The structure of the root of the plant. Features of the structure of the root
Living organisms are studied by the science of biology. The structure of the root of the plant is considered in one of the sections of botany.
The root is an axial vegetative organplants. It is characterized by unlimited apical growth and radial symmetry. Features of the structure 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 include strengthening the plant in the soil, participating in vegetative propagation, stock and synthesis of organic nutrients. But the most important function ensuring 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 is.
- The main root. Its formation comes from the germinal root, when the seed of the plant begins to germinate.
- Complementary roots. They can appear on different parts of the plant (stem, leaves).
- Lateral roots. They form branches, starting from the previously appeared roots (main or subordinate).
Types of root systems
The root system is a community of all roots thatare present in the plant. In this case, the appearance of this set in different plants can vary greatly. The reason for this is the presence or absence, as well as the varying degrees of development and severity of different types of roots.
Depending on this factor, several types of root systems are distinguished.
- Core root system. The name speaks for itself. The main root acts as a rod. It is well expressed in size and length. The structure of the root for this type is characteristic of dicotyledons. This is sorrel, carrots, beans, etc.
- Uterine root system. For this type of characteristic features. The external structure of the root, which is the main, does not differ from that of the lateral ones. It does not stand out in the general mass. Formed from the embryonic root, it does not grow very long. The urinary root system is characteristic of monocotyledonous plants. These are cereals, garlic, tulip, etc.
- Root system of mixed type. 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, the subordinate roots are also highly developed. It is typical for a tomato, cabbage.
Historical development of the root
If to argue from the point of view of phylogeneticroot development, then its appearance occurred much later than the formation of the stem and leaf. Most likely, the push for this was the emergence of plants on land. In order to gain a foothold in a solid substrate, 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.
Formation and development of the root systemis 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 kidneys. Its growth is due to an increase in length. At the point of growth, it is covered with a root sheath.
The growth process is associated with cell divisioneducational tissue. It is under the root sheath, which performs the function of protecting delicate dividing cells from damage. The case itself is a collection of thin-walled living cells, in which the process of renewal is constantly taking place. That is, with the progress of the root in the soil, the old cells gradually slough off, and new ones grow in their place. Also located outside the cage cells give off a special mucus. It facilitates the progress of the root in a solid soil substrate.
It is generally known that depending on the environmentthe structure of plants is very different. For example, aquatic plants do not have a root cap. In the process of evolution, they formed another device - a water pocket.
The structure of the root of the plant: the zone of division, the zone of growth
Cells, emerging from the educational tissue, eventually become differentiated. Thus, the root zones are formed.
The division zone. It is represented by cells of the educational tissue, which subsequently give rise to all other types of cells. The size of the zone is 1 mm.
The zone of growth. It is represented by a smooth section, the length of which is from 6 to 9 mm. It follows immediately behind the division zone. Cells are characterized by intensive growth, during which they are strongly extended in length, and gradual differentiation. It should be noted that the process of division in this zone is almost not carried out.
This part of the root is severalcentimeters are also often called the zone of root hairs. This name reflects the features of the structure 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 suction zone is the place where theactive absorption of water, which contains dissolved mineral substances. The activity of cells of the root hairs, in this case, can be compared with the operation of pumps. This process is very energy-consuming. Therefore, cells of the suction zone contain a large number of mitochondria.
It is very important to pay attention to one morefeature of root hairs. They are able to release a special mucus containing coal, malic and citric acids. Slime promotes dissolution of mineral salts in water. Particles of the soil due to mucus like glued to the root hairs, facilitating the absorption of nutrients.
Structure of the root hair
The increase in the area of the suction zone occurs precisely due to the root hairs. For example, their quantity in rye reaches 14 billion, forming a total length of up to 10,000 kilometers.
The appearance of the root hairs makes them look likeon a white fluff. They do not live long - from 10 to 20 days. The formation of new plants in the plant takes very little time. For example, the formation of root hairs in young seedlings of apple trees takes place within 30-40 hours. The site where these unusual outgrowths have died out can still suck up water for some time, and then it is covered by a cork, and this ability is lost.
If we talk about the structure of the hairscap, then,First of all, it is necessary to distinguish its subtlety. This feature helps the hair to absorb nutrients. Its cell is almost entirely 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 slimy cover, which helps to glue root hairs with small particles of soil substrate. Due to this, the hydrophilicity of the soil rises.
The transverse structure of the root in the suction zone
The zone of root hairs is also often called the zonedifferentiation (specialization). This is not accidental. It is here on the cross-section that you can see a certain layering. It is caused by the differentiation of the layers inside the root.
The table "Root structure on a transverse section" is presented below.
|Rhizoderma||One layer of cells of the integumentary tissue that are capable of forming root hairs.|
|Primary cortex||Several layers of cells of the main tissue that are involved in the transport of nutrients from the root hairs to the central axial cylinder.|
|Pericycles||Cells of the educational tissue that participate in the primary formation of lateral and accessory roots.|
|Central Axial Cylinder||Conductive tissues (bast, wood), forming in their totality a radial conductive bundle.|
It should be noted that inside the crust there is alsodistinction. Its outer layer is called the exoderm, the inner one 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 takes place. Also, in the parenchyma, some organic substances vital for the plant are synthesized. Thus, the internal structure of the root allows us to fully appreciate the significance and importance of the functions that each layer performs.
Area of conduction
Located above the suction zone. The largest and the most durable part of the root. It is here that the movement of substances important for the life of the plant organism takes place. This is possible due to the good development of conductive tissues in this zone. The internal structure of the root in the conduction zone determines its ability to transport substances in both directions. On the ascending current (upward) there is a movement of water with mineral compounds dissolved in it. And organic compounds that participate in the vital functions of the root cells are delivered downward. The zone of holding is the place of formation of lateral roots.
The structure of the root of the bean sprout clearly illustrates the main stages of the process of root plant formation.
Features of the structure of the root of the plant: the ratio of ground and underground parts
For many plants this development is typicalThe root system, which leads to its predominance over the terrestrial part. An example can serve as cabbage, the root of which in depth can grow by 1.5 meters. Its width can be up to 1, 2 meters.
The root system of the apple tree grows so much that it takes up space, the diameter of which 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 sandy areasand rocky soils, have very long roots. This is due to the fact that in such soils water and organic substances are very deep. During the evolution of plants for a long time adapted to such conditions, 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's thorn can be 20 meters deep.
The root hairs of wheat branch so muchIt is strong that their total length can reach 20 km. However, this is not a limiting value. Unlimited apical root growth in the absence of strong competition with other plants can increase this value several times more.
Modifications of roots
The structure of the root of some plants can vary,forming the so-called modifications. This is a kind of adaptation of plant organisms in specific habitats. Below is a description of some of the modifications.
Root tubers are characteristic for dahlia, a cleaner and some other plants. They are formed due to the thickening of the accessory and lateral roots.
Ivy and kampsis also differ in their characteristicsstructure of these vegetative organs. They have so-called root-hooks, which allow them to cling to a number of standing plants and other supports that are in their reach.
Air roots, which are very long and absorb water, are found in monsters and orchids.
Growing upwardly upward respiratory roots participate in the function of breathing. There are cypress marsh, willow and brittle.
Some representatives of the flora that forma separate group of plant parasites, there are devices that help penetrate the host's stem. These are the so-called sucker roots. Characteristic for the mistletoe of white, dodder.
In vegetable crops such as carrots, beets, radishes, there are root crops, which are formed by the growth of the main root, inside which nutrients are stored.
Thus, the features of the structure of the root of the plant, leading to the formation of alterations, depend on many factors. The main habitat and evolutionary development.