Functions of the main organs of plants. General characteristics of higher plants. Differences between higher plants and lower ones. Classification of plants according to their life forms, description of plants

The plant kingdom amazes with its greatness and diversity. Wherever we go, no matter what corner of the planet we find ourselves in, we can find representatives of the plant world everywhere. Even the ice of the Arctic is no exception for their habitat. What is this plant kingdom? The types of its representatives are diverse and numerous. What are the general characteristics of the plant kingdom? How can they be classified? Let's try to figure it out.

General characteristics of the plant kingdom

All living organisms can be divided into four kingdoms: plants, animals, fungi and bacteria.

The characteristics of the plant kingdom are as follows:

• are eukaryotes, that is, plant cells contain nuclei;
• are autotrophs, that is, they form organic substances from inorganic substances during photosynthesis using the energy of sunlight;
• lead a relatively sedentary lifestyle;
• unlimited growth throughout life;
• contain plastids and cell walls made of cellulose;
• starch is used as a reserve nutrient;
• presence of chlorophyll.

Botanical classification of plants

The plant kingdom is divided into two subkingdoms:

• lower plants;
• higher plants.

Subkingdom "lower plants"

This subkingdom includes algae - the simplest in structure and the most ancient plants. However, the world of algae is very diverse and numerous.

Most of them live in or on the water. But there are algae that grow in the soil, on trees, on rocks and even in ice.

The body of algae is a thallus or thallus, which has neither roots nor shoots. Algae do not have organs or various tissues; they absorb substances (water and mineral salts) over the entire surface of the body.

The subkingdom “lower plants” consists of eleven divisions of algae.

Significance for humans: release oxygen; are eaten; used to produce agar-agar; are used as fertilizers.

Subkingdom "higher plants"

Higher plants include organisms that have well-defined tissues, organs (vegetative: root and shoot, generative) and individual development (ontogenesis) which are divided into embryonic (embryonic) and postembryonic (post-embryonic) periods.

Higher plants are divided into two groups: spore plants and seed plants.

Spore-bearing plants spread through spores. Reproduction requires water. Seed plants spread by seeds. Water is not needed for reproduction.

Spore plants are divided into the following sections:

• bryophytes;
• lycophytes;
• horsetails;
• fern-like.

Seeds are divided into the following sections:

• angiosperms;
• gymnosperms.

Let's look at them in more detail.

Department "bryophytes"

Bryophytes are low-growing herbaceous plants, the body of which is divided into a stem and leaves; they have a kind of roots - rhizoids, the function of which is to absorb water and anchor the plant in the soil. Besides photosynthetic and ground tissue, mosses have no other tissues. Most mosses are perennial plants and grow only in moist areas. Bryophytes are the most ancient and simplest group. At the same time, they are quite diverse and numerous and are second only to angiosperms in the number of species. There are about 25 thousand of their species.

Bryophytes are divided into two classes - liver and phyllophytes.

Liverworts are the most ancient mosses. Their body is a branched flat thallus. They live mainly in the tropics. Representatives of liverworts: mosses Merchantia and Riccia.

Leafy mosses have shoots that consist of stems and leaves. A typical representative is cuckoo flax moss.

In mosses, sexual and asexual reproduction is possible. Asexual can be either vegetative, when the plant reproduces by parts of stems, thallus or leaves, or spore-bearing. During sexual reproduction in bryophytes, special organs are formed in which immobile eggs and motile sperm mature. Sperm move through the water to the eggs and fertilize them. Then a capsule with spores grows on the plant, which, after maturation, scatter and spread over long distances.

Mosses prefer damp places, but they grow in deserts, on rocks, and in tundras, but they are not found in the seas and on highly saline soils, in shifting sands and glaciers.

Importance for humans: peat is widely used as fuel and fertilizer, as well as for the production of wax, paraffin, paints, paper, and in construction it is used as a heat-insulating material.

Divisions "mocophytes", "tail-like" and "fern-like"

These three divisions of spore plants have similar structure and reproduction, most of them grow in shady and moist places. Woody forms of these plants are very rare.

Ferns, club mosses and horsetails are ancient plants. 350 million years ago they were large trees, they made up the forests on the planet, in addition, they are the sources of coal deposits at the present time.

The few plant species of the fern, horsetail and lycophyte divisions that have survived to this day can be called living fossils.

Externally different types mosses, horsetails and ferns are different from each other. But they are similar in internal structure and reproduction. They are more complex in structure than mossy plants (they have more tissue in their structure), but simpler than seed plants. They belong to spore plants, since they all form spores. Both sexual and asexual reproduction are also possible for them.

The most ancient representatives of these orders are club mosses. Nowadays, club moss can be found in coniferous forests.

Horsetails are found in the Northern Hemisphere, now they are represented only by herbs. Horsetails can be found in forests, swamps and meadows. A representative of the horsetails is horsetail, which usually grows in acidic soils.

Ferns are a fairly large group (about 12 thousand species). Among them there are both grasses and trees. They grow almost everywhere. Representatives of ferns are ostrich and bracken.

Significance for humans: ancient pteridophytes gave us deposits of coal, which is used as fuel and valuable chemical raw materials; some species are used for food, used in medicine, and used as fertilizers.

Department "angiosperms" (or "flowering")

Flowering plants are the most numerous and highly organized group of plants. There are more than 300 thousand species. This group makes up the bulk of the planet's vegetation. Almost all representatives of the plant world that surround us in everyday life, both wild and garden plants, are representatives of angiosperms. Among them you can find all life forms: trees, shrubs and grasses.

The main difference between angiosperms is that their seeds are covered with a fruit formed from the ovary of the pistil. The fruit protects the seed and promotes its distribution. Angiosperms produce flowers, the organ of sexual reproduction. They are characterized by double fertilization.

Flowering plants dominate the vegetation cover as the most adapted to modern living conditions on our planet.

Value for humans: used for food; release oxygen into the environment; used as building materials and fuel; used in the medical, food, and perfume industries.

Department "gymnosperms"

Gymnosperms are represented by trees and shrubs. There are no herbs among them. Most gymnosperms have leaves in the form of needles. Among gymnosperms, a large group of conifers stands out.

About 150 million years ago, conifers dominated the planet's vegetation.

Significance for humans: form coniferous forests; release large amounts of oxygen; used as fuel, building materials, shipbuilding, and furniture manufacturing; used in medicine and in the food industry.

Diversity of flora, plant names

The above classification continues; departments are divided into classes, classes into orders, followed by families, then genera and, finally, plant species.

The plant kingdom is huge and diverse, so it is customary to use botanical names for plants that have a double name. The first word in the name means the genus of plants, and the second means the species. This is what the taxonomy of the well-known chamomile will look like:

Kingdom: plants.
Department: flowering.
Class: dicotyledonous.
Order: astroflora.
Family: Asteraceae.
Genus: chamomile.
Type: chamomile.

Classification of plants according to their life forms, description of plants

The plant kingdom is also classified according to life forms, that is, according to the external appearance of the plant organism.

• Trees are perennial plants with lignified aerial parts and a distinct single trunk.
• Shrubs are also perennial plants with lignified aerial parts, but, unlike trees, they do not have a clearly defined one trunk, and branching begins near the ground and several equal trunks are formed.
• Shrubs are similar to shrubs, but are low-growing - no higher than 50 cm.
• Subshrubs are similar to shrubs, but differ in that only the lower parts of the shoots are lignified, and the upper parts die off.
• Lianas are plants with clinging, climbing and climbing stems.
• Succulents are perennial plants with leaves or stems that store water.
• Herbs are plants with green, succulent and non-woody shoots.

Wild and cultivated plants

Humans have also contributed to the diversity of the plant world, and today plants can also be divided into wild and cultivated.

Wild - plants in nature that grow, develop and spread without human help.

Cultivated plants come from wild plants, but are obtained through selection, hybridization or genetic engineering. These are all garden plants.

Tests

660-01. The specialized organ of air nutrition of the plant is
A) green leaf
B) root vegetable
B) flower
D) fruit

Answer

660-02. What role do roots play in the life of a plant?
A) form organic substances from inorganic ones
B) cool the plants
C) store organic matter
D) absorb carbon dioxide and release oxygen

Answer

660-03. The main function of the root is
A) stocking nutrients
B) soil nutrition of plants
B) absorption of organic matter from the soil
D) oxidation of organic substances

Answer

660-04. What is the most important role of the leaf in the life of a plant?
A) ensures the evaporation of water
B) performs a supporting function
B) used as a protective organ
D) absorbs water and mineral salts

Answer

660-05. Under what conditions can water rise upward in a plant?
A) in the absence of water evaporation
B) with constant evaporation of water
B) only during the daytime
D) only with closed stomata

Answer

660-06. The main role of leaves in plant life is
A) breathing
B) storing
B) photosynthetic
D) vegetative propagation

Answer

660-07. Evaporation of water by leaves promotes
A) the movement of mineral salts in the plant
B) supply leaves with organic substances
B) absorption of carbon dioxide by chloroplasts
D) increasing the rate of formation of organic substances

Answer

660-08. The main function of the stem is
A) aerial nutrition of plants
B) storage of water and nutrients
B) conduction of water and nutrients
D) evaporation of water

Answer

660-09. Which of the following is an adaptation to dry living conditions?
A) wide leaves
B) many stomata
B) fleshy stems
D) creeping stems

Answer

660-10. Fungi that form mycorrhizae are obtained from plant roots
A) water
B) antibiotics
B) mineral salts
D) organic substances

Answer

660-11. The role of the stem in the life of the plant is
A) strengthening the plant in the soil
B) the formation of organic substances
B) the movement of substances throughout the plant
D) absorption of water and mineral salts

The Earth's biosphere includes at least 5 (most likely 20 and perhaps even 50) million. various types Living creatures. The flora is rich and diverse (over 500 thousand species). The kingdom of Plants (Vegetabilia, Plantae or Phytobiota) is often divided into three subkingdoms: Red algae, or Crimson algae (Rhodobionta), True algae (Phycobionta) and Higher plants, or Embryonic organisms (Embryobionta). The first two subkingdoms are classified as lower plants (thallaceae, or thallus plants - Thallophyta). This group unites the most simply organized plants (unicellular, colonial and multicellular) living in the aquatic environment, especially in the seas and oceans. In some modern systems of the organic world it has only historical meaning, since previously eukaryotic unicellular, mobile forms, and now all lower plants are often included in the kingdom Protista.

Higher plants are also called shoots, or leafy plants (Cormobionta, Cormophyta); telomic (Telobionta, Telomophyta); land plants.

The subkingdom of Higher plants is characterized by the following main features.

Mainly terrestrial lifestyle. Higher plants are inhabitants of the air. In the course of a long evolutionary process, new species emerged that were adapted to life in terrestrial conditions. The presence of aquatic forms among higher plants (pondweed, elodea, watercolor and others) is a secondary phenomenon.

Entering terrestrial habitat conditions gave a powerful impetus to the restructuring of the entire organization of the plant. In terrestrial conditions, plant lighting has improved, which has activated the process of photosynthesis, led to an increase in assimilates, the volume of plants as a whole, and necessitated their further morphological division. The vegetative body of the plant turned out to be divided into two parts (aboveground and underground), performing different functions. Thus, higher plants are characterized by morphological division into two main vegetative organs: root and shoot. The stem and leaves are components of the shoot (as if they were organs of the same order). All leafy higher plants belong to the morphological group - shoots. Among modern plants of this group, highly organized forms predominate, well adapted to the varied living conditions of land. They are characterized by numerous modifications of the main organs and their components (tubers, stolons, spines, tendrils, scales, bulbs and others). There are also a number of primitive representatives with a simpler organization that have no roots. Leafy bryophytes (cuckoo flax and others) are primarily rootless plants. To absorb water, they form rhizoids. Bladderwort is a secondary rootless plant (it lives in the upper layers of water).

Not all higher plants have their aerial parts divided into vegetative organs. Liver mosses are often represented by a green dichotomously branching plate creeping along the ground and attached to it by rhizoids. They make up the morphological group of thallus, or thallus plants.

Higher plants are characterized by more complex anatomical differentiation of tissues. The air environment is characterized by great variability of many environmental factors and their greater contrast. In terrestrial conditions, plants have developed a complex system of integumentary tissues. The most important specialized integumentary tissue, without which the development of land is impossible, is the epidermis. In evolutionary terms, it has a very ancient origin. The body of the first known land plants (rhiniophytes) was covered with epidermis, which had stomata to regulate gas exchange and transpiration. Subsequently, secondary (periderm) and tertiary integumentary (rhytidome) tissues were formed.

In the terrestrial environment, in most higher plants, the complexes of conductive, mechanical, excretory, internal boundary and other types of tissues also received the most complex development.

For the normal functioning of underground and above-ground organs, rapid movement of water, minerals and organic substances is necessary. This is achieved by the development of special conductive tissues inside the body of higher plants: xylem, or wood, phloem, or phloem. In an upward direction, along the xylem, water moves with minerals dissolved in it, absorbed from the soil by the roots and organic substances produced by the roots themselves. In a downward direction, through the phloem, assimilation products, mainly carbohydrates, move. Specialized water-conducting elements of xylem are formed - tracheids, and then tracheae, or vessels. Ringed and spiral tracheids and vessels make up the protoxylem, pores, with different types and lateral porosity (staircase, opposite, regular, sometimes random) - metaxylem. The most ancient type of pore tracheids is scalariform. They are characteristic of the metaxylem of most higher spore plants.

Among spore plants, scalariform vessels are present in the metaxylem of some ferns (for example, bracken). Vessels are also found in the secondary xylem of highly organized gymnosperms (Ephedra, Gnetum and Welwitschia). However, in the noted ferns and gymnosperms, the vessels are few in number and the main functional load is borne by the tracheids. They were already discovered in rhinophytes.

It is believed that elements transporting assimilation products in the process of evolution of the plant world appeared before water conductors. In rhinia, elongated thin-walled cells with plasmodesmal tubules and pores were found, which may have participated in the conduction of solutions of organic substances. In leaf-stemmed mosses, this function is performed by long, thin-walled cells, slightly expanded at the ends. Several such cells form a longitudinal single-row cord. The rest of the higher spores and gymnosperms are characterized by the formation of sieve cells. Only angiosperms form sieve tubes, the segments of which arise from sieve cells. The process of their transformation is similar to the process of transformation of tracheids into vascular segments. Sieve tubes conduct photosynthetic products more efficiently than sieve cells. In addition, each segment is accompanied by one or more companion cells.

Conducting elements, mechanical tissues and parenchyma are grouped into regular combinations - vascular-fibrous bundles (radial, concentric, collateral, bicollateral). The most common are collateral, open (dicots) and closed types (monocots). A central cylinder—stele—emerges, first in the form of the simplest protostele. Subsequently, due to the increase and complication of the structure of the stem, siphonostele, dictyostele, eustele and ataxostele are formed.

In higher plants, mechanical tissues also received powerful development. When living in an aquatic environment, the need for these tissues was small, since water supported their bodies well. In an air environment, the density of which is many times less than water, mechanical tissues provide plant resistance to static (gravity) and dynamic (i.e., rapidly changing) loads (wind gusts, rain impacts, animal impacts, etc.). During the process of evolution, specialized mechanical tissues (sclerenchyma and collenchyma) arose and developed in connection with the progressive dismemberment and increase in plant mass.

Like organs, tissues did not appear and develop immediately. Thallus higher plants lack a developed conducting system. Mechanical tissues are also poorly developed. Having small sizes and living in humid conditions, the strength of these plants is largely ensured by the elasticity of the membranes that make up their living cells, saturated with water. The study of extinct fossil plants reveals a whole series of intermediate forms, showing the emergence and stages of development of certain organs and tissues.

Spores of higher plants have a more complex structure than those of lower plants (algae). They are motionless, without flagella. The spores of higher spore plants (bryophytes, lycophytes, horsetails, pteridophytes and psiloteformes) are covered with a multilayer cell membrane (sporoderm). It consists of two main layers: a hard outer layer (exosporium) and a thin inner layer (endosporium). Characteristic feature exosporia, consisting of cellulose, is the presence of sporollinin, a high-molecular compound with exceptional stability; similar in physical and chemical properties to cutin. In lower plants, zoospores and aplanospores (devoid of flagella) are formed. They do not have a polysaccharide shell. Exosporium is extremely durable, waterproof, and resistant to high temperatures, chemicals, exposure to microorganisms. Therefore, spores of terrestrial plants can remain viable for a long time (sometimes for decades). This helps to survive periods unfavorable for germination, which is especially important in terrestrial conditions. Due to their microscopic size, they are often transported over considerable distances. Thus, sharp adaptive changes in the structure of the spores were necessary under living conditions on land. With the help of spores, the dispersal of species and the transfer of unfavorable conditions. The spore shells (especially its outer layers) are also well preserved in geological strata, in a fossil state. Many long-extinct plants are known only from remains of their sporoderm.

More primitive higher plants produce identical spores (isospores) both in size and physiological characteristics (morphologically homosporous plants). Under favorable conditions, isospores “germinate” – they divide, and bisexual shoots (gametophytes) are formed. In mosses, horsetails, ferns and psilotes they live independently, regardless of the sporophyte. They feed differently: autotrophically (terrestrial, green), mycotrophically - symbiosis with fungi (underground, colorless) and mixotrophically (semi-underground) shoots.

However, among terrestrial plants there are many morphologically heterosporous forms that produce spores that differ in size and always in functional features(heterospores). When germinating, small-sized spores (microspores) give rise to male shoots, while large ones (megaspores) give rise to female shoots. They are formed on one or on different individuals, respectively, in micro- and megasporangia.

Modern horsetails are characterized by physiological diversity. Identical spores on substrates of different trophicity and water supply form different types of shoots - male (under poor growth conditions), female and bisexual (under favorable growth conditions). This is due to the fact that the egg accumulates nutrients necessary for the developing embryo after fertilization. The physiological diversity of modern horsetails is an “echo” of the morphological diversity of their ancestors.

In the process of evolution, heterosporousness is accompanied by a reduction in shoots, especially male ones. Often they consist of only a single cell of the vegetative body and one antheridium. The female germ, in addition to the formation of the egg, must ensure the safety of the zygote and the development of the embryo, which in the early stages is not capable of independent living. In heterosporous lycophytes and pteridophytes, the prothalla develops inside the megaspore or partially protrudes beyond the shell. They are more reliably protected than the bisexual shoots of morphologically homosporous plants. Megaspores of lycophytes and pteridophytes also perform the function of species dispersal. In seed plants, the megaspore never leaves the mother sporophyte.

Land plants are characterized by the formation of fundamentally new multicellular reproductive organs, or organs of asexual and sexual processes (i.e., sporangia and gametangia). This is due to the protection of spores and gametes from external influences in a complex terrestrial habitat. The outer layers are sterilized (a wall is formed); only internal tissues are capable of producing spores and gametes. The wall firmly retains moisture and protects developing spores and gametes from drying out. This feature is one of the most important in conditions of terrestrial existence.

The wall of the sporangium can be single-layered or multilayered. The number of spores in sporangia varies. In homosporous higher plants, only 8 spores are very rarely formed in the sporangium, usually at least 32 spores. Many have twice or four times as many, some primitive ferns have up to 15,000 spores. In heterosporous forms, at least 32 microspores are also formed in each microsporangium. However, a megasporangium usually produces one megaspore.

The reproductive organs of higher plants are always of two types: male - antheridia and female - archegonia. In the antheridium, male germ cells (male gametes) are formed - sperm, and in the archegonium - female germ cells (female gametes) - the egg. Antheridia are oval or spherical shape. Under the single-layer wall of the antheridium, spermatogenic tissue is formed, from the cells of which flagellated spermatozoa are formed. By the time they mature, in the presence of moisture, the wall opens, and spermatozoa move towards the archegonia with the help of flagella.

Archegonia are flask-shaped. The upper narrow part is the neck, the lower widened part is the abdomen. Under the protection of a single-layer wall, cervical tubular cells develop inside the neck, and one or two abdominal tubular cells and a large spherical egg cell develop in the abdomen. By the time the egg matures, the cervical, abdominal tubular cells, as well as the upper wall cells become mucus. Some of the mucus is secreted beyond the archegonium. Mucus contains substances that have a positive chemotactic effect on sperm. They swim to the archegonium through the mucus of the neck and move towards the egg.

In the life cycle, sporangia and gametangia are confined to its different phases of development (forms, or generations). A reduction of gametangia in heterosporous forms is also observed. In all gymnosperms, antheridia are reduced; archegonia are reduced in Gnetum and Welwitschia. In all angiosperms, gametangia are not formed at all.

In higher plants, isogametes and heterogametes (motile germ cells of different sexes that differ in size), which are found in lower plants, do not form. Sexual differentiation in higher plants intensified and led to sharp dimorphism of gametes. The eggs accumulate nutrients and are therefore larger and more immobile. Sperm and sperm are almost devoid of reserve nutrients. Thus, higher plants are characterized by anisogametes that differ in size and degree of mobility.

Gamete dimorphism is of great biological importance. The uneven distribution of nutrients between male and female gametes ensures larger number gamete fusions than with uniform distribution between gametes of the same mass of nutrients. During the evolution of plants, gamete dimorphism increased.

With increasing sexual differentiation, the number of male gametes in the gametangium increased, and the number of female gametes, on the contrary, decreased. An archegonium appeared with one large and immobile egg cell. A large number of eggs in the archegonia can only be in abnormal cases. An increase in sperm count increased the likelihood of sexual intercourse. It was accompanied by a decrease in their size, which facilitated the movement of sperm in the thinnest films of water. The concentration of nutrients in one large egg contributes to the development of more complete offspring.

Land plants are characterized by oogamy. The process of fertilization (syngamy) occurs inside the archegonium. In primitive higher plants, fertilization occurs in damp weather, during rain or heavy dew. Motile male gametes with flagella (spermatozoa) move independently in a film of water and reach the archegonia. In most gymnosperms and all angiosperms, as a result of adaptation to life on land, a special type of oogamy arose - siphonogamy. Male gametes lose mobility. The fertilization process occurs without the presence of a drop-liquid medium. The function of delivering and protecting male gametes is carried out by the gametophyte (pollen grain) itself, due to the formation of the pollen tube. These achieve greater reliability of the fertilization process.

As a result of the sexual process, a zygote is formed, which gives rise to a multicellular embryo of higher plants. Like the zygote, all cells of the embryo are characterized by a diploid set of chromosomes, containing the hereditary material of the parents of a non-identical genetic nature. This ensures the emergence of more genetically diverse offspring due to the recombination of parental genes. Favorable conditions are created for natural selection. This is precisely the biological role of the sexual process.

The embryo is a young sporophyte of the next generation. Subsequently, the adult sporophyte gradually forms. The peculiarity of higher plants - the presence of a multicellular embryo - made it possible for the German botanist W. Zimmermann, the Soviet botanist A. Takhtadzhyan and the American A. Cronquist to name the subkingdom of higher plants - embryonic organisms (Embryobionta).

In higher plants, at critically early stages, a young embryo (sporophyte) develops inside the female gametangium under the protection of the mother. In higher spore plants, the mother organism is the gametophyte, and in seed plants, the sporophyte itself (since the gametophyte is extremely reduced).

Higher plants are characterized by a heteromorphic life cycle (Fig. 1). In spore plants it continues from spore to spore, in seed plants it continues from seed to seed. Includes two reproductive processes: asexual (spore formation) and sexual. Characteristic feature of higher plants is the presence of a correct change of development phases, or alternation of generations: sexual (gametophyte = prothallus = haplonta = haplophase) and asexual (sporophyte = diplonta = diplophase). As noted above, in many higher plants (mosses, horsetails, ferns, etc.), these generations are, as it were, separate physiologically independent organisms, and the reproductive processes are separated not only spatially, but also in time.

Rice. 1. Scheme of the life cycle of a morphologically homosporous plant - club moss (Lycopodium clavatum): 1 – sporophyte (adult plant); 2 – sporophyll with sporangium; 3–6 – development of spores from the mother cell (sporocyte) by meiosis; 7 – dispute; 8 – spore germination; 9 – bisexual gametophyte (thallus); 10 – antheridium; 11 – sperm; 12 – archegonium with egg; 13 – archegonium with egg and sperm; 14 – divisions of the zygote (development of the embryo); 15 – remains of the outgrowth; 16 – young sporophyte.

1–7,14,16 – organs and structures of the sporophyte; 8–13,15 – organs and structures of the growth.

In mosses and, especially in seed plants, one of the generations is subordinate to the other and, physiologically, is, as it were, reduced to its organ. In mosses the gametophyte dominates, in all other higher plants the sporophyte dominates, often reaching large sizes. In all higher plants, the place of reduction division (meiosis) is during the formation of spores. From one diploid spore mother cell, a tetrad of haploid spores (4 meiospores) is formed.

The saprophyte completes ontogenetic development with the formation of a multicellular sporangium with spores. In most higher plants, with the exception of bryophytes, sporangia arise on special organs - sporangophores (carriers of sporangia). The origin, structure and shape of sporangiophores are varied. More often they have a flat, leaf-like shape and are called sporophylls.

After germination of haploid spores, a haploid sexual generation is formed - the gametophyte. Only in bryophytes, a protonema (pregrowth) develops from spores - a filamentous or lamellar formation that gives rise to a gametophyte. The cycle repeats.

Unlike lower plants, spores in higher plants do not carry out the process of reproduction (“reproduction of their own kind”). Even in cases where spores (in morphologically homosporous) and megaspores (in morphologically heterosporous) plants perform the function of dispersal, bisexual or female gametophytes (thallusts) are formed from them - generations that, in their morphological, cytological and functional characteristics, differ sharply from the sporophyte , in whose sporangia it was formed.

Uncharacteristic of higher plants and sexual reproduction. An individual similar to the parent does not develop from the zygote, and the next generation of the heteromorphic life cycle is a sporophyte.

The appearance of new individuals of a species occurs only as a result of a combination of two reproductive processes - sporulation and the sexual process. In higher spore plants, reproduction occurs as a result of gameto-sporia (if the gametophyte is dominant - bryophytes) or sporogamy (if the sporophyte is dominant - the rest are spore-bearing), (Sautkina, Poliksenova, 2001). In higher spore plants, sporulation and the sexual process are separated spatially and occur in different generations.

During the evolution of seed plants, a large aromorphosis occurs - a special type of megasporangium (megasinangium) appears - the ovule (ovule). The processes of formation of megaspores, the female gametophyte, the formation of gametes (eggs), the process of fertilization, and the development of the embryo occur in a single organ. As a result, the ovule itself turns into a seed. Sporulation and the sexual process are no longer separable, and on their basis a special type of reproduction arises - seed reproduction. In angiosperms, these processes are combined not only spatially but also temporally. Both processes follow each other very quickly, almost without interruption. The shoots are greatly reduced, and the periods of their development are sharply shortened. Angiosperms clearly demonstrate the end result of heterosporousness - a reduction in the duration of the life cycle. The megaspore has also lost the ability to disperse the species; this function is performed by the seed.

Most higher plants are characterized by vegetative propagation. The exception is many gymnosperms, and among angiosperms - annual and biennial plants. Forms of natural vegetative propagation extremely diverse and often specialized, especially in angiosperms. Higher plants can reproduce using vegetative organs (thalli, roots, shoots) and their parts. A widespread non-specialized form of vegetative propagation is fragmentation, both as a result of the influence of random mechanical factors (the influence of wind, currents, movement and gnawing of animals, etc.), and as a result of the death of some cells. Specialized forms of vegetative propagation are also widely characteristic of the haploid and diploid generations, when they are dominant. In spore plants, brood buds, twigs, leaves, brood bodies, rooting shoots, adventitious (adventitious) buds (ferns), underground rhizomes and other devices are formed. Daughter organisms of angiosperms always develop from buds, which are formed on various parts of the vegetative organs (roots, stems, leaves). Their occurrence is often associated with mechanical damage to the organ (natural and artificial). Widespread specialized organs of vegetative propagation of flowering plants are rhizomes, underground and aboveground stolons (tendrils), bulbs, corms, tubers, root cones and others.

Higher plants originated from algae, since in the geological history of the plant world the era of higher plants was preceded by the era of algae. These hypotheses appeared at the end of the 19th century (F. Bower, F. Fritsch, R. Wettstein). The first reliable land plants are known only from spores and date back to the beginning of the Silurian period of the Paleozoic era (430 million years ago). Based on preserved microfossils or organ imprints, land plants have been described from Upper Silurian and Lower Devonian deposits. The first higher plants are united in the group of rhinophytes. Despite the morphological and anatomical simplicity of their structure, they were typical terrestrial plants. They had cutinized epidermis with stomata, a developed conducting system, and multicellular sporangia with spores with durable protective membranes. Therefore, it can be assumed that the process of land development began much earlier - in the early Paleozoic (in the Ordovician or Cambrian periods).

Higher plants have a complex common features, which suggests the unity of their origin from one ancestral group (monophyletic origin). However, there are many followers of the views on polyphyletic origin, including within certain groups of higher plants (bryophytes, angiosperms). According to their views, the original group of algae had different types of reproduction cycles and gave rise to two independent lines of evolution.

For a long time, brown algae were considered as the original group of higher plants (G. Schenk, G. Potonier). A supporter of these views was also K.I. Meyer. They are characterized by complex development cycles, including heteromorphic ones. There are all types of alternation of generations. This is one of the most complex groups of algae, both externally and internally. The thallus is characterized by a multicellular, often complexly divided thallus into stem- and leaf-like organs. Many brown algae have a tissue structure (assimilation, storage, mechanical and conducting tissues are distinguished). Representatives of this division contain multicellular sporangia and gametangia. However, in nature the law of the “unspecialized ancestor” often operates. In addition, the first higher plants were characterized by a primitive external and internal structure. One of the difficulties in accepting this hypothesis is also the differences in pigment composition and reserve nutrients: brown algae have chlorophyll A and C (the latter is not detected in plants), the additional pigment fucoxanthin, reserve products are laminarin and hexahydric alcohol manitol (they do not have starch) . Brown algae are also exclusively marine and not freshwater organisms. Among the archegonial plants there are no representatives of marine flora. Among angiosperms alone, 20–30 species live in salt waters. There is no doubt that these are secondary aquatic, highly organized plants.

With the advent of new information in the second half of the twentieth century, green algae again began to be considered as the ancestors of higher plants (L. Stebbins; M. Shafedo et al.). Both higher plants and green algae are characterized by the presence of similar pigments (the main photosynthetic pigment is chlorophyll A, auxiliary pigments are chlorophyll B, α- and β-carotene, similar xanthophylls); their plastids have a well-defined system of internal membranes. The product of assimilation (the main storage carbohydrate) is starch, which is deposited in chloroplasts, and not in the cytoplasm, as in other photosynthetic eukaryotes. In higher plants and some green algae, the most important component of the cell wall is cellulose. There is also a similarity between some rhinophytes and some green algae in terms of their branching patterns. Some modern chaetophorans (order Chaetophorales) have multichambered gametangia. There is also a similarity in life cycles some representatives. Along with motile zoospores, green algae also have immobile aplanospores, so characteristic of higher plants. They live mainly in freshwater bodies of water, but are also found on land. Morphological and ecological diversity, the variety of their life strategies allowed them to evolve in different directions. So, according to the majority of modern botanists, the probable ancestors of higher plants could be freshwater or brackish water multicellular green algae with a heterotrichous (variegated) thallus structure.

The hypothesis of the origin of higher plants from organisms similar to living characeae has also become widespread. Both groups are brought together by the nature of the formation of the intercellular pectin plate (phragmoplate is involved - a system of microtubules located in the equatorial plane of the mitotic spindle). The directions of development are also the same - from the center to the periphery (centrifugally). A similar type of formation of the intercellular plate is also found among some representatives of the Ulothrix class, characterized by a variety of thallus structures (filamentous, less often lamellar or tubular).

Along with the complex morphological division of the structure of the thallus, charophytes are characterized by multicellular organs of sexual reproduction, like higher plants. Important Features They are also the presence of the protonema stage, or preadolescent, in the development process, the haploid nature of the thallus (zygotic reduction). They live in reservoirs with fresh and brackish water. Some are confined to terrestrial wet habitats. Remains of fossil charophyte algae are known from deposits of the Silurian period of the Paleozoic era. It is also believed that they could have originated from some highly organized whorled green algae, similar to modern chaetophorans.

Other views on the origin of higher plants have been translated in the literature. It is believed that their ancestors could have been some hypothetical group that combined the characteristics of brown and green algae. There are other less common hypotheses.

It has also been suggested that the transition of the algal ancestor of higher plants to the conditions of terrestrial existence was significantly facilitated by symbiosis with fungi (theory of symbiogenesis). As is known, symbiosis with fungi is widespread in nature. At the intracellular level with underground organs (endomycorrhiza), it is characteristic of most higher plants. At the beginning of the Paleozoic era, complex multicellular algae began to populate coastal land as part of an endomycorrhizal association. Studies of the remains of the most ancient higher plants have shown that ethdomycorrhiza was no less common among them than among modern ones. The presence of fungal hyphae in the tissues of the underground organ probably contributed to a more intensive use of minerals, especially phosphates, contained in nutrient-poor substrates of the early Paleozoic era. In addition, it is assumed that this could also provide better water absorption and help increase the resistance of higher plants to drying out, which is extremely important in living conditions on land. Similar relationships can be observed in the example of modern plants, which were the first to colonize extremely poor soils. Species with endomycorrhizae have a much greater chance of survival under such conditions. Thus, it is possible that not just one organism, but a whole symbiotic complex was the first to settle on land.

There were several prerequisites for the appearance of land plants. The independent course of evolution of the plant world prepared the emergence of new and more advanced forms. As a result of photosynthesis by algae, the oxygen content in the planet's atmosphere increased, which allowed the development of life on land. In the Proterozoic era (900 million years ago), the oxygen concentration in the atmosphere was only 0.001 of modern level, in the Cambrian (the first period of the Paleozoic era) - 0.01, and in the Silurian - already 0.1. The increase in oxygen content correlated with the formation of the ozone layer, which blocks some ultraviolet radiation. At the initial stages of the development of life on Earth, it contributed to the formation of biological macromolecules and at the same time acted as a factor limiting evolution in the absence of a sufficient amount of oxygen in the atmosphere. It is necessary primarily for nuclear and cell division.

The appearance of terrestrial plants coincides in time with the development of the process of metabolism of phenolic compounds, including tannins, anthocyanins, flavonoids, etc. They regulate growth processes, contribute to the development of protective reactions of plants, including from mutagenic factors - ionizing radiation, ultraviolet radiation, some chemical substances.

Recently, the hypothesis that lower organisms - various algae, fungi and bacteria - were the first to master the land, forming together terrestrial ecosystems, is gaining more and more supporters. They prepared the substrate, which was later assimilated by plants. Paleosols have been known since the early Precambrian.

According to the famous expert on fossil flora S.V. Meyena (1987) more likely that the process of formation of higher plants did not occur during the emergence of algae on land, but in the algal population of land. The time of their formation should be attributed to the previous periods of the Silurian.

At first Paleozoic era Large mountain-building processes took place over vast areas. The Scandinavian Mountains, Sayan Mountains, Altai, the northern part of the Tien Shan, etc. arose. This caused the gradual shallowing of many seas and the appearance of land in place of former shallow reservoirs. As the seas became shallower, multicellular algae that inhabited shallow waters remained on land for longer periods. Only those plants survived that were able to adapt to new living conditions. The ancestors of higher plants first had to adapt to life in brackish water, then in fresh water, in estuaries, in shallow waters or on the wet shores of reservoirs.

The new habitat was fundamentally different from the original aquatic one. It is characterized by: solar radiation, moisture deficiency, complex contrasts of a two-phase soil-air environment. One of the key moments of the early stage of reaching land was the formation of spores with strong protective covers, since moisture deficiency was the main critical factor for the development of the earth's surface. The spores were able to spread across land surfaces by wind and survive dry conditions. For spores to disperse, the sporangia must be raised above the substrate. Therefore, the development of the sporophyte was accompanied by an increase in its size. This required more air and mineral nutrition products. The resulting increase in the surface of the plant was achieved by dismembering it in the most in a simple way– forked branching of aboveground and underground axes. As plants increased in size and differentiation, structures emerged that facilitate more efficient spore release and dispersal. Another important evolutionary processes contributing to the development of land were the biosynthesis of cutin by plants and the formation of a generally complex specialized tissue - the epidermis with stomata. It is able to protect land plants from drying out and carry out gas exchange. Higher plants stabilized their moisture content and became relatively independent of fluctuations in atmospheric and soil humidity. In lower land plants, water metabolism is not stabilized. The intensity of their life processes completely depends on the presence of moisture in the habitat. When drought occurs, they lose moisture and fall into suspended animation.

The morphological division of land plants originated from the heterotrichous thallus of green algae. It is believed that their creeping parts gave rise to thallus (thallus) forms, and the ascending parts gave rise to radial ones. Lamellar thalli turned out to be biologically unpromising, since they would cause increased competition for light. The ascending sections, on the contrary, received further development and subsequently formed radial branching axial structures.

Since the emergence of higher plants on land, they have developed in two main directions and formed two main evolutionary branches: haploid and diploid.

The haploid branch of the evolution of higher plants is characterized by the progressive development of the gametophyte and is represented by bryophytes. Along with ensuring the sexual process, the gametophyte performs the main functions of vegetative organs - photosynthesis, water supply and mineral nutrition. They gradually improved, became more complex, increasing the assimilation surface, and were morphologically dissected to provide nutrition and spore formation for the developing sporophyte. The sporophyte, on the contrary, underwent reduction. Basically, it is limited to sporulation and is not an independently living generation. To better disperse spores, he developed various devices.

The sexual process in bryophytes occurs in the presence of droplet-liquid moisture (male gametes are motile - biflagellate sperm). Therefore, the gametophyte is often associated with wet habitats and cannot reach large sizes. The haploid gametophyte also has less genetic potential than the diploid sporophyte. Therefore, the line of evolution of higher plants with the dominance of the gametophyte is lateral, dead-end.

In all other higher plants, the sporophyte dominates the reproductive cycle. The diploid set of chromosomes, along with the activation of assimilation, expanded the possibilities of formative processes. The sporophyte in terrestrial conditions turned out to be much more viable.

The turning point in the evolution of land plants was the emergence of the ability of cells to synthesize lignin. They formed conductive and supporting tissues. Since the Devonian period, the underground parts of the sporophyte have turned into roots, performing the functions of absorption and anchorage. Leaves have formed on the above-ground parts of higher plants. Thus, as higher plants increased in body size, anatomical and morphological differentiation led to the formation of complex, specialized tissues and organs. This strengthened the position of higher plants in the terrestrial environment and contributed to more efficient photosynthesis. Abundant branching and the creation of large sporophyte sizes have repeatedly led to the colossal productivity of diaspores and their effective settlement. Most terrestrial plant communities are dominated by sporophytes.

The gametophyte, on the contrary, gradually became smaller and simpler during evolution. In homosporous mosses, horsetails, and ferns, gametophytes have the appearance of a tiny undifferentiated or poorly differentiated green thallus, called a prothallium, or prothallium. The maximum reduction of gametophytes is associated with the separation of the sexes. Their purpose is limited to the implementation of the main function - ensuring the sexual process. Both types of unisexual gametophytes (male and female) are much smaller than gametophytes of homosporous land plants. In heterosporous they develop under the spore shell, and in homosporous they develop outside it.

The reduction and simplification of unisexual gametophytes occurred at an accelerated pace during evolution. They lost chlorophyll and their development occurred due to the nutrients of the sporophyte. The greatest reduction of the gametophyte is observed in seed plants. The male gametophyte is represented by a pollen grain, the female gametophyte in gymnosperms is the primary haploid endosperm, and in angiosperms it is the embryo sac of the ovule.

At the first stages of the development of land by land plants, there was no competition. The uniformity and abundance of spores in geological deposits indicates their insignificant diversity and their rapid development of land. In Devonian times (400–345 million years ago), higher spore plants of the diploid line of evolution became more numerous and diverse. For the first time, morphological diversity appears. Subsequently, it appears repeatedly in various unrelated groups of vascular plants. Diversity has important biological significance. In more highly organized plants, ovules, seeds, etc. arise only on the basis of heterospory.

A sharp differentiation of plant forms occurred in the Middle Devonian. Low-growing rhiniophytes are replaced by tree-like tall (up to 40 m in height) forms of lycophytes and horsetails. In the late Devonian period, tree-like plants formed real forests. Over a relatively short period (Late Devonian – Carboniferous (Carboniferous)), representatives of many taxonomic groups of pteridophytes appear. They began to dominate the habitable part of the land. The planet began to turn green. This period is rightly called the time of ferns. The vegetation cover reached its most luxuriant development at the end of the Carboniferous period. Tall tree-like lycophytes (lepidodendrons, sigillaria, etc.), horsetails (calamites), pteridophytes and seed ferns formed lush plant communities, in many ways similar to the flora of modern tropics. At this time, pine-like animals appeared.

At the end of the Paleozoic era (Permian period), gymnosperms began to predominate almost everywhere on land. They replaced the fern-like species that had dominated until then. The greatest diversity of gymnosperm forms existed in the Mesozoic (the era of gymnosperms). It is believed that the sharp change in floras is largely associated with the increasing dryness of the climate. Gymnosperms with a more developed conducting system turned out to be more adapted to changed living conditions. Important adaptive features are characterized by the process of internal fertilization with the help of a pollen tube, which is characteristic of many representatives. And finally, they developed ovules and seeds that nourished the sporophyte embryo and protected it from the vicissitudes of land life. These are the main biological advantages of seed plants

Even more adapted to the conditions environment are flowering or angiosperm plants. The variety of their sizes, life forms, adaptations to pollination, to the spread of diaspores, to endure unfavorable climatic periods, etc. is striking. All these features enable flowering plants to fully realize their evolutionary and adaptation potential. They turned out to be the only group of plants capable of forming complex multi-layered communities (especially in lowland forests of the tropics), consisting mainly, and sometimes almost entirely, of their representatives. This contributed to more intensive and complete use of habitats, as well as more successful conquest of territories. No group of plants has been able to develop such a variety of adaptations to certain environmental factors. Only they managed to re-develop the marine environment - dozens of representatives of angiosperms grow in the salty waters of shallow seas along with algae. Having appeared at the beginning of the Cretaceous period of the Mesozoic era (this is judged by their reliably determined fossil remains), by the end of the Cretaceous they usually dominate most ecosystems. In a relatively short period of geological time, estimated at ten to two million years, they underwent basic evolutionary differentiation and spread widely throughout the globe, quickly reaching the Arctic and Antarctica. Their dominance in land cover continues to this day. The course of biosphere processes of metabolism and energy transformation, the gas composition of the atmosphere, climate, water regime of land, and the nature of soil processes depend on their vital activity. Most land animals exist only thanks to angiosperms. They form their habitat and are connected with them by various trophic and other consortial connections. Many groups of animals arose only when flowering plants began to dominate the land. Many arthropods (especially insects) and some vertebrates (especially birds) are characterized by evolution associated with angiosperms. Man as a biological species was able to arise and exist only thanks to the abundance of angiosperms.

As in the plant world, a parallel direction of evolution is observed in the animal world - from oviparous to viviparous. In plants - from spore-forming to seed-forming. Seed plants replaced spore plants. After all, the vast majority of spores, not finding favorable conditions, die. The spores do not have an adequate supply of nutrients. The development of the gametophyte and the process of fertilization in spores also require certain conditions, which cannot always be provided on land. Seeds usually have a supply of nutrients (in gymnosperms it is the primary haploid endosperm, in angiosperms it is the secondary triploid endosperm, perisperm, or in the embryo itself). The seed coat, often formed from the tissues of the integument (teguments), is reliable protection from adverse environmental influences. A seed is much more adaptable than a spore (one cell). Most seeds are characterized by a more or less long dormant period. The dormant period is of great biological importance, as it makes it possible to survive unfavorable times of the year, and also contributes to more distant settlement. The seed is the most adapted plant organ for dispersal.

Meanwhile, the gametophyte generation gradually decreased in size and became increasingly dependent on the sporophyte for nutrition and protection.

Thus, the appearance of terrestrial, or higher plants, marked the beginning of a new era in the life of the planet. The development of land by plants was accompanied by the appearance of new animal species. The conjugate evolution of plants and animals has led to a colossal diversity of life forms on Earth and changed its appearance. Higher plants are also widely used by humans in the economy and everyday life. Moreover, almost all cultivated plants, with the exception of some red (porphyry, etc.) and green algae (chlorella, scenedesmus, etc.) are higher plants.

The subkingdom of higher plants unites at least 350 thousand species. Most taxonomists divide them into 8 divisions: Bryophytes, Rhiniformes, Mocophytes, Equisetaceae, Pteridophytes, Psilotformes, Gymnosperms, Angiosperms, or Flowering plants. However, in modern academic publications the number of divisions varies from 5 to 14. Studying fossil plants, paleobotanists (S.V. Meyen and others) note that between the lycophytes, horsetails and pteridophytes there are more than single genera that occupy intermediate position, combine the characteristics of various departments, bringing them together. Therefore, they are often combined into one department. In addition, a common specificity of their reproduction cycle is the sequential alternation of independently living heteromorphic generations. Rhiniformes, on the contrary, are often divided into 2 or 3 independent sections, and bryophytes - into 3 or 4 sections. This also applies to gymnosperms, which are divided into 5 divisions (A.L. Takhtadzhyan). Recently, two new divisions of the most ancient seed plants were identified - Archaeopteridophyta and Archaeospermatophyta (N.S. Snigirevskaya).

Based on the presence of vessels and (or) tracheids, representatives of all divisions, with the exception of bryophytes, are often called higher vascular plants (Tracheophyta). Bryophytes do not have a developed internal conducting system. Gymnosperms and angiosperms are classified as seed plants, the remaining divisions are classified as higher spore plants. In addition to bryophytes and seed plants, representatives of other divisions are sometimes grouped into the group of spore-bearing vascular plants. Due to the reduction of archegonia, angiosperms are opposed to all other divisions - archegonial plants.

An analysis of plant habitats given in the “Identifier of Higher Plants of Belarus” showed that the flora of Belarus contains about 1220 local or native vascular plants. As a result of the violation of the integrity of the vegetation cover, due to active human economic activity, the natural flora is depleted and at the same time it is enriched due to alien or adventive species. Some species are introduced accidentally, especially during transport (rail, road, water, air). About a third of the territory of Belarus is occupied by cultivated plants (food, fodder, medicinal, ornamental, technical). Many of them penetrate synanthropic habitats (wastelands, landfills, roadsides of railways, highways, and field roads, etc.). According to the results of research by D.I. Tretyakov, the adventitious fraction of the flora includes more than 800 species. In addition to vascular plants, the flora of Belarus contains about 430 species of bryophytes (G.F. Rykovsky, O.M. Maslovsky). Thus, currently there are over 2,450 species of higher plants in the flora of Belarus.

In conditions of intensive use of natural resources, the problem of protecting flora is becoming increasingly urgent. She happens to be integral part environmental protection natural environment. This complex system measures for rational use, restoration and multiplication of natural resources. On modern stage development of society, human economic activity is one of the decisive factors determining the state of natural resources. The creation of a scientific system of measures that corresponds to the basic laws of development of nature and society and their implementation in practice is the subject of nature conservation. The Red Book is the main document in accordance with which the legal protection of rare and endangered species is carried out. The Red Book of Belarus contains 171 species of higher plants (including 15 bryophytes, 12 vascular spores and 144 seed plants: 1 gymnosperm species, 143 angiosperms). Since 2000, work has been carried out to prepare the third edition of the Red Book of Belarus, which plans to include 200 species of higher vascular plants. Work is underway to create a Green Book of Belarus, which determines the status of rare and endangered plant communities. Existing system specially protected natural areas of Belarus as of June 1, 2004 include about 1,500 objects (including 1 biosphere reserve, 5 national parks, reserves of republican and local significance, etc.). They occupy about 8% of the territory of Belarus, which is close to the optimal level according to international recommendations.

Higher plants include all terrestrial leafy plants that reproduce by spores or seeds.

The main differences between higher and lower plants:

1) Habitat: the lower ones have water, the higher ones have mostly land.

2) Development of various tissues in higher plants- conductive, mechanical, integumentary, of which organs are composed.

3) The presence of vegetative organs in higher plants:

- Root- fixation in the soil and water-mineral nutrition

- Sheet- photosynthesis

- Stem- transport in-in (ascending and descending currents)

(stem with leaves + buds = shoot)

4) Higher plants have covering tissue– epidermis, which performs protective functions

5) Enhanced mechanical stability of the stem of higher plants due to the thick cell wall, impregnated with lignin.

6) Reproductive organs: in most lower plants they are unicellular, in higher plants they are multicellular. The reproductive organs of higher plants are formed in different generations: gametophyte(antheridia and archegonia) and on sporophyte(sporangia).

Based on the characteristics that higher plants have, they are called: stomatal, embryonic, shoot, tellome and vascular plants.

Vascular plants- all higher plants, with the exception of mosses.

Higher plants originated from green, freshwater or brackish water heterotrichous algae. The first higher plants were rhiniophytes– leafless, biochotomous plants. The terminal branches of these plants were called tellomes.

In the development cycle of all higher plants, with the exception of mosses, sporophyte Only in mosses the gametophyte predominates over the sporophyte.

There are plants : 1) Homosporous– they form identical spores and each spore germinates into a different-sex gametophyte.

2) Heterosporous- from a female spore a female gametophyte is formed, from a male spore a male gametophyte is formed.

A spore is a mononuclear, haploid cell (n) with 2 membranes.

Spore plants:

Rhiniophytes – fossil plants (Rhyniophyta)

Bryophytes

Psilotophid

Moss-moss

Horsetails

Ferns

Water is required for fertilization

Higher seed plants:

Department Flowering (Angiosperms)

No water is needed for fertilization

1. General characteristics of the department Bryophyta Department Bryophyta - Bryophyta

Bryophytes- the most primitive, oldest group of higher plants, appeared about 400 million years ago.

Number of types: Currently, bryologists have described about 20 thousand species of mosses.

Moss habitat: Bryophytes are distributed everywhere (they settle on soil, rocks, stumps, trees), except for seas and highly saline soils, and are found even in Antarctica. Mosses prefer shaded, moist places.

Body structure of mosses: mosses are low-growing perennial herbaceous plants ranging in size from 1 mm to several centimeters, less often up to 60 cm or more. The body of mosses is either divided into a stem (caulidia) and small leaves (phylloids), such as sphagnum and cuckoo flax, or is represented by a thallus not divided into organs (marschantia). A characteristic feature of all bryophytes- lack of roots. Absorption of water and attachment to the substrate is carried out by rhizoids, which are outgrowths of the epidermis. The absorption and evaporation of water occurs over the entire surface of the gametophyte.

Bryophytes do not have a developed conducting system (tracheids, vessels, sieve tubes). There are both monoecious and dioecious plants. Their internal structure is relatively simple. Bryophytes, like all higher plants, are characterized by the correct alternation of sexual and asexual generations. The development cycle is dominated by the haploid gametophyte (it constitutes the main body of the plant). Sporophyte does not contain chlorophyll and is attached to the gametophyte for life and feeds on it.

The development of mosses is very interesting. Fertilization is only possible in the presence of water, since sperm can move in it. On one plant, male cells with flagella are formed, on another plant, at the very tops, large female cells mature. During rain or fog, mobile male cells in a drop of water rush towards female cells and merge with them. From a fertilized female cell (zygote), a sporophyte develops, which is called sporogon(he is box with a leg, expanded at the bottom into the foot - haustoria, with the help of which he, sticking to the gametophyte, lives at the expense of it).

(calyptra-remnant of the abdomen of the archegonia)

The relationship between gametophyte and sporophyte is very limited. The gametophyte not only nourishes, but also protects the sporophytic generation, helps in dispersing spores (“false leg” raises the capsule above the plant, the archegonium, bursting with its abdomen, covers the capsule).

A huge number of spores are formed in the box. Each spore is smaller than a grain of semolina. When the spores ripen, the lid of the box opens, or small pores form in it, through which the spores fly free. Once in favorable conditions, the spore germinates. The individual life of bryophytes begins with the germination of a spore. Most often, when the spore swells, the exine bursts, and the intine, together with the contents of the spore, is stretched and gives rise to a single-row filament or a single-layer plate bearing rhizoids. This initial stage of gametophyte development is called protonema(from Greek protos - primary, nema - thread). It either gradually turns into an adult thallus gametophyte (in liverworts), or buds form on the protonema, giving rise to an adult leafy gametophyte).

Vegetatively Bryophytes reproduce with the help of special organs (brood buds, leaves, parts of leaves, twigs); the sporophyte (leg) is also capable of vegetative reproduction.

Mosses are capable of accumulating many substances, including radioactive ones. Some bryophytes (Sphagnum) have antibiotic properties and are used in medicine. Peat deposits, formed mainly by sphagnum mosses, have long been exploited as a source of fuel and organic fertilizers. The bryophyte department is divided into three classes: 1) Horn flowers(Anthocerotaceae); 2 )Liverworts(multiple marching); 3)Leaf mosses(cuckoo flax, sphagnum).

An organ is a part of a plant that has a certain external (morphological) and internal (anatomical) structure in accordance with the function it performs. There are vegetative and reproductive organs of the plant.

The main vegetative organs are the root and shoot (stem with leaves). They provide the processes of nutrition, conduction and dissolved substances, as well as vegetative propagation.

Reproductive organs (spore-bearing spikelets, strobili or cones, flower, fruit, seed) perform functions associated with sexual and asexual reproduction of plants, and ensure the existence of the species as a whole, its reproduction and distribution.

The division of the plant body into organs and the complication of their structure occurred gradually in the process of development of the plant world. The body of the first land plants - rhinophytes, or psilophytes - was not divided into roots and leaves, but was represented by a system of branching axial organs - telomes. As plants reached land and adapted to life in the air and soil, their telomes changed, which led to the formation of organs.

In algae, fungi and lichens, the body is not differentiated into organs, but is represented by a thallus, or thallus of a very diverse appearance.

During the formation of organs, some general patterns are revealed. As the plant grows, the size and weight of the body increase, cell division occurs and they stretch in a certain direction. The first stage of any neoplasm is the orientation of cellular structures in space, i.e. polarity. In higher seed plants, polarity is already detected in the zygote and the developing embryo, where two rudimentary organs are formed: a shoot with an apical bud and a root. The movement of many substances occurs along conductive paths in a polar manner, i.e. in a certain direction.

Another pattern is symmetry. It manifests itself in the location of the side parts in relation to the axis. There are several types of symmetry: radial - two (or more) planes of symmetry can be drawn; bilateral - only one plane of symmetry; in this case, a distinction is made between the dorsal (dorsal) and ventral (ventral) sides (for example, leaves, as well as organs that grow horizontally, i.e., having plagiotropic growth). , growing vertically - orthotropic - have radial symmetry.

In connection with the adaptation of the main organs to new specific conditions, a change in their functions occurs, which leads to their modifications, or metamorphoses (tubers, bulbs, spines, buds, flowers, etc.). In plant morphology, homologous and similar organs are distinguished. Homologous organs have the same origin, but may differ in shape and function. Similar organs perform the same functions and have the same appearance, but different in origin.

The organs of higher plants are characterized by oriented growth ( , which is a reaction to the unilateral action of external factors (light, gravity, humidity). The growth of axial organs towards light is defined as positive (shoots) and negative (main root) phototropism. Oriented growth of axial organs of a plant, caused by the unilateral action of gravity, is defined as geotropism.Positive geotropism of the root causes its directed growth towards the center, negative geotropism of the stem - from the center.

The shoot and root are present in rudimentary form in the embryo located in the mature seed. The embryonic shoot consists of an axis (embryo stalk) and cotyledon leaves, or cotyledons. The number of cotyledons in the embryo of seed plants ranges from 1 to 10-12.

At the end of the embryo axis there is a shoot growth point. It is formed by a meristem and often has a convex surface. This is the cone of growth, or apex. At the top of the shoot (apex) the rudiments of leaves are laid in the form of tubercles or ridges following the cotyledons. Typically, the leaf primordia grow faster than the stem, with the young leaves covering each other and the growth point, forming a bud of the embryo.

The part of the axis where the bases of the cotyledons are located is called the cotyledon node; the remaining portion of the embryonic axis, below the cotyledons, is called the hypocotyl, or subcotyledon. Its lower end passes into the embryonic root, which is so far represented only by a growth cone.

As the seed germinates, all organs of the embryo gradually begin to grow. The embryonic root emerges from the seed first. It strengthens young plant in the soil and begins to absorb water and dissolved in it minerals, giving rise to the main root. The area at the border between the main root and the stem is called the root collar. In most plants, the main root begins to branch, and lateral roots of the second, third and higher orders appear, which leads to the formation of a root system. Adventitious roots can form quite early on the hypocotyl, in old sections of the root, on the stem, and sometimes on the leaves.

Almost simultaneously, a first-order shoot, or main shoot, develops from the embryonic bud (apex), which also branches, forming new shoots of the second, third and higher orders, which leads to the formation of the main shoot system.

As for the higher spore shoots (moss mosses, horsetails, ferns), their body (sporophyte) develops from the zygote. The initial stages of the life of the sporophyte take place in the tissues of the growths (gametophytes). An embryo develops from the zygote, consisting of a rudimentary shoot and a root pole.

So, the body of any higher plant consists of shoot and (except for mossy) root systems, built from repeating structures - shoots and roots.

In all organs of a higher plant, three tissue systems - integumentary, conductive and basal - continue continuously from organ to organ, reflecting the integrity of the plant organism. The first system forms the outer protective cover of plants; the second, including phloem and xylem, is immersed in the system of basic tissues. The fundamental difference in the structure of the root, stem and leaf is determined by the different distribution of these systems.

During primary growth, which begins near the tips of the roots and stems, the primary ones are formed, which make up the primary body of the plant. Primary xylem and primary phloem and associated parenchyma tissues form the central cylinder, or stele, of the stem and root of the primary plant body. There are several types of steles.