Living organisms are studying the science of biology. The structure of the plant root is considered in one of the sections of botany.
The root is the axial vegetative organ of the plant. It is characterized by unlimited apical growth and radial symmetry. The structural features of the root depend on many factors. This is the evolutionary origin of the plant, its belonging to a particular class, its habitat. The main functions of the root are plant strengthening in the soil, participation in vegetative propagation, supply and synthesis of organic nutrients. But the most important function that ensures the vital activity of the plant organism is soil nutrition, which is carried out in the process of active absorption from the substrate of water containing dissolved mineral salts.
Types of roots
The external structure of the root is largely due to what type it belongs to.
- The main root. Its formation comes from the germinal root, when the seed of the plant begins to germinate.
- Adnexal roots. They can appear on various parts of the plant (stem, leaves).
- Lateral roots. They form the branching, starting from previously appeared roots (main or subordinate).
Types of root systems
The root system is the community of all the roots that a plant has. Moreover, the appearance of this combination in different plants can vary greatly. The reason for this is the presence or absence, as well as a different degree of development and severity of various types of roots.
Depending on this factor, several types of root systems are distinguished.
- Rod root system. The name speaks for itself. The main root acts as a core. It is well expressed in size and length. The root structure of this type is characteristic of dicotyledonous plants. This is sorrel, carrots, beans, etc.
- The fibrous root system. This type has its own characteristics. The external structure of the root, which is the main one, is no different from that of the lateral ones. It does not stand out in the total mass. Formed from the germinal root, it does not grow very long. The urolithic root system is characteristic of monocotyledonous plants. These are cereals, garlic, tulip, etc.
- The mixed root system. Its structure combines the features of the two types described above. The main root is well developed and stands out against the general background. But at the same time, accessory roots are also highly developed. Characteristic for tomato, cabbage.
Historical Root Development
If we argue from the point of view of the phylogenetic development of the root, then its appearance occurred much later than the formation of the stem and leaf. Most likely, the impetus for this was the release of plants on land. In order to gain a foothold in a solid substrate, the representatives of the ancient flora needed something that could serve as a support. In the process of evolution, root-like underground branches first formed. Later they gave rise to the development of the root system.
Root case
The formation and development of the root system is carried out throughout the life of the plant. The structure of the root of the plant does not provide for the presence of leaves and buds. Its growth is carried out by increasing in length. At the growth point, it is covered with a root cap.
The growth process is associated with cell division of the educational tissue. It is she who is under the root cover, performing the function of protecting delicate dividing cells from damage. The case itself is a collection of thin-walled living cells in which the renewal process is constantly taking place. That is, when the root is advanced in the soil, the old cells gradually desquamate, and new ones grow in their place. Also located outside the case cells secrete a special mucus. It facilitates root advancement in a solid soil substrate.
It is well known that, depending on the habitat, the structure of plants varies greatly. For example, aquatic plants do not have a root cap. In the process of evolution, they formed another device - a water pocket.
Plant root structure: division zone, growth zone
Cells, emerging from educational tissue, begin to differentiate over time. Thus, root zones are formed.
Division zone. It is represented by cells of educational tissue, which subsequently give rise to all other types of cells. The size of the zone is 1 mm.
Growth area. It is represented by a smooth section, the length of which is from 6 to 9 mm. Follows immediately after the division zone. The cells are characterized by intensive growth, during which they are strongly extended in length, and gradual differentiation. It should be noted that the division process in this area is almost not carried out.
Suction zone
This section of the root, several centimeters in length, is also often called the zone of root hairs. This name reflects the structural features of the root in this area. There are outgrowths of skin cells, the size of which can vary from 1 mm to 20 mm. This is the root hairs.
The absorption zone is a place where active absorption of water is carried out, which contains dissolved minerals. The activity of root hair cells, in this case, can be compared with the operation of pumps. This process is very energy consuming. Therefore, the cells of the absorption zone contain a large number of mitochondria.
It is very important to pay attention to one more feature of root hairs. They are able to secrete a special mucus containing carbonic, malic and citric acids. Mucus promotes the dissolution of mineral salts in water. Particles of the soil, thanks to the mucus, seem to stick to the root hairs, facilitating the process of absorption of nutrients.
Root hair structure
The increase in the area of the absorption zone occurs precisely due to root hairs. For example, their number in rye reaches 14 billion, forming a total length of up to 10,000 kilometers.
The appearance of root hairs makes them look like a white fluff. They do not live long - from 10 to 20 days. It takes very little time for the plant organism to form new ones. For example, the formation of root hairs in young apple seedlings takes 30-40 hours. The area where these unusual outgrowths died out can still absorb water for some time, and then the cork covers it, and this ability is lost.
If we talk about the structure of the shell of the hair, then, first of all, it is necessary to highlight its subtlety. This feature helps the hair absorb nutrients. Its cell is almost completely occupied by a vacuole surrounded by a thin layer of cytoplasm. The core is located at the top. The space near the cell is a special mucous membrane that promotes gluing of root hairs with small particles of soil substrate. Due to this, the hydrophilicity of the soil increases.
The transverse structure of the root in the absorption zone
The zone of root hairs is also often called the zone of differentiation (specialization). This is no coincidence. It is here that in the cross section you can see a certain layering. It is due to the delimitation of layers within the root.
The table “The structure of the root in the cross section” is presented below.
| Layer | Structure, functions |
| Rhizoderma | One layer of integumentary tissue cells that are able to form root hairs. |
| Primary bark | Several layers of cells of the main tissue that are involved in the transport of nutrients from root hairs to the central axial cylinder. |
| Pericycle | Cells of educational tissue that are involved in the primary formation of lateral and adnexal roots. |
| Central axial cylinder | Conductive tissues (bast, wood), forming in their entirety a radial conductive beam. |
It should be noted that there is also a distinction within the cortex. Its outer layer is called the exoderm, the inner layer is the endoderm, and between them is the main parenchyma. It is in this intermediate layer that the process of directing solutions of nutrients to the vessels of wood occurs. Also, some vital substances for the plant are synthesized in the parenchyma. Thus, the internal structure of the root allows you to fully appreciate the significance and importance of the functions that each of the layers performs.
Holding area
Located above the suction zone. The longest and most durable root section. It is here that the movement of substances important for the life of the plant organism occurs. This is possible due to the good development of conductive tissues in this area. The internal structure of the root in the conduction zone determines its ability to transport substances in both directions. The upward current (upward) is the movement of water with mineral compounds dissolved in it. And down are delivered organic compounds that are involved in the vital activity of root cells. The area of conduct is the site of lateral root formation.
The structure of the root of the bean sprout clearly illustrates the main stages of the process of formation of the plant root.
Features of the structure of the plant root: the ratio of ground and underground parts
Many plants are characterized by such a development of the root system, which leads to its predominance over the ground part. An example is headed cabbage, the root of which can grow 1.5 meters deep. Its width can be up to 1, 2 meters.
The root system of the apple tree grows so much that it occupies a space whose diameter can reach 12 meters.
And in the alfalfa plant, the height of the ground part does not exceed 60 cm. While the root length can be more than 2 meters.
All plants living in areas with sandy and rocky soils have very long roots. This is due to the fact that in such soils, water and organic matter are very deep. In the process of evolution, the plants adapted to such conditions for a long time, and the structure of the root gradually changed. As a result, they began to reach the depth where the plant organism can stock up with the substances necessary for growth and development. So, for example, the root of a camel spine can be 20 meters deep.
Wheat root hairs branch so strongly that their total length can reach 20 km. However, this is not a limit. Unlimited apical root growth in the absence of strong competition with other plants can increase this value by several times.
Root Modifications
The root structure of some plants can change, forming the so-called modifications. This is a kind of adaptation of plant organisms in specific living conditions. Below is a description of some of the modifications.
Root tubers are characteristic of dahlia, chistyak and some other plants. They are formed due to thickening of the accessory and lateral roots.
Ivy and campsys are also distinguished by structural features of these vegetative organs. They have so-called trailing roots that allow them to cling to nearby plants and other supports that are within their reach.
Aerial roots, characterized by a long length and absorbing water, are found in monstera and orchids.
Vertically growing respiratory roots are involved in the breathing function. There are cypress bog, willow brittle.
Some representatives of the flora, forming a separate group of parasite plants, have devices that help penetrate into the stem of the host. These are the so-called sucker roots. Characteristic for white mistletoe, dodder.
Such vegetable crops as carrots, beets, radishes, have root crops, which were formed due to the growth of the main root, inside which nutrients are stored.
Thus, the structural features of the root of the plant, leading to the formation of modifications, depend on many factors. The main ones are habitat and evolutionary development.