Plants have a root. Plant roots

What are plants?
Both plants and animals are made up of cells. Cells produce chemical substances, on which growth and livelihood depends. In addition, both plants and animals use gases, water and minerals for their life processes. Both plants and animals pass by life cycles during which they are born, grow, multiply and die. But plants have one very significant difference: they are not able to move from place to place, since the roots are fixed in one place. They have the ability to carry out a special process called photosynthesis. For this process, plants use the energy of solar radiation contained in the air. carbon dioxide as well as water and minerals from the soil - and from all this they develop their own nutrition. Animals cannot do this. To obtain the energy necessary for life, they must search for food, eat plants or other animals.
The waste product of photosynthesis is oxygen, a gas that all animals need to breathe. And this means that if there was no plant life, then there would be no animal life on Earth either.

What do plants eat?
This is not to say that plants eat - in the literal sense, meaning, for example, the food of animals. Green plants obtain food for themselves through a chemical process known as photosynthesis, in which energy from the sun's radiation, carbon dioxide and water are used to produce substances called monosaccharides. Then these monosaccharides are converted into starches, proteins or fats, and these, in turn, provide the plant with the necessary energy for vital processes to occur and plants to grow. The plant food we buy in stores is a mixture of minerals that plants need to grow. These minerals include nitrogen, phosphorus and potassium. As a rule, the plant is able to extract them from the soil on which it grows: it absorbs them through the roots along with water. But farmers, gardeners and everyone who grows plants add minerals in addition to make the plants stronger and stronger.

Do all plants have roots?
The simplest plants have no roots. For example, unicellular green algae float on the surface of the water. In the same way, many seaweeds float on the surface of the water, which are algae more large species... The same algae that attach to the seabed do so with special anchoring structures that are not true roots. Seaweed assimilates water and minerals from the sea using all of its parts. Likewise, simple plants such as mosses form a dense, low carpet in low places and absorb the necessary moisture directly from their surroundings. Instead of roots, they have filamentous outgrowths (they are called rhizoids), and with the help of these outgrowths they cling to trees or stones. But all plants are more complex shapes- ferns, conifers (coniferous plants) and flowering plants - have stems and roots. Stems and roots are an internal distribution system that is able to carry water and minerals from where the plant takes them to wherever they are needed.

Do all plants have leaves?
The simplest plants such as algae have no leaves. Mosses have some kind of leaves in which photosynthesis takes place, but these are not real leaves,
Plants of more complex types have leaves. The shape of the leaf is often determined by the environmental conditions in which the plants grow. Usually, where there is a lot of sunlight and water, the leaves are wide and flat, forming a large surface on which photosynthesis can take place. However, in places where it is dry and cold, serious problem not excluded due to moisture loss. For example, the elongated, needle-shaped leaves of conifers (including pines) help retain water. Due to this, such plants are able to live in very dry and cold places, far to the north and at high altitudes.

If the plants are cut, do they feel it?
Plants do not have nervous system and they don't feel when they are being cut. But plants feel the power of attraction, light and touch.

How are seeds obtained?
In conifers (coniferous plants) and in flowering trees there are seeds.
Conifers - pine, spruce, fir, cypress, have male and female cones. Male cones have pollen sacs that release millions of tiny particles of pollen - male reproductive cells - into the air. The wind carries them to the female cones, which have reproductive cells in the ovules. The ovules are sticky, and pollen sticks to them. When the male and female cells meet, fertilization occurs, and seeds are generated in the scales of the female cone. As the seeds grow, the cone grows in size. When the seeds are ripe (which usually takes a couple of years), the bud opens and releases them. The seeds have a hard shell and a certain amount of food inside for use in the initial stage of growth (if the seed falls on a place suitable for growth); in addition, the seeds are equipped with wings that help them fly in the wind. Seed formation in flowering plants is somewhat more complicated. Male cells develop in stamens and “travel” inside hard pollen grains. Female cells, ovules, develop deep in the ovary of a flower and are enclosed in a pistil. Top part The pistil (called the stigma) is long and sticky, making it a good target for pollen. After the pollen enters the stigma, a small tube grows from the pollen grain. The male cell passes through this tube and reaches the ovule. Fertilization occurs and seeds begin to develop.
Wind, water, insects and other animals help transfer pollen from one flower to another.

How do seeds become plants?
If the seeds simply fall down into the soil under the parent tree, they will have to fight for their survival - for sunlight, water and minerals. This means that in order to start growing, turning into new plants, most seeds need to look for other places, traveling in the wind, on water, or with the help of insects and animals. Some seeds, such as conifers and maples, have wings. Others, like dandelion seeds, are equipped with parachutes made of delicate hairs. And in fact, and in another case, the seeds can, thanks to these features, fly in the wind over long distances; they sometimes land in places suitable for germination. Other seeds are carried by water: thanks to their hard, waterproof shell, coconuts, for example, can swim miles across the sea before they find a shore with suitable conditions for germination. Animals are excellent seed distributors. They carry seeds to different places in the mouth (as a squirrel does when storing supplies for the winter); sometimes the seeds cling to animal fur or feathers.
Some seeds can wait for years for the right moment to germinate, and some never get this opportunity.

Why do the flowers have bright colors?
Reproduction of many flowering plants depends on whether insects and birds carry pollen from one plant to another, and plants can attract specific animals with their bright or aromatic flowers. Nourishing pollen and flower nectar form an important part of the diet of many creatures. When birds and insects come to the flower to eat, pollen sticks to their legs and bodies. Flying in search of food to flowers of other plants of the same species, insects and birds leave some of the pollen in them, and thus cross-pollination occurs. In plants pollinated by the wind, flowers are usually small, inconspicuous, without bright colors (and many have no nectar), since they do not need to attract the attention of insects and birds to spread their pollen.

Why do flowers differ from one another?
What a flower looks like depends a lot on the way it is pollinated. Flowers that are pollinated by the wind are usually small, inconspicuous, without bright colors, since they do not need to attract the attention of insects and birds to spread their pollen. Flowers, on the other hand, which depend on pollen-carrying creatures for pollination, should attract insects and birds to help cross-pollinate. And these flowers often adapt - in terms of color, smell or shape - to specific insects or animals. Many flowers that attract bees have special parts that serve as "landing platforms" so that bees arriving to them can rest on such platforms while they feed. Bees can distinguish most colors (except red), and bright flowers they are attracted. Butterflies love many of the colors that attract bees. Butterflies also have elongated mouthpieces, and butterflies also like to "land" when they feed. However, large wings prevent butterflies from diving deep into the flower. Therefore, butterflies prefer flat, wide flowers and those that grow in clusters. Butterflies are attracted to flowers of all kinds of bright colors. But moths, which look like butterflies, are nocturnal, that is, they are active at night. Therefore, flowers that attract moths are mostly light in color or White color, that is, one that is clearly distinguishable in the dark. And since moths prefer to flutter in the air rather than “land” on a flower, they don't need “landing platforms” on the flowers they fly to.

Why do some flowers smell like perfume?
Flowers have a scent, so they attract those they need for cross-pollination. Some insects and other animals that get their food from flowers have a keen sense of smell. Bees, for example, have sensitive odor detectors in their antennae. Therefore, most flowers pollinated by bees have a smell: Flowers that open only at night often have strong smell, which helps those who receive their food from them - for example, night moths, to find them in the dark. However, not all flowers have a pleasant smell. Some flowers smell like rotting meat or other decaying substances, thus attracting flies to them. Flowers that have an unpleasant (from a human point of view) odor also attract bats, which need plants for food.

Why are some plants poisonous?
Plants cannot escape from "predators" - animals that will eat them, so some plants have developed other methods of defense. Many plants have poisonous parts. Rhubarb leaves, for example, are very dangerous to eat, although the stems of these plants are quite safe and tasty. Scientists believe that plants often have one venomous part to ward off predators; other parts remain harmless and safe for pollinating animals.

Why do some plants have thorns?
As mentioned above, plants are deprived of the opportunity to escape from hungry animals, so they produce different shapes protection. In some plants, some parts are poisonous, others have thorns and various sharp outgrowths, with the help of which they protect themselves from animals that want to eat them. The thorns hurt the animals trying to get close to such plants, and they try to stay away from them.

How can desert plants live without water?
In a real desert, where it never rains, plants cannot live. But in places where cacti and other desert plants grow, it still rains sometimes - even if it happens once every couple of years. When it rains, desert plants quickly absorb water from their roots, storing it in thick leaves and stems. And this accumulated moisture allows them to wait for the next rain.

Are mushrooms plants?
Mushrooms are not actually plants. They do not have true roots, leaves, and stems, and they lack the chlorophyll that plants use to make their own food (which is why they are not green and they do not need sunlight). Mushrooms feed mainly on the dead flesh of plants and animals, thus cleaning the environment and enriching the soil.

What is the most dangerous mushroom?
Most dangerous mushroom- death cap. It is often found near birches and oaks. Even a small piece of this mushroom can lead to death, which occurs in 6-15 hours. The poison of many mushrooms is destroyed by boiling, but the poison of the pale toadstool is not destroyed by heat treatment.

How long do trees live?
For a long time, it was believed that the oldest living trees in the world are sequoias, which grow in the central Pacific coast of the United States of America. Some of these trees are almost 4,000 years old. However, several decades ago, it was discovered conifer tree that lives even longer: the bristlecone pine, native to the United States of America in the states of Nevada, Arizona and southern California. The oldest of these living trees is 4,600 years old.

Why do some trees drop their leaves in autumn?
The loss of leaves prepares such trees for a lack of water in winter time: There is little moisture in cold dry air, and snow can only give water after it has melted. In addition, since the soil freezes in winter, it is difficult for the tree to get water from its roots. In the spring and summer, gases and moisture escape from the tree through thousands of microscopic stomata in the leaves. Without leaves, a tree can retain maximum water. Also, if the trees did not drop their leaves, then the mass of snow on the leaves of the tree branches most likely would not withstand and break.

What are vegetables?
Vegetables are the parts of plants that we eat: roots, stems, leaves. Carrots and potatoes are essentially roots. Asparagus are the stems of plants. Cabbage, spinach, salads are the leaves. V Everyday life we also call many fruits vegetables - zucchini, tomatoes, cucumbers and so on.

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

1. Root functions
Root Is an underground organ of a plant.
The main functions of the root:
- supporting: the roots fix the plant in the soil and hold it throughout its life;
- nutritious: through the roots the plant receives water with dissolved mineral and organic substances;
- storing: in some roots they can accumulate nutrients.

2. Types of roots

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

3. Types of root system

The roots of one plant are root system... The root system is pivotal and fibrous. In the tap root system, the main root is well developed. Most dicotyledonous plants (beets, carrots) have it. Have perennial plants the main root can die off and nutrition occurs at the expense of 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. There is no main root in it. Monocotyledonous plants have such a system, for example, cereals, onions.

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

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

Root cap has more dark color, this is the very tip of the root. Root cap cells protect the root apex from damage by solid soil particles. The cap cells 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 area looks like a cannon, because root hairs are very small. Root hair cells, like other cells, have a cytoplasm, a nucleus, and vacuoles with cell sap. These cells are short-lived, die off quickly, and in their place new ones are formed from the younger superficial cells located closer to the root tip. The task of the root hairs is to absorb water with dissolved nutrients. The suction zone is constantly moving due to cell renewal. It is delicate and easily damaged when transplanted. The cells of the underlying tissue are present here.

Zone ... It is located above the suction, does not have root hairs, the surface is covered with integumentary tissue, and there is a conductive tissue in the thickness. The cells of the conduction zone are vessels through which water with solutes moves to the stem and leaves. There are also vascular cells through which organic matter from the leaves enters the root.

The whole root is covered with cells mechanical tissue, 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 found. The length of the roots is influenced by moisture, soil composition, permafrost.

Long roots are formed in plants in arid places. This is especially true for desert plants. So in a camel thorn, the root system reaches 15-25 m in length. In wheat in non-irrigated fields, the roots reach 2.5 m in length, and in irrigated fields - 50 cm, and their density increases.

Permafrost limits the growth of roots in depth. For example, in the tundra near dwarf birch roots only 20 cm. Roots are shallow, branched.

In the process of adapting to environmental conditions, the roots of plants have changed and began to perform additional functions.

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

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

3. Attachment roots (suckers) - adventitious measles that develop in plants in tropical places. They allow you to attach to vertical supports (to a wall, rock, tree trunk), bringing 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 the young lateral roots, which facilitates the assimilation nitrogen gas soil air. Such roots take the form 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 - found in orchids, bromeliads, some ferns, monstera.

Aerial support roots are adventitious roots that form on tree branches and reach the ground. Occur in banyan, ficus.

6. Stilted roots. Plants growing in the intertidal zone develop stilted roots. They hold large leafy shoots high above the water on unsteady muddy ground.

7. Respiratory roots are formed in plants that do not have enough oxygen to breathe. Plants grow in excessively humid places - in swampy swamps, creeks, sea estuaries. The roots grow vertically upward and emerge to the surface, absorbing air. Examples include brittle willow, marsh cypress, 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 enter the cells. their salt content in them is less than in the soil. The rate at which the root hairs absorb water is called the suction force. If the concentration of substances in the soil nutrient solution is higher than inside the cell, then the water will leave the cells and plasmolysis will occur - the plants will wither. This phenomenon is observed in dry soil conditions, as well as with excessive application mineral fertilizers... Root pressure can be confirmed by a series of experiments.

The plant with roots is dipped into a glass of water. Pour on top of the water to protect it from evaporation thin layer vegetable oil and mark the level. After a day or two, the water in the container dropped below the mark. Therefore, the roots sucked in the water and brought it up to the leaves.

Purpose: to find out the main function of the root.

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

Purpose: to find out how temperature affects the functioning of the root.

One glass should be with warm water(+ 17-18 ° C), and the other with cold (+ 1-2 ° C). In the first case, water is released abundantly, in the second - little, or completely stops. This is proof that temperature has a profound effect on the functioning of the root.

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

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

2 - Mineral nutrition

The physiological role of minerals is very important. They are the basis for synthesis organic compounds and directly affect the metabolism; serve as catalysts for biochemical reactions; affect cell turgor and protoplasm permeability; are the centers of electrical and radioactive phenomena in plant organisms. Using the root is carried out mineral nutrition plants.

3 - Breathing roots

For normal growth and development of a plant, it is necessary that Fresh air.

Purpose: to check the presence of respiration at the roots.

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

It has been established that the normal development of plants is possible only if the nutrient solution contains 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 macronutrients, their concentration in the plant is 10-2-10%. For the normal development of plants, 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 applied to the soil.

The plant grows and develops normally if all the necessary nutrients are contained in the environment surrounding the roots. Soil is such a medium for most plants.

1. What role do roots play in plant life?

2. How do roots differ from rhizoids?

Rhizoid is a filamentous root-like formation in mosses, lichens, some algae and fungi, which serves to fix them on the substrate and absorb water and nutrients from it. Unlike true roots, rhizoids do not have conductive tissues.

3. Do all plants have roots?

The simplest plants have no roots. For example, unicellular green algae float on the surface of the water. Likewise, many algae, which are algae of larger species, float on the surface of the water.

Simple plants such as mosses absorb the moisture they need directly from their surroundings. Instead of roots, they have filamentous outgrowths (rhizoids), and with the help of these outgrowths they cling to trees or stones. But all plants of more complex forms - ferns, conifers and flowering plants- have stems and roots.

To learn how to distinguish between types of root systems, complete the lab.

Core and fibrous root systems

1. Consider the root systems of the plants proposed to you. How do they differ?

There are two types of root systems - pivotal and fibrous. The root system, in which the main root, similar to the core, is most developed, is called the core root.

2. Read in the textbook which root systems are called pivotal and which are fibrous.

3. Select tap root plants.

Most dicotyledonous plants, such as sorrel, carrots, beets, etc., have a core root system.

4. Select plants with a fibrous root system.

A fibrous root system is characteristic of monocotyledonous plants - wheat, barley, onions, garlic, etc.

5. By the structure of the root system, determine which plants are monocotyledonous, which are dicotyledons.

6. Fill in the table "The structure of root systems in different plants."

Questions

1. What functions does the root perform?

The roots anchor the plant in the soil and hold it firmly throughout its life. Through them, the plant receives water and minerals dissolved in it from the soil. In the roots of some plants, storage substances can be deposited and accumulated.

2. Which root is called the main one, and which ones are called adventitious and lateral?

The main root develops from the embryonic root. The roots that form on the stems, and in some plants and on the leaves, are called adventitious. Lateral roots extend from the main and adventitious roots.

3. Which root system is called pivotal, and which is called fibrous?

The root system, in which the main root, similar to the core, is most developed, is called the core root.

Fibrous is the root system of the adventitious and lateral roots. The main root in plants with a fibrous system is underdeveloped or dies off early.

Think

When growing corn, potatoes, cabbage, tomatoes and other plants, hilling is widely used, that is, the lower part of the stem is sprinkled with earth (Fig. 6). Why do they do this?

For the appearance of adventitious roots and improving plant nutrition, loosening the soil. In potatoes, this operation stimulates the formation of tubers, because its root system grows better in breadth than in depth.

Tasks

1. Have indoor plants coleus and pelargonium, adventitious roots are easily formed. Carefully cut off a few side shoots with 4-5 leaves. Delete two bottom sheets and place the shoots in glasses or jars of water. Watch for the formation of adventitious roots. After the roots are 1 cm long, plant the plants in pots with nutritious soil. Water them regularly.

2. Record the observations and discuss with other students.

Coleus cuttings root very well in water. After putting them in water, white roots will appear in a couple of weeks (or maybe even earlier).

The time for cutting the roots in pelargonium is 5-15 days. The root system develops in three to four weeks, after which the plants can be planted in separate pots.

3. Germinate radish, pea or bean seeds and wheat kernels. You will need them in the next lesson.

1. Rinse the grain 2-3 times

2. Pour with purified water (the volume of water is 1.5 - 2 times the volume of grain)

3. Soak for 10-12 hours at a temperature of 16-21 C˚ (the duration of soaking depends on the temperature - the higher the temperature, the less you need to soak)

4. Rinse 2 times

5. Place the lid on leaking

6. Watering at least 3 times a day (3-4 days) GRAIN SHOULD NOT FLY !!! THE WATER MUST BE DRAINED FULLY !!!

1. Rinse the seeds;

2. Put the seeds in a container so that they occupy no more than half of its height;

3. Pour water over the seeds so that the water is on top of the seeds by at least 2 centimeters;

4. After about 8 hours, drain the water and rinse the seeds, which should have changed somewhat;

5. Cover them with damp gauze or some other clean damp cloth (already without water).

The root in plants performs various mechanical and physiological functions... The most important of them are: absorption of water, organic and mineral substances from the soil and their transfer to roots and leaves. In addition, the roots help the plant to gain a foothold in the soil, it is less sensitive to influences atmospheric phenomena(strong wind, rain, etc.). They practically grow together with, therefore, quite often when the plant is pulled out from the tiny hairs, soil particles remain.

With the help of the roots, the plant is connected with the organisms that inhabit the layer (mycorrhiza). This required part plant organism helps in synthesis and accumulates substances useful for plant growth. In addition, the root is responsible for vegetative propagation - the formation of a new plant, which appears by the disintegration of tubers or rhizomes in the mother.

But not all plants have the same roots. A fairly common structure is the taproot. Such an underground structure of a plant organism has one large rod, from which a large number of small hairs. There is a tuft, in which there are several large rod hairs (for example, many types of herbs). Such plants are extremely useful for the soil, since their dense structure is from erosion.

Everyone knows plants that, as they grow, accumulate many useful substances in the roots. Sweet potatoes are a prime example. In addition, there are plants that do not need soil. So, some types of orchids are on trees, and they receive all the necessary substances and moisture from the air, and, for example, poison ivy is attached to trees with the help of aerial roots.

Core root system

The tap root system is characterized by a developed main root. It has the shape of a rod, and it is because of this similarity given type and got its name. The lateral roots of such plants are extremely weak. The root has the ability to grow indefinitely, and the main root in taproot plants reaches impressive sizes. This is necessary to optimize the extraction of water and nutrients from soils, where groundwater occurs at significant depths. Many species have a core root system - trees, shrubs, and herbaceous plants: birch, oak, dandelion, sunflower,.

Fibrous root system

In plants with a fibrous root system, the main root is practically undeveloped. Instead, they are characterized by numerous branching adventitious or lateral roots of approximately the same length. Often, in plants, the main root first grows, from which the lateral roots begin to depart, but in the process of further development of the plant, it dies off. A fibrous root system is characteristic of plants that reproduce vegetatively. It usually occurs in - coconut tree, orchids, paparotnikovid, cereals.

Mixed root system

A mixed or combined root system is also often distinguished. Plants belonging to this type have a well-differentiated main root and multiple lateral and adventitious roots. This structure of the root system can be observed, for example, in strawberries and strawberries.

Root modifications

The roots of some plants are so modified that it is difficult at first glance to attribute them to any type. These modifications include root crops - thickening of the main root and lower part of the stem, which can be seen in turnips and carrots, as well as root tubers - thickening of lateral and adventitious roots, which can be observed in sweet potatoes. Also, some roots can serve not for the absorption of water with salts dissolved in it, but for breathing (respiratory roots) or additional support (stilted roots).

The roots fix the plant in the soil, provide soil water-mineral nutrition, sometimes serve as a place for the deposition of reserve nutrients. In the process of adaptation to environmental conditions, the roots of some plants acquire additional functions and are modified.

What are the types of roots

In plants, there are main, adventitious and lateral roots. When a seed germinates, an embryonic root first develops from it, which later becomes the main root. On the stems and leaves of some plants, adventitious roots grow. Lateral roots can also extend from the main and adventitious roots.

Root systems

All plant roots fold into a root system, which is tap and fibrous. In the core system, the main root is more developed than the others and resembles a core, while in the fibrous system it is insufficiently developed or dies off early. The first is most typical for, the second - for monocots. However, the main root is usually well expressed only in young dicotyledonous plants, and in old ones it gradually dies off, giving way to adventitious roots growing from the stem.

How deep are the roots

The depth of the roots in the soil depends on the growing conditions of the plant. Wheat roots, for example, grow on dry fields by 2.5 m, and on irrigated fields - no more than half a meter. However, in the latter case, the root system is more dense.

The tundra plants themselves are undersized, and their roots are concentrated at the surface due to permafrost. In a dwarf birch, for example, they are at a maximum depth of about 20 cm. The roots of desert plants, on the contrary, are very long - this is necessary to reach groundwater... For example, a leafless barnyard is rooted in the soil by 15 m.

Root modifications

To adapt to conditions environment the roots of some plants have changed and acquired additional functions. So, the roots of radish, beets, turnips, turnips and rutabagas, formed by the main root and lower parts stem, store nutrients. The thickening of the lateral and adventitious roots of the cleaver and dahlias became root tubers. Ivy attachment roots help the plant to attach to a support (wall, tree) and bring the leaves to the light.

Phylogenetically, the root arose later than the stem and leaf - in connection with the transition of plants to life on land and probably originated from root-like underground branches. The root has no leaves or buds arranged in a certain order. It is characterized by apical growth in length, its lateral ramifications arise from internal tissues, the growth point is covered with a root cap. The root system is formed throughout the life of a plant organism. Sometimes the root can serve as a place of deposition in the supply of nutrients. In this case, it is modified.

Types of roots

The main root is formed from the embryonic root during seed germination. Lateral roots extend from it.

Adventitious roots develop on stems and leaves.

Lateral roots are branches of any root.

Each root (main, lateral, adventitious) has the ability to branch, which significantly increases the surface of the root system, and this contributes to better strengthening plants in the soil and improve its nutrition.

Types of root systems

There are two main types of root systems: pivotal, with a well-developed main root, and fibrous. The fibrous root system consists of a large number of adventitious roots of the same size. The entire mass of roots consists of lateral or adventitious roots and looks like a lobe.

The highly branched root system forms a huge absorbing surface. For example,

the total length of the roots of winter rye reaches 600 km;
length of root hairs - 10,000 km;
total root surface - 200 m 2.

This is many times the area of the above-ground mass.

If the plant has a well-expressed main root and adventitious roots develop, then a mixed root system is formed (cabbage, tomato).

External structure of the root. Internal structure of the root

Root zones

Root cap

The root grows in length at its tip, where young cells of the educational tissue are located. The growing part is covered with a root cap that protects the root tip from damage and makes it easier for the root to move through the soil during growth. The latter function is carried out due to the property of the outer walls of the root cap to be covered with mucus, which reduces friction between the root and soil particles. They can even push apart soil particles. The cells of the root cap are alive and often contain starch grains. The cells of the cap are constantly renewed due to division. Participates in positive geotropic reactions (direction of root growth towards the center of the Earth).

The cells of the division zone are actively dividing, the length of this zone in different types and different roots of the same plant are not the same.

A stretch zone (growth zone) is located behind the division zone. The length of this zone does not exceed a few millimeters.

As the linear growth is completed, the third stage of root formation begins - its differentiation, a zone of differentiation and specialization of cells (or a zone of root hairs and absorption) is formed. In this zone, the outer layer of the epiblema (rhizoderm) with root hairs, the layer of the primary cortex and the central cylinder are already distinguished.

Root hair structure

Root hairs are highly elongated outgrowths of the outer cells that cover the root. The number of root hairs is very large (per 1 mm 2 from 200 to 300 hairs). Their length reaches 10 mm. Hair is formed very quickly (in young apple seedlings in 30-40 hours). Root hairs are short-lived. They die off after 10-20 days, and new ones grow on the young part of the root. This ensures the development of new soil horizons by the root. The root grows continuously, forming more and more new areas of root hairs. The hairs can not only absorb ready-made solutions of substances, but also contribute to the dissolution of some soil substances, and then suck them in. The area of the root, where the root hairs have died off, is able to absorb water for some time, but then it becomes covered with a cork and loses this ability.

The hair sheath is very thin, which facilitates the absorption of nutrients. Almost the entire hair cell is occupied by a vacuole surrounded by a thin layer of cytoplasm. The nucleus is at the top of the cell. A mucous membrane forms around the cell, which promotes adhesion of root hairs with soil particles, which improves their contact and increases the hydrophilicity of the system. The absorption is facilitated by the release of acids (carbonic, malic, citric) by the root hairs, which dissolve mineral salts.

Root hairs also play a mechanical role - they serve as a support for the root apex, which passes between soil particles.

Under a microscope, on a transverse section of the root in the absorption zone, its structure at the cellular and tissue levels is visible. On the surface of the root is the rhizoderm, below it is the bark. The outer layer of the cortex is the exoderm, inward from it is the main parenchyma. Its thin-walled living cells perform a storage function, carry out solutions of nutrients in a radial direction - from the suction tissue to the vessels of the wood. They also synthesize a number of organic substances vital for the plant. The inner layer of the cortex is endoderm. Nutrient solutions from the cortex into the central cylinder through the endoderm cells pass only through the protoplast of the cells.

The bark surrounds the central cylinder of the root. It borders on a layer of cells that retain their ability to divide for a long time. This is the pericycle. Pericycle cells give rise to lateral roots, adventitious buds and secondary educational tissues... Inward from the pericycle, in the center of the root, are the conductive tissues: bast and wood. Together they form a radial conductive bundle.

The conductive system of the root conducts water and minerals from the root to the stem (upward current) and organic matter from the stem to the root (downward current). It consists of vascular fibrous bundles. The main components of the bundle are sections of the phloem (along which substances move to the root) and xylem (along which substances move from the root). The main conducting elements of phloem are sieve tubes, xylems are trachea (vessels) and tracheids.

Root vital processes

Root water transport

Absorption of water by root hairs from the soil nutrient solution and carrying it in the radial direction along the cells of the primary cortex through the passage cells in the endoderm to the xylem of the radial conducting bundle. The intensity of water absorption by root hairs is called the suction force (S), it is equal to the difference between osmotic (P) and turgor (T) pressure: S = P-T.

When the osmotic pressure is equal to the turgor pressure (P = T), then S = 0, water stops flowing into the cell of the root hair. If the concentration of substances in the soil nutrient solution is higher than inside the cell, then the water will leave the cells and plasmolysis will occur - the plants will wither. This phenomenon is observed in dry soil conditions, as well as with excessive application of mineral fertilizers. Inside the root cells, the sucking force of the root increases from the rhizoderm towards the central cylinder, so the water moves along the concentration gradient (i.e., from a place with a higher concentration of it to a place with a lower concentration) and creates root pressure, which raises the water column along the vessels of the xylem forming an upward current. This can be found on leafless spring trunks when "sap" is being collected, or on cut tree stumps. The outflow of water from wood, fresh stumps, leaves is called "crying" of plants. When the leaves bloom, they also create a sucking force and attract water to themselves - a continuous column of water is formed in each vessel - capillary tension. The root pressure is the lower motor of the water current, and the sucking force of the leaves is the upper one. This can be confirmed with the help of simple experiments.

Absorption of water by the roots

Target: figure out the basic function of the root.

What do we do: a plant grown on wet sawdust, shake off its root system and put its roots in a glass of water. Pour a thin layer of vegetable oil over the water to protect it from evaporation and mark the level.

What we observe: in a day or two, the water in the container dropped below the mark.

Result: therefore, the roots sucked in the water and brought it up to the leaves.

One more experiment can be done to prove the absorption of nutrients by the root.

What do we do: Cut off the stem of the plant, leaving a stump 2-3 cm high.Place a rubber tube 3 cm long on the stump, and put a curved glass tube 20-25 cm high on the upper end.

What we observe: the water in the glass tube rises and flows out.

Result: this proves that the root absorbs water from the soil into the stem.

Does the water temperature affect the rate of water absorption by the root?

Target: find out how temperature affects the work of the root.

What do we do: one glass should be with warm water (+ 17-18 ° C), and the other with cold (+ 1-2 ° C).

What we observe: in the first case, water is released abundantly, in the second - little, or completely stops.

Result: this is proof that temperature has a profound effect on the functioning of the root.

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

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

Mineral nutrition

The physiological role of minerals is very important. They are the basis for the synthesis of organic compounds, as well as factors that change the physical state of colloids, i.e. directly affect the metabolism and structure of the protoplast; serve as catalysts for biochemical reactions; affect cell turgor and protoplasm permeability; are the centers of electrical and radioactive phenomena in plant organisms.

It has been established that the normal development of plants is possible only if the nutrient solution contains three non-metals - nitrogen, phosphorus and sulfur and - and four metals - potassium, magnesium, calcium and iron. Each of these elements has an individual meaning and cannot be replaced by another. These are macronutrients, their concentration in the plant is 10 -2 –10%. For the normal development of plants, 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 applied to the soil.

The plant grows and develops normally if all the necessary nutrients are contained in the environment surrounding the roots. Soil is such a medium for most plants.

Breathing roots

For normal growth and development of the plant, it is necessary that fresh air flows to the root. Let's check if this is so?

Target: does the root need air?

What do we do: take two identical vessels with water. We will place developing seedlings in each vessel. We saturate the water in one of the vessels with air every day using a spray bottle. Pour a thin layer of vegetable oil on the surface of the water in the second vessel, as it delays the flow of air into the water.

What we observe: after a while, the plant in the second vessel will stop growing, wither, and eventually die.

Result: the death of the plant occurs due to the lack of air necessary for the respiration of the root.

Root modifications

Some plants store reserve nutrients in the roots. They accumulate carbohydrates, mineral salts, vitamins and other substances. Such roots grow strongly in thickness and acquire an unusual appearance... Both the root and the stem are involved in the formation of root crops.

Roots

If storage substances accumulate in the main root and at the base of the stem of the main shoot, root crops (carrots) are formed. Root-forming plants are mainly biennials. In the first year of life, they do not bloom and accumulate many nutrients in root crops. On the second, they bloom quickly, using accumulated nutrients and form fruits and seeds.

Root tubers

In dahlia, reserve substances accumulate in the adventitious roots, forming root tubers.

Bacterial nodules

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

Stilted

Stilted roots develop near the tidal ramp. They hold large leafy shoots high above the water on unsteady muddy ground.

Air

Tropical plants living on tree branches develop aerial roots. They are often found in orchids, bromeliads, and some ferns. Aerial roots hang freely in the air, not reaching the ground and absorbing moisture that falls on them from rain or dew.

Retracting

In bulbous and corms, such as crocuses, among the numerous filamentous roots, there are several thicker, so-called retracting roots. Shrinking, such roots pull the corms deeper into the soil.

Columnar

The ficus develops columnar aerial roots, or support roots.

Soil as a habitat for roots

The soil for plants is the medium from which it receives water and nutrients. The amount of minerals in the soil depends on specific features parent rock, the activity of organisms, from the life of the plants themselves, from the type of soil.

Soil particles compete with the roots for moisture, retaining it on their surface. This is the so-called bound water, which is subdivided into hygroscopic and film water. It is held by the forces of molecular attraction. The moisture available to the plant is represented by capillary water, which is concentrated in the small pores of the soil.

Antagonistic relations develop between the moisture and the air phase of the soil. The more large pores in the soil, the better the gas regime of these soils, the less moisture the soil retains. The most favorable water-air regime is maintained in structural soils, where water and air are located simultaneously and do not interfere with each other - water fills capillaries inside structural aggregates, and air fills large pores between them.

The nature of the interaction between the plant and the soil is largely related to the absorption capacity of the soil - the ability to retain or bind chemical compounds.

The microflora of the soil decomposes organic matter to simpler compounds, participates in the formation of the soil structure. The nature of these processes depends on the type of soil, chemical composition plant residues, physiological properties of microorganisms and other factors. Soil animals take part in the formation of the soil structure: annelids, insect larvae, etc.

As a result of the totality of biological and chemical processes in the soil, a complex complex of organic substances is formed, which is united by the term "humus".

Aquatic culture method

What salts the plant needs, and what effect they have on its growth and development, was established by experiment with aquatic crops. The aquatic culture method is the cultivation of plants not in soil, but in aqueous solution mineral salts. Depending on the goal in the experiment, you can exclude an individual salt from the solution, reduce or increase its content. It was found that fertilizers containing nitrogen promote the growth of plants containing phosphorus - the early ripening of fruits, and those containing potassium - the fastest outflow of organic matter from the leaves to the roots. In this regard, fertilizers containing nitrogen are recommended to be applied before sowing or in the first half of summer, containing phosphorus and potassium - in the second half of summer.

With the help of the method of aquatic cultures, it was possible to establish not only the plant's need for macronutrients, but also to clarify the role of various microelements.

Currently, there are cases when plants are grown using hydroponics and aeroponics.

Hydroponics - growing plants in containers filled with gravel. Nutrient solution containing necessary elements, is fed into the vessels from the bottom.

Aeroponics is an aerial plant culture. With this method, the root system is in the air and is automatically (several times within an hour) sprayed with a weak solution of nutrient salts.