The evolution of the animal and plant world gradually led to the complication of their organization. Therefore, the modern variety of species is so great that it simply amazes the imagination. The increasing complexity of the internal structure is reflected in every evolutionary branch.
This especially affected plants that were able to transform from lower underwater species to higher representatives settled throughout the globe, having a complex internal and external structure. A major role in this was played by the development of special structures - tissues, which make up the bulk of the individuals of this kingdom.
Meristems: definition and concept
In total, five main types of tissue of plant organisms can be distinguished. Among them are the following:
- meristems, or educational tissues;
- stocking;
- conductive;
- mechanical;
- the main ones.
Each of them has a special structure, various types of cells, and performs a certain important function in the life of the plant. Educational tissue deserves special attention, because it is it that gives rise to almost everything else and provides the main distinguishing feature of plants from other living organisms - unlimited growth throughout life.
If you give a more accurate biological definition of this type of tissue, it will sound like this: educational tissue, or meristem, is the general name for a special type of tissue that consists of cells active throughout life, constantly dividing and providing growth and development of the plant as a whole.
In addition, it is meristems that give rise to many other types of tissues in the body. For example, mechanical, conductive, integumentary and other. Due to them, the wounded areas are healed on the plant body, and the lost structures (leaves, parts of the stem, root) are quickly restored. It is safe to say that educational tissue is one of the most important, which allows plants to exist. Therefore, its structure and functions will be considered in more detail.
Educational tissue cells. general information
Two main types of cells that make up the meristems can be distinguished:
- Polygonal, or isodiametric. They contain a very large core, which occupies almost the entire internal space. They have ribosomes, mitochondria, and small vacuoles scattered throughout the cytoplasm. The shell is quite thin. Between themselves are located quite friable. Such cells form eumeristems. They give rise to all types of tissues, except conductive.
- Prosenchymal cells. On the contrary, they have very large vacuoles filled with cell sap. Between themselves are connected more densely, the shape is elongated, cubic or prismatic. The educational tissue built from them gives rise to conductive systems, cambium and procambium plants.
Thus, depending on the type of cells that form the tissue, the function it performs is also determined.
Two more types of meristem cells can also be distinguished:
- Initial - actively dividing cells throughout life, ensuring the accumulation of the total mass of educational tissue. They also give rise to another group.
- Derived cells - may differ from the previous ones in shape, size, number of vacuoles and other parameters.
These types of structures in some plant species may generally be indistinguishable, at least morphologically.
In general, the structure of educational tissue allows us to distinguish several types that make up its classification.
Meristem classification
The basis can be put several different signs. The first of these is the morphology of the cells that make up the tissue. According to this feature, they distinguish:
- lamellar meristems - cells of a cubic shape with a single-layer membrane forming integumentary tissue;
- columnar educational tissue - form the core of stems and tree trunks, prismatic cells with a dense shell;
- massive meristems - give rise to growth in thickness, represented by polygonal cells.
The next sign for classification is the ability to differentiate into other structures. On this basis, all meristems can be divided into six groups:
- Embryonic educational tissue. Her name speaks for itself. Forms the primary tissue of the embryo.
- Apical meristems, also called apical. Form: procambium, epidermis, conductive tissue, parenchyma.
- Wound educational tissue. They are formed at the sites of damage and provide quick restoration of the lost organ or healing of the wound.
- Intercalary - provide insert growth of plants in height and width.
- Lateral or lateral - provide a thickening of the axial structures of the body due to the deposition of cambium or pellogen.
- Marginal meristem - it is she who forms the sheet canvas.
The last classification by which all meristems can be divided into two groups is genetic. According to it they are divided into:
- primary - associated with germinal and apical tissues;
- secondary - cambium, procambium and others.
Obviously, various signs of classification confirm the importance of the structures in question, especially their role in plant life.
Plate meristem
This is an educational tissue whose functions are to form the epidermis of a plant. It is lamellar meristems that create integumentary tissues that protect the body from external influences, maintain a certain shape and structure.
Cells of lamellar educational tissue are located in one row, very intensively divided, and perpendicular to the working body. As a result, the external epidermis of the plant is formed.
Columnar fabric
Another name for these fabrics is core. They received it for its elongated prismatic shape of the cells that make up the structure of the cells, which are located closely with each other and have a fairly thick shell.
Columnar tissue gives rise to and completely forms the core of the stems and trunks of plants. Cells of this tissue also divide perpendicular to the axial organs.
Massive meristems. a brief description of
Features of the educational tissue, which is called massive, is that it allows the plant to accumulate a mass of undifferentiated cells, which lead to a thickening and growth of mass. In this case, this happens quite evenly.
In the future, each part of the cell mass is transformed into a particular tissue, that is, it specializes and will fulfill its function. Thus, for example, sporangium and other tissues are formed.
Functions of the educational tissue of plants
The role played by the meristems is enormous. You can identify several basic most important functions that perform the tissue in question:
- Provide the plant unlimited growth throughout life.
- They give rise to differentiation and specialization of all other types of tissues in the body.
- Provide the normal development of plants.
- Eliminate damage and restore lost structures.
However, the main function of the educational tissue is to repeatedly divide the cells and accumulate them in large mass for the possibility of constant use by parts of the plant, and therefore, to maintain its growth and activity throughout life. It is for this reason that there are no such tissues in the body of animals and humans. After all, they grow only to genetically determined (originally laid down in the genome) sizes.
Apical meristem
This educational tissue, the functions and structure of which we will consider, is one of the most important of all types of meristems. There are a number of reasons for this.
- It is the apical tissue that is also called apical tissue, since after the development of the embryo it remains in the growth cone (top of the shoot).
- The apical meristem allows the stem and roots to grow in length.
- Over time, it is the apical tissue that is transformed into the floral and meristem of the inflorescence, allowing flowers to form with all its parts.
- It gives rise to all other types of educational tissues.
Therefore, we are talking about a high degree of significance of the apical meristems in plant life.
This type of fabric has several derivatives that it forms in the body of the plant. They are as follows:
- integumentary tissue;
- protoderm;
- procambium;
- conductive tissue;
- basic;
- massive.
Along with the apical, lateral or lateral meristems are also significant. They give rise to cambium and pellogen, form the so-called annual rings, which are clearly visible on transverse sections of stems and trunks.
Primary educational tissue
These include those that are first laid in the body of the embryo. First of all, it is the meristem of the embryo and apical (apical). Some of them persist throughout life, while others die off, forming the primary body of the plant.
Since we have already examined the apical meristems in more detail above, it makes no sense to repeat everything again. Primary tissues are apical educational structures.
Secondary meristems
This group includes a massive meristem, which allows the plant to increase mass at later stages of development. This is an educational tissue, the functions of which are mainly in the formation of thickenings of the axial organs of plants.
A special role in this is played by cambium and pellogen. Most often, secondary meristems come into effect after the apical growth of the plant ends, but there are exceptions. As, for example, in the case of cambium.
Also important is the value of wound meristems, which lead to the formation of callus - the mass of cells. They tighten the place of injury or damage to the plant.