Department Angiosperms (Flowering) plants
OPTION 1
For each task, choose one correct answer from the four proposed.
A1. The generative organ of angiosperms is
2) stem
3) flower
A2. One of the essential features of angiosperms, which is unique to this group of plants, is
1) presence of flowers
2) propagation by seeds
3) soil nutrition
4) carrying out photosynthesis in the light
AZ. Vessels in flowering plants are formed by tissue cells
1) cover
2) conductive
3) storage
4) mechanical
A4. A modified shoot of a flowering plant is
3) flower
4) stem
A5. The ovules of flowering plants are located in
1) sepals
2) pistil ovary
3) corolla petal
4) anther stamen
A6. Develops from the fertilized egg of flowering plants
1) filament
2) seed embryo
3) stigma
4) sperm
A7. After double fertilization in flowering plants, the ovule develops
1) seed
4) inflorescence
B1.
A. The root system of flowering plants includes the main, lateral and adventitious roots.
B. Leaves on tropical flowering plants persist throughout the life of the plant.
1) Only A is correct
2) Only B is correct
3) Both judgments are correct
4) Both judgments are incorrect
B2. Choose three true statements. Traits of monocots
1) one cotyledon per seed
2) parallel veining of leaves
3) reticulate venation of leaves
4) tap root system
5) fibrous root system
6) five-membered flower
BZ. Establish a correspondence between the family of flowering plants and its class.
PLANT FAMILY
A, Cereals
B. Rosaceae
B. Legumes
G. Liliaceae
D. Solanaceae
FLOWER CLASS
1) Monocots
2) Dicotyledons
B4.
2) Psilophytes (the first land plants)
3) Algae
4) Flowering plants
5) Ferns
Answer: 3, 2, 5, 1, 4.
IN 1. Assignment to work with picture 3.
A. Which family does the flowering plant shown in Figure 3 belong to?
1) Cereals
2) Legumes
3) Liliaceae
4) Cruciferous
B.
1) reticulate venation
2) parallel veining
3) compound sheet
4) round shape
IN.
1) single flowers
2) the presence of an inflorescence
3) bright corolla
4) juicy fruits
OPTION 2
A1. The ovule of angiosperms is located
1) on the reverse side of the sheet
2) under the bark of the stem
3) in the ovary of the pistil
4) at the top of the shoot
A2. The thickness of the tree trunk in flowering plants is determined by the functioning
3) cambium
4) cores
AZ. As a result of the division of cambium cells in the stem, the formation of
3) cores
4) tree rings
A4. The main parts of a flower include
1) pestle
3) cup
4) receptacle
A5. A flower that contains a pistil and a stamen is called
1) pistillate
2) staminate
3) same-sex
4) bisexual
A6. Spermine, which is formed from
1) pollen grain
2) stigma
3) corolla petals
4) filament
A7. In the seeds of flowering plants, the endosperm is
1) embryo
3) water supply
4) supply of nutrients
B1. Are the following statements true?
A. A poplar shoot consists of a stem, leaves and buds.
B. Self-pollination occurs between two flowers of plants of the same species.
1) Only A is correct
2) Only B is correct
3) Both judgments are correct
4) Both judgments are incorrect
B2. Choose three true statements. Signs of dicotyledonous plants
1) arc venation of leaves
2) reticulate venation of leaves
3) two cotyledons in the seed
4) fibrous root system
5) tap root system
6) the number of flower parts is a multiple of three
BZ. Establish a correspondence between the type of plant and the class to which it belongs.
PLANT TYPE
A. Homemade apple tree
B. Potatoes
B. Rye
G. Leek
D. White cabbage
FLOWER CLASS
1) Monocots
2) Dicotyledons
Write down the corresponding numbers in the table.
B4. Establish the sequence of stages of evolution in the plant world.
1) Ferns
2) Multicellular algae
3) Psilophytes (the first land plants)
4) Flowering plants
Answer: 5, 2, 3, 1, 6, 4.
IN 1. Assignment to work with picture 4.
A. What family does the flowering plant shown in the picture belong to?
1) Cereals
2) Legumes
3) Rosaceae
4) Compositae
B. Features of the structure of the leaves of this plant
1) arc venation
2) parallel veining
3) reticulate venation
4) needle shape
IN. Characteristics of the generative organs of this plant
1) the number of flower parts is a multiple of three
2) the number of flower parts is a multiple of five
3) simple perianth
4) the rim is missing
Textile- a group of cells that are structurally and functionally interconnected with each other, similar in origin, structure and performing certain functions in the body.
Tissues arose in higher plants in connection with their access to land and reached the greatest specialization at angiosperms, in which up to 80 species are distinguished. The most important plant tissues:
Educational,
Integumentary,
Conductive,
Mechanical
Basic.
Fabrics can be simple and complex. Plain fabricsconsist of one type of cell (for example, collenchyma, meristem), andcomplex- from cells of different structures that perform, in addition to basic functions, additional functions (epidermis, xylem, phloem, etc.).
Educational fabrics, or meristems, are embryonic tissues. Thanks to their long-lasting ability to divide (some cells divide throughout life), meristems participate in the formation of all permanent tissues and thereby form the plant, and also determine its long-term growth.
The cells of educational tissue are thin-walled, multifaceted, tightly closed, with dense cytoplasm, a large nucleus and very small vacuoles. They are capable of dividing in different directions.
According to the origin of meristems, there are primary and secondary. The primary meristem is the embryo of the seed, and in an adult plant it remains at the tip of the roots and tips of the shoots, which makes it possible for them to grow in length. Further growth of the root and stem in diameter (secondary growth) is ensured secondary meristems- cambium and phellogen. Based on their location in the plant body, apical (apical), lateral (lateral), intercalary (intercalary) and wound (traumatic) meristems are distinguished.
Integumentary tissues located on the surface of all plant organs. They perform a mainly protective function - they protect plants from mechanical damage, penetration of microorganisms, sudden temperature fluctuations, excessive evaporation, etc. Depending on their origin, three groups of integumentary tissues are distinguished - epidermis, periderm and crust.
Epidermis (epidermis, skin)- primary integumentary tissue located on the surface of leaves and young green shoots (Fig. 8.1). It consists of a single layer of living, tightly packed cells that do not have chloroplasts. The cell membranes are usually tortuous, which ensures their strong closure. The outer surface of the cells of this tissue is often covered with a cuticle or waxy coating, which is an additional protective device. The epidermis of leaves and green stems contains stomata that regulate transpiration and gas exchange in the plant.
Periderm- secondary integumentary tissue of stems and roots, replacing the epidermis in perennial (less often annual) plants (Fig. 8.2.). Its formation is associated with the activity of the secondary meristem - phellogen (cork cambium), the cells of which divide and differentiate in the centrifugal direction (outward) into the cork (phellema), and in the centripetal direction (inward) - into a layer of living parenchyma cells (phelloderm). Cork, phellogen and phelloderm make up the periderm.
Rice. 8.1. Leaf epidermis of various plants: a-chlorophytum; 6 - common ivy: in - fragrant geranium; G - white mulberry; 1- epidermal cells; 2 - stomatal guard cells; 3 - stomatal fissure.
Figure 8.2. Periderm of elderberry stem (a - cross section of a shoot, b - lentils): I-performing fabric; 2 - remnants of the epidermis; 3 -cork (phellema); 4 - phellogen; 5 - phelloderm.
The cells of the cork are impregnated with a fat-like substance - suberin - and do not allow water and air to pass through, so the contents of the cell die and it fills with air. The multilayer cork forms a kind of stem cover that reliably protects the plant from adverse environmental influences. For gas exchange and transpiration of living tissues lying under the plug, the latter has special formations - lentils; These are gaps in the plug filled with loosely arranged cells.
Crust formed in trees and shrubs to replace cork. In the deeper tissues of the cortex, new areas of phellogen are laid down, forming new layers of cork. As a result, the outer tissues are isolated from the central part of the stem, deformed and die. On the surface of the stem, a complex of dead tissues gradually forms, consisting of several layers of cork and dead sections of bark. A thick crust provides more reliable protection for the plant than cork.
Conductive fabrics ensure the movement of water and nutrients dissolved in it throughout the plant. There are two types of conductive tissue - xylem (wood) and phloem (bast).
Xylem is the main water-conducting tissue of higher vascular plants, ensuring the movement of water with minerals dissolved in it from the roots to the leaves and other parts of the plant (ascending current). It also performs a supporting function. The xylem consists of tracheids and tracheae (vessels) (Fig. 8.3), wood parenchyma and mechanical tissue.
Tracheids They are narrow, highly elongated dead cells with pointed ends and lignified membranes. The penetration of solutions from one tracheid into another occurs by filtration through pores - recesses covered with a membrane. Liquid flows through the tracheids slowly, since the pore membrane prevents the movement of water. Tracheids are found in all higher plants, and in most horsetails, club mosses, ferns and gymnosperms they serve as the only conducting element of the xylem. Angiosperms have vessels along with tracheids.
Figure 8.3. Elements of xylem (a) and phloem (6): 1-5 - ringed, spiral, scalariform and porous (4, 5) trachea, respectively; 6 - ringed and porous tracheids; 7 - sieve tube with companion cell.
Trachea (vessels)- these are hollow tubes consisting of individual segments located one above the other. In the segments, through holes are formed on the transverse walls - perforations, or these walls are completely destroyed, due to which the speed of the flow of solutions through the vessels increases many times over. The shells of the vessels are impregnated with lignin and give the stem additional strength. Depending on the nature of the thickening of the membranes, tracheas are distinguished as ringed, spiral, scalariform, etc. (see Fig. 8.3).
Phloem conducts organic substances synthesized in the leaves to all plant organs (downward current). Like xylem, it is a complex tissue and consists of sieve tubes with companion cells (see Fig. 8.3), parenchyma and mechanical tissue. Sieve tubes are formed by living cells located one above the other. Their transverse walls are pierced with small holes, forming a kind of sieve. The cells of the sieve tubes are devoid of nuclei, but contain cytoplasm in the central part, strands of which pass through through holes in the transverse partitions into neighboring cells. Sieve tubes, like vessels, stretch along the entire length of the plant. Companion cells are connected to the segments of the sieve tubes by numerous plasmodesmata and, apparently, perform some of the functions lost by the sieve tubes (enzyme synthesis, ATP formation).
Xylem and phloem are in close interaction with each other and form special complex groups in plant organs - vascular bundles.
Mechanical fabrics ensure the strength of plant organs. They form a frame that supports all plant organs, resisting their fracture, compression, and rupture. The main characteristics of the structure of mechanical tissues, ensuring their strength and elasticity, are the powerful thickening and lignification of their membranes, close closure between cells, and the absence of perforations in the cell walls.
Mechanical tissues are most developed in the stem, where they are represented by bast and wood fibers. In roots, mechanical tissue is concentrated in the center of the organ.
Depending on the shape of the cells, their structure, physiological state and the method of thickening of the cell membranes, two types of mechanical tissue are distinguished: collenchyma and sclerenchyma (Fig. 8.4).
Rice. 8.4. Mechanical fabrics: a -angular collenchyma; 6- sclerenchyma; V -- sclereids from cherry plum fruits: 1 - cytoplasm, 2-thickened cell wall, 3 - pore tubules.
Collenchyma is represented by living parenchyma cells with unevenly thickened membranes, making them especially well adapted for strengthening young growing organs. Being primary, collenchyma cells easily stretch and practically do not interfere with the elongation of the part of the plant in which they are located. Collenchyma is usually located in separate strands or a continuous cylinder under the epidermis of the young stem and leaf petioles, and also borders the veins in dicotyledonous leaves. Sometimes collenchyma contains chloroplasts.
Sclerenchyma consists of elongated cells with uniformly thickened, often lignified membranes, the contents of which die in the early stages. The membranes of sclerenchyma cells have high strength, close to the strength of steel. This tissue is widely represented in the vegetative organs of land plants and forms their axial support.
There are two types of sclerenchyma cells: fibers and sclereids. Fibers- these are long thin cells, usually collected in strands or bundles (for example, bast or wood fibers). Sclereids - these are round, dead cells with very thick, lignified membranes. They form the seed coat, nut shells, seeds of cherries, plums, and apricots; they give the flesh of pears their characteristic coarse character.
Main fabric, or parenchyma, consists of living, usually thin-walled cells that form the basis of organs (hence the name tissue). It houses mechanical, conductive and other permanent tissues. The main tissue performs a number of functions, and therefore they distinguish between assimilation (chlorenchyma), storage, pneumatic (aerenchyma) and aquiferous parenchyma (Fig. 8.5).
Figure 8.5. Parenchymal tissues: 1-3 - chlorophyll-bearing (columnar, spongy and folded, respectively); 4-storage (cells with starch grains); 5 - pneumatic, or aerenchyma.
Cells assimilation tissues contain chloroplasts and perform the function of photosynthesis. The bulk of this tissue is concentrated in the leaves, a smaller part in young green stems.
In cells storing proteins, carbohydrates and other substances are deposited in the parenchyma. It is well developed in the stems of woody plants, in roots, tubers, bulbs, fruits and seeds. Plants of desert habitats (cacti) and salt marshes have aquifer parenchyma, which serves to accumulate water (for example, large specimens of cacti from the genus Carnegia contain up to 2-3 thousand liters of water in their tissues). Aquatic and marsh plants develop a special type of basic tissue - pneumatic parenchyma, or aerenchyma. Aerenchyma cells form large air-bearing intercellular spaces, through which air is delivered to those parts of the plant whose connection with the atmosphere is difficult
Onion scales under a microscope
Biology test Department Angiosperms for 7th grade students. The test includes 2 options, each option consists of 3 parts (Part A, Part B, Part C). Part A has 7 tasks, Part B has 4 tasks, Part C has 1 task.
1 option
A1. The generative organ of angiosperms is
1) root
2) stem
3) flower
4) leaf
A2. One of the essential features of angiosperms, which is unique to this group of plants, is
1) presence of flowers
2) propagation by seeds
3) soil nutrition
4) carrying out photosynthesis in the light
A3. Vessels in flowering plants are formed by tissue cells
1) cover
2) conductive
3) storage
4) mechanical
A4. A modified shoot of a flowering plant is
1) seed
2) sheet
3) flower
4) stem
A5. The ovules of flowering plants are located in
1) sepals
2) pistil ovary
3) corolla petal
4) anther stamen
A6. Develops from the fertilized egg of flowering plants
1) filament
2) seed embryo
3) stigma
4) sperm
A7. After double fertilization in flowering plants, the ovule develops
1) seed
2) fruit
3) flower
4) inflorescence
B1.
A. The root system of flowering plants includes the main, lateral and adventitious roots.
B. Leaves on tropical flowering plants persist throughout the life of the plant.
1) Only A is correct
2) Only B is correct
3) Both judgments are correct
4) Both judgments are incorrect
B2. Choose three true statements. Traits of monocots
1) one cotyledon per seed
2) parallel veining of leaves
3) reticulate venation of leaves
4) tap root system
5) fibrous root system
6) five-membered flower
B3. Establish a correspondence between the family of flowering plants and its class.
Flowering plant family
A. Cereals
B. Rosaceae
B. Legumes
G. Liliaceae
D. Solanaceae
1. Monocots
2. Dicotyledons
B4. Establish the sequence of stages of evolution in the plant world
B1. Drawing assignment.
1) Cereals
2) Legumes
3) Liliaceae
4) Cruciferous
1) reticulate venation
2) parallel veining
3) compound sheet
4) round shape
1) single flowers
2) the presence of an inflorescence
3) bright corolla
4) juicy fruits
Option 2
A1. The ovule of angiosperms is located
1) on the reverse side of the sheet
2) under the bark of the stem
3) in the ovary of the pistil
4) at the top of the shoot
A2. The thickness of the tree trunk in flowering plants is determined by the functioning
1) bark
2) bast
3) cambium
4) cores
A3. As a result of the division of cambium cells in the stem, the formation of
1) bast
2) peel
3) cores
4) tree rings
A4. The main parts of a flower include
1) pestle
2) whisk
3) cup
4) receptacle
A5. A flower that contains a pistil and a stamen is called
1) pistillate
2) staminate
3) same-sex
4) bisexual
A6. Sperm cells, which are formed from
1) pollen grain
2) stigma
3) corolla petals
4) filament
A7. A 7. In the seeds of flowering plants, the endosperm is
1) embryo
2) cover
3) water supply
4) supply of nutrients
B1. Are the following statements true?
A. A poplar shoot consists of a stem, leaves and buds.
B. Self-pollination occurs between two flowers of plants of the same species.
1) Only A is correct
2) Only B is correct
3) Both judgments are correct
4) Both judgments are incorrect
B2. Choose three true statements. Signs of dicotyledonous plants
1) arc venation of leaves
2) reticulate venation of leaves
3) two cotyledons in the seed
4) fibrous root system
5) tap root system
6) the number of flower parts is a multiple of three
B3. Establish a correspondence between the type of plant and the class to which it belongs.
Type of flowering plant
A. Homemade apple tree
B. Potatoes
B. Rye
G. Leek
D. White cabbage
1. Monocots
2. Dicotyledons
B4. Establish the sequence of stages of evolution in the plant world.
1) Ferns
2) Multicellular algae
3) Psilophytes (the first land plants)
4) Flowering plants
5) Unicellular algae
6) Gymnosperms
B1. Drawing assignment
A. What family does the flowering plant shown in the picture belong to?
1) Cereals
2) Legumes
3) Rosaceae
4) Compositae
B. Features of the structure of the leaves of this plant
1) arc venation
2) parallel veining
3) reticulate venation
4) needle shape
B. Characteristics of the generative organs of this plant
1) the number of flower parts is a multiple of three
2) the number of flower parts is a multiple of five
3) simple perianth
4) the rim is missing
Answers to the biology test Department Angiosperms
1 option
A1. 3
A2. 1
A3. 2
A4. 3
A5. 2
A6. 2
A7. 1
B1. 1
B2. 125
B3. 12212
B4. 32514
IN 1. 122
Option 2
A1. 3
A2. 3
A3. 4
A4. 1
A5. 4
A6. 1
A7. 4
B1. 1
B2. 235
B3. 22112
B4. 523164
IN 1. 332
In biology, tissue is a group of cells that have a similar structure and origin, and also perform the same functions. In plants, the most diverse and complex tissues developed during the process of evolution in angiosperms (flowering plants). Plant organs are usually formed from several tissues. There are six types of plant tissues: educational, basic, conductive, mechanical, integumentary, secretory. Each tissue includes subtypes. Between tissues, as well as inside them, there are intercellular spaces - spaces between cells.
Educational fabric
Due to the division of cells of the educational tissue, the plant increases in length and thickness. In this case, some of the cells of the educational tissue differentiate into cells of other tissues.
The cells of educational tissue are quite small, tightly adjacent to each other, have a large core and a thin membrane.
Educational tissue in plants is found in growth cones root (root tip) and stem (stem apex), occurs at the bases of internodes, and educational tissue also makes up cambium(which ensures the growth of the stem in thickness).
Cells of the root growth cone. The photo shows the process of cell division (chromosome divergence, dissolution of the nucleus).
Parenchyma or ground tissue
Parenchyma includes several types of tissues. There are assimilative (photosynthetic), storage, water-bearing and air-bearing basic tissue.
Photosynthetic tissue consists of cells containing chlorophyll, i.e. green cells. These cells have thin walls and contain a large number of chloroplasts. Their main function is photosynthesis. Assimilation tissue makes up the pulp of leaves, is part of the bark of young tree stems and grass stems.
In cells storage tissue nutrient reserves accumulate. This tissue makes up the endosperm of seeds and is part of tubers, bulbs, etc. The core of the stem, the internal cells of the stem and root bark, and the succulent pericarp also usually consist of storage parenchyma.
Aquifer parenchyma characteristic only of a number of plants, usually in arid habitats. Water accumulates in the cells of this tissue. Aquiferous tissue can be found both in the leaves (aloe) and in the stem (cacti).
Air tissue characteristic of aquatic and marsh plants. Its peculiarity is the presence of a large number of intercellular spaces containing air. This facilitates gas exchange for the plant when it is difficult.
Conductive fabric
The common function of various conductive tissues is to conduct substances from one plant organ to another. In the trunks of woody plants, conductive tissue cells are located in the wood and phloem. Moreover, in the wood there are vessels (trachea) and tracheids, along which the aqueous solution moves from the roots, and in the phloem - sieve tubes, through which organic substances move from photosynthetic leaves.
Vessels and tracheids are dead cells. The aqueous solution rises through the vessels faster than through the tracheids.
Sieve tubes are living but anucleate cells.
cover tissue
The integumentary tissue includes the skin (epidermis), cork, and crust. The skin covers the leaves and green stems; these are living cells. The plug consists of dead cells impregnated with a fat-like substance that does not allow water or air to pass through.
The main functions of any integumentary tissue are to protect the internal cells of the plant from mechanical damage, drying out, penetration of microorganisms, and temperature changes.
Cork is a secondary covering tissue, as it occurs in place of the skin of the stems and roots of perennial plants.
The crust consists of cork and dead layers of the main tissue.
Mechanical fabric
Mechanical tissue cells are characterized by highly thickened lignified membranes. The functions of mechanical tissue are to give strength and elasticity to the body and organs of plants.
In the stems of angiosperms, the mechanical tissue can be located in one continuous layer or in separate strands spaced from each other.
In leaves, the fibers of the mechanical tissue are usually located next to the fibers of the conductive tissue. Together they form the veins of the leaf.
Secretory or excretory tissue of plants
Secretory tissue cells secrete different substances, and therefore the functions of this tissue are different. Excretory cells in plants line resin and essential oil passages and form peculiar glands and glandular hairs. Flower nectaries belong to the secretory tissue.
Resins perform a protective function when the plant stem is damaged.
Nectar attracts pollinating insects.
There are secretory cells that remove metabolic products, for example, oxalic acid salts.
Almost all multicellular living organisms are composed of various types of tissues. This is a collection of cells, 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 plant. They are different. Let's look at them.
What kind of animal tissues can there be?
Animal tissues are of the following types:
- nervous;
- muscular;
- epithelial;
- connecting.
All of them, except the first, are divided into 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 includes types such as loose fibrous, dense fibrous, reticular, blood and lymph, fat, bone and cartilage.
Diversity of plant tissues
Plant tissues are of the following types:
- main;
- cover;
- mechanical;
- educational.
All types of plant tissues combine several types. Thus, the main ones include assimilation, storage, aquifer and air-bearing. combines such species as bark, cork and epidermis. Conductive tissues include phloem and xylem. Mechanical is divided into collenchyma and sclerenchyma. Educational ones include lateral, apical and intercalary.
All tissues perform specific functions, and their structure corresponds to the role they perform. This article will examine in more detail the conductive tissue and the structural features of its cells. Let's 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 differs. 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 belonging to more than one type differ.
The role of xylem is to conduct solutions of chemical substances from the root upward to all other organs of the plant.
And the function of phloem is to conduct solutions in the opposite direction - from certain plant organs along the stem down to the root.
What is xylem?
It is also called wood. Conductive tissue of this type consists of two different conductive elements: tracheids and vessels. It also includes mechanical elements - wood fibers, and basic elements - wood parenchyma.
How are xylem cells organized?
Conducting tissue cells 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 conducting element of the cell - the vessel - consists of several cells, which are called vascular segments. These cells are located one above the other. At the junction of segments of the same vessel there 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 vessels occurs much faster than through tracheids.
The cells of both conducting elements are dead and do not contain protoplasts (protoplasts are the contents of the cell, excluding the nucleus, organelles 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 neighboring conducting elements.
The walls of the conductive elements have thickenings that give the cell strength. Depending on the type of these thickenings, conductive elements are divided into spiral, ringed, ladder, mesh and point-pore.
Functions of 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, ensuring the strength of the xylem.
The elements 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 with 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.
How does the xylem of different plants differ?
Since tracheids arose much earlier in the process of evolution than vessels, these conducting elements are also present in lower land plants. These are spore-bearing plants (ferns, mosses, mosses, horsetails). Most gymnosperms also have only tracheids. However, some gymnosperms also have vessels (they are present in Gnetaceae). Also, as an exception, the named elements are also present in some ferns and horsetails.
But angiosperms (flowering) plants all have both tracheids and blood vessels.
What is phloem?
Conductive tissue of this type is also called bast.
The main part of the phloem is sieve-like conducting elements. Also in the structure of the bast there are mechanical elements (phloem fibers) and elements of the main tissue (phloem parenchyma).
The peculiarities of the conducting tissue of this type are that the cells of the sieve elements, unlike the conducting elements of the xylem, remain alive.
Structure of sieve elements
There are two types of them: sieve cells and the former are elongated in length and have pointed ends. They are permeated with through holes through which substances are transported. Sieve cells are more primitive than multicellular sieve elements. They are characteristic of plants such as spores and gymnosperms.
In angiosperms, conducting elements are represented by sieve tubes, consisting of many cells - segments of the sieve elements. The through holes of two adjacent cells form sieve-like plates.
Unlike sieve cells, the mentioned structural units of multicellular conducting elements lack nuclei, but they still remain alive. An important role in the structure of the phloem of angiosperms is also played by companion cells located next to each cell segment of the sieve elements. The companions contain both organelles and nuclei. Metabolism occurs in them.
Considering that phloem cells are living, this conducting tissue cannot function for a long time. In perennial plants, its life span is three to four years, after which the cells of this conducting tissue die.
Additional phloem elements
In addition to sieve cells or tubes, this conducting tissue also contains ground tissue elements and mechanical elements. The latter are represented by bast (phloem) fibers. They perform a supporting function. Not all plants have phloem fibers.
The elements of the main tissue are represented by phloem parenchyma. It, like the xylem parenchyma, plays 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 plant conduction system
Xylem and phloem are always located nearby and form bundles. Depending on how the two types of conductive tissue are positioned 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: centrifloem and centoxylem.
The conductive tissue of the root usually has radial bundles. In them, xylem rays extend from the center, and phloem is located between the xylem rays.
Collateral bundles are more characteristic of angiosperms, while concentric bundles are more characteristic of spores and gymnosperms.
Conclusion: Comparison of Two Types of Conductive Fabrics
As a conclusion, we present a table that briefly summarizes the basic data on two types of conducting plant tissues.
| Xylem | Phloem | |
| Structure | Consists of conductive elements (trachea and vessels), wood fibers and wood parenchyma. | Consists of conducting elements (sieve cells or sieve tubes), phloem fibers and phloem parenchyma. |
| Features of conducting cells | Dead cells that lack plasma membranes, organelles and nuclei. They have an elongated shape. They are located one above the other and do not have horizontal partitions. | Living ones 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 | Conducting substances dissolved in water upward: from the root to the plant organs. | Downward transport of chemical solutions: from the terrestrial organs of plants to the roots. |
Now you know everything about the conducting tissues of plants: what they are, what functions they perform and how their cells are structured.