Just like animals, plants have different tissues in their bodies. Organs are built from them, which, in turn, form systems. The structural unit as a whole is still the same - the cell.
However, the tissues of plants and animals differ from each other both in structure and in their functions. Therefore, let's try to figure out what these structures are in representatives of the flora. Let's take a closer look at what the mechanical tissue of plants is.
Plant tissues
In total, 6 groups of tissues in the plant body can be distinguished.
- Educational includes wound, apical, lateral and insertion types. Designed to restore the structure of plants, various types of growth, takes part in the formation of other tissues, forms new cells. Depending on the function performed, it becomes clear where the areas with the educational tissue will be localized: leaf petioles, internodes, root tip, upper part of the stem.
- The main one consists of different types of parenchyma (columnar, air-bearing, spongy, storage, aquifer), as well as the photosynthetic part. The function matches the name:storage of water, accumulation of reserve nutrients, photosynthesis, gas exchange. Localization in leaves, stems, fruits.
- Conductive tissues - xylem and phloem. The main purpose is the transportation of minerals and water to the leaves and stem and the return delivery of nutrient compounds to the places of accumulation. They are located in the vessels of wood, specialized cells of the bast.
- Integumentary tissues include three main varieties: cork, crust, epidermis. Their role is primarily protective, as well as transpiration and gas exchange. Location in the body of the plant: the surface of the leaves, bark, root.
- Excretory tissues produce juice, nectars, metabolic products, moisture. They are located in specialized structures (nectaries, lactifers, hairs).
- The mechanical tissue of plants, its structure and functions will be discussed in more detail below.
Mechanical fabrics: general characteristics
Complex and heterogeneous weather conditions, climatic catharsis, not always mild changes in nature - from all this a person is protected by a home. And often it is plants that become such a refuge for animals. And who will save them? What makes them able to withstand heavy winds, earthquakes, volcanic eruptions and hail, snowfalls and tropical downpours? It turns out that the structure included in the composition - mechanical fabric - helps them survive.
This structure is not always evenly distributed in the same plant. Also, its content is not the samedifferent representatives. But to one degree or another, everyone has it. The mechanical tissue of plants has its own special structure, classification and functions.
Functional relevance
One name of this structure speaks of the role and importance it has for plants - mechanical strength, protection, support. Often, mechanical fabric is equated with reinforcement. That is, it is a kind of skeleton, a skeleton that gives support and strength to the entire plant organism.
These functions of mechanical tissue are extremely important. Due to their presence, the plant is able to endure the strongest bad weather, while maintaining the integrity of all parts. You can often see how the trees sway from strong gusts of wind. However, they do not break, showing miracles of plasticity and strength. This is due to the fact that the mechanical properties of tissues work. You can also see the stability of shrubs, tall grasses, semi-shrubs, small trees. They are all held up like stoic tin soldiers.
Of course, this is explained by the structural features of cellular structures and varieties of mechanical tissues. You can divide them into groups.
Classification
There are three main types of such structures, each of which has its own structural features of the mechanical tissue.
- Collenchyma.
- Sclerenchyma.
- Sclereids (often considered part of sclerenchyma).
Each of the listed tissues can be formed fromprimary and secondary meristem. All mechanical tissue cells have thick, strong cell walls, which largely explains the ability to perform the listed functions. The contents of each cell can be either alive or dead.
Collenchyma and its structure
The evolution of this type of structure comes from the basic tissues of plants. Therefore, collenchyma most often contains the pigment chlorophyll and is capable of photosynthesis. This tissue is formed only in young plants, lining their organs immediately under the cover, sometimes a little deeper.
A prerequisite for collenchyma is cell turgor, only in this case it is able to perform the functions of reinforcement and support assigned to it. Such a state is possible, since all cells of this tissue are alive, growing and dividing. The shells are very thickened, but pores remain through which moisture is taken and a certain turgor pressure is set.
Also, the structure of mechanical tissues of this type implies several types of cell articulation. On this basis, it is customary to distinguish three types of collenchyma.
- Plate. Cell walls are thickened fairly evenly, arranged tightly to each other, parallel to the stem. Elongated in shape (an example of a plant containing this type of tissue is the sunflower).
- Angular collenchyma - shells are thickened unevenly, in the corners and in the middle. These parts interlock with each other, forming small spaces (buckwheat, pumpkin, sorrel).
- Loose - the name speaks for itself. The cell walls are thickened, but their connection- with large intercellular spaces. Often performs a photosynthetic function (belladonna, coltsfoot).
Once again, it should be pointed out that collenchyma is the tissue of only young, one-year-old plants and their shoots. The main places of localization in the body of the plant are petioles and main veins, in the stem on the sides in the form of a cylinder. This mechanical tissue contains only living, non-lignified cells that do not interfere with the growth of plants and their organs.
Performed functions
In addition to photosynthesizing, one can also call the support function as the main one. However, it does not play such a big role in this as sclerenchyma. Nevertheless, the tensile strength of collenchyma is comparable to the strength of metals (aluminum, for example, and lead).
In addition, the functions of this type of mechanical tissue are also explained by the ability to form secondary lignified shells in old plant organs.
Sclerenchyma, cell types
Unlike collenchyma, the cells of this tissue most often have lignified membranes, strongly thickened. Living content (protoplast) dies over time. Often the cell structures of sclerenchyma are impregnated with a special substance - lignin, which increases their strength many times over. The fracture strength of sclerenchyma is comparable to that of structural steel.
The main types of cells that make up such a tissue are as follows:
- fiber;
- Sclereids;
- structures that make up conductive tissues, xylem and phloem - bast fibers andwood (libriform).
Fibers are elongated and pointed upwards prosenchymal structures with strongly thickened and lignified shells, very few pores. They are localized at the end of plant growth processes: internodes, stem, central part of the root, petioles.
Bast and wood fibers are of great importance as accompanying conductive tissues surrounding them.
The peculiarities of the structure of the mechanical tissue of sclerenchyma are that all cells are dead, with a well-formed woody membrane. All together they give colossal resistance to plants. Sclerenchyma is formed from the primary meristem, cambium and procambium. It is localized in trunks (stems), petioles, roots, pedicels, receptacle, stalks and leaves.
Role in the plant organism
The function of the mechanical tissue of sclerenchyma is obvious - providing an integral strong framework with sufficient strength, elasticity and strength to withstand dynamic and static influences from the mass of the crown (for trees) and natural disasters (for all plants).
The function of photosynthesis for sclerenchyma cells is uncharacteristic due to the death of their living contents.
Sclereids
These structural elements of mechanical tissue are formed from ordinary thin-walled cells by the gradual death of the protoplast, sclerification (lignification) of the membranes and their multiple thickening. Such cells develop in two ways:
- frommain meristem;
- from the parenchyma.
You can verify the strength and rigidity of sclereids by marking the places of their localization in plants. They make up nut shells, fruit pits.
The shape of these structures can be very different. So, allocate:
- short rounded stony cells (brachysclereids);
- branched;
- strongly elongated - fibrous;
- osteosclereids - shaped like human tibia bones.
Often such structures are found even in the pulp of fruits, which protects them from being eaten by various birds and animals. Sclereids of all types make up the features of mechanical tissues, help them perform support functions.
Value for plants
The role of such cells is not only in reinforcing functions. Sclereids also help plants:
- protect seeds from temperature extremes;
- avoid fruit damage by bacteria and fungi, as well as animal bites;
- to form, in combination with other mechanical tissues, a full-fledged stable mechanical framework.
Presence of mechanical tissues in different plants
The distribution of these types of tissues is not the same in different representatives of the flora. So, for example, the least sclerenchyma contains lower aquatic plants - algae. After all, for them the function of support is played by water, its pressure.
Also not too woody and stock uplignin tropical plants, all representatives of wet habitats. But the inhabitants of arid conditions acquire mechanical tissues to the maximum. This is reflected in their ecological name - sclerophytes.
Collenchyma is more typical for annual dicotyledonous representatives. Sclerenchyma, on the contrary, is mostly formed in monocotyledonous perennial grasses, shrubs and trees.
