This is a complete explanation of the epidermal tissue starting from the meaning, function, characteristics, and structure of the tissue.
Definition of Epidermis
The epidermis is the tissue found in the plant body which is located on the outside. Epidermal tissue plays a role to cover all parts of the plant body from roots, stems, to leaves. Usually, this section contains only two layers of cells that are flat and tightly shaped.
For your information, the word epidermis comes from the Greek, where epi means above or covers and derma means skin. This tissue usually consists of rows of single cells that protect and cover the entire young plant body. In general, the function of the epidermis is as a protector.
In addition, this network also serves as a place of exchange of substances. It should be noted that the location of the epidermal tissue is on the upper and lower surfaces of the leaves. The leaf epidermis does not have chloroplasts except for the stomata guard cells.
Epidermal Tissue Function
Previously we have explained that the function of the epidermis is to protect the tissues that are in it. In addition, the epidermal tissue also serves as a place of exchange of substances. This tissue also functions as a protector when there is loss of water caused by evaporation, mechanical damage such as being trampled, or due to changes in temperature and also loss of various nutrients due to rain, wind, and so on.
However, the cells present in the epidermis sometimes have special functions and characteristics related to the main function of the covered organ. Epidermal tissue can develop and then be modified to form root hairs, spina, and also cover cells in the stomata. Like the skin of the human body, the epidermis in plants is the main protection from physical damage and pathogenic organisms .
At the top of the leaf surface, there is an epidermis that functions to form a thick layer called the cuticle layer, for example, found in banana leaves and taro leaves. Then there are those who have fine hairs like those found in durian leaves. Leaf mouths or stomata are modifications of the epidermis for gas exchange.
Then on the epidermis of the stem, there is a section that forms a thick layer and a layer of hair or trichomes. This layer also serves as protection. For the root epidermis, some are modified to become root hairs. This root hair will absorb salt water and minerals.
Characteristics of the Epidermis
Below are the characteristics of the epidermis that you need to know:
- Composed of living cells
- Does not have chlorophyll
- There is only 1 single cell layer
- They vary in size, shape, and arrangement, but are usually tightly packed and do not have intercellular spaces
- The outer epidermal cell wall adjacent to the air will experience thickening. Meanwhile, for the inner epidermal cell walls that are adjacent to other tissues, the cell walls will remain thin
Epidermal Tissue Structure
Epidermal tissue structure consists of tightly packed cells without intercellular spaces. These cells are also thin-walled and extend parallel to the root axis. The cell wall is composed of pectin and cellulose which functions to absorb water. When the epidermis peels off because it is old, the cell wall will be thickened with suberin and cutin.
Absorption occurs at the tip of the root. In the epidermis layer (outer surface) will form a bulge in the form of hair and root hairs. The cells will form root hairs that are on the back that cover the entire area or can be up to several centimeters.
After knowing what the epidermis is, its functions, characteristics, and structure, other information that we will explain is about epidermis derivatives. Epidermal derivatives or modifications are additional tools or structures that exist in the epidermis. Although derived from the epidermis, in fact these additional tools have functions that are not the same and even opposite to the function of the epidermis itself.
The various types of epidermal derivatives include the following:
Stomata are gaps in the epidermis that are bounded by two guard cells in which there are chloroplasts. Its function and shape is opposite to that of the epidermis. The functions of the stomata are:
- As a way of respiration or breathing
- As a way of entry of carbon dioxide or CO2 from the air that occurs in the process of photosynthesis
- As a way of transpiration or evaporation
Trichomes are hairs that have one or many cells originating from epidermal cells. These cells have larger and denser structures like spines or warts. Trichomes are composed of epidermal cells or tissues in the epidermis (emergency). There are several types of trichomes, namely:
- Trichomes that do not produce secretions or are non-glandular
- Trichomes that produce secretions or glands
Meanwhile, the functions of the trichomes are as follows:
- The function of the trichomes on the leaves is to reduce the occurrence of evaporation, disturbances from animals and humans, and to function as a continuation of the stimulus
- In nectarines or flowers, it functions to secrete honey, attract insects, and help in the pollination process
- The function of the trichomes in seeds is to prevent insects that will damage the seeds, absorb water so that it accelerates the growth process to become sprouts
- Meanwhile, the function of the trichomes on the stem is to reduce evaporation and to climb (in rattan and cactus).
Litokis is the part that is located in the epidermis of Ficus. Litocysts have centripetal thickenings composed of cellulose stalks with deposits or depositions. Carbonate that has a honeycomb shape is called systolite.
4. Fan Cell
Fan cells or also called buliform cells have a large size when compared to epidermal cells. These cells have a fan-like shape and have tipped walls and have large vacuoles. The walls are composed of pectin and cellulose. The outer wall is covered by cuticle and contains cutin.
When the air is hot, the water in the fan cell will evaporate. Then the cells will shrink, causing the upper surface area of the leaf to be smaller than the lower surface area. This causes the leaves to curl and reduces further evaporation.
5. Lenti Sel
In some plants there are spots on the surface of the stem. These spots are called lenti cells. Lenti cells occur when the surface of the stem contains a stoma. When the stoma is no longer functioning, it has a different function and becomes lenti cells or cork pores.
Velamen are dead cells present in the epidermis of aerial roots and hanging roots in orchid plants. Velamen function to store air and water. There are those who argue that the epidermis with velamen as a double epidermis or multiple epidermis.
7. Water Parenkin
Water parenchyma are several layers of cells in the inner epidermis of leaves in xerofia plants. This layer is composed of large cells with thin walls and a large central vacuole. In xerofia plants, parenkin is used to store water. The epidermis and water parenchyma are called double epidermis.
8. Silica Cells and Cork Cells
These two cells are successively formed in pairs along the length of the leaf. The fully expanded silica cell contains silica bodies in the form of an isotropic silica mass with microscopic granules in the center. Meanwhile, the cork cell walls contain suberin and dense organic matter.