Plant roots. Types of root system. Functions of the root. Root zones. Modification of roots. Functions of the root Function of the root as a plant organ

A root is an underground organ of a plant. The main functions of the root are:

Supporting: roots anchor the plant in the soil and hold it throughout its life;

Nutritional: through the roots the plant receives water with dissolved minerals and organic substances;

Storage: Some roots can store nutrients.

Types of roots

There are main, adventitious and lateral roots. When a seed germinates, the embryonic root appears first and turns into the main one. Adventitious roots may appear on the stems. Lateral roots extend from the main and adventitious roots. Adventitious roots provide the plant with additional nutrition and perform a mechanical function. They develop when hilling, for example, tomatoes and potatoes.

Functions of roots:

They absorb water and mineral salts dissolved in it from the soil and transport them up the stem, leaves and reproductive organs. The suction function is performed by root hairs (or mycorrhizae) located in the suction zone.

Fixes the plant in the soil.

Nutrients (starch, inulin, etc.) are stored in the roots.

There is symbiosis with soil microorganisms - bacteria and fungi.

Vegetative propagation of many plants occurs.

Some roots have a function respiratory organ(Monstera, Philodendron, etc.).

The roots of a number of plants perform the function of “stilted” roots (ficus banyan, pandanus, etc.).

The root is capable of metamorphosis (thickenings of the main root form “root crops” in carrots, parsley, etc.; thickenings of lateral or adventitious roots form root tubers in dahlias, groundnuts, chistyak, etc., shortening of roots in bulbous plants). The roots of one plant are the root system. The root system can be taprooted or fibrous. Well developed in the tap root system main root. The majority has it dicotyledonous plants(beets, carrots). U perennial plants the main root can die, and nutrition occurs through the lateral roots, so the main root can only be traced in young plants. The fibrous root system is formed only by adventitious and lateral roots. It does not have a main root. Monocot plants, for example, cereals and onions, have such a system. Root systems take up a lot of space in the soil. For example, in rye, the roots spread 1-1.5 m wide and penetrate up to 2 m deep. Metamorphoses of the root system associated with living conditions: * Aerial roots. * Stilt roots. * Respiratory roots. * Board-shaped roots. * Roots - supports. (columnar). *Roots - trailers.

10. Root metamorphoses and the functions they perform. The influence of environmental factors on the formation and development of the root system of plants. Mycorrhiza. Mushroom root. Attached to plants and are in a state of symbiosis. Fungi living on roots use carbohydrates that are formed as a result of photosynthesis; in turn deliver water and minerals.

Nodules. The roots of leguminous plants thicken, forming outgrowths, due to bacteria from the genus Rhizobium. Bacteria are able to fix atmospheric nitrogen, converting it into a bound state; some of these compounds are absorbed by higher plants. Thanks to this, the soil is enriched with nitrogenous substances. Retractile (contractile) roots. Such roots are capable of drawing regeneration organs into the soil to a certain depth. Retraction (geophily) occurs due to the reduction of typical (main, lateral, adventitious roots) or only specialized contractile roots.. Board-shaped roots. These are large plagiotropic lateral roots, along the entire length of which a flat outgrowth is formed. Such roots are characteristic of trees in the upper and middle layers of the tropical rain forest. The process of formation of a plank-shaped outgrowth begins at the oldest part of the root - the basal one. Columnar roots. Characteristic of tropical ficus bengal, ficus sacred, etc. Some of the aerial roots hanging down exhibit positive geotropism - they reach the soil, penetrate into it and branch, forming an underground root system. Subsequently, they turn into powerful pillar-like supports. Stilt and respiratory roots. Mangrove plants that develop stilted roots are rhizophores. Stilt roots are metamorphosed adventitious roots. They are formed in seedlings on the hypocotyl, and then on the stem of the main shoot. Respiratory roots. The main adaptation to life on unstable silty soils in conditions of oxygen deficiency is a highly branched root system with respiratory roots - pneumatophores. The structure of pneumatophores is associated with the function they perform - ensuring gas exchange of roots and supplying their internal tissues with oxygen. Aerial roots are formed in many tropical herbaceous epiphytes. Their aerial roots hang freely in the air and are adapted to absorb moisture in the form of rain. To do this, velamen is formed from the protodermis, which absorbs water. Storage roots. Root tubers form due to metamorphosis of lateral and adventitious roots. Root tubers function only as storage organs. These roots combine the functions of storing and absorbing soil solutions. Root crop is an axial orthotropic structure formed by a thickened hypocotyl (neck), the basal part of the main root and the vegetative part of the main shoot. However, the activity of the cambium is limited. Further, the thickening of the root continues due to the pericycle. Cambium is added and a ring of meristematic tissue is formed.

Environmental factor may limit their growth and development. For example, with regular cultivation of the soil, the annual cultivation of any crop on it, the supply of mineral salts is depleted, so the growth of plants in this place stops or is limited. Even if all other conditions necessary for their growth and development are present. This factor is designated as limiting.
For example, the limiting factor for aquatic plants most often is oxygen. For sunny plants, for example sunflowers, this factor most often becomes sunlight (lighting).
The combination of such factors determines the conditions for the development of plants, their growth and the possibility of existence in a certain area. Although, like all living organisms, they can adapt to their living conditions. Let's look at how this happens:
Drought, high temperatures
Plants that grow in hot, dry climates, such as deserts, have strong root systems to be able to obtain water. For example, shrubs belonging to the Juzgun genus have 30-meter roots that go deep into the ground. But cacti have roots that are not deep, but widely spread under the surface of the soil. They collect water from a large surface of the soil during rare, short rains.
Collected water must be saved. Therefore, some succulent plants retain moisture in their leaves, branches, and trunks for a long time.
Among the green inhabitants of the desert there are those who have learned to survive even with many years of drought. Some, called ephemerals, live only a few days. Their seeds germinate, bloom and bear fruit as soon as the rain passes. At this time, the desert looks very beautiful - it blooms.
But lichens, some mosses and ferns, can live in a dehydrated state for a long time, until a rare rain falls.
Cold, wet tundra conditions
Here the plants adapt to very harsh conditions. Even in summer it rarely gets above 10 degrees Celsius. Summer lasts less than 2 months. But even during this period there are frosts.
There is little precipitation, so the snow cover that protects the plants is small. A strong gust of wind can completely expose them. But permafrost retains moisture and there is no shortage of it. Therefore, the roots of plants growing in such conditions are superficial. Plants are protected from cold by the thick skin of the leaves, a waxy coating on them, and a plug on the stem.
Due to the polar day in the tundra in summer, photosynthesis in the leaves continues around the clock. Therefore, during this time they manage to accumulate a sufficient, durable supply of necessary substances.
Interestingly, trees growing in tundra conditions produce seeds that grow once every 100 years. Seeds grow only when there is suitable conditions- after two warm summer seasons in a row. Many have adapted to reproduce vegetatively, for example, mosses and lichens.
sunlight
Light is very important for plants. Its amount affects their appearance and internal structure. For example, forest trees that grow tall enough to get enough light have a less spreading crown. Those who are in their shadow develop worse, are more oppressed. Their crowns are more spreading, and the leaves are arranged horizontally. This is necessary in order to catch as much sunlight as possible. Where there is enough sun, the leaves are arranged vertically to avoid overheating.

11. External and internal structure of the root. Root growth. Absorption of water from the soil by roots. The root is the main organ of a higher plant. The root is an axial organ, usually cylindrical in shape, with radial symmetry, and geotropic. It grows as long as the apical meristem, covered with a root cap, is preserved. On the root, unlike the shoot, leaves never form, but, like the shoot, the root branches, forming root system.

The root system is the collection of roots of one plant. The nature of the root system depends on the ratio of the growth of the main, lateral and adventitious roots. The root system distinguishes between the main (1), lateral (2) and adventitious roots (3)

main root develops from the embryonic root.

Subordinate clauses are called the roots developing on the stem part of the shoot. Adventitious roots can also grow on leaves.

Lateral roots occur on roots of all types (main, lateral and accessory)

Internal structure of the root. At the tip of the root there are cells of educational tissue. They actively share. This section of the root, about 1 mm long, is called division zone . The root division zone is externally protected from damage by the root cap. The cells of the cap secrete mucus, which envelops the root tip, facilitating its passage through the soil.

Above the division zone there is a smooth section of the root about 3-9 mm long. Here the cells no longer divide, but strongly elongate (grow) and thereby increase the length of the root - this stretch zone , or growth zone root

Above the growth zone there is a section of the root with root hairs - these are long outgrowths of the cells of the outer covering of the root. With their help, the root absorbs (sucks) water with dissolved mineral salts from the soil. The root hairs act like little pumps. This is why the root area with root hairs is called suction zone or absorption zone The absorption zone occupies 2-3 cm on the root. Root hairs live for 10-20 days. The root hair cell is surrounded by a thin membrane and contains cytoplasm, a nucleus and a vacuole with cell sap. Under the skin there are large round cells with thin membranes - the cortex. The inner layer of the cortex (endoderm) is formed by cells with suberized membranes. Endoderm cells do not allow water to pass through. Among them there are living thin-walled cells - passage cells. Through them, water from the bark enters the conducting tissues, which are located in the central part of the stem under the endodermis. Conductive tissues in the root form longitudinal cords, where sections of xylem alternate with sections of phloem. The xylem elements are located opposite the passage cells. The spaces between xylem and phloem are filled with living parenchyma cells. Conductive tissues form a central or axial cylinder. With age, educational tissue, the cambium, appears between xylem and phloem. Thanks to the division of cambium cells, new elements of xylem and phloem, mechanical tissue, are formed, which ensures the growth of the root in thickness. At the same time, the root acquires additional functions - support and storage of nutrients. Above is venue area root, through the cells of which water and mineral salts absorbed by root hairs move to the stem. The conduction zone is the longest and strongest part of the root. There is already a well-formed conducting tissue here. Water with dissolved salts rises through the cells of the conducting tissue to the stem - this rising current, and from the stem and leaves to the root, organic substances necessary for the life of root cells move - this is downward current.The roots most often take the form: cylindrical (horseradish); conical or conical (in dandelion); thread-like (in rye, wheat, onions).

From the soil, water enters the root hairs by osmosis, passing through their membranes. This fills the cell with water. Some of the water enters the vacuole and dilutes the cell sap. Thus, different densities and pressures are created in neighboring cells. A cell with a more concentrated vacuolar sap takes some of the water from a cell with a dilute vacuolar sap. This cell transfers water through a chain through osmosis to another neighboring cell. In addition, part of the water passes through the intercellular spaces, like capillaries between the cells of the cortex. Having reached the endodermis, water rushes through the passage cells into the xylem. Since the surface area of the endodermal passage cells is much less area On the surface of the root skin, significant pressure is created at the entrance to the central cylinder, which allows water to penetrate the xylem vessels. This pressure is called root pressure. Thanks to root pressure, water not only enters the central cylinder, but also rises into the stem to a considerable height.

Root growth:

The root of a plant grows throughout its life. As a result, it constantly increases, going deeper into the soil and moving away from the stem. Although roots have unlimited growth capacity, they almost never have the opportunity to use it to its full potential. In the soil, the plant's roots are interfered with by the roots of other plants, and there may not be enough water and nutrients. However, if a plant is grown artificially in very favorable conditions, then it is capable of developing roots of enormous mass.

The roots grow from their apical part, which is located at the very bottom of the root. When the root tip is removed, its growth in length stops. However, the formation of many lateral roots begins.

The root always grows downwards. Regardless of which way the seed is turned, the root of the seedling will begin to grow downward. Absorption of water from the soil by roots: Water and minerals are absorbed by the epidermal cells near the tip of the root. Numerous root hairs, which are outgrowths of epidermal cells, penetrate into cracks between soil particles and increase the absorption surface of the root many times over.

12. Escape and its functions. Structure and types of shoots. Branching and growth of shoots. The escape- this is an unbranched stem with leaves and buds located on it - the rudiments of new shoots that arise in a certain order. These primordia of new shoots ensure the growth of the shoot and its branching. Shoots are vegetative and spore-bearing

The functions of vegetative shoots include: the shoot serves to strengthen the leaves on it, ensures the movement of minerals to the leaves and the outflow organic compounds, serves as a reproductive organ (strawberry, currant, poplar), serves as a storage organ (potato tuber), and spore-bearing shoots perform the function of reproduction.

Monopodial-growth occurs due to the apical bud

Sympodial- shoot growth continues at the expense of the nearest lateral bud

False dichotomous-after the apical bud dies, shoots grow (lilac, maple)

Dichotomous- from the apical bud two lateral buds are formed, giving two shoots

Tillering– This is branching in which large lateral shoots grow from the lowest buds located near the surface of the earth or even underground. As a result of tillering, a bush is formed. Very dense perennial bushes are called turfs.

Structure and types of shoots:

Types:

The main shoot is a shoot that develops from the bud of the seed embryo.

Lateral shoot is a shoot that appears from a lateral axillary bud, due to which the stem branches.

An elongated shoot is a shoot with elongated internodes.

Shortened shoot - a shoot with shortened internodes.

A vegetative shoot is a shoot that bears leaves and buds.

Generative shoot - a shoot bearing reproductive organs - flowers, then fruits and seeds.

Branching and growth of shoots:

Branching- This is the formation of lateral shoots from axillary buds. A highly branched system of shoots is obtained when lateral shoots grow on one shoot, and the next lateral shoots grow on them, and so on. In this way, as much air supply as possible is captured.

The growth of shoots in length is due to the apical buds, and the formation of lateral shoots occurs due to the lateral (axillary) and adventitious buds

13. Structure, functions and types of kidneys. Diversity of buds, development of shoots from the bud. Bud- a rudimentary, not yet developed shoot, at the top of which there is a growth cone.

Vegetative (leaf bud)- a bud consisting of a shortened stem with rudimentary leaves and a growth cone.

Generative (flower) bud- a bud represented by a shortened stem with the rudiments of a flower or inflorescence. A flower bud containing 1 flower is called a bud. Types of kidneys.

There are several types of buds in plants. They are usually divided according to several criteria.

1. By origin:* axillary or exogenous (arise from secondary tubercles), form only on the shoot* subordinate clauses or endogenous (arising from the cambium, pericycle or parenchyma). An axillary bud occurs only on the shoot and can be recognized by the presence of a leaf or leaf scar at its base. An adventitious bud appears on any plant organ, serving as a reserve bud for various types of damage.

2. By location on the shoot:* apical(always axillary) * lateral(can be axillary and accessory).

3) By duration:* summer, functioning* wintering, i.e. in a state of winter dormancy* sleeping, those. being in a state of long-term, even long-term, dormancy.

These buds are clearly distinguishable in appearance. Summer buds have a light green color, the growth cone is elongated, because There is intensive growth of the apical meristem and the formation of leaves. The outside of the summer bud is covered with green young leaves. With the onset of autumn, growth in the summer bud slows down and then stops. The outer leaves stop growing and specialize into protective structures - bud scales. Their epidermis becomes lignified, and sclereids and containers with balms and resins are formed in the mesophyll. The kidney scales, glued together with resins, hermetically seal the access of air inside the kidney. in spring next year the wintering bud turns into an active summer bud, which turns into a new shoot. When the overwintering bud awakens, the meristem cells begin to divide and the internodes lengthen; as a result, the bud scales fall off, leaving leaf scars on the stem, the totality of which forms a bud ring (a trace from the overwintering or dormant bud). From these rings you can determine the age of the shoot. Some of the axillary buds remain dormant. These are living buds, they receive nutrition, but do not grow, so they are called dormant. If the shoots located above them die, then the dormant buds can “wake up” and produce new shoots. This ability is used in agricultural practice and in floriculture when shaping the appearance of plants.

14. Anatomical structure of the stem of herbaceous dicotyledonous and monocotyledonous plants. The structure of the stem of a monocot plant. The most important of the monocotyledonous plants are cereals, the stem of which is called a culm. Despite its small thickness, the straw has significant strength. It consists of nodes and internodes. The latter are hollow inside and have the greatest length at the top and the shortest at the bottom. The most tender parts of the culm are located above the nodes. In these places there is educational tissue, so the cereals grow at their internodes. This growth of cereals is called intercalary growth. The stems of monocotyledonous plants have a well-defined bunch structure. Vascular-fibrous bundles closed type(without cambium) are distributed throughout the entire thickness of the stem. On the surface, the stem is covered with a single-layer epidermis, which subsequently becomes lignified, forming a layer of cuticle. Located directly under the epidermis, the primary cortex consists of a thin layer of living parenchyma cells with chlorophyll grains. Deep from the parenchyma cells there is a central cylinder, which begins on the outside with mechanical sclerenchyma tissue of pericyclic origin. Sclerenchyma gives the stem strength. The main part of the central cylinder consists of large parenchyma cells with intercellular spaces and randomly located fibrovascular bundles. The shape of the tufts on the cross section of the stem is oval; all areas of wood gravitate closer to the center, and bast areas - to the surface of the stem. There is no cambium in the vascular-fibrous bundle, and the stem cannot thicken. Each bundle is surrounded on the outside by mechanical fabric. The maximum amount of mechanical tissue is concentrated around fascicles near the surface of the stem.

Anatomical structure of the stems of dicotyledonous plants already in early age differs from the structure of monocots (Fig. 1). The vascular bundles here are located in one circle. Between them is the main parenchymal tissue, forming the medullary rays. The main parenchyma is also located inward from the bundles, where it forms the core of the stem, which in some plants (buttercup, angelica, etc.) turns into a cavity, in others (sunflower, hemp, etc.) is well preserved. The structural features of the vascular-fibrous bundles of dicotyledonous plants are that they are open, that is, they have tufted cambium, consisting of several regular rows of lower dividing cells; inside of them appear cells from which secondary wood is formed, and outwards - cells from which secondary bast (phloem) is formed.. Parenchyma cells of the main tissue surrounding the bundle, often filled with storage substances; various vessels that conduct water; cambial cells, from which new bundle elements arise; sieve tubes that conduct organic matter, and mechanical cells (bast fibers) that give strength to the bundle. The dead elements are water-conducting vessels and mechanical tissues, and all the rest are living cells that have a protoplast inside. By dividing cambium cells in the radial direction (that is, perpendicular to the surface of the stem), the cambial ring lengthens, and by dividing them in the tangential direction (that is, parallel to the surface of the stem), the stem thickens. 10-20 times more cells are deposited towards the wood than towards the bast, and therefore the wood grows much faster than the bast.
The classes Dicotyledons and Monocots are divided into families. Plants of each family have general signs. In flowering plants, the main characteristics are the structure of the flower and fruit, the type of inflorescence, as well as the features of the external and internal structure of the vegetative organs.

15. Anatomical structure of the stem of woody dicotyledonous plants. Annual shoots of linden are covered with epidermis. By autumn they become lignified and the epidermis is replaced by cork. During the growing season, a cork cambium is laid under the epidermis, which forms a cork on the outside, and phelloderm cells inside. These three integumentary tissues form the integumentary complex of the periderm. The cells of the epidermis gradually become within 2-3 years they peel off and die. Under the periderm is the primary cortex. The outer layers are represented by cells of lamellar chlorophyll-bearing collenchisma, then there is chlorophyll-bearing parenchyma and a weakly defined endoderm.

Most of the stem consists of tissues formed by the activity of the cambium. The boundaries of bark and wood run along the cambium. All tissues lying outside the cambium are called bark. The bark can be primary and secondary. The primary has already been described, the secondary bark consists of phloem, or phloem, and heart-shaped rays. Phloem is trapezoidal in shape. and the medullary rays are presented in the form of triangles, the apices of which converge towards the center of the stem to the core.

The medullary rays penetrate the wood through and through. These are the primary medullary rays, through which water and organic substances move in a rational direction. The medullary rays are represented by parenchyma cells, inside which by autumn reserve nutrients (starch) are deposited, which are spent in the spring on the growth of young shoots.

In the phloem, layers of hard bast (bast fibers) and soft (living thin-walled elements) alternate. The bast (slerenchyma) fibers of the bast are represented by dead prosenchymal cells with thick lignified walls. The soft bast consists of sieve tubes with companion cells (conductive tissue) and phloem parenchyma , in which nutrients (carbohydrates, fats, etc.) accumulate. In the spring, these substances are spent on the growth of shoots. Organic substances move through the sieve tubes. In the spring, when the bark is cut, the juice flows out. The cambium is represented by one dense ring of thin-walled rectangular cells with a large nucleus and cytoplasm. In autumn, the cambium cells become thick-walled and its activity ceases.

To the center of the stem inward from the cambium, wood is formed, consisting of vessels (tracheas), tracheids, wood parenchyma and sclerenchyma wood (libriforms). Libriforms are a collection of narrow, thick-walled and lignified cells of mechanical tissue. Wood is deposited in the form of annual rings (a combination of spring and autumn elements of wood) wider in spring and summer and narrower in autumn, as well as in dry summer. On a transverse cut of a tree, the relative age of the tree can be determined by the number of growth rings. In the spring, during the period of sap flow, water with dissolved mineral salts rises through the vessels of the wood.

In the central part of the stem there is a core, consisting of parenchyma cells and surrounded by small vessels of primary wood.

16. Leaf, its functions, parts of the leaf. Variety of leaves. The outside of the sheet is covered peel. It is formed by a layer of transparent cells of the integumentary tissue, tightly adjacent to each other. The skin protects the internal tissues of the leaf. The walls of its cells are transparent, which allows light to easily penetrate into the leaf.

On the lower surface of the leaf, among the transparent cells of the skin, there are very small paired green cells, between which there is a gap. Couple guard cells And stomatal fissure between them they call stomata . Moving apart and closing, these two cells either open or close the stomata. Gas exchange occurs through the stomata and moisture evaporates.

When there is insufficient water supply, the plant stomata are closed. As water enters the plant, they open.

A leaf is a lateral flat organ of a plant that performs the functions of photosynthesis, transpiration and gas exchange. Leaf cells contain chloroplasts with chlorophyll, in which the “production” of organic substances - photosynthesis - takes place in the light from water and carbon dioxide.

Functions Water for photosynthesis comes from the root. Some of the water evaporates from the leaves to prevent overheating of the plants. sun rays. During evaporation, excess heat is consumed and the plant does not overheat. The evaporation of water by leaves is called transpiration.

Leaves absorb from the air carbon dioxide, and release oxygen produced during photosynthesis. This process is called gas exchange.

Leaf parts

External structure leaf. In most plants, a leaf consists of a blade and a petiole. The lamina is the expanded lamellar part of the leaf, hence its name. The leaf blade performs the main functions of the leaf. At the bottom it turns into a petiole - the narrowed stem-like part of the leaf.

With the help of a petiole, the leaf is attached to the stem. Such leaves are called petiolate. The petiole can change its position in space, and along with it the leaf blade also changes position, which finds itself in the most favorable lighting conditions. The petiole contains vascular bundles that connect the vessels of the stem with the vessels leaf blade. Thanks to the elasticity of the petiole, the leaf blade can more easily withstand the impact of raindrops, hail, and gusts of wind on the leaf. In some plants, at the base of the petiole there are stipules that look like films, scales, small leaves (willow, rose hips, hawthorn, white acacia, peas, clover, etc.). The main function of stipules is to protect young developing leaves. The stipules may be green, in which case they are similar to the leaf blade, but usually much smaller. In peas, meadow cherry and many other plants, stipules remain throughout the life of the leaf and perform the function of photosynthesis. In linden, birch, and oak, filmy stipules fall off at the young leaf stage. In some plants - caragana tree, white acacia - they are modified into spines and perform protective function, protecting plants from damage by animals.

There are plants whose leaves do not have petioles. Such leaves are called sessile. They are attached to the stem by the base of the leaf blade. Sessile leaves of aloe, carnation, flax, tradescantia. In some plants (rye, wheat, etc.), the base of the leaf grows and covers the stem. This enlarged base is called the vagina.

One of the most important parts of the plant is the root. It is this that ensures the normal functioning of trees, grasses, shrubs and even aquatic flora. Often the above-ground part of the plant is just the tip of the iceberg. Much of it may be underground. It is no coincidence that the roots are so large, because they have very important functions. Let's take a closer look at the amazing features of the plant world.

Functions of roots

The roots of each plant perform a range of tasks that may vary from species to species, but in most cases these tasks are the same for both trees and their smaller relatives. The roots of trees and other above-ground plants help them stay upright and resist wind and animals. This is especially true for big trees due to their mass and height. The root system helps them attach to the bottom and also prevents some of them from flipping over.

Another function of roots is nutritional. They absorb water from the soil and deliver it to the right places. They also synthesize some amino acids, alkaloids and other elements that plants need. Some of the flora representatives generally store useful material directly in the roots (mostly starch and other carbohydrates). Also, do not forget about such a thing as mycorrhiza - a symbiosis of a plant with fungi. The root plays a key role in it. such that some plants reproduce with its help - by root suckers.

Types of roots

Depending on the structure and function assigned to them, there are different types of roots. The first one is the main one. It grows directly from the seed when it germinates, to then become the main axis of the entire root system. In addition to the main root, there are also subordinate roots. They form from a variety of places - on stems, sometimes on leaves, and in some cases even on flowers. Another type is lateral roots. They emerge from the main or adventitious roots and branch laterally, forming more and more shoots.

Root systems

All the roots that the plant has form the root system. Depending on the role of various roots in the life of their owner, two types of systems are distinguished - taproot and fibrous. The first is distinguished by its focus on the main root, which grows most intensively. In this type, the main core develops much more efficiently than the side ones. However, this difference can be seen mainly in initial stage growth. Over time, the lateral roots begin to inexorably catch up with their main brother, and in old plants they are even larger than the main one. The rod system is typical mainly for

The second type is distinguished by features of the root opposite to the tap root. Such a system is called fibrous. It is characteristic of and distinguished by its numerous adventitious and lateral processes that fill the space under the plant. In this case, the main root is usually poorly developed or practically undeveloped.

Root. Root structure

Each root is divided into several zones, each of which is responsible for its own unique functions. One of most important places- division zone. It is located at the tip of each root and is responsible for its growth in length. Here, myriads of small cells constantly multiply. This process allows this part of the root to perform its difficult task. But the division zone is useless without the root cap, which is located at the end of each root. It consists of layers of fused cells that protect dividing cells from mechanical damage. In addition, the root cap secretes a kind of mucus that promotes the advancement of roots in the soil.

The next segment of the root is the elongation zone. It is located immediately behind the division area and is distinguished by the fact that its cells are constantly growing, although the process of division is almost completely absent in them. Then there is the suction zone - the place where water and minerals are drawn from the soil. This happens thanks to the myriads of tiny hairs covering this area. They significantly increase the total absorption area. At the same time, each hair works like a pump, sucking everything necessary from the soil. Next comes the conduction zone, which is responsible for transporting water with minerals to the top. Also from here the elements responsible for the vital activity of the root system descend. This part is very strong and it is from it that the lateral roots grow.

Cross section

If you cut the root, you can see the layers that make it up. First comes the skin, which is only one cell wide. Under it you can see the base of the root - the parenchyma. It is through its loose tissue that water and minerals enter the axial cylinder. It is formed by the pericambium - the educational structure that usually surrounds

Around the conducting cylinder there are tightly closed endodermal cells. They are waterproof, which forces life-giving moisture with minerals to move upward. But how then does the liquid get inside? This occurs thanks to special passage cells located on the endoderm. In most cases, the roots of grass, trees, and shrubs have this structure, although sometimes there are differences.

Mycorrhiza

Often, the roots of trees are the site of their symbiosis with other life forms. Fungi become the most common partners of plants.

This phenomenon is called mycorrhiza, which stands for “fungus root.” It's hard to believe, but most trees depend on a fruitful union with mycelium. Our usual birches, maples and oaks benefit greatly from this symbiosis.

When the mycelium interacts with the roots, an exchange occurs in which the mycelium gives essential minerals to the tree, receiving carbohydrates in return. This evolutionary move has allowed many plant species to live in conditions unsuitable for their species. Moreover, some representatives of the flora would not exist at all if it were not for mycorrhiza. In addition to symbiosis with fungi, there is a beneficial cooperation with bacteria, which the root resorts to. The structure of the root in this case will differ from what we are used to. On it you can find nodules in which special bacteria live, supplying the tree with atmospheric nitrogen.

Conclusion

One of the most important parts of any plant is the root. The structure of the root is ideally suited for the tasks it performs. The root system is an amazing mechanism that nourishes plants. It is not for nothing that various mystical movements believe that the tree combines the powers of heaven and earth. Its above-ground part absorbs sunlight, and the roots receive nutrition from the soil.

The significance of the root system is not obvious, since the main attention is drawn to the above-ground part of the plant: foliage, trunk, flower, stem. At the same time, the root remains in the shadows, modestly fulfilling its honorable mission.

In addition to the main root, many plants have numerous adventitious roots. The totality of all the roots of a plant is called the root system. In the case when the main root is slightly expressed, and the adventitious roots are significantly expressed, the root system is called fibrous. If the main root is significantly expressed, the root system is called tap root.

Some plants deposit reserve nutrients in the roots, such formations are called roots.

Basic functions of the root

Supporting (fixing the plant in the substrate);
Absorption, conduction of water and minerals;
Supply of nutrients;
Interaction with the roots of other plants, fungi, microorganisms living in the soil (mycorrhiza, legume nodules).
Synthesis of biologically active substances

In many plants, the roots perform special functions (aerial roots, sucker roots).

Origin of the root

The body of the first plants that came onto land was not yet divided into shoots and roots. It consisted of branches, some of which rose vertically, while others pressed against the soil and absorbed water and nutrients. Despite their primitive structure, these plants were provided with water and nutrients, since they were small in size and lived near water.

In the course of further evolution, some branches began to go deeper into the soil and gave rise to roots adapted to more advanced soil nutrition. This was accompanied by a profound restructuring of their structure and the appearance of specialized tissues. Root formation was a major evolutionary advance that enabled plants to colonize drier soils and produce large shoots that rose upward toward the light. For example, bryophytes do not have real roots; their vegetative body small sizes- up to 30 cm, mosses live in damp places. Ferns develop true roots, this leads to an increase in the size of the vegetative body and to the flourishing of this group during the Carboniferous period.

Modifications and specialization of roots

The roots of some buildings tend to metamorphose.

Root modifications:

Root vegetable- modified succulent root. The main root and Bottom part stem. Most root plants are biennial.
Root tubers(root cones) are formed as a result of thickening of the lateral and adventitious roots.
Roots-holds- peculiar adventitious roots. With the help of these roots, the plant “glues” to any support.
Stilt roots- act as a support.
Aerial roots- lateral roots, growing downwards. Absorb rainwater and oxygen from the air. Formed in many tropical plants under conditions of high humidity.
Mycorrhiza- cohabitation of the roots of higher plants with fungal hyphae. With such mutually beneficial cohabitation, called symbiosis, the plant receives water with nutrients dissolved in it from the fungus, and the fungus receives organic substances. Mycorrhiza is characteristic of the roots of many higher plants, especially woody ones. Fungal hyphae, entwining thick lignified roots of trees and shrubs, perform the functions of root hairs.
Bacterial nodules on the roots of higher plants- cohabitation of higher plants with nitrogen-fixing bacteria - they are modified lateral roots adapted to symbiosis with bacteria. Bacteria penetrate through the root hairs into young roots and cause them to form nodules. With such symbiotic cohabitation, bacteria convert nitrogen contained in the air into a mineral form available to plants. And plants, in turn, provide bacteria with a special habitat in which there is no competition with other types of soil bacteria. Bacteria also use substances found in the roots of higher plants. More often than others, bacterial nodules form on the roots of plants of the legume family. Due to this feature, legume seeds are rich in protein, and members of the family are widely used in crop rotation to enrich the soil with nitrogen.
Storage roots- root vegetables consist mainly of storage tissue (turnips, carrots, parsley).
Breathing roots- in tropical plants - perform the function of additional respiration.

Features of the structure of roots

The collection of roots of one plant is called the root system.

Root systems include roots of various natures.

There are:

main root,
lateral roots,
adventitious roots.

The main root develops from the embryonic root. Lateral roots occur on any root as a side branch. Adventitious roots are formed by the shoot and its parts.

Types of root systems

In the tap root system, the main root is highly developed and clearly visible among other roots (characteristic of dicotyledons). In the fibrous root system, at the early stages of development, the main root, formed by the embryonic root, dies, and the root system is composed of adventitious roots (typical of monocots). The taproot system usually penetrates deeper into the soil than the fibrous root system, but the fibrous root system better entwines adjacent soil particles, especially in its upper fertile layer. The branched root system is dominated by equally developed main and several lateral roots (in tree species, strawberries).

Young root ending zones

Different parts of the root perform different functions and differ in appearance. These parts are called zones.

The outside tip of the root is always covered with a root cap, which protects the delicate cells of the meristem. The cap consists of living cells that are constantly renewed. The cells of the root cap secrete mucus, which covers the surface of the young root. Thanks to mucus, friction with the soil is reduced; its particles easily stick to the root ends and root hairs. In rare cases, the roots lack a root cap (aquatic plants). Under the cap there is a division zone, represented by educational tissue - the meristem.

The cells of the division zone are thin-walled and filled with cytoplasm; there are no vacuoles. The division zone can be distinguished on a living root by its yellowish color; its length is about 1 mm. Following the division zone is a stretch zone. It is also small in length, only a few millimeters, stands out with a light color and is seemingly transparent. The cells of the growth zone no longer divide, but are able to stretch in the longitudinal direction, pushing the root end deeper into the soil. Within the growth zone, cells are divided into tissues.

The end of the growth zone is clearly visible by the appearance of numerous root hairs. Root hairs are located in the suction zone, the function of which is clear from its name. Its length ranges from several millimeters to several centimeters. Unlike the growth zone, sections of this zone no longer shift relative to the soil particles. Young roots absorb the bulk of water and nutrients using root hairs.

Root hairs appear in the form of small papillae - cell outgrowths. After a certain time, the root hair dies off. Its lifespan does not exceed 10-20 days.

Above the absorption zone, where the root hairs disappear, the conduction zone begins. Through this part of the root, water and solutions of mineral salts absorbed by root hairs are transported to the higher lying parts of the plant.

Anatomical structure of the root

In order to become familiar with the system of absorption and movement of water along the root, it is necessary to consider the internal structure of the root. In the growth zone, cells begin to differentiate into tissues, and in the absorption and conduction zone, conductive tissues are formed, ensuring the rise of nutrient solutions to the above-ground part of the plant.

Already at the very beginning of the root growth zone, the mass of cells differentiates into three zones: rhizoderm, cortex and axial cylinder.

Rhizoderma- integumentary tissue that covers the outside of young root endings. It contains root hairs and is involved in absorption processes. In the absorption zone, the rhizoderm passively or actively absorbs elements of mineral nutrition, expending energy in the latter case. In this regard, rhizoderm cells are rich in mitochondria.

Literature

V. Chub. Underground life of plants. Roots. // Floriculture, November-December 2007, No. 6, p. 46 - 51.

Wikimedia Foundation. 2010.

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Questions:
1. Root functions
2.Types of roots
3.Types of root system
4. Root zones
5. Modification of roots
6. Life processes at the root

1. Root functions
Root- This is the underground organ of the plant.
Main functions of the root:
- supporting: roots anchor the plant in the soil and hold it throughout its life;
- nutritious: through the roots the plant receives water with dissolved minerals and organic substances;
- storage: nutrients can accumulate in some roots.

2. Types of roots

3. Types of root system

The roots of one plant are the root system. The root system can be taprooted or fibrous. The taproot system has a well-developed main root. Most dicotyledonous plants (beets, carrots) have it. In perennial plants, the main root may die, and nutrition occurs through the lateral roots, so the main root can only be traced in young plants.

The fibrous root system is formed only by adventitious and lateral roots. It does not have a main root. Monocot plants, for example, cereals and onions, have such a system.

Root systems take up a lot of space in the soil. For example, in rye, the roots spread 1-1.5 m wide and penetrate up to 2 m deep.

4. Root zones
In a young root, the following zones can be distinguished: root cap, division zone, growth zone, suction zone.

Root cap has a darker color, this is the very tip of the root. The cells of the root cap protect the root tip from damage by solid soil particles. The cells of the cap are formed by the integumentary tissue and are constantly renewed.

Suction zone has many root hairs, which are elongated cells no more than 10 mm long. This zone looks like a cannon, because... root hairs are very small. Root hair cells, like other cells, have cytoplasm, a nucleus and vacuoles with cell sap. These cells are short-lived, die quickly, and in their place new ones are formed from younger surface cells located closer to the tip of the root. The task of root hairs is to absorb water and dissolved nutrients. The absorption zone is constantly moving due to cell renewal. It is delicate and easily damaged during transplantation. The cells of the main tissue are present here.

Venue area . It is located above the suction, has no root hairs, the surface is covered with integumentary tissue, and in the thickness there is conductive tissue. The cells of the conduction zone are vessels through which water and dissolved substances move into the stem and into the leaves. Here there are also vascular cells through which organic substances from the leaves enter the root.

The entire root is covered with mechanical tissue cells, which ensures the strength and elasticity of the root. The cells are elongated, covered with a thick membrane and filled with air.

5. Modification of roots

The depth of root penetration into the soil depends on the conditions in which the plants are located. The length of the roots is affected by humidity, soil composition, and permafrost.

Long roots form in plants in dry places. This is especially true for desert plants. Thus, the root system of camel thorn reaches 15-25 m in length. In wheat on non-irrigated fields, the roots reach a length of up to 2.5 m, and on irrigated fields - 50 cm and their density increases.

Permafrost limits the depth of root growth. For example, in the tundra dwarf birch roots are only 20 cm. The roots are superficial, branched.

In the process of adaptation to environmental conditions, plant roots changed and began to perform additional functions.

1. Root tubers act as a storehouse of nutrients instead of fruits. Such tubers arise as a result of thickening of the lateral or adventitious roots. For example, dahlias.

2. Root vegetables - modifications of the main root of plants such as carrots, turnips, and beets. Root crops are formed bottom stem and top part main root. Unlike fruits, they do not have seeds. Root crops are biennial plants. In the first year of life, they do not bloom and accumulate a lot of nutrients in the roots. On the second, they quickly bloom, using the accumulated nutrients and forming fruits and seeds.

3. Trailer roots (suckers) are adventitious roots that develop in plants in tropical areas. They allow you to attach to vertical supports (to a wall, rock, tree trunk), bringing the foliage to the light. An example would be ivy and clematis.

4. Bacterial nodules. The lateral roots of clover, lupine, and alfalfa are peculiarly changed. Bacteria settle in young lateral roots, which promotes the absorption of gaseous nitrogen from the soil air. Such roots take on the appearance of nodules. Thanks to these bacteria, these plants are able to live in nitrogen-poor soils and make them more fertile.

5. Aerial roots are formed in plants growing in humid equatorial and tropical forests. Such roots hang down and absorb rainwater from the air - they are found in orchids, bromeliads, some ferns, and monstera.

Aerial buttress roots are adventitious roots that form on tree branches and reach the ground. Occurs in banyan and ficus trees.

6. Stilt roots. Plants growing in the intertidal zone develop stilted roots. They hold large leafy shoots on unstable muddy soil high above the water.

7. Respiratory roots are formed in plants that lack oxygen for respiration. Plants grow in excessively moist places - in marshy swamps, creeks, sea estuaries. The roots grow vertically upward and reach the surface, absorbing air. Examples include brittle willow, swamp cypress, and mangrove forests.

6. Life processes at the root

1 - Absorption of water by roots

The absorption of water by root hairs from the soil nutrient solution and its conduction through the cells of the primary cortex occurs due to the difference in pressure and osmosis. Osmotic pressure in the cells forces minerals to penetrate into the cells, because. their salt content is less than in the soil. The intensity of water absorption by root hairs is called suction force. If the concentration of substances in the soil nutrient solution is higher than inside the cell, then water will leave the cells and plasmolysis will occur - the plants will wither. This phenomenon is observed in conditions of dry soil, as well as with excessive application of mineral fertilizers. Root pressure can be confirmed through a series of experiments.

A plant with roots is lowered into a glass of water. Pour a thin layer over the water to protect it from evaporation. vegetable oil and mark the level. After a day or two, the water in the tank dropped below the mark. Consequently, the roots sucked up the water and brought it up to the leaves.

Goal: find out the basic function of the root.

We cut off the stem of the plant, leaving a stump 2-3 cm high. We put a rubber tube 3 cm long on the stump, and on the upper end we put a curved glass tube 20-25 cm high. Water in glass tube rises and flows out. This proves that the root absorbs water from the soil into the stem.

Goal: find out how temperature affects root function.

One glass should be with warm water (+17-18ºС), and the other with cold water (+1-2ºС). In the first case, water is released abundantly, in the second - little, or stops altogether. This is proof that temperature greatly influences root function.

Warm water is actively absorbed by the roots. Root pressure increases.

Cold water is poorly absorbed by the roots. In this case, root pressure drops.

2 - Mineral nutrition

The physiological role of minerals is very great. They are the basis for the synthesis of organic compounds and directly affect metabolism; act as catalysts for biochemical reactions; affect cell turgor and protoplasm permeability; are centers of electrical and radioactive phenomena in plant organisms. The root provides mineral nutrition to the plant.

3 - Root Breathing

For normal height and the development of the plant, it is necessary that fresh air reaches the roots.

Goal: check for breathing at the roots.

Let's take two identical vessels with water. Place developing seedlings in each vessel. Every day we saturate the water in one of the vessels with air using a spray bottle. Pour a thin layer of vegetable oil onto the surface of the water in the second vessel, as it delays the flow of air into the water. After some time, the plant in the second vessel will stop growing, wither, and eventually die. The death of the plant occurs due to a lack of air necessary for the root to breathe.

It has been established that normal plant development is possible only if there is nutrient solution three substances - nitrogen, phosphorus and sulfur and four metals - potassium, magnesium, calcium and iron. Each of these elements has an individual meaning and cannot be replaced by another. These are macroelements, their concentration in the plant is 10-2–10%. For normal plant development, microelements are needed, the concentration of which in the cell is 10-5–10-3%. These are boron, cobalt, copper, zinc, manganese, molybdenum, etc. All these elements are present in the soil, but sometimes in insufficient quantities. Therefore, mineral and organic fertilizers are added to the soil.

The plant grows and develops normally if the environment surrounding the roots contains all the necessary nutrients. This environment for most plants is soil.

The roots of the vast majority of plants perform six main functions:

Roots hold the plant in a certain position. This function is obvious for terrestrial plants; it is especially significant for large trees with a large mass of branches and leaves. In many aquatic plants, fastening to the bottom allows the leaves to be advantageously distributed in space. In floating plants, such as duckweed, the roots prevent the plant from turning over.

The roots provide soil nutrition to the plant, absorbing water from the soil with minerals dissolved in it, and conducting substances to the shoot (Fig. 1).

In some plants, reserve nutrients such as starch and other carbohydrates are stored in the main root.

In the roots, the formation of certain substances necessary for the plant body occurs. Thus, in the roots, nitrates are reduced to nitrites, and some amino acids and alkaloids are synthesized.

Roots can carry out symbiosis with fungi and microorganisms living in the soil (mycorrhiza, nodules of representatives of the legume family).

With the help of roots, vegetative propagation can be carried out (for example, by root suckers). Plants such as dandelion, plum, raspberry, and lilac reproduce by root suckers.

Absorption of water and minerals by the root

This function arose in plants in connection with their access to land.

The absorption of water and minerals by the plant occurs independently of each other, since these processes are based on different mechanisms of action. Water passes into the root cells passively, and minerals enter the root cells mainly as a result of active transport, which involves energy expenditure.

Rice. 1. Horizontal water transport:

1 - root hair; 2 - apoplastic pathway; 3 - symplastic path; 4 - epiblema (rhizoderm); 5 - endoderm; 6 - pericycle; 7 - xylem vessels; 8 - primary cortex; 9 - plasmodesmata; 10 - Casparian belts.

Water enters the plant mainly according to the law of osmosis. Root hairs have a huge vacuole with concentrated cell sap, which has a high osmotic potential, which ensures the flow of water from the soil solution into the root hair.

Horizontal transport of substances

Water enters the plant body through rhizoderm, the surface of which is greatly enlarged due to the presence of root hairs.

In this zone, in the conducting cylinder of the root, the root conducting system is formed - xylem vessels, which is necessary to ensure the upward flow of water and minerals.

Water with mineral salts is absorbed by root hairs. The endoderm pumps these substances into the conducting cylinder, creating root pressure and preventing water from escaping. Water with salts enters the vessels of the conducting cylinder and rises through the transpiration current along the stem to the leaves.

VERTICAL TRANSPORT OF SUBSTANCES

Roots carry water and minerals to the ground organs of the plant.

Vertical movement of water occurs through dead xylem cells that are unable to push water to the leaves. This movement is supported by the transpiration function of the leaves.

Definition

Root pressure- the force with which the root pumps water into the stem.

The root actively pumps mineral and organic substances into xylem vessels; as a result, increased osmotic pressure occurs in the root vessels relative to the pressure of the soil solution. The root pressure can reach 3 atm. Evidence of the presence of root pressure is, for example, guttation(release of water droplets from leaves).

OSMOSIS AND TURGOR

The flow of water from the soil into the root and its movement along the stem is determined by the difference in osmotic pressure.

The pressure of the cell sap solution exerted on the cytoplasm and cell walls is called osmotic.

Since the concentration of organic and mineral substances inside the root hair is higher than in the soil, the environment in relation to the cell sap of the root hairs is a hypotonic solution. By absorbing water, the hair cell dilutes the concentration of cell sap. Gradually, the cell sap of the hairs becomes hypotonic in relation to the deeper located cells of the cortex. And water, entering them from root hairs, also reduces the concentration of substances in the juice. Now, in the next groups of cells, the concentration of juice will be higher than in the previous ones. As water is absorbed, the concentration of sap from the cortex cells to the xylem vessels will increase. However, due to the fact that water leaves the root hair, the concentration of organic matter in it increases again, which ensures further absorption of water from the soil. The outer membrane of the cells of the root skin and root hair is a semi-permeable membrane, permeable to the soil solution and almost impermeable to substances dissolved in the cell sap.

The one-way passage of solutions through semi-permeable membranes that separate solutions of different concentrations is called osmosis.

Osmotic pressure is opposed by the pressure of a stretched cell wall - turgorous. The intensity of water absorption by the outer root cells depends on the suction force with which water penetrates into the cell vacuole.

Definition

Sucking force is the difference between osmotic and turgor pressures.

The suction force of all the root hairs of the root creates root pressure, due to which water enters the vessels and rises. The force with which water flows from the root to the stem is called root pressure.

Thus, the movement of water and salts dissolved in it is facilitated by the suction force of root hairs, root pressure, the adhesion force between water molecules and the walls of blood vessels, as well as the suction force of leaves, which, constantly evaporating water, attract it from the roots.

Expand

In the living cells of the root, the first selection of substances allowed into the plant occurs. The participation of living cells in the acceptance of substances determines the selective ability of the plant, due to which various substances are absorbed into different quantities. Since intake is highly dependent on consumption, the plant takes in some salts and then others at different stages of development. The more developed the root system, the more active the absorption of water and salts.

Situations often arise when plant roots perform some additional functions or one of the main functions requires more development. In such cases, modifications of the roots are formed (see Modifications of plant organs).