What tissue represents the division zone? Plant roots

In a longitudinal section, the following root zones (plant root areas) are distinguished:

• Growth zone with root cap;
• zone of elongation and beginning of cell differentiation;
• suction zone;
• conductive zone.

Root zones

Growth

The growth zone (division zone) of the root occupies the tip 2-3 mm long. This is a zone of actively dividing cells, the root meristem. All root tissues arise from this educational tissue.

Growth area covered root cap, which protects it from damage and facilitates the advancement of the root in the soil. The cells of the cap have increased turgor. As the roots deepen in the soil, they are erased, their outer layer is peeled off, and new cells grow from the inside due to the root meristem.

Sprains

In the elongation zone, the cells greatly increase in the longitudinal direction and become cylindrical. Large vacuoles appear in them. The combined growth of cells in this zone creates a force that forces the root deeper into the soil.

This zone is also small and occupies a few millimeters. In its upper part, cells begin to specialize, finally turning into vessels, tracheids and other types of root cells in the suction zone.

Suction

The root absorption zone ranges in length from a few millimeters to several centimeters. Its surface is protected by integumentary tissue - skin with root hairs. Under the skin is the root bark, surrounding its central part with a conducting system.

The conductive zone is the entire rest of the root, from the suction zone to the plant stem. This area has a denser integumentary tissue, is thickened, the number of vessels and sieve tubes is increased due to the activity of the cambium.

The root conduction zone is an intermediary between the suction zone and the above-ground part of the plant.

Summary table of the structure and functions of root zones

Zone name	Structural features	Functions
Division zone	Small living cells that divide quickly	The beginning of all other zones and root tissues
Growth zone	Cells grow and increase in size	Provides basic root growth
Suction zone	The outer layer is represented by cells with root hairs	Provides absorption of water with beneficial substances dissolved in it
Venue area	Conductive tissues are well developed	Transport

Internal structure of a plant root

Outer covering tissue of the root - skin- differs from the skin of the stem and leaf in the presence of root hairs, the absence of stomata and cuticle, easy permeability to water, and absorption capacity.

The skin cells are arranged in one layer. Many of them have root hairs - elongated cylindrical outgrowths of the outer wall of skin cells, ranging from 0.15 mm to 1 cm in length with a diameter of hundredths of a millimeter. The cell nucleus passes into the root hair and is usually located at its very end.

In addition to the nucleus, the cytoplasm of the root hair contains vacuoles with cell sap and colorless plastids. The surface of the hairs is covered with a mucous substance that glues them to soil particles.

Root hairs short-lived. They are formed in 30-40 hours, live for 10-20 days, then die off. To replace them, new ones are formed in the young part of the root, and the area with dead hairs becomes a conductive zone. The number of root hairs per 1 mm2 reaches several hundred (for example, in corn - 425, in peas - 230). Thanks to their presence, the suction surface of the root increases tens of times.

Root bark, adjacent to the skin from the inside, consists of cells of the main tissue arranged in several rows. Cortical cells have different sizes. Directly under the skin they are large, and in deeper layers they are smaller.

The innermost layer of the bark ( endoderm), enclosing the central part of the root (central cylinder) with a conducting system, consists of one row of densely packed cells. Their outer walls (from the bark side) are thin, while the lateral and internal walls are thickened and impermeable to water and gases.

Between the thick-walled cells there is a small number of thin-walled cells located opposite the vessels of the central cylinder. These are passage cells; they conduct water from the root bark into the vessels of the central cylinder.

Central cylinder occupies the middle part of the stem and consists of various tissues. Its outer layer, adjacent to the endoderm from the inside, consists of thin-walled parenchyma cells and is called the pericycle, or root layer.

Pericycle cells (secondary educational tissue) periodically divide and give rise to lateral roots, root parenchyma, adventitious buds of root shoots, and cambium.

Further, towards the center of the axial cylinder, there is a closed vascular-fibrous bundle, in which sections of phloem and xylem alternate, located radially. The center of the axial cylinder of the root in most plant species is occupied by one large or several small vessels. In some species, the center is occupied by cells of the main tissue (parenchyma), which also fills the gaps between the phloem and xylem areas.

The absorption zone is the functionally most important part of the root, since its main function is carried out here - the absorption of water and minerals. The structure of the root in the suction zone is best adapted to fulfill this role. The root tissues are arranged in concentric circles, which is typical for axial organs, and exhibit a high degree of specialization. In a cross section, two main structural regions of the root are distinguishable - the primary cortex and the central cylinder. The central, or axial, cylinder, in accordance with its name, occupies a central position, the primary cortex surrounds it in a ring.

The outside of the root is covered with a skin - the epidermis, which has a special purpose. This is suction fabric. Compared to the epidermis of above-ground organs, the root skin differs in some features - the absence of a cuticle and stomata, and the presence of root hairs. For this reason, the primary integumentary tissue of the root also has special names - epiblema(from Greek epiblema - bedspread) and rhizoderm(from Greek risus - root, derma - skin).

Skin cells are living, parenchymal, thin-walled, with a wall layer of cytoplasm. They are remarkable in that they form long thin growths on the outside - root hairs. A root hair is part of an epidermal cell. Epidermal cells that form hairs are called trichoblasts, cells that do not form them are called atrichoblasts. Trichoblasts are distinguished by their smaller size, dense cytoplasm and large nucleus. The shape of the root hair in a damp chamber is cylindrical; in the soil it becomes deformed. Its length is tenths of a millimeter, rarely 1.2-1.5 mm, diameter - 5-15 microns. The number of root hairs is very large: in a favorable environment - 200 - 300 per 1 mm 2 of surface. Due to root hairs, the suction surface of the root increases many times, close contact with soil particles is achieved and the suction process is facilitated. Root hairs actively influence the soil, promoting the dissolution of poorly soluble compounds.

Root hairs do not last long - 2-3 days, then they die off and form anew on the younger part of the root. Thus, root hairs move to new soil horizons.

Primary cortex- parenchymal tissue. It is called the cortex due to its peripheral position, and primary due to its origin from the primary meristem. In the suction zone it accounts for most of the cross section. The cells of the primary cortex are round in cross section, neither cylindrical or prismatic in longitudinal section, slightly elongated along the root. The cell membranes are relatively thin, the cytoplasm lies wall-to-wall, inclusions, organic and mineral, are common. The cells are arranged loosely, forming a large number of intercellular spaces, which, according to the theory of “free space”, along with the cell membranes, are the main bed of water flow. In the bark of some plants there are lacticifers and other receptacles for secretions. All these signs indicate high physiological activity of the primary cortex. Mechanical tissues within the cortex - stony cells and sclerenchyma - are rare.

The outer and inner boundary layers differ from the main mass of the crust. The outer layer underlying the epidermis is called exodermis(from Greek exo - outside, derma - skin). The exoderm can be single-layered. In this case, it consists of large polygonal cells, which suberize relatively early. In multilayered exodermis, the cells are smaller than the main cells of the cortex. The cell walls of the exodermis have characteristic thickenings. The exoderm is especially well developed in monocotyledonous plants. In them, it forms a stronger integumentary tissue (of primary origin) instead of the epidermis.

The inner layer of the cortex, bounding the central cylinder, is called endoderm(from the Greek endon - inside, derma). Its cells are highly specialized both morphologically and functionally. They are characterized by partial suberization of cell walls, which occurs to a lesser extent in dicotyledonous plants, and more significantly in monocotyledonous plants. The endoderm is a single layer of regularly shaped cells that develop from the periblema. In the embryonic phase, endodermal cells have meristematic activity; due to their division, the main parenchyma of the primary cortex is formed. With further development of cells, their functions and structure change. In the absorption zone, a suberized strip appears on the transverse and radial walls of the endoderm, which is called the Casparian belt. On transverse sections, suberized areas are visible in the form of points on the radial walls - Casparian spots.

The function of the endoderm is undoubtedly associated with the flow of water and mineral salts into the central cylinder. If in the cortex water moves freely through the intercellular spaces and cellulose cell membranes, then partially suberized endodermal cells interrupt its “uncontrolled” flow. The penetration of water into the central cylinder becomes possible only through the protoplast of the cell, which regulates this process.

In later phases of root development, the endodermis protects the central cylinder from loss of substances.

In monocotyledonous plants, the morphological development of the endodermis does not end with the formation of the Casparian belt. Subsequently, the cell walls thicken significantly and become lignified, with the inner tangential and radial walls becoming thicker, while the outer tangential wall remains relatively thin. The thickened part of the cell membrane takes on a characteristic horseshoe-shaped appearance.

In different plants and in different organs, the endoderm develops differently. In the root it is more developed, in the stem it is weaker, and sometimes it does not develop at all.

The endodermal ring contains a small number of non-suberized cells called pass cells. Their number corresponds to the number of xylem rays in the central cylinder against which they are located. It is assumed that passage cells are formed from already differentiated xylem cells; they do not form a continuous vertical cord, but alternate with suberized cells.

In dicotyledonous plants, the primary cortex is short-lived; as a rule, it exists only in the absorption zone, i.e. during the primary structure of the root. As a result of the development of secondary tissues in the branching zone, the primary bark dies and sloughs off. Root shedding occurs. In monocotyledonous plants, which do not have a secondary structure, the primary cortex is permanently preserved.

Central cylinder (axial cylinder, stele)- part of the axial organ where conducting tissues are located. In the central cylinder of the root, conducting tissues form a radial conducting bundle. Xylem, represented by vessels, is arranged in rays, the number of which varies in different plants, but is constant for a given species. There can be two, four, five, or even more than a hundred xylem rays. Accordingly, based on the number of xylem, the roots are called di-, tetra-, or polyarch. For example, the roots of beets, carrots, some poppies, and nettles have two rays of xylem. Pumpkin has four xylem rays, beans have five. Tetrarchic roots are considered primary.

The external vessels in the xylem rays are the first to differentiate. These are the smallest narrow-lumen vessels in the root xylem. They form protoxylem. The vessels lying closer to the center develop later, forming metaxylem. Metaxylem vessels are larger than protoxylem vessels and have a different type of cell wall thickening. Thus, the development of primary xylem in the root proceeds in a centripetal manner. The central position in the axial cylinder is occupied by the largest metaxylem vessels or core, consisting of cells with thickened membranes.

Phloem is represented by sieve tubes, which are located in separate islands between the xylem rays. The very first elements of phloem - delicate small sieve tubes - form protophloem. Larger sieve tubes appear after them - metaphloem. Phloem and xylem do not touch. Between them are undifferentiated cells, from which the cambium subsequently develops.

Xylem and phloem are in direct contact with the bark. In the stem, as will be seen later, these tissues are arranged differently. This peculiar arrangement of conducting tissues is explained by the functional significance of the root. Water coming from the bark directly enters the xylem, bypassing the phloem. With the flow of water, some substances that are used in the synthetic processes occurring in it also enter the root. These materials necessary for synthesis are accumulated by the phloem.

The outermost layer of the central cylinder, underlying the endoderm, is called the pericycle (from the Greek peri - around, kyklos - around). This is one or more layers of parenchyma cells. Physiologically, the pericycle is a potential educational tissue. From it, lateral roots and adventitious buds are formed, if they are characteristic of this plant at all, and the cambium and cork cambium partially develop. The pericycle is a direct continuation of the apical meristem.

Thus, the general plan of the primary structure of the root and the morphological differentiation of tissues reveal a high degree of specialization and adaptability of the root to the functions of absorption and conduction of water.

3. "Root zone" test
BOTANY TESTS

INTERACTIVE CARDS:
1. Internal structure of the root
2. Root zones
3. Root growth

KOREN
Root	An axial vegetative organ of a plant, possessing unlimited apical growth, positive geotropism, having a radial structure and never bearing leaves. The apex of the root is protected by the root cap.
Root meaning	Fixation of the plant in the soil, absorption of water and mineral salts, storage of organic substances, synthesis of amino acids and hormones, respiration, symbiosis with fungi and nodule bacteria, vegetative propagation (in root-offspring plants).
main root	A root developing from an embryonic root.
Adventitious root	A root developing from a stem or leaf.
Lateral root	Branch of the main, lateral or adventitious root.
Root system
Tap root system	The main root with all the lateral roots and their branches.
Adventitious root system	Adventitious roots with all lateral roots and their branches.
Tap root system	Root system with a well-defined tap root.
Fibrous root system	The root system is represented mainly by adventitious roots, in which the main root is not distinguished.
Root vegetable	A modified thickened main root, bearing a shortened shoot at the base and performing the function of storing nutrients (carrots).
Root tuber	A modified thickened lateral or adventitious root that performs the function of storing nutrients (dahlia).
Root zones	Structures that successively replace each other as the root grows in length.
Division zone	The growth cone, represented by the apical educational tissue, ensures the growth of the root in length due to continuous cell division.
Stretch zone	The zone of the root where cell size increases and their specialization begins.
Suction zone	A zone that moves as it grows, where cells specialize into various tissues and water is absorbed from the soil using root hairs.
Venue area	The root zone located above the absorption zone, where water and mineral salts move through the vessels, and carbohydrates through the sieve tubes. The root in this area is covered with cork tissue.
Root cap

CRIB.
Source: http://www.hpora.ru/
Root is the underground part of the vegetative body of a plant, anchoring it in the soil. Appeared for the first time in vascular plants.

Root functions:

1. Absorbing - water with substances dissolved in it is transported through the xylem to above-ground organs, where it is included in the processes of photosynthesis.
2. Conductive - water and nutrients move through the xylem and phloem of the root.
3. Storage - synthesized organic substances return through the phloem from terrestrial organs to the root and are stored.
4. Synthetic - many amino acids, hormones, alkaloids, etc. are synthesized at the root.
5. Anchor - fix the plant in the ground.

The root consists of a main root and lateral roots. The primary root is formed in the embryo; it is oriented downward and becomes the main one in gymnosperms and flowering plants. Lateral roots form on the main root.

The root is an axial organ that has radial symmetry and grows in length indefinitely due to the activity of the apical (apical) meristem. It differs from the stem in that leaves never grow on it, and the apical meristem is covered with a sheath.

Types of root systems:

* Tap root system - includes main and lateral roots, characteristic of dicotyledonous flowering and gymnosperm plants.
* Fibrous - formed from adventitious roots that grow from the lower part of the shoot.

Soil, its importance for plant life:

Soil is composed of solid particles derived from parent rock, the type of which determines the mineral composition of the soil. The water content in the soil is the main factor for plant development. Soils consisting of particles of different sizes are considered most favorable for water retention. Living soil components (microorganisms, fungi, invertebrates and small vertebrates) help improve soil fertility. Thus, nitrogen-fixing bacteria and blue-green algae enrich the soil with bound nitrogen, and mycorrhizal fungi stimulate the mineral nutrition of plants. It is very important to have organic residues in the soil, which are constantly subject to mineralization by microorganisms and are a continuous source of soil nutrition. The more organic residues in the soil, the more fertile it is.

Internal structure of the root. The conducting system of the root (sieve tubes and vessels) is located radially in the center of the root, forming an axial cylinder with the cells of the main tissue. The vessels transport water with substances dissolved in it to the ground organs of the plant from the root hairs. Between the strands of blood vessels there are sieve tubes. They serve to transport organic solutions from the above-ground parts of the plant to the root cells. Between the phloem and xylem there is educational tissue - the cambium, the cells of which continuously divide, ensuring the growth of the root in thickness. Absorption of water with substances dissolved in it occurs in the zone of root hairs. A root hair is an outgrowth of a cell; it lives for about 20 days and is replaced by a new one.

Root zones in a longitudinal section:

1. Root cap:
2. Division zone - dividing cells of educational tissue.
3. Growth zone - carries out root growth in length.
4. Suction zone - located above the growth zone. Its surface is covered with outgrowths of external cells - root hairs, which absorb water from the soil with substances dissolved in it. The root hairs are covered with mucus, which dissolves the mineral particles of the soil, and the roots adhere firmly to the substrate. Lateral roots are formed in this zone.
5. Conduction zone - in the center of the root there is conductive tissue formed by wood (xylem) and phloem (phloem). The zone is characterized by constant growth. It accounts for most of the root length. Here the root thickens due to the division of cambium cells. In the area of ​​conduction, the root branches.

Root zones

Root zone	Features of cells	What tissue is it formed from?	Function
Root cap	Cells are dead and easily mucus	cover	Protects against mechanical damage, mucilage promotes root advancement in the soil
Division zone	Cells are small and constantly dividing	educational	Cells constantly divide to support root growth
Growth zone	The cells are young, growing, that is, elongating	educational	The cells stretch, causing the root to grow in length.
Suction zone	The zone is represented by root hairs. A root hair is an elongated cell	Main, suction	Root hairs absorb mineral salts dissolved in water
Venue area	The zone is represented by vessels - these are dead cells	conductive	Through the vessels of the root, minerals dissolved in water move from bottom to top of the stem

Root modifications.
Roots. Due to the strong growth of parenchyma or due to the activity of additional layers of cambium, the root thickens and is modified into a root crop. In radishes, beets and turnips, most of the root crop is formed by the overgrown base of the stem; In carrots, on the contrary, the main part of the root crop is formed by the main root. Root vegetables are adapted for storing nutrients.
Other modifications: root tubers (dahlia),
aerial roots (corn).
root roots (ivies)

Control questions

1. What is a root?
2. What functions does the root perform?
3. What are the types of roots?
4. What is the root system?
5. What types of root systems are distinguished in monocots? dicotyledonous plants?
6. What zones does the root consist of? What function does each of them perform?
7. What is a root cap? Describe its functions and structural features.
8. What modified roots do you know?
9. What are the similarities and differences in the structure of the roots of carrots, radishes and beets?

Pictures from the site were used

The science of biology studies living organisms. The structure of a plant root is discussed in one of the branches of botany.

The root is the axial vegetative organ of the plant. It is characterized by unlimited apical growth and radial symmetry. The structural features of the root depend on many factors. This is the evolutionary origin of the plant, its belonging to one class or another, its habitat. The main functions of the root include strengthening the plant in the soil, participation in vegetative propagation, and the supply and synthesis of organic nutrients. But the most important function ensuring the vital activity of the plant organism is soil nutrition, which is carried out in the process of active absorption of water containing dissolved mineral salts from the substrate.

Types of roots

The external structure of the root is largely determined by what type it belongs to.

• Main root. Its formation occurs from the embryonic root when the plant seed begins to germinate.
• Adventitious roots. They can appear on different parts of the plant (stem, leaves).
• Lateral roots. It is they who form branches, starting from previously appeared roots (main or subordinate).

Types of root systems

The root system is the community of all the roots that a plant has. Moreover, the appearance of this aggregate can vary greatly among different plants. The reason for this is the presence or absence, as well as the different degrees of development and severity of different types of roots.

Depending on this factor, several types of root systems are distinguished.

• The name speaks for itself. The main root acts as a rod. It is well defined in size and length. The root structure of this type is typical for sorrel, carrots, beans, etc.
• This type has its own characteristics. The external structure of the main root is no different from that of the lateral ones. He doesn't stand out in the crowd. Formed from an embryonic root, it grows for only a short time. The fibrous root system is characteristic of monocotyledonous plants. These are cereals, garlic, tulip, etc.
• Mixed root system. Its structure combines the features of the two types described above. The main root is well developed and stands out against the general background. But at the same time, adventitious roots are also highly developed. Typical for tomatoes and cabbage.

Historical development of the root

If we think from the point of view of the phylogenetic development of the root, then its appearance occurred much later than the formation of the stem and leaf. Most likely, the impetus for this was the emergence of plants on land. In order to gain a foothold in a solid substrate, representatives of the ancient flora needed something that could serve as a support. In the process of evolution, root-like underground branches were first formed. Later they gave rise to the development of the root system.

Root cap

The formation and development of the root system occurs throughout the life of the plant. The structure of the plant root does not provide for the presence of leaves and buds. Its growth is due to an increase in length. At the point of growth it is covered with a root cap.

The growth process is associated with educational tissue. It is she who is located under the root cap, which performs the function of protecting delicate dividing cells from damage. The case itself is a collection of thin-walled living cells in which the process of renewal constantly occurs. That is, as the root moves through the soil, old cells gradually peel off, and new ones grow in their place. Also, the cells of the cap located outside secrete a special mucus. It facilitates the advancement of the root in a solid soil substrate.

It is well known that the structure of plants varies greatly depending on the habitat. For example, aquatic plants do not have a root cap. In the process of evolution, they developed another device - a water pocket.

Plant root structure: division zone, growth zone

Cells that emerge begin to differentiate over time. In this way, root zones are formed.

Division zone. It is represented by cells of educational tissue, which subsequently give rise to all other types of cells. Zone size - 1 mm.

Growth zone. It is represented by a smooth section, the length of which ranges from 6 to 9 mm. It follows immediately after the division zone. The cells are characterized by intensive growth, during which they become greatly elongated in length, and gradual differentiation. It should be noted that the division process in this zone is almost not carried out.

Suction zone

This section of the root, several centimeters long, is also often called the root hair zone. This name reflects the structural features of the root in this area. There are outgrowths of skin cells, the size of which can vary from 1 mm to 20 mm. These are root hairs.

The suction zone is the place where the active absorption of water, which contains dissolved minerals, occurs. The activity of root hair cells, in this case, can be compared to the operation of pumps. This process is very energy-intensive. Therefore, the cells of the absorption zone contain a large number of mitochondria.

It is very important to pay attention to one more feature of root hairs. They are able to secrete special mucus containing carbonic, malic and citric acids. Mucus helps dissolve mineral salts in water. Thanks to mucus, soil particles seem to stick to the root hairs, facilitating the absorption of nutrients.

Root hair structure

The increase in the area of ​​the absorption zone occurs precisely due to the root hairs. For example, their number in rye reaches 14 billion, forming a total length of up to 10,000 kilometers.

The appearance of root hairs makes them look like white fluff. They do not live long - from 10 to 20 days. It takes very little time for the plant organism to form new ones. For example, the formation of root hairs in young apple tree seedlings takes 30-40 hours. The area where these unusual growths died off can still absorb water for some time, and then it is covered with a plug, and this ability is lost.

If we talk about the structure of the hair sheath, then, first of all, we should highlight its thinness. This feature helps the hair absorb nutrients. Its cell is almost completely occupied by a vacuole, surrounded by a thin layer of cytoplasm. The core is located at the top. The space near the cell is a special mucous sheath that promotes the gluing of root hairs with small particles of soil substrate. Due to this, the hydrophilicity of the soil increases.

Transverse structure of the root in the suction zone

The root hair zone is also often called the zone of differentiation (specialization). This is no coincidence. It is here that a certain layering can be seen in the cross section. It is caused by the delimitation of layers inside the root.

The table “Root structure in a cross section” is presented below.

It should be noted that there is also a distinction within the cortex. Its outer layer is called exoderm, the inner layer is called endoderm, and between them is the main parenchyma. It is in this intermediate layer that the process of directing nutrient solutions into the vessels of the wood occurs. Also, some organic substances vital for the plant are synthesized in the parenchyma. Thus, the internal structure of the root allows us to fully assess the significance and importance of the functions that each of the layers performs.

Venue area

Located above the suction zone. The longest and most durable section of the root. It is here that the movement of substances important for the life of the plant organism occurs. This is possible due to the good development of conductive tissues in this area. The internal structure of the root in the conduction zone determines its ability to transport substances in both directions. The ascending current (upward) moves water with mineral compounds dissolved in it. And organic compounds are delivered down, which participate in the life of root cells. The conduction zone is where lateral roots form.

The structure of the bean seedling root clearly illustrates the main stages of the process of plant root formation.

Features of the structure of the plant root: the ratio of above-ground and underground parts

Many plants are characterized by such development of the root system, which leads to its predominance over the ground part. An example is cabbage, the root of which can grow 1.5 meters deep. Its width can be up to 1.2 meters.

It grows so much that it occupies a space whose diameter can reach 12 meters.

And in the alfalfa plant, the height of the ground part does not exceed 60 cm. While the length of the root can be more than 2 meters.

All plants that live in areas with sandy and rocky soils have very long roots. This is due to the fact that in such soils water and organic matter are very deep. In the process of evolution, plants adapted to such conditions for a long time, and the structure of the root gradually changed. As a result, they began to reach the depth where the plant organism can stock up on the substances necessary for growth and development. For example, the root can be 20 meters deep.

Wheat root hairs branch so strongly that their total length can reach 20 km. However, this is not the limit value. Unlimited apical growth of roots in the absence of strong competition with other plants can increase this value several times more.

Root modifications

The structure of the roots of some plants can change, forming so-called modifications. This is a kind of adaptation of plant organisms in specific living conditions. Below is a description of some of the modifications.

Root tubers are characteristic of dahlia, chistyak and some other plants. They are formed due to thickening of adventitious and lateral roots.

Ivy and campsis also differ in the structural features of these vegetative organs. They have so-called hitch roots, which allow them to cling to nearby plants and other supports that are within their reach.

Monsteras and orchids are distinguished by their long length and absorb water.

Respiratory roots growing vertically are involved in the respiratory function. Available in brittle willow.

Vegetable crops such as carrots, beets, and radishes have root crops that are formed due to the growth of the main root, inside which nutrients are stored.

Thus, the structural features of the plant root that lead to the formation of modifications depend on many factors. The main ones are habitat and evolutionary development.

Root cap and division zone

1) In which part of the root is the cap located, why is it needed and what cells is it represented by? The cap is located directly at the tip of the root; it plays a protective role. It consists of several layers, while the outer layer has mucus, its cells are constantly torn off.

2) How does the cover restore its dimensions? Due to the division zone - the place where the educational tissue is located, which is constantly dividing.

3) What is the significance of the division zone besides replenishing the cap cells? It forms all the other cells of the root.

Growth zone (stretching)

1) What is the location of the growth zone in the root? Located behind the division zone, in front of the suction zone.

2) What tissue cells are part of the growth zone? What are their features? It partially includes cells of educational tissue, but there are also cells that have finished dividing and are simply growing. The cells grow by absorbing moisture and forming large vacuoles, so this section of the root elongates.

3) What is the function of the growth zone? It pushes the division zone forward, deep into the soil, along with the root cap.

4) What tissue cells can the grown cells of the growth zone turn into? One part of the cells will turn into cells of the integumentary tissue, the second will become cells of the main tissue, and finally, the remaining part will be cells of the conducting tissue.

5) How can we experimentally prove that the root grows from the apex, due to the division zone and the growth zone? Let's put two pairs of dash marks on the bean (or fava bean) sprout - the first at the top of the root, the second at its base. Literally a day later we will see that the distance between the marks has increased only at the top of the root. The conclusion is simple - the root is characterized precisely by apical growth.

Suction zone

1) Root hairs are located in this zone. What structure do their cells have? The cell walls are thin, mucous, and the central vacuoles are large. The length of the hairs is from 0.1 to 1.5 millimeters, but sometimes they can reach 8-9 mm, for example, this is characteristic of wheat.

2) Why are hairs needed? During development, they tightly adhere to microscopic lumps of soil, and the mucus contained on them actively dissolves minerals in the soil. Thus, multiple hairs increase the previously small suction surface of the root by tens and sometimes hundreds of times. However, the root hair does not live long, a few days at most.

3) Where do root hairs die and where do new root hairs grow? They die off at the end of the suction zone, new ones appear near the growth zone. We conclude that the suction zone is constantly growing, penetrating into new layers of soil. However, in general, the suction zone remains the same length.

Internal structure of the root in the suction zone

1) The outer layer of cells, the skin (called rhizoderm or epiblema), is formed by root hairs.

2) Root cortex cells are the next layer. They are living, thin-walled cells, between which there are large intercellular spaces.

3) Three layers can be distinguished in the cortex - the outer dense one (it is adjacent to the skin, and in the conduction zone it takes on the functions of the skin after it dies), the center of the cortex of large cells, the inner part of the cortex (represented by one layer of interlocking cells). Substances, such as vitamins, starch, and proteins, can be stored in the root bark.

4) Conductive tissues in the center of the root: the central cylinder, which includes wood and bast. Wood vessels of the central cylinder - what are they? Long hollow tubes, without living contents, with lignified walls, through which water moves with the necessary mineral salts it contains. The sieve tubes of bast are built from living cells, which are characterized by transverse partitions in the form of a sieve (hence the name), but without a nucleus. There is no core at the root. How are the wood and bast arranged in the central cylinder in the suction zone? The wood is in the center, its rays reaching the periphery of the central cylinder. Different types of plants have from three to several dozen rays. The bast is located between the rays of the wood.

Venue area

1) What happens to the cells of the outer layer of the cortex after the root hairs die? They also die, and the dead ones protect the internal parts of the root from damage and bacteria. Such a section of the root can no longer absorb, but only conducts substances.

2) Is the venue area growing? Yes. And it also accounts for most of the length of long-lived roots.