difference Between Guard Cell and Epidermal Cell

Function

Guard Cell: A pair of guard cells form a stoma, which is involved in the gas exchange of plants with the near atmosphere.

Epidermal Cell: Epidermal cells provide a protection to the plant from the external environment.

Shape

Guard Cell: Guard cell is bean-shaped in monocots and dumbbell-shaped in dicots.

Epidermal Cell: Epidermal cells are rectangular or tubular-shaped.

Size

Guard Cell: Guard cell is small.

Epidermal Cell: Epidermal cell is large.

Chloroplasts

Guard Cell: Guard cell consists of chloroplasts.

Epidermal Cell: Epidermal cell lacks chloroplasts.

Cell Wall

Guard Cell: Inner cell wall of the guard cell is thicker than the outer cell wall of guard cells.

Epidermal Cell: The outer cell wall is thicker than the inner cell wall of epidermal cells.

Origin

Guard Cell: Guard cells are differentiated from epidermal cells.

Epidermal Cell: Epidermal cells are differentiated from protoderm.

Location

Guard Cell: Guard cells are found in the epidermis of leaves and stems.

Epidermal Cell: Epithelial cells are found in the epidermis of leaves, stems, and roots.

Cutin

Guard Cells: No cutin is found in guard cells.

Epidermal Cells: Cutin is found in the cell wall of the epidermal cells.

In Roots

Guard Cells: No guard cells are found in roots.

Epidermal Cells: Epidermal cells in root are involved in the water and ion absorption from the soil.

Conclusion

Guard cells and epidermal cells are two types of parenchyma cells found in the epidermis. Guard cells regulate the size of the stoma, which in turn regulate the gas exchange of plants with the external environment and the amount of the water loss from plants. Hence, the exchanging gasses are carbon dioxide, oxygen, and moisture. Guard cells possess chloroplasts, involved in the photosynthesis as well. Epidermal cells are living cells covering the outside surface of the herbaceous plants. They contain a thick covering of cutin, which reduces the water loss from plants. Epidermal cells in roots are specialized for water and ion absorption. Thus, the main difference between guard cell and epidermal cell is their roles and functions.

Reference:
1. Lawson, Tracy. “Guard cell photosynthesis and stomatal function.” New Phytologist. Blackwell Publishing Ltd, 03 Dec. 2008. Web. 11 Apr. 2017.
2. “The Epidermal Tissue System of Plants (With Diagrams).” Biology Discussion. N.p., 16 Oct. 2015. Web. 11 Apr. 2017.
3. “Plant Cells, Tissues, and tissue systems.” Plant Cells. N.p., n.d. Web. 11 Apr. 2017.

Image Courtesy:
1.” Opening and Closing of Stoma” By Ali Zifan – Own work; Used information from:Campbell Biology (10th Edition) by: Jane B. Reece & Steven A. Wasserman.and [1]., (CC BY-SA 4.0) via Commons Wikimedia
2. “Stomata” by ACJ1 (CC BY-SA 2.0) via Flickr