Plant tissue. Types of Plant Tissue

The works describing animal and plant tissue appeared in the XVII century. The first anatomical botanists - Gru and Malpigi - studied the most important of them, and also introduced concepts such as prozenchyme and parenchyma. In general, biology is engaged in 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: tissue. Classification

The structure separation scheme 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 of the same origin, homogeneous composition and perform one task. Classification of structures is carried out according to different criteria. For example, plant tissues include:

• The main ones.
• Conductive.
• Meristem (educational).
• Coverslips.
• Excreting.
• Mechanical.

If plant tissues are composed of cells with more or less the same structure and tasks, then 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 (pellogen, cambium) and primary (pericycle, procambium).
• Wounded.
• Insertion.

Types of plant tissue of the main species include storage and assimilation parenchyma. Conducting structures are considered phloem (bast) and xylem (wood).

Cover (border) plant tissue:

• External: secondary (periderm), primary (epidermis), tertiary (ritidum, or peel); velamen, rhizoderma.
• Internal: exo- and endoderm, parietal cells from conducting bundles of leaves.

Mechanical structures (skeletal, supporting) are divided into sclerenchyma (scleroids, fibers), collenchyma. And the last group is the excretory (secretory) tissue of the plant organism.

Educational Structures: General

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 on the tops of stems, tips of roots and other places. Due to the presence of a plant cell in this tissue, there is a continuous growth of culture and the formation of permanent elements and organs.

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), and wound. Also, the structures are divided into secondary and primary. The latter include apical types of plant tissue. These structures determine the growth of culture in length. In higher low-organized plants (ferns, horsetails), apical meristems are characterized by weak severity. They are represented by only one initial or initial cell. In angiosperms and gymnosperms, apical meristems are quite well expressed. They are represented by many of the initial cells that form the growth cones. Lateral structures are usually secondary. Thanks to them, the roots, stems (axial organs as a whole) grow in thickness. Lateral types of plant tissue are pellogen and cambium. Thanks to the activity of the former, cork is formed in the roots and stems. This group also includes aeration tissue - lentils. Lateral meristem, like cambium, structural elements of bast and wood are formed. In adverse life periods of plants, a slowdown or complete cessation of cambium activity occurs. Insertion meristems are usually primary. They are preserved as separate sites in areas of active growth: at the base of internodes and petioles of cereal leaves, for example.

Cover structures

The functions of plant tissues of this group are to protect the culture from the adverse effects of environmental factors. Negative effects, in particular, should be considered excessive evaporation, solar overheating, drying wind, mechanical damage, penetration of bacteria and pathogenic fungi into the interior. There is primary and secondary integumentary tissue. The first category includes the epiblema and the skin (epidermis). Secondary integumentary tissues are the felloderma, cork cambium, and cork.

Structural Features

All organs in annual plants are covered with peel, in perennial woody crops in the current growing season - green shoots, in general, on plantations - grassy aboveground parts. The latter, in particular, are leaves, flowers, stems.

Plant tissue structure: epidermis

Its composition, as a rule, includes one layer of closed structural elements. In this case, the intercellular space is absent. The epidermis is quite easy to remove and is a transparent thin film. This is living tissue, which includes a gradual layer of protoplast with a core and leukoplasts, a large vacuole. The latter occupies almost the entire cell. The outer wall of the structural elements of the epidermis is more thickened, and the inner and side 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 the pores. In different plants, epidermal cells differ in size and shape. Many monocotyledonous cultures have structural elements elongated in length. Most dicotyledonous plantations have winding side walls. 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. Water plants with leaves floating on the surface (water lilies, egg 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.

Stomata

These are highly specialized formations in the epidermis. The stomata consist of 2 closing cells and a gap - the formation between them. Structural elements have a lunar shape. They regulate the size of the slit-like formation. It, in turn, can be closed and opened 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. On the contrary, it is closed at night. This phenomenon is noted in dry times, and with wilting leaves. It is due to the ability of stomata to store moisture inside.

Main structures

The parenchyma occupies most of the space between other permanent tissues in the stem, roots and other organs of plants. The main structures mainly consist of living elements having various forms. Cells can be found thin-walled, but sometimes thickened, lignified, with simple pores, and a wall cytoplasm are also found. The parenchyma consists of the pulp of leaves and fruits, the core of rhizomes and stems, their bark. There are several subgroups of this fabric. So, among the main structures distinguish: air-bearing, water-bearing, storage and assimilation. The functions of plant tissues in this category are to store nutrient compounds.

Chlorophyll-bearing parenchyma

Chlorenchyma - assimilation tissue - the structure in which photosynthesis occurs. Its elements are distinguished by thin walls. They have a core and chloroplasts. The latter, like the cytoplasm, are located gradually. Chlorenchyma is located directly under the skin. Mostly it is concentrated in green young shoots and leaves.

Aerenhima

The air-bearing tissue is a structure with sufficiently developed intercellular spaces in various organs. Most of all, it is characteristic of marshy, aquatic and coastal-aquatic crops, whose roots are in oxygen-poor silt. Air reaches the lower organs using the transmission organs. In addition, communication between the intercellular spaces and the atmosphere is carried out by means of peculiar pneumatic ducts. Due to aerenchyma, the specific gravity of the plant is reduced. This, apparently, explains the ability of aquatic crops to maintain a vertical position, and leaves - to be on the surface.

Aquifer structure

This fabric retains moisture in the stems and leaves of succulent plants and crops in saline areas. The first, for example, include cacti, crassulaceae, agave, aloe and others. To the second - comb, sarsazan, hodgepodge and others. This fabric 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. This, 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 core, seed germ, endosperm and other areas.

Mechanical cover

Supporting tissues act as a kind of reinforcement or "stereo" (from the Greek. "Solid", "durable"). The main objective of the structures is to provide resistance to dynamic and static loads. In accordance with this, the 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 on the periphery, in separate areas, or in a continuous cylinder.

Collenheim

It is a simple primary supporting tissue with living cellular contents: cytoplasm, nucleus, and sometimes chloroplasts. Three categories of collenchyma are distinguished: loose, lamellar and angular. This classification is carried out in accordance with the nature of the thickening of cells. If it is in the corners, then the structure is angular, if parallel to the surface of the stem and evenly enough, then this is a plate-like collenchyma. Formed tissue from the main meristem and is located under the epidermis at a distance of one or more layers from it.

Sklerenheim

This mechanical tissue is considered quite common. It consists of structural elements with lignified and uniformly thickened walls and slit-like pores in small quantities. The cells in the sclerenchyma are elongated in length, they are characterized by a prosenchymal shape with pointed ends.

Conductive structures

These tissues transport nutrients. It is carried out in two directions. The transpiration (ascending) current of aqueous solutions and salts 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-shaped tubes of the phloem. Conductive tissue can be compared in some way with the circulatory system of people, since it has radial and axial networks. Nutrients enter every cell in the body.

Excretory fiber

Secretory tissues are special formations with the ability to excrete or isolate droplet-liquid medium and metabolic products. The latter are called secrets. If they leave the plant, then external secretion tissues participate, and if they remain inside - accordingly, internal structures participate. 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. Intra-secretory structures are presented in the form of resinous passages, idioblasts, essential oil channels, lactis, receptacles for secretions, glands and other things.

Plant tissue table