Almost all multicellular living organisms are composed of various types of tissue. This is a collection of cells similar in structure, united by common functions. For plants and animals, they are not the same.
A variety of tissues of living organisms
First of all, all tissues can be divided into animal and vegetable. They are different. Let's look at them.
What can be animal tissue?
Animal tissues are of the following types:
- Nervous
- muscle
- epithelial;
- connecting.
All of them, except the first, are divided into types. Muscle tissue is smooth, striated, and cardiac. Epithelial is divided into single-layer, multi-layer - depending on the number of layers, as well as cubic, cylindrical and flat - depending on the shape of the cells. Connective tissue combines such species as loose fibrous, dense fibrous, reticular, blood and lymph, fat, bone and cartilage.
Plant tissue variety
Plant tissues are of the following types:
- main;
- coverslip;
- conductive fabric;
- mechanical;
- educational.
All types of plant tissues combine several types. So, the main ones are assimilation, storage, water-bearing and air-bearing. Integumentary tissues combine such species as cortex, cork and epidermis. Conductive tissue includes phloem and xylem. Mechanical is divided into collenchyma and sclerenchyma. Educational ones include lateral, apical and insertive.
All tissues perform certain functions, and their structure corresponds to the role that they perform. This article will examine in more detail the conductive tissue, the structural features of its cells. We will also talk about its functions.
Conductive fabric: structural features
These tissues are divided into two types: phloem and xylem. Since they are both formed from the same meristem, they are located next to each other in the plant. However, the structure of the conductive tissues of the two species is different. Let's talk more about the two types of conductive tissue.
Conductive tissue functions
Their main role is the transport of substances. However, the functions of conductive tissues belonging to more than one species differ.
The role of xylem is carrying out solutions of chemicals from the root up to all other organs of the plant.
And the function of the phloem is to conduct solutions in the opposite direction - from certain organs of the plant along the stem down to the root.
What is xylem?
It is also called wood. Conductive tissue of this species consists of two different conductive elements: tracheid and blood vessels. Also, its composition includes mechanical elements - wood fibers, and the main elements - wood parenchyma.
How are xylem cells arranged?
Conducting tissue cells are divided into two types: tracheids and segments of blood vessels. A tracheid is a very long cell with undisturbed walls, in which there are pores for the transport of substances.
The second conductive element of the cell - the vessel - consists of several cells, which are called segments of the vessels. These cells are located one above the other. Through the joints of the segments of the same vessel are through holes. They are called perforations. These openings are necessary for the transport of substances through the vessels. The movement of various solutions through the vessels is much faster than through the tracheids.
The cells of both conductive elements are dead and do not contain protoplasts (protoplasts are the contents of the cell, with the exception of the cell wall, that is , it is the nucleus, organoids and cell membrane). There are no protoplasts, since if they were in the cell, the transport of substances through it would be very difficult.
Through vessels and tracheids, solutions can be transported not only vertically, but also horizontally - to living cells or adjacent conductive elements.
The walls of the conductive elements have thickenings that give the cell strength. Depending on the type of these thickenings, the conductive elements are divided into spiral, ring, stair, mesh and pore-pore.
The functions of the mechanical and basic elements of xylem
Wood fibers are also called librioform. These are elongated cells that have thickened lignified walls. They perform a supporting function that ensures the strength of the xylem.
Elements of the main tissue in the xylem are represented by wood parenchyma. These are cells with lignified membranes in which simple pores are located. However, at the junction of the parenchyma cell with the vessel, there is a bordered pore, which connects to its simple pore. Wood parenchyma cells, unlike vascular cells, are not empty. They have protoplasts. The xylem parenchyma performs a reserve function - it stores nutrients.
What is the difference between xylem of different plants?
Since tracheids in the process of evolution arose much earlier than blood vessels, these conductive elements are also present in lower terrestrial plants. This is a spore (ferns, mosses, crowns, horsetails). Most gymnosperms also have only tracheids. However, some gymnosperms also have vessels (they are present in oppressive ones). Also, as an exception, these elements are present in some ferns and horsetails.
But angiosperms (flowering) plants all have tracheids and vessels.
What is phloem?
Conductive tissue of this species is also called bast.
The main part of the phloem is sieve-like conductive elements. Also in the structure of the bast there are mechanical elements (phloem fibers) and elements of the main tissue (phloem parenchyma).
Features of the conductive tissue of this species are that the cells of the sieve elements, in contrast to the conductive elements of the xylem, remain alive.
The structure of sieve elements
There are two types: sieve cells and sieve tubes. The former are elongated and have pointed ends. They are penetrated by through holes, through which the transport of substances occurs. Sieve cells are more primitive than multicellular sieve elements. They are characteristic of plants such as spore and gymnosperms.
In angiosperms, conductive elements are represented by sieve tubes, consisting of many cells - segments of sieve elements. The through holes of two adjacent cells form sieve plates.
Unlike sieve cells, in the mentioned structural units of multicellular conducting elements there are no nuclei, but they still remain alive. An important role in the structure of the phloem of angiosperms is also played by companion glue, located next to each cell-segment of sieve elements. Companions have both organoids and nuclei. They have a metabolism.
Given that the phloem cells are living, this conductive tissue cannot function for long. In perennial plants, the period of its life is three to four years, after which the cells of this conductive tissue die.
Additional phloem elements
In addition to sieve cells or tubes, elements of the main tissue and mechanical elements are also present in this conductive tissue. The latter are represented by bast (phloem) fibers. They perform a supporting function. Not all plants have phloem fibers.
Elements of the main tissue are represented by phloem parenchyma. She, like the xylem parenchyma, plays a backup role. It contains substances such as tannins, resins, etc. These elements of the phloem are especially developed in gymnosperms.
Phloem of various plant species
In lower plants, such as ferns and mosses, it is represented by sieve cells. The same phloem is characteristic of most gymnosperms.
Angiosperms have multicellular conductive elements: sieve tubes.
The structure of the plant conductive system
Xylem and phloem are always located nearby and form bundles. Depending on how the two types of conductive tissue are located relative to each other, several types of bundles are distinguished. The most common are collateral. They are arranged in such a way that the phloem lies on one side of the xylem.
There are also concentric beams. In them, one conductive tissue surrounds another. They are divided into two types: centrofloemic and centroxylem.
The conductive root tissue usually has radial bundles. In them, the rays of xylem depart from the center, and the phloem is located between the rays of xylem.
Collateral bundles are more characteristic for angiosperms, and concentric ones for spore and gymnosperms.
Conclusion: a comparison of two types of conductive tissue
As a conclusion, we present a table in which the main data on two types of conductive plant tissues are abbreviated.
Conductive plant tissue | Xylem | Phloem |
| Structure | It consists of conductive elements (trachea and blood vessels), wood fibers and wood parenchyma. | It consists of conductive elements (sieve cells or sieve tubes), phloem fibers and phloem parenchyma. |
| Conducting Cell Features | Dead cells that do not have plasma membranes, organoids, and nuclei. They have an elongated shape. They are located one above the other and do not have horizontal partitions. | Live nuclear-free cells, in the walls of which there are a large number of through holes. |
| Additional items | Wood parenchyma and wood fibers. | Phloem parenchyma and phloem fibers. |
| Functions | Carrying substances dissolved in water up: from the root to the organs of plants. | Transportation of chemical solutions down: from the ground organs of plants to the root. |
Now you know everything about the conducting tissues of plants: what they are, what functions they perform and how their cells are arranged.