Almost all multicellular living organisms are composed of various types of tissues. This is a collection of cells that are similar in structure, united by common functions. They are not the same for plants and animals.
Diversity of tissues of living organisms
First of all, all tissues can be divided into animal and vegetable. They are different. Let's take a look at them.
What can animal tissue be like?
Animal tissues are of the following types:
- nervous;
- muscular;
- epithelial;
- connective.
All of them, except for the first one, are divided into types. Muscle tissue is smooth, striated and cardiac. Epithelial is divided into single-layer, multilayer - depending on the number of layers, as well as cubic, cylindrical and flat - depending on the shape of the cells. Connective tissue combines such types as loose fibrous, dense fibrous, reticular, blood and lymph, adipose, bone and cartilage.
Diversity of plant tissues
Plant tissues are of the following types:
- main;
- integumentary;
- conductive fabric;
- mechanical;
- educational.
All types of plant tissues combine sever altypes. So, the main ones include assimilation, storage, aquifer and air. Integumentary tissues combine such types as bark, cork and epidermis. Conductive tissues include phloem and xylem. Mechanical is divided into collenchyma and sclerenchyma. Educational include lateral, apical and insertion.
All tissues perform certain functions, and their structure corresponds to the role they perform. This article will discuss 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 types is different. Let's talk more about the two types of conductive fabrics.
Functions of conductive tissues
Their main role is the transport of substances. However, the functions of conductive tissues that are not of the same species differ.
The role of xylem is to carry chemical solutions from the root up to all other plant organs.
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. The conductive tissue of this type consists of two different conductive elements: tracheids and vessels. It also includes mechanical elements - wood fibers, and the main elements- wood parenchyma.
How are xylem cells arranged?
The cells of the conductive tissue are divided into two types: tracheids and vascular segments. A tracheid is a very long cell with intact 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 vascular segments. These cells are located one above the other. Through holes are located at the junctions of the segments of the same vessel. They are called perforations. These holes 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, the nucleus, organelles and cell membrane). There are no protoplasts, because 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 neighboring conductive elements.
The walls of the conductive elements have thickenings that give the cage strength. Depending on the type of these thickenings, the conductive elements are divided into spiral, annular, ladder, mesh and point-pore.
Functions of mechanical and basic elements of xylem
Wood fibersalso 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 wood parenchyma. These are cells with lignified shells, in which simple pores are located. However, at the junction of the parenchyma cell with the vessel, there is a fringed pore that connects to its simple pore. Wood parenchyma cells, unlike vascular cells, are not empty. They have protoplasts. The xylem parenchyma performs a reserve function - nutrients are stored in it.
How does the xylem of different plants differ?
Since tracheids in the process of evolution arose much earlier than vessels, these conductive elements are also present in lower land plants. These are spores (ferns, mosses, club mosses, horsetails). Most gymnosperms also possess only tracheids. However, some gymnosperms also have vessels (they are present in the gneatids). Also, as an exception, these elements are present in some ferns and horsetails.
But angiosperms (flowering) plants all have both tracheids and vessels.
What is phloem?
The conductive tissue of this type is also called bast.
The main part of the phloem - sieve 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 conductivetissues of this type lie in the fact that the cells of the sieve elements, unlike the conductive elements of the xylem, remain alive.
Structure of sieve elements
There are two types: sieve cells and sieve tubes. The former are elongated and have pointed ends. They are permeated with 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 spores and gymnosperms.
In angiosperms, the conducting 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, there are no nuclei in the mentioned structural units of multicellular conducting elements, but they still remain alive. An important role in the structure of the phloem of angiosperms is also played by satellite cells located next to each cell-segment of sieve elements. Companions contain both organelles and nuclei. They are metabolized.
Given that phloem cells are alive, this conductive tissue cannot function for a long time. In perennial plants, its life span is three to four years, after which the cells of this conductive tissue die.
Additional phloem elements
In addition to sieve cells or tubes, this conductive tissue also containsbasic fabric elements and mechanical elements. 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. It, like the xylem parenchyma, performs a reserve role. It stores substances such as tannins, resins, etc. These phloem elements 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 conducting elements: sieve tubes.
Structure of the conducting system of a plant
Xylem and phloem are always located side by side 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 collaterals. They are arranged in such a way that the phloem lies on one side of the xylem.
There are also concentric bundles. In them, one conductive tissue surrounds another. They are divided into two types: centrophloem and centroxylem.
The conductive tissue of the root usually has radial bundles. In them, the xylem rays depart from the center, and the phloem is located between the xylem rays.
Collateral bundles are more characteristic of angiosperms, and concentric bundles are more characteristic of spore and gymnosperms.
Conclusion: comparison of two types of conductive fabrics
As a conclusion, we present a table that summarizes the basic data on two types of conductive plant tissues.
| Xylem | Phloem | |
| Building | Consists of conductive elements (tracheas and vessels), wood fibers and wood parenchyma. | Consists of conductive elements (sieve cells or sieve tubes), phloem fibers and phloem parenchyma. |
| Features of conducting cells | Dead cells lacking plasma membranes, organelles and nuclei. They have an elongated shape. They are located one above the other and do not have horizontal partitions. | Living nuclear-free cells with a large number of through holes in their walls. |
| Additional items | Wood parenchyma and wood fibers. | Phloem parenchyma and phloem fibers. |
| Functions | Carrying substances dissolved in water up: from the root to the plant organs. | Transport of chemical solutions down: from the ground organs of plants to the root. |
Now you know everything about the conductive tissues of plants: what they are, what functions they perform and how their cells are arranged.
