Works describing animal and plant tissues appeared in the 17th century. The first botanists-anatomists - Gru and Malpighi - investigated the most important of them, and also introduced such concepts as prosenchyma and parenchyma. In general, biology deals with the study of structures. Fabrics have differences in composition, tasks, origin. Next, we consider in more detail the main features of these structures. The article will present a table of plant tissues. In it you can see the main categories of structures, their location and tasks.
Biology: tissues. Classification
The scheme for the division of structures in accordance with physiological tasks was developed by Haberlandt and Schwendener at the turn of the 19th-20th centuries. Plant tissues are groups of elements that have the same origin, homogeneous composition and perform the same task. Structures are classified according to different criteria. For example, plant tissues include:
- Main.
- Conductive.
- Meristems (educational).
- Integuments.
- Excretory.
- Mechanical.
If plant tissues consist ofcells that have more or less the same structure and tasks, they are called simple. If the elements are not the same, then the whole system is called complex or complex. Types of plant tissue of one category or another are divided, in turn, into groups. For example, educational structures include:
- Apical.
- Lateral - secondary (phellogen, cambium) and primary (pericycle, procambium).
- Wound.
- Insert.
Types of plant tissue of the main type include storage and assimilation parenchyma. Phloem (bast) and xylem (wood) are considered conductive structures.
Integumentary (borderline) plant tissues:
- External: secondary (periderm), primary (epiderm), tertiary (rhytidoma, or crust); velamen, rhizoderma.
- Internal: exo- and endoderm, parietal cells from vascular leaf bundles.
Mechanical structures (skeletal, supporting) are divided into sclerenchyma (sclereids, fibers), collenchyma. And the last group is the excretory (secretory) tissues of the plant organism.
Educational Structures: Overview
These plant tissues (meristems) are groups of constantly young, actively dividing cells. They are located on the growth sites of various organs. For example, they can be found on the tops of stems, the tips of roots, and other places. Due to the presence of a plant cell in this tissue, there is a continuous growth of the culture and the formation of permanentelements and bodies.
Features of the meristem
Depending on the location of the educational tissue of the plant cell, it can be apical (apical), lateral (lateral), intercalary (intercalary), wound. Structures are also divided into secondary and primary. The latter include the apical types of plant tissue. These structures determine the growth of culture in length. In higher low-organized plants (ferns, horsetails), the apical meristems are weakly expressed. They are represented by only one initial, or initial cell. In angiosperms and gymnosperms, the apical meristems are quite well expressed. They are represented by many initial cells that form growth cones. Lateral structures are usually secondary. Thanks to them, the growth of roots, stems (axial organs as a whole) in thickness is carried out. Lateral types of plant tissue are phellogen and cambium. Thanks to the activity of the first, cork is formed in the roots and stems. This group also includes ventilation fabric - lentils. The lateral meristem, like the cambium, forms the structural elements of bast and wood. In unfavorable life periods of plants, the activity of the cambium slows down or completely stops. Intercalated meristems are usually primary. They are preserved as separate patches in areas of active growth: at the base of the internodes and petioles of cereal leaves, for example.
Integumentary structures
Functions of plant tissues of thisgroups are to protect the culture from the adverse effects of environmental factors. Negative influences, in particular, should be considered excessive evaporation, solar overheating, drying wind, mechanical damage, penetration of bacteria and pathogenic fungi. There is primary and secondary integumentary tissue. The first category includes epiblema and skin (epidermis). Phelloderma, cork cambium, cork are considered secondary integumentary tissues.
Features of structures
All organs of annual plants are covered with skin, green shoots of perennial tree crops in the current growing season, in general, herbaceous above-ground parts of plantations. The latter, in particular, are leaves, flowers, stems.
Structure of plant tissues: epidermis
As a rule, it consists of one layer of closed structural elements. In this case, there is no intercellular space. The epidermis is quite easily removed and is a transparent thin film. This is a living tissue, which includes a gradual layer of protoplast with a nucleus and leukoplasts, a large vacuole. The latter occupies almost the entire cell. The outer wall of the structural elements of the epidermis is thicker, while the inner and lateral walls are thin. The latter have pores. The main task of the epidermis is the regulation of transpiration and gas exchange. It is carried out to a greater extent through the stomata. Inorganic compounds and water penetrate through the pores. In different plants, epidermal cells differ in size and shape. Many monocot crops have structural elements that are elongated in length. Most dicot plantations have winding sidewalls. This increases the density of their connection with each other. The structure of the epidermis in the upper and lower parts of the leaf is different. There are more stomata below than above. Aquatic plants with leaves floating on the surface (water lilies, capsules) have their own characteristics. Their stomata are present only on the upper part of the plate. But in plants completely submerged in water, these formations are absent.
Stoma
These are highly specialized formations in the epidermis. The stomata consist of 2 guard cells and a gap - the formation between them. Structural elements have a crescent shape. They regulate the size of the slit formation. It, in turn, can close and open in accordance with the turgor pressure in the closing elements, depending on the concentration of carbon dioxide in the atmosphere and other factors. During the day, stomatal cells take part in photosynthesis. During this period, turgor pressure is high, and the slit-like formation is open. At night, on the contrary, it is closed. This phenomenon is observed both in dry times and with wilting of leaves. It is due to the ability of stomata to store moisture inside.
Basic Structures
The parenchyma occupies most of the space between other permanent tissues in the stem, roots and other plant organs. The main structures are predominantly composed of living elements that have a variety of forms. Cells may be thin-walled, but sometimes thickened,lignified, with simple pores, parietal cytoplasm. The parenchyma consists of the pulp of leaves and fruits, the core of rhizomes and stems, their bark. There are several subgroups of this tissue. So, among the main structures are: air-bearing, aquifer, storage and assimilation. The function of plant tissues in this category is to store nutrient compounds.
Chlorophyllon-bearing parenchyma
Chlorenchyma - assimilation tissue - the structure in which photosynthesis takes place. Its elements are distinguished by thin walls. They contain a nucleus and chloroplasts. The latter, like the cytoplasm, are located in the wall. Chlorenchyma is located directly under the skin. It is mainly concentrated in green young shoots and leaves.
Aerenchyma
Air-bearing tissue is a structure with sufficiently developed intercellular spaces in various organs. Most of all, it is characteristic of swampy, aquatic and coastal aquatic crops, whose roots are in oxygen-poor silt. Air reaches the lower organs with the help of transmission organs. In addition, communication between the intercellular spaces and the atmosphere is carried out through peculiar pneumatodes. Due to aerenchyma, the specific gravity of the plant decreases. This, apparently, explains the ability of aquatic crops to maintain an upright position, and leaves - to be on the surface.
Aquifer
This fabric retains moisture in the stems and leaves of succulent plants and crops in saline areas. The first, for example, include cacti, fat women, agave, aloe and others. To the second- comb, sarsazan, hodgepodge and others. This tissue is well developed in sphagnum moss.
Storage structures
In these tissues, at a certain point in the development of culture, metabolic products begin to be deposited. These are, in particular, fats, carbohydrates and others. Cells in storage tissue are usually thin-walled. The structure is widely represented in root thickenings, bulbs, tubers, stem cores, germs, endosperm and other areas.
Mechanical covers
Supporting fabrics act as a kind of reinforcement or "stereo" (from the Greek. "solid", "durable"). The main task of structures is to provide resistance to dynamic and static loads. In accordance with this, tissues have a certain structure. In terrestrial crops, they are more developed in the axial section of the shoot - the stem. Cells can be located along the periphery, separate areas or a solid cylinder.
Collenchyma
It is a simple primary supporting tissue with living cellular content: cytoplasm, nucleus, sometimes chloroplasts. There are three categories of collenchyma: loose, lamellar and angular. Such a classification is carried out in accordance with the nature of the thickening of the cells. If it is in the corners, then the structure is angular, if it is parallel to the surface of the stem and fairly evenly, then this is a lamellar collenchyma. The tissue is formed from the main meristem and is located under the epidermis at a distance of one or more layers from it.
Sclerenchyma
This mechanical fabric is considered quite common. It consists of structural elements with lignified and evenly thickened walls and a small amount of slit-like pores. Cells in sclerenchyma are elongated in length, they are characterized by a prosenchymal shape with pointed ends.
Conductive structures
These tissues provide the transport of nutrient compounds. It is carried out in two directions. The transpiration (ascending) current of aqueous solutions and s alts goes through the tracheids and vessels from the roots to the leaves along the stem. Assimilation (descending) movement occurs from the upper parts to the underground through special sieve tubes of the phloem. The conductive tissue can be compared in some way to the human circulatory system, as it has a radial and an axial network. Nutrients penetrate every cell in the body.
Excretory fibers
Secretory tissues are special formations that have the ability to secrete or isolate in themselves a drop-liquid medium and metabolic products. The latter are called secrets. If they leave the plant, then external secretion tissues are involved in this, and if they remain inside, then internal structures are involved, respectively. The formation of liquid products is associated with the activity of membranes and the Golgi complex. Secrets of this type are designed to protect plants from destruction by animals, damage by pathogens or insects. Intrasecretorystructures are presented in the form of resin ducts, idioblasts, essential oil channels, lactifers, receptacles for secretions, glands and others.
Table of Plant Tissues
| Name | Location | Functions |
| Apical | Root tips (growth cones), shoot points | Growth in the length of organs due to cell division, the formation of tissues of the root, leaves, stem, flowers |
| Side | Between wood and bast roots and stems | Stem and root growth in thickness; cambium deposits wood cells inside and bast outward |
| Skin (epidermis) | Covering the leaves, green stems, all parts of the flower | Protection of organs from fluctuations in temperature, drying out, damage. |
| Cork | Covering overwintering tubers, stems, roots, rhizomes | |
| Crust | Covering the underside of tree trunks | |
| Vessels | Xylem (wood) running along the veins of leaves, roots, stems | Carrying water and minerals from soil to root, stem, leaves, flowers |
| Sieve tubes | Phloem (bast), located along the veins of the leaves, root, stem | Holding organiccompounds in root, stem, flowers from leaves |
| Vascular fibrous bundles | The central cylinder of the stem and root; flower and leaf veins | Carrying on wood mineral compounds and water; on the bast - organic products; strengthening organs, uniting them into a single whole |
| Mechanical | Around the vascular fibrous vascular bundles | Strengthening organs through scaffolding |
| Assimilation | Green stems, leaf pulp. | Gas exchange, photosynthesis. |
| Reserve | Roots, fruits, tubers, bulbs, seeds | Storage of proteins, fats, etc. (starch, sugar, fructose, glucose) |
