Plants. plant roots

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 neither leaves nor buds arranged in a certain order. It is characterized by apical growth in length, its lateral branches arise from internal tissues, the growth point is covered with a root cap. root system formed throughout the life of the plant organism. Sometimes the root can serve as a place of deposition in the reserve nutrients. In this case, it is modified.

Root types

The main root is formed from the germinal root during seed germination. It has lateral roots.

Adventitious roots develop on stems and leaves.

Lateral roots are branches of any roots.

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

Types of root systems

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

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

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

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

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

External structure of the root. The internal structure of the root

Root zones

root cap

The root grows in length with its tip, where the young cells of the educational tissue are located. The growing part is covered with a root cap that protects the tip of the root from damage and facilitates the movement of the root in 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 living, often containing grains of starch. The cells of the cap are constantly updated due to division. Participates in positive geotropical 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 is different types and at different roots the same plant is not the same.

Behind the division zone there is an extension zone (growth zone). The length of this zone does not exceed a few millimeters.

As 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.

The structure of the root hair

Root hairs are highly elongated outgrowths of the outer cells covering the root. The number of root hairs is very high (from 200 to 300 hairs per 1 mm2). Their length reaches 10 mm. Hairs are formed very quickly (in young seedlings of an apple tree in 30-40 hours). Root hairs are short-lived. They die off in 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 continuously grows, forming more and more new areas of root hairs. Hair can not only absorb ready solutions substances, but also to promote the dissolution of certain soil substances, and then absorb them. The area of ​​the root where the root hairs have died off is able to absorb water for some time, but then becomes covered with cork and loses this ability.

The sheath of the hair 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 sheath is formed around the cell, which promotes gluing of root hairs with soil particles, which improves their contact and increases the hydrophilicity of the system. Absorption is facilitated by the secretion of acids (carbonic, malic, citric) by root hairs, which dissolve mineral salts.

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

Under a microscope on a cross section of the root in the absorption zone, its structure is visible at the cellular and tissue levels. On the surface of the root is the rhizoderm, below it is the bark. outer layer cortex - exoderm, inward from it - the main parenchyma. Its thin-walled living cells perform a storage function, conduct nutrient solutions in the radial direction - from the absorbing tissue to the vessels of the wood. They also synthesize a number of vital organic substances for the plant. The inner layer of the cortex is the endoderm. Nutrient solutions coming from the cortex to the central cylinder through the cells of the endoderm 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 the ability to divide for a long time. This is the pericycle. Pericycle cells give rise to lateral roots, adnexal buds, and secondary educational tissues. Inward from the pericycle, in the center of the root, there are conductive tissues: bast and wood. Together they form a radial conducting beam.

The conducting 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 the sections of the phloem (through which substances move to the root) and xylem (through which substances move from the root). The main conducting elements of the phloem are sieve tubes, xylems are tracheas (vessels) and tracheids.

Root life processes

Water transport at the root

Absorption of water by root hairs from the soil nutrient solution and its conduction in the radial direction along the cells of the primary cortex through the passage cells in the endodermis to the xylem of the radial vascular bundle. The intensity of water absorption by the root hairs is called the suction force (S), it is equal to the difference between the 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 root hair cell. 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 immoderate application. mineral fertilizers. Inside the root cells, the sucking power of the root increases from the rhizoderm towards the central cylinder, so water moves along the concentration gradient (i.e., from a place with a higher concentration to a place with a lower concentration) and creates a root pressure that raises a column of water along the xylem vessels , forming an upward current. It can be found on spring leafless trunks when "sap" is harvested, or on cut stumps. The outflow of water from wood, fresh stumps, leaves, is called the "weeping" 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. Root pressure is the lower motor of the water current, and the sucking power of the leaves is the upper one. You can confirm this with the help of simple experiments.

Absorption of water by roots

Target: find out the main function of the root.

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

What we observe: after a day or two, the water in the tank 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, proving the absorption of nutrients by the root.

What we do: 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 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 temperature of the water affect the rate of absorption of water by the root?

Target: find out how temperature affects root operation.

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

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 strong effect on root performance.

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

It has been established that the normal development of plants is possible only in the presence of three non-metals in the nutrient solution - nitrogen, phosphorus and sulfur and - and four metals - potassium, magnesium, calcium and iron. Each of these elements has an individual value 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 found 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 the environment surrounding the roots contains all the necessary nutrients. Soil is such an environment for most plants.

Root breath

For normal growth and development of a plant, it is necessary that the root receive Fresh air. Let's check if it is?

Target: do roots need air?

What we do: Let's take two identical vessels with water. We place developing seedlings in each vessel. We saturate the water in one of the vessels every day with air using a spray bottle. On the surface of the water in the second vessel, pour a thin layer of vegetable oil, 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

In some plants, reserve nutrients are deposited 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 reserve 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 mostly biennials. In the first year of life, they do not bloom and accumulate a lot of nutrients in root crops. On the second, they quickly bloom, using the accumulated nutrients and form fruits and seeds.

root tubers

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

bacterial nodules

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

stilted

A ramp growing in the intertidal zone develops stilted roots. High above the water, they hold large leafy shoots on unsteady muddy ground.

Air

At 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 from rain or dew that falls on them.

Retractors

In bulbs and tubers bulbous plants, for example, in crocuses, among the numerous thread-like roots, there are several thicker, so-called retracting roots. Reducing, such roots draw the corm deeper into the soil.

Pillar-shaped

Ficus develop columnar above-ground roots, or support roots.

Soil as a habitat for roots

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

Soil particles compete with roots for moisture, holding it on their surface. This is the so-called bound water, which is divided into hygroscopic and film. 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 the capillaries inside the structural aggregates, and air fills the large pores between them.

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

Soil microflora decomposes organic matter into simpler compounds, participates in the formation of 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 a combination of biological and chemical processes in the soil, a complex complex of organic substances is formed, which is combined by the term "humus".

Water culture method

What salts a plant needs, and what effect they have on its growth and development, was established by experiment with aquatic cultures. The aquatic culture method is the cultivation of plants not in soil, but in an aqueous solution of mineral salts. Depending on the goal in the experiment, you can exclude a separate salt from the solution, reduce or increase its content. It was found that fertilizers containing nitrogen promote the growth of plants, those containing phosphorus - the earliest ripening of fruits, and those containing potassium - the fastest outflow of organic matter from leaves to 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.

Using the method of water cultures, it was possible to establish not only the need of a plant for macroelements, but also to find out the role of various microelements.

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

Hydroponics is the cultivation of plants in pots filled with gravel. Nutrient solution containing necessary elements, is fed into the vessels from below.

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

The root is one of the main organs of the plant. It performs the function of absorption from the soil with elements of mineral nutrition dissolved in it. The root anchors and holds the plant in the soil. In addition, the roots are of metabolic importance. As a result of the primary synthesis, amino acids, hormones, etc. are formed in them, which are quickly included in the subsequent biosynthesis that occurs in the stem and leaves of the plant. Reserve nutrients can be deposited in the roots.

The root is an axial organ with a radially symmetrical anatomical structure. The root grows in length indefinitely due to the activity of the apical meristem, the delicate cells of which are almost always covered by the root cap. Unlike the shoot, the root is characterized by the absence of leaves and, therefore, dismemberment into nodes and internodes, as well as the presence of a cap. The entire growing part of the root does not exceed 1 cm.

The root cap, about 1 mm long, consists of loose thin-walled cells, which are constantly replaced by new ones. At the growing root, the cap is practically updated every day. The exfoliating cells form a slime that facilitates the movement of the root tip in the soil. The functions of the root cap are to protect the growing point and provide the roots with positive geotropism, which is especially pronounced at the main root.

A dividing zone about 1 mm in size, composed of meristem cells, adjoins the cap. The meristem in the process of mitotic divisions forms a mass of cells, providing root growth and replenishing the cells of the root cap.

The division zone is followed by the stretch zone. Here, the length of the root increases as a result of cell growth and the acquisition of a normal shape and size by them. The extension of the stretch zone is several millimeters.

Behind the stretch zone is the suction or absorption zone. In this zone, the cells of the primary integumentary root - the epiblema - form numerous root hairs that absorb the soil solution of minerals. The absorption zone is several centimeters long, it is here that the roots absorb the bulk of the water and salts dissolved in it. This zone, like the two previous ones, gradually moves, changing its place in the soil with the growth of the root. As the root grows, the root hairs die, the absorption zone appears on the newly growing root area, and the absorption of nutrients occurs from the new soil volume. In place of the former absorption zone, a conduction zone is formed.

The primary structure of the root

The primary structure of the root arises as a result of differentiation of the meristem of the apex. In the primary structure of the root near its tip, three layers are distinguished: the outer one is the epiblem, the middle one is the primary cortex, and the central axial cylinder is the stele.

Internal tissues naturally and in a certain sequence arise in the division zone in the apical meristem. There is a clear division into two sections. The outer section, originating from the middle layer of initial cells, is called Periblem. The inner section comes from the upper layer of initial cells and is called the Pleroma.

The pleroma gives rise to a stele, while some cells turn into vessels and tracheids, others into sieve tubes, others into core cells, etc. Periblema cells turn into the primary root cortex, consisting of parenchymal cells of the main tissue.

From the outer layer of cells - dermatogen - the primary integumentary tissue - epiblema, or rhizoderm - is isolated on the root surface. It is a single layer fabric reaching full development in the absorption zone. The formed rhizoderm forms the thinnest numerous outgrowths - root hairs. The root hair is short-lived and only in the growing state actively absorbs water and substances dissolved in it. The formation of hairs contributes to an increase in the total surface of the suction zone by 10 or more times. The length of the hair is not more than 1 mm. Its shell is very thin and consists of cellulose and pectin.

The primary cortex that emerged from the periblem consists of living thin-walled parenchymal cells and is represented by three distinct layers: endoderm, mesoderm, and exoderm.

Directly to the central cylinder (stele) adjoins the inner layer of the primary cortex - the endoderm. It consists of one row of cells with thickenings on the radial walls, the so-called Casparian bands, which are interspersed with thin-walled cells - through cells. Endoderm controls the flow of substances from the cortex to the central cylinder and vice versa.

Outward from the endoderm is the mesoderm - the middle layer of the primary cortex. It consists of loosely arranged cells with a system of intercellular spaces through which intensive gas exchange takes place. In the mesoderm, plastic substances are synthesized and moved to other tissues, reserve substances accumulate, and mycorrhiza is located.

The outer part of the primary cortex is called the exoderm. It is located directly under the rhizoderm, and as the root hairs die off, it appears on the root surface. In this case, the exoderm can perform the function of an integumentary tissue: thickening and corking of the cell membranes and the death of the cell contents occur. Among the corked cells, there remain non-corked cells through which substances pass.

The outer layer of the stele adjacent to the endoderm is called the pericycle. Its cells retain the ability to divide for a long time. In this layer, the lateral roots are laid, therefore the pericycle is called the root layer.

The roots are characterized by alternation of xylem and phloem sections in the stele. Xylem forms a star (with different number rays in different groups of plants), and between its rays is the phloem. In the very center of the root there may be xylem, sclerenchyma, or thin-walled parenchyma. Alternation of xylem and phloem along the periphery of the stele - salient feature root, which distinguishes it sharply from the stem.

The primary root structure described above is characteristic of young roots in all groups of higher plants. In club mosses, horsetails, ferns and representatives of the class Monocotyledons of the Department of Flowering Plants, the primary structure of the root is preserved throughout its life.

Secondary structure of the root

In the roots of gymnosperms and dicots angiosperms the primary structure of the root is preserved only until the beginning of its thickening as a result of the activity of secondary lateral meristems - cambium and phellogen (cork cambium). The process of secondary changes begins with the appearance of layers of cambium under the areas of the primary phloem, inward from it. The cambium arises from the poorly differentiated parenchyma of the central cylinder. Inside, it deposits elements of the secondary xylem (wood), outside - elements of the secondary phloem (bast). At first, the cambium layers are separated, but then they close and form a continuous layer. This is due to the division of pericycle cells against xylem rays. The cambial regions arising from the pericycle are formed only by the parenchymal cells of the medullary rays, the remaining cells of the cambium form the conducting elements - xylem and phloem. This process can continue for a long time, and the roots reach a considerable thickness. In the perennial root, in its central part, there remains a distinctly expressed primary ray xylem.

The cork cambium (phellogen) also appears in the pericycle. It lays out layers of cells of the secondary integumentary tissue - corks. The primary cortex (endoderm, mesoderm and exoderm), isolated by a cork layer from the internal living tissues, dies.

Root systems

The totality of all the roots of a plant is called the root system. Its composition involves the main root, lateral and adventitious roots.

The root system is rod or fibrous. The tap root system is characterized by the predominant development of the main root in length and thickness, and it stands out well from other roots. In the tap root system, in addition to the main and lateral roots, adventitious roots can also occur. Most dicotyledonous plants have a tap root system.

In all monocotyledonous plants and in some dicotyledonous plants, especially those that reproduce vegetatively, the main root dies off early or develops poorly, and the root system is formed from adventitious roots that arise at the base of the stem. Such a root system is called fibrous.

For the development of the root system great importance have soil properties. The soil affects the structure of the root system, the growth of its roots, the depth of penetration and their spatial distribution in the soil.

The secretions of the roots create in the soil around it a zone teeming with bacteria, fungi and other microorganisms, which is called the rhizosphere. The formation of surface, deep and other root systems reflects the adaptation of plants to the conditions of soil water supply.

In addition, in any root system there are continuous changes associated with the age of plants, the change of seasons, etc.

Root specializations and metamorphoses

In addition to the main functions, the roots can perform some others, while the roots undergo modifications, their metamorphoses.

In nature, the phenomenon of symbiosis of the roots of higher plants with soil fungi is widespread. The ends of the roots, braided from the surface with hyphae of the fungus or containing them in the root bark, are called mycorrhiza (literally - "fungal root"). Mycorrhiza is external, or ectotrophic, internal, or endotrophic, and external-internal.

Ectotrophic mycorrhiza replaces the plant's root hairs, which usually do not develop. External and external-internal mycorrhiza was noted in woody and shrubby plants (for example, in oak, maple, birch, hazel, etc.).

Internal mycorrhiza develops in many species of herbaceous and woody plants (for example, in many species of cereals, onions, walnut, grapes, etc.). Species of such families as Heather, Wintergreen and Orchids cannot exist without mycorrhiza.

The symbiotic relationship between a fungus and an autotrophic plant is manifested in the following. Autotrophic plants provide the fungal symbiont with soluble carbohydrates available to it. In turn, the fungal symbiont supplies the plant with the most important mineral substances (the nitrogen-fixing fungal symbiont delivers nitrogen compounds to the plant, quickly ferments sparingly soluble reserve nutrients, bringing them to glucose, the excess of which increases the absorption activity of the roots.

In addition to mycorrhiza (mycosymbiotrophy), in nature there is a symbiosis of roots with bacteria (bacteriosymbiotrophy), which does not have such widespread like the first one. Sometimes growths called nodules form on the roots. Inside the nodules there are many nodule bacteria that have the ability to fix atmospheric nitrogen.

storage roots

Many plants are able to store reserve nutrients (starch, inulin, sugar, etc.) in their roots. Modified roots that perform the function of storage are called "root crops" (for example, in beets, carrots, etc.) or root cones (strongly thickened adventitious roots of dahlia, chistyak, lyubka, etc.). There are numerous transitions between root crops and root cones.

Retractor or contractile roots

In some plants, there is a sharp reduction in the root in the longitudinal direction at its base (for example, in bulbous plants). Retracting roots are widespread in angiosperms. These roots cause rosettes to fit tightly to the ground (for example, in plantain, dandelion, etc.), the underground position of the root neck and vertical rhizome, and provide some deepening of the tubers. Thus retracting roots help shoots to find the best depth in the soil. In the Arctic, retracting roots ensure the survival of an unfavorable winter period by flower buds and renewal buds.

aerial roots

Aerial roots develop in many tropical epiphytes (from the families of Orchids, Aronnikovs and Bromeliads). They have aerenchyma and can absorb atmospheric moisture. On swampy soils in the tropics, trees form respiratory roots (pneumatophores), which rise up above the soil surface and supply underground organs with air through a system of holes.

Trees growing along the shores of tropical seas as part of mangroves in the tidal zone form stilted roots. Due to the strong branching of these roots, the trees remain stable on unsteady ground.

What are plants?
Both plants and animals are made up of cells. Cells produce chemicals that grow and function. In addition, both plants and animals for their life processes use gases, water and minerals. Both plants and animals go through life cycles during which they are born, grow, reproduce and die. But plants have one very significant difference: they are not able to move from place to place, because their 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, carbon dioxide contained in the air, as well as water and minerals from the soil - and from all this they produce their own food. Animals cannot do this. To obtain the energy necessary for life, they must seek 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 were no plant life, then there would be no animal life on Earth either.

What do plants eat?
It cannot be said that plants eat - in the literal sense, meaning, for example, the food of animals. Green plants make their own food through a chemical process known as photosynthesis, which uses energy from the sun, carbon dioxide, and water to produce substances called monosaccharides. These monosaccharides are then converted into starches, proteins, or fats, which, in turn, provide the plant with the necessary energy for vital processes to take place 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, a plant is able to extract them from the soil in which it grows: it absorbs them through the roots along with water. But farmers, gardeners and all who grow plants add minerals in addition to make the plants stronger and stronger.

Do all plants have roots?
The simplest plants do not have roots. For example, single-celled 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 seaweeds that attach themselves to the seafloor do so with the help of special “attachment” formations that are not true roots. Seaweed absorbs water and minerals from the sea using all of its parts. Similarly, 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 (cone-bearing 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 where they are needed.

Do all plants have leaves?
The simplest plants such as algae do not have leaves. Mosses have some kind of leaves in which photosynthesis takes place, but these are not real leaves,
Plants over complex types have leaves. The shape of the leaf is often determined by the environmental conditions in which the plants grow. Typically, where there is plenty of sunlight and water, the leaves are broad and flat, providing a large surface area on which photosynthesis can take place. However, in places where it is dry and cold, serious problem not ruled out 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 in the north and at high altitudes.

If plants are cut, do they feel it?
Plants don't have nervous system and they don't feel when they're being cut. But plants feel gravity, light and touch.

How are seeds obtained?
In coniferous trees (cone-bearing plants) and in flowering trees there are seeds.
Coniferous trees - pines, spruces, firs, cypresses, have male and female cones. Male cones have pollen sacs that release millions of tiny pollen particles, the 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 born in the scales of the female cone. As the seeds grow, the cone increases in size. When the seeds are ripe (usually it takes a couple of years), the cone opens and releases them. Seeds have a hard shell and some nutrition inside for use in the initial stage of growth (if the seed gets into 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. The male cells develop in the stamens and "travel" being enclosed in hard pollen grains. The female cells, the ovules, develop deep in the ovary of the flower and are enclosed in the pistil. Top part the pistil (called the stigma) is long and sticky, making it a good target for pollen. After the pollen hits the stigma, a small tube grows from the pollen grain. The male cell passes through this tubule and reaches the ovule. Fertilization occurs and seeds begin to develop.
Wind, water, insects and other animals help to 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 survival - for sunlight, water and minerals. So, in order to start growing, turning into new plants, most seeds need to look for other places, traveling by wind, by 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 of delicate hairs. In both cases, the seeds can, thanks to these features, fly long distances downwind; sometimes they land in places suitable for germination. Other seeds are dispersed by water: thanks to a hard waterproof shell coconuts, for example, can sail many miles in the sea before finding a shore with suitable conditions for germination. Animals are excellent seed dispersers. They spread seeds to different places in the mouth (as a squirrel does when preparing stocks for the winter); sometimes the seeds cling to the fur or feathers of animals.
Some seeds are able to wait years for the right moment to germinate, and some never get that opportunity.

Why do flowers have bright colors?
Reproduction of many flowering plants depends on insects and birds transferring pollen from one plant to another, and plants may attract specific animals with their bright or fragrant flowers. The nutritious pollen and nectar of flowers form an important part of the diet of many creatures. When birds and insects come to the flower to eat, the pollen sticks to their legs and bodies. Flying in search of food to the flowers of other plants of the same species, insects and birds leave part of the pollen in them, and thus cross-pollination occurs. Wind-pollinated plants usually have small, inconspicuous flowers that are not brightly colored (and many lack nectar) because they do not need to attract the attention of insects and birds to spread their pollen.

Why are flowers different from one another?
The way a flower looks depends largely on the way it is pollinated. Wind-pollinated flowers are usually small, nondescript, and not brightly colored, as they do not need to attract the attention of insects and birds to disperse their pollen. But flowers that rely on pollen-carrying creatures to pollinate should attract insects and birds to help cross-pollinate. And such flowers are often adjusted - in terms of color, smell or shape - to specific insects or animals. Many of the flowers that attract bees have special parts that serve as "landing platforms" so that bees flying to them can rest on such platforms while they feed. Bees can distinguish most colors (except red) and are attracted to bright colors. Butterflies like many of the same flowers that attract bees. Butterflies also have elongated mouthparts, and butterflies are also not averse to "landing" when they feed. However, the large wings prevent the butterflies from diving deep inside 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, i.e., one that is clearly distinguishable in the dark. And because moths prefer to float in the air rather than "land" on a flower, they don't need "landing platforms" on the flowers they land on.

Why do some flowers smell like perfume?
The flowers are fragrant, so they attract those they need to cross-pollinate. 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 a strong smell, which helps to find them in the dark for those who feed from them - for example, nocturnal moths. However, not all flowers have a pleasant smell. Some flowers have the smell of rotting meat or other decaying matter, thus attracting flies. Flowers that have an unpleasant (from a human point of view) smell also attract bats needing plants for food.

Why are some plants poisonous?
Plants cannot run away from "predators" - animals that will eat them, so some plants have developed other ways 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 scare away predators; other parts remain harmless and safe for pollinating animals.

Why do some plants have spines?
As mentioned above, plants are unable to escape from hungry animals, so they develop different forms of protection. In some plants, certain parts are poisonous, others have spines and various sharp outgrowths with which they protect themselves from animals that want to eat them. Thorns hurt animals trying to get close to such plants, and they try to stay away from them.

How can plants in the desert 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's raining, desert plants quickly absorb water through 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 don't have true roots, leaves, or stems, and they lack the chlorophyll that plants use to make their own food (which is why they aren't green and don't need sunlight). Mushrooms feed mainly on the dead flesh of plants and animals, thus purifying the environment and enriching the soil.

What is the most dangerous mushroom?
The most dangerous mushroom is the pale grebe. It is often found near birches and oaks. Even small piece of this fungus can lead to death, which occurs after 6-15 hours. The poison of many mushrooms is destroyed by boiling, but the poison of the pale grebe 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 part of the Pacific coast in the United States of America. Some of these trees are almost 4,000 years old. However, decades ago, it was discovered conifer tree, which lives even longer: it is a spiny pine that grows in the United States of America in the states of Nevada, Arizona and southern California. The oldest of these living trees is 4600 years old.

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

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

1. What role do roots play in plant life?

2. How do roots differ from rhizoids?

Rhizoid - 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 do not have roots. For example, single-celled green algae float on the surface of the water. Similarly, many algae, which are larger species of algae, float on the surface of the water.

Simple plants such as mosses absorb the necessary moisture 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.

Rod and fibrous root systems

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

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

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

3. Select plants with a tap root system.

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

4. Select plants with fibrous root systems.

The fibrous root system is characteristic of monocot plants - wheat, barley, onions, garlic, etc.

5. Based on the structure of the root system, determine which plants are monocots and which are dicots.

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, reserve substances can be deposited and accumulated.

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

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

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

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

Fibrous is called the root system of 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 it?

For the appearance of adventitious roots and improve 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. Do indoor plants coleus and pelargonium easily form adventitious roots. Carefully cut off a few side shoots with 4-5 leaves. Remove the bottom two leaves and place the shoots in glasses or jars of water. Watch for the formation of adventitious roots. After the roots reach 1 cm, plant the plants in pots with nutrient soil. Water them regularly.

2. Record the results of your observations and discuss with other students.

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

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

3. Sprout seeds of radishes, peas or beans and wheat grains. You will need them in the next lesson.

1. Rinse the grain 2-3 times

2. Fill 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 soaking is needed)

4. Rinse 2 times

5. Cover the lid leaking

6. Watering at least 3 times a day (3-4 days) GRAIN SHOULD NOT FLOAT!!! WATER MUST GO 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 the seeds with water so that the water is at least 2 centimeters above the seeds;

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

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