The main stages of historical development and complexity of the plant world on earth. The main stages of the development of the plant world - Knowledge Hypermarket The appearance of the main groups of plants in the process of evolution

The emergence of unicellular and multicellular algae, the emergence of photosynthesis: the emergence of plants on land (psilophytes, mosses, ferns, gymnosperms, angiosperms).

The development of the plant world took place in 2 stages and is associated with the appearance of lower and higher plants. According to the new taxonomy, algae are classified as lower (and previously included bacteria, fungi and lichens. Now they are separated into independent kingdoms), and mosses, pteridophytes, gymnosperms and angiosperms are classified as higher.

In the evolution of lower organisms, two periods are distinguished, which differ significantly in the organization of the cell. During period 1, organisms similar to bacteria and blue-green algae dominated. The cells of these life forms did not have typical organelles (mitochondiria, chloroplasts, Golgi apparatus, etc.). The cell nucleus was not limited by the nuclear membrane (this is a prokaryotic type of cellular organization). Period 2 was associated with the transition of lower plants (algae) to an autotrophic type of nutrition and with the formation of a cell with all the typical organelles (this is a eukaryotic type of cellular organization, which was preserved at subsequent stages of development of the plant and animal world). This period can be called the period of dominance of green algae, unicellular, colonial and multicellular. The simplest of multicellular organisms are filamentous algae (ulotrix), which do not have any branching in their body. Their body is a long chain consisting of individual cells. Other multicellular algae are dissected by a large number of outgrowths, so their body is branched (in Chara, in Fucus).

Multicellular algae, due to their autotrophic (photosynthetic) activity, have evolved in the direction of increasing their body surface for better absorption nutrients from the aquatic environment and solar energy. Algae have a more progressive form of reproduction - sexual reproduction, in which the beginning of a new generation is given by a diploid (2n) zygote, combining the heredity of 2 parental forms.

The 2nd evolutionary stage of plant development must be associated with gradual transition them from an aquatic to a terrestrial lifestyle. The primary terrestrial organisms turned out to be psilophytes, which were preserved as fossil remains in Silurian and Devonian deposits. The structure of these plants is more complex compared to algae: a) they had special organs of attachment to the substrate - rhizoids; b) stem-like organs with wood surrounded by phloem; c) rudiments of conducting tissues; d) epidermis with stomata.

Starting with psilophytes, it is necessary to trace 2 lines of evolution of higher plants, one of which is represented by bryophytes, and the second by ferns, gymnosperms and angiosperms.

The main thing that characterizes bryophytes is their predominance in the cycle individual development gametophyte above sporophyte. The gametophyte is everything green plant capable of self-feeding. The sporophyte is represented by a capsule (cuckoo flax) and is completely dependent on the gametophyte for its nutrition. The dominance of the moisture-loving gametophyte in mosses under the conditions of an air-terrestrial lifestyle turned out to be impractical, so mosses became a special branch of the evolution of higher plants and have not yet given rise to perfect groups of plants. This was also facilitated by the fact that the gametophyte, compared to the sporophyte, had poor heredity (haploid (1n) set of chromosomes). This line in the evolution of higher plants is called gametophytic.

The second line of evolution on the path from psilophytes to angiosperms is sporophytic, because in ferns, gymnosperms and angiosperms the sporophyte dominates in the cycle of individual plant development. It is a plant with a root, stem, leaves, sporulation organs (in ferns) or fruiting organs (in angiosperms). Sporophyte cells have a diploid set of chromosomes, because they develop from a diploid zygote. The gametophyte is greatly reduced and is adapted only for the formation of male and female germ cells. In flowering plants, the female gametophyte is represented by the embryo sac, which contains the egg. The male gametophyte is formed when pollen germinates. It consists of one vegetative and one generative cell. When pollen germinates, 2 sperm appear from the generative cell. These 2 male reproductive cells are involved in double fertilization in angiosperms. The fertilized egg gives rise to a new generation of the plant - the sporophyte. The progress of angiosperms is due to the improvement of the reproductive function.

The book outlines a pressing problem of modern natural science - the origin of life. It is written on the basis of the most modern data from geology, paleontology, geochemistry and cosmochemistry, which refutes many traditional but outdated ideas about the origin and development of life on our planet. The extreme antiquity of life and the biosphere, commensurate with the age of the planet itself, allows the author to conclude: the origin of the Earth and life is a single interconnected process.

For readers interested in geosciences.

Book:

Plants, as typical representatives of photoautotrophic organisms of our planet, arose during a long evolution, which originates from the primitive inhabitants of the illuminated zone of the sea - planktonic and benthic prokaryotes. Comparing paleontological data with data on the comparative morphology and physiology of living plants, we can generally outline the following: chronological sequence their appearance and development:

1) bacteria and blue-green algae (prokaryotes);

2) cyan, green, brown, red, etc. algae (eukaryotes, like all subsequent organisms);

3) mosses and liverworts;

4) ferns, horsetails, mosses, seed ferns;

6) angiosperms, or flowering plants.

Bacteria and blue-green algae were found in the most ancient preserved deposits of the Precambrian; algae appeared much later, and only in the Phanerozoic do we encounter the lush development of higher plants: lycophytes, horsetails, gymnosperms and angiosperms.

Throughout the Cryptozoic period, predominantly single-celled organisms—various types of algae—developed in primary reservoirs in the euphotic zone of ancient seas.

The main representatives of prokaryotes discovered in the Precambrian had autotrophic nutrition - through photosynthesis. The most favorable conditions for photosynthesis were created in the illuminated part of the sea at a depth from the surface to 10 m, which also corresponded to the conditions of shallow benthos.

To date, the study of Precambrian microfossils has advanced, and accordingly, a large amount of factual material has been accumulated. In general, the interpretation of microscopic specimens is a difficult task that cannot be resolved unambiguously.

Trichome bacteria, which differ sharply from mineral formations of a similar shape, are best identified and identified. The obtained empirical material on microfossils allows us to conclude that they can be compared with living cyanobacteria.

Stromatolites, as biogenic structures of the distant past of the planet, were formed during the accumulation of a thin sediment of calcium carbonate captured by photosynthetic organisms of microbiological associations. Microfossils in stromatolites consist almost exclusively of prokaryotic microorganisms, mainly related to blue-green algae - cyanophytes. When studying the remains of benthic microorganisms composing stromatopites, one interesting feature of fundamental importance was revealed. Microfossils of different ages change their morphology little and generally indicate the conservation of prokaryotes. Microfossils related to prokaryotes remained almost constant for quite some time. for a long time. In any case, we have before us an established fact - the evolution of prokaryotes was much slower than that of higher organisms.

So, in the course of geological history, prokaryotic bacteria exhibit maximum persistence. Persistent forms include organisms that have been preserved unchanged during the process of evolution. As G. A. Zavarzin notes, since ancient communities of microorganisms show significant similarities with modern ones developing in hydrotherms and in areas of evaporite formation, this makes it possible to more thoroughly study the geochemical activity of these communities using modern natural and laboratory models, extrapolating them to the distant Precambrian time.

The first eukaryotes arose in planktonic associations open waters. The end of the exclusive dominance of prokaryotes dates back to approximately 1.4 billion years ago, although the first eukaryotes appeared much earlier. Thus, according to the latest data, the appearance of fossil organic remains from black shales and carbonaceous formations of the Upper Lake region indicates the appearance of eukaryotic microorganisms 1.9 billion years ago.

From the date of 1.4 billion years ago to our time, the Precambrian fossil record expands significantly. This date marks the appearance of relatively large forms related to planktonic eukaryotes and called “acritarchs” (translated from Greek as “creatures”). unknown origin"). It should be noted that the acritarcha group is proposed as an undefined systematic category denoting Microfossils of different origins, but similar in external morphological characters. Acritarchs from the Precambrian and Lower Paleozoic are described in the literature. Most acritarchs were probably single-celled photosynthetic eukaryotes - the shells of some ancient algae. Some of them could still have a prokaryotic organization. The planktonic nature of acritarchs is indicated by their cosmopolitan distribution in sediments of the same age. The most ancient acritarchs from the Early Riphean deposits of the Southern Urals were discovered by T.V. Yankauskas.

Over the course of geological time, the size of acritarchs increased. According to observational data, it turned out that the younger the Precambrian Microfossils, the larger they are. It is assumed that a significant increase in the size of acritarchs was associated with an increase in the size of the eukaryotic cell organization. They could have appeared as independent organisms or, more likely, in symbiosis with others. L. Margelis believes that eukaryotic cells were assembled from pre-existing prokaryotic cells. However, for the survival of eukaryotes, it was necessary that the habitat be saturated with oxygen and, as a consequence, aerobic metabolism arose. Initially, free oxygen released during photosynthesis of cyanophytes accumulated in limited quantities in shallow water habitats. The increase in its content in the biosphere caused a reaction on the part of organisms: they began to populate oxygen-free habitats (in particular, anaerobic forms).

Data from Precambrian micropaleontology indicate that in the Middle Precambrian, even before the appearance of eukaryotes, cyanophytes constituted a relatively small part of the plankton. Eukaryotes needed free oxygen and increasingly competed with prokaryotes in those areas of the biosphere where free oxygen appeared. Based on available micropaleontological data, it can be judged that the transition from prokaryotic to eukaryotic flora of ancient seas occurred slowly and both groups of organisms coexisted together for a long time. However, this coexistence occurs in a different proportion in the modern era. By the beginning of the Late Riphean, many autotrophic and heterotrophic forms of organisms had already spread.

As they developed, organisms moved for nutrients to deeper and more distant areas of the sea. The fossil record notes a sharp increase in the diversity of large spheroidal forms of eukaryotic acritarchs in Late Riphean times, 900-700 million years ago. About 800 million years ago, representatives of a new class of planktonic organisms appeared in the World Ocean - goblet-shaped bodies with massive shells or outer covers mineralized with calcium carbonate or silica. At the beginning of the Cambrian period, significant shifts occurred in the evolution of plankton - a variety of microorganisms arose with a complex sculptured surface and improved buoyancy. They gave rise to true spiny acritarchs.

The appearance of eukaryotes created an important prerequisite for the emergence of multicellular plants and animals in the Early Riphean (about 1.3 billion years ago). For the Belta series from the Precambrian of the western states of North America, they were described by C. Walcott. But what type of algae they belong to (brown, green or red) is still unclear. Thus, the extremely long era of dominance of bacteria and related blue-green algae was replaced by an era of algae that reached a significant variety of shapes and colors in the waters of the ancient oceans. During the Late Riphean and Vendian, multicellular algae became more diverse; they were compared with brown and red algae.

According to Academician B.S. Sokolov, multicellular plants and animals appeared almost simultaneously. Various representatives of aquatic plants are found in Vendian sediments. The most prominent place is occupied by multicellular algae, the thalli of which often overflow the strata of Vendian sediments: mudstones, clays, sandstones. Macroplanktonic algae, colonial algae, spiral-filamentous algae Volymella, felt algae and other forms are often found. Phytoplankton is very diverse.

For most of Earth's history, plant evolution took place in aquatic environments. It was here that aquatic vegetation originated and went through various stages of development. In general, algae are a large group of lower aquatic plants that contain chlorophyll and produce organic matter through photosynthesis. The body of the algae has not yet been differentiated into roots, leaves and other characteristic parts. They are represented by unicellular, multicellular and colonial forms. Reproduction is asexual, vegetative and sexual. Algae are part of plankton and benthos. Currently, they are classified as a plant subkingdom Thallophyta, in which the body is composed of a relatively uniform tissue - thallus, or Thallus. The thallus consists of many cells that are similar in appearance and function. IN historical aspect algae went through the longest stage in the development of green plants and, in the general geochemical cycle of matter in the biosphere, played the role of a giant generator of free oxygen. The emergence and development of algae was extremely uneven.

Green algae (Chlorophyta) are a large and widespread group of predominantly green plants, which falls into five classes. In appearance they are very different from each other. Green algae come from green flagellated organisms. This is evidenced by transitional forms - pyramidomonas and chlamydomonas, mobile unicellular organisms that live in waters. Green algae reproduce sexually. Some groups of green algae achieved great development during the Triassic period.

Flagellates (Flagellata) are united in a group of microscopic single-celled organisms. Some researchers attribute them to the plant kingdom, others to the animal kingdom. Like plants, some flagellates contain chlorophyll. However, unlike most plants, they do not have a separate cellular system and are able to digest food with the help of enzymes, and also live in the dark, like animal organisms. In all likelihood, flagellates existed in the Precambrian, but their undisputed representatives were found in Jurassic deposits.

Brown algae (Phaeophyta) are distinguished by the presence of brown pigment in such quantities that it actually masks chlorophyll and gives plants the appropriate color. Brown algae belong to benthos and plankton. The largest algae reach 30 m in length. Almost all of them grow in salt water, which is why they are called sea grass. Brown algae include sargassum algae - floating planktonic forms with a large number of bubbles. In fossil form they are known from the Silurian.

Red algae(Rhodophyta) have this color due to the red pigment. These are predominantly marine plants, highly branched. Some of them have a calcareous skeleton. This group is often called cullipora. They exist today, and have been known in fossil form since the Lower Cretaceous. Somipores, which are close to them, with larger and wider cells, appeared in the Ordovician.

Charovaya algae(Charophyta) are a very unique and rather highly organized group of multicellular plants that reproduce sexually. They are so different from other algae that some botanists classify them as leaf-stem algae due to the emerging tissue differentiation. Charodic algae are green in color and currently live in fresh water and in brackish water bodies. They avoid seawater with normal salinity, but it can be assumed that in the Paleozoic they inhabited the seas. Some charophytes develop spores impregnated with calcium carbonate. Characeae are among the important rock-forming organisms of freshwater limestones.

Diatoms(Diatomeae) - typical representatives of plankton. They have an oblong shape and are covered on the outside with a shell made of silica. The first remains of diatoms were found in Devonian sediments, but they may be older. In general, diatoms are a relatively young group. Their evolution has been studied better than other algae, since flint shells and valves of diatoms can be preserved in a fossil state for a very long time. In all likelihood, diatoms come from flagellates, which are yellow in color and are capable of depositing in their shells a small amount of silica. In modern times, diatoms are widespread in fresh and sea ​​waters, are occasionally found in moist soils. Remains of diatoms are known in Jurassic deposits, but it is possible that they appeared much earlier. Fossil diatoms from the Early Cretaceous reached the modern era without interruption in sedimentation.

Very important event, which contributed to a sharp acceleration in the rate of evolution of the entire living population of our planet, was the emergence of plants from the marine environment onto land. The emergence of plants on the surface of continents can be considered a true revolution in the history of the biosphere. The development of terrestrial vegetation created the prerequisites for animals to reach land. However, the massive transition of plants to land was preceded by a long preparatory period. It can be assumed that plant life on land appeared a very long time ago, at least locally - in a humid climate on the coasts of shallow bays and lagoons, where changes in water level periodically brought aquatic vegetation onto land. The Soviet naturalist L. S. Berg was the first to express the idea that the land surface was not a lifeless desert neither in the Cambrian nor in the Precambrian. The prominent Soviet paleontologist L. Sh. Davitashvili also admitted that in the Precambrian the continents probably already had some kind of population consisting of low-organized plants and, possibly, even animals. However, their total biomass was negligible.

To live on land, plants had to not lose water. It should be borne in mind that in higher plants - mosses, pteridophytes, gymnosperms and flowering plants, which currently make up the bulk of terrestrial vegetation, only roots, root hairs and rhizoids come into contact with water, while the rest of their organs are in the atmosphere and evaporate water the entire surface.

Plant life flourished most on the shores of lagoon lakes and swamps. Here a type of plant appeared, the lower part of which was in the water, and the upper part in the air, under direct rays of the sun. Somewhat later, with the penetration of plants onto non-flooded land, their very first representatives developed a root system and were able to consume groundwater. This contributed to their survival during dry periods. Thus, new circumstances led to the division of plant cells into tissues and the development of protective devices that did not exist in the ancestors that lived in water.

Fig. 14. Development and genetic connections various groups of land plants

The massive conquest of the continents by plants occurred during the Silurian period of the Paleozoic era. First of all, these were psilophytes - peculiar spore-bearing plants resembling club mosses. Some of the twisting stems of psilophytes were covered with bristly leaves. Psilophytes were devoid of roots, and mostly leaves. They consisted of branching green stems up to 23 cm high and rhizomes stretching horizontally in the soil. Psilophytes, as the first reliable sushi plants, created entire green carpets on moist soil.

Probably, the production of organic matter from the first land vegetation was insignificant. The vegetation of the Silurian period undoubtedly originated from the algae of the sea and itself gave rise to the vegetation of the subsequent period.

After the conquest of the land, the development of vegetation led to the formation of numerous and varied forms. Intensive separation of plant groups began in the Devonian and continued in subsequent geological time. The general pedigree of the most important plant groups is given in Fig. 14.

Mosses originated from. seaweed Their early stage of development is very similar to some green algae. However, there is an assumption that mosses originated from simpler representatives of brown algae, adapted to life on damp rocks or in soils in general.

On the surface of the Early Paleozoic continents, the age of algae gave way to the age of psilophytes, which gave rise to vegetation that was reminiscent in appearance and size of modern thickets of large mosses. The dominance of psilophytes was replaced in the Carboniferous period by the dominance of fern-like plants, which formed fairly extensive forests on marshy soils. The development of these plants contributed to the fact that the composition atmospheric air changed. A significant amount of free oxygen was added and a mass of nutrients necessary for the emergence and development of land vertebrates accumulated. At the same time, huge masses of coal were accumulated. The Carboniferous period was characterized by an exceptional flourishing of terrestrial vegetation. Tree-like mosses appeared, reaching a height of 30 m, huge horsetails, ferns, and conifers began to appear. During the Permian period, the development of terrestrial vegetation continued, which significantly expanded its habitats.

The period of dominance of ferns gave way to the period of cone-bearing coniferous plants. The surface of the continents began to take on a modern appearance. At the beginning of the Mesozoic era, conifers and cycads became widespread, and in the Cretaceous period they appeared flowering plants. At the very beginning of the Early Cretaceous era, Jurassic forms of plants still existed, but then the composition of the vegetation changed greatly. At the end of the Early Cretaceous era, many angiosperms are found. From the very beginning of the Late Cretaceous era, they pushed aside gymnosperms and took a dominant position on land. In general, in the terrestrial flora there is a gradual replacement of the Mesozoic vegetation of gymnosperms (conifers, cycads, ginkgos) by vegetation of the Cenozoic appearance. The vegetation of the Late Cretaceous era is already characterized by the presence of a significant number of modern flowering plants such as beech, willow, birch, plane tree, laurel, and magnolia. This restructuring of vegetation prepared a good food base for the development of higher terrestrial vertebrates - mammals and birds. The development of flowering plants was associated with the flowering of numerous insects that played important role in pollination.

The onset of a new period in the development of plants did not lead to the complete destruction of ancient plant forms. Some organisms of the biosphere were preserved. With the advent of flowering plants, bacteria not only did not disappear, but continued to exist, finding new sources of nutrition in the soil and in the organic matter of plants and animals. Algae of different groups changed and developed along with higher plants.

Coniferous forests, which appeared in the Mesozoic, still grow today along with deciduous ones. They provide shelter to fern-like plants, since these ancient inhabitants of the foggy and humid climate of the Carboniferous period are afraid of open places illuminated by the sun.

Finally, it should be noted that there are persistent forms in the modern flora. The most persistent were certain groups of bacteria, which remained virtually unchanged since the Early Precambrian. But from more highly organized forms of plants, genera and species were also formed, which have changed little to date.

It should be noted that there is an undoubted presence in the modern flora of relatively highly organized multicellular plant genera. Late Paleozoic and Mesozoic forms of plants, which lived without changes for tens and hundreds of millions of years, are, of course, persistent. Thus, at present, “living fossils” (Fig. 15) from the groups of ferns, gymnosperms and mosses have been preserved among the plant world. The term “living fossil” was first used by Charles Darwin, citing the East Asian gymnosperm tree as an example Ginkgo biloba. From the world of terrestrial plants, living fossils include the most famous fern palms, ginkgo tree, araucaria, mammoth tree, or sequoia.

As noted by the expert on fossil flora A. N. Krshptofovich, many genera of plants, lords of ancient forests, also existed for an extremely long time, especially in the Paleozoic; for example, Sigillaria, Lepidodendron, Calamites - at least 100-130 million years. The same number - Mesozoic ferns 11 conifers Metasequoia. The genus Ginkgo is more than 150 million years old, and the modern species Ginkgo biloba, if we include the essentially indistinguishable form Ginkgo adiantoides, is about 100 million years old.

Living fossils of the modern plant world can otherwise be called phylogenetically conserved types. Plants that are well studied in paleobotanical terms and classified as living fossils are conservative groups. They have not changed at all or have changed very little compared to related forms of the geological past.

Naturally, the presence of living fossils in modern flora raises the problem of their formation in the history of the biosphere. Conservative organizations are present in all major phylogenetic branches and exist in a wide variety of conditions: in deep and shallow sea zones, in ancient tropical forests, in open steppe expanses and in all bodies of water without exception. The most important condition for the existence of evolutionarily conservative organisms - the presence of habitats with a constant living environment. However, stable living conditions are not decisive. The presence of only certain forms, and not all communities of flora and fauna, indicates other factors in the preservation of living fossils. The study of their geographical distribution indicates that they are confined to strictly defined territories, and are characterized by geographic isolation. Thus, Australia, the islands of Madagascar and New Zealand- These are typical areas of distribution of terrestrial living fossils.

In its evolution, the plant world creates the general appearance of the ancient landscapes in which the development of the animal world took place. Therefore, the division of geological time can be carried out on the basis of the succession of various plant forms. The German paleobotanist W. Zimmermann, back in 1930, divided the entire geological past from the point of view of the development of the plant world into six eras. He gave them a letter designation and arranged them in sequence from ancient eras to younger ones.

A comparison of the usual geological time scale, constructed primarily from paleozoological data, with the plant development scale is presented in Table. eleven.

Planet Earth was formed more than 4.5 billion years ago. The first single-celled life forms appeared perhaps about 3 billion years ago. At first it was bacteria. They are classified as prokaryotes because they do not have a cell nucleus. Eukaryotic (those with nuclei in cells) organisms appeared later.

Plants are eukaryotes capable of photosynthesis. In the process of evolution, photosynthesis appeared earlier than eukaryotes. At that time it existed in some bacteria. These were blue-green bacteria (cyanobacteria). Some of them have survived to this day.

According to the most common hypothesis of evolution, plant cell formed by the entry into a heterotrophic eukaryotic cell of a photosynthetic bacterium that was not digested. Further, the process of evolution led to the appearance of a single-celled eukaryotic photosynthetic organism with chloroplasts (their predecessors). This is how unicellular algae appeared.

The next stage in the evolution of plants was the emergence of multicellular algae. They reached great diversity and lived exclusively in water.

The surface of the Earth did not remain unchanged. Where the earth's crust rose, land gradually emerged. Living organisms had to adapt to new conditions. Some ancient algae were gradually able to adapt to a terrestrial lifestyle. In the process of evolution, their structure became more complex, tissues appeared, primarily integumentary and conductive.

The first land plants are considered to be psilophytes, which appeared about 400 million years ago. They have not survived to this day.

Further evolution of plants, associated with the complication of their structure, took place on land.

During the time of the psilophytes, the climate was warm and humid. Psilophytes grew near bodies of water. They had rhizoids (like roots), with which they anchored themselves in the soil and absorbed water. However, they did not have true vegetative organs (roots, stems and leaves). The movement of water and organic substances throughout the plant was ensured by the emerging conductive tissue.

Later, ferns and mosses evolved from psilophytes. These plants have more complex structure, they have stems and leaves, they are better adapted to living on land. However, just like psilophytes, they remained dependent on water. During sexual reproduction, in order for the sperm to reach the egg, they need water. Therefore, they could not “go” far from wet habitats.

During the Carboniferous period (approximately 300 million years ago), when the climate was humid, ferns reached their dawn, and many of their tree forms grew on the planet. Later, dying off, it was they who formed coal deposits.

When the climate on Earth began to become colder and drier, ferns began to die out en masse. But some of their species before this gave rise to the so-called seed ferns, which in fact were already gymnosperms. In the subsequent evolution of plants, seed ferns became extinct, giving rise to other gymnosperms. Later, more advanced gymnosperms appeared - conifers.

The reproduction of gymnosperms no longer depended on the presence of liquid water. Pollination occurred with the help of wind. Instead of sperm (mobile forms), they formed sperm (immobile forms), which were delivered to the egg special education pollen grain. In addition, gymnosperms produced not spores, but seeds containing a supply of nutrients.

The further evolution of plants was marked by the appearance of angiosperms (flowering plants). This happened about 130 million years ago. And about 60 million years ago they began to dominate the Earth. Compared to gymnosperms, flowering plants are better adapted to life on land. We can say that they began to take more advantage of the environment. So their pollination began to occur not only with the help of the wind, but also with the help of insects. This increased pollination efficiency. Angiosperm seeds are found in fruits, which allow them to spread more efficiently. In addition, flowering plants have more complex tissue structure, for example, in a conducting system.

Currently, angiosperms are the most numerous group of plants in terms of the number of species.

The first plant organisms arose in the wild in very distant times. The first living beings were microscopically small lumps of mucus. Much later, some of them developed a green color, and these living organisms began to look like unicellular algae. Single-celled creatures gave rise to multicellular organisms, which, like single-celled organisms, arose in water. From unicellular algae, various multicellular algae developed.

The surface of the continents and the ocean floor have changed over time. New continents rose and previously existing ones sank. Due to vibrations of the earth's crust, land appeared in place of the seas. The study of fossil remains shows that the plant world of the Earth also gradually changed.

The transition of plants to a terrestrial lifestyle, according to scientists, was associated with the existence of land areas that were periodically flooded and cleared of water. The receding water was retained in the depressions. They either dried up or filled with water again. The drainage of these areas occurred gradually. Some algae have developed adaptations for living outside of water.

The climate at that time was globe was humid and warm. The transition of some plants from an aquatic to a terrestrial lifestyle began. The structure of these plants gradually became more complex. They gave rise to the first land plants. The oldest group of known land plants are psilophytes.

The development of the plant world on Earth is a long-term process, which is based on the transition of plants from an aquatic to a terrestrial way of life.

Psilophytes already existed 420-400 million years ago, and later became extinct. Psilophytes grew along the banks of reservoirs and were small multicellular green plants. They had no roots, stems, or leaves. The role of roots was played by rhizoids. Psilophytes, unlike algae, have a more complex internal structure- presence of integumentary and conductive tissues. They reproduced by spores.

From psilophytes came bryophytes and ferns, which already had stems, leaves and roots. The heyday of ferns was about 300 million years ago during the Carboniferous period. The climate at this time was warm and humid. At the end of the Carboniferous period, the Earth's climate became noticeably drier and colder. Tree ferns, horsetails and club mosses began to die out, but by this time primitive gymnosperms appeared - descendants of some ancient ferns. According to scientists, the first gymnosperms were seed ferns, which later became completely extinct. Their seeds developed on the leaves: these plants did not have cones. Seed ferns were tree-like, liana-like and herbaceous plants. Gymnosperms originated from them.

Living conditions continued to change. Where the climate was more severe, ancient gymnosperms gradually died out and were replaced by more advanced plants - ancient conifers, then they were replaced by modern conifers: pine, spruce, larch, etc.

The transition of plants to land is closely connected not only with the appearance of such organs as stems, leaves, roots, but, mainly, with the appearance of seeds, a special method of reproduction of these plants. Plants that reproduced by seeds were better adapted to life on land than plants that reproduced by spores. This became especially clear when the climate became less humid.

On the growths developing from spores (in mosses, mosses, ferns), female and male gametes (sex cells) are formed - eggs and sperm. In order for fertilization to occur (after the fusion of gametes), atmospheric or groundwater, in which sperm move towards eggs.

Gymnosperms do not need free water for fertilization, since it occurs inside the ovules. In them, male gametes (sperm) approach female gametes (eggs) through pollen tubes growing inside the ovules. Thus, fertilization in spore plants is completely dependent on the availability of water; in plants that reproduce by seeds, this dependence is not present.

Angiosperms - descendants of ancient gymnosperms - appeared on Earth over 130-120 million years ago. They turned out to be the most adapted to life on land, since only they have special reproductive organs - flowers, and their seeds develop inside the fruit and are well protected by the pericarp.

Thanks to this, angiosperms quickly spread throughout the Earth and occupied a wide variety of habitats. For more than 60 million years, angiosperms have dominated the Earth. In Fig. 67 shows not only the sequence of appearance of certain plant divisions, but also their quantitative composition, where angiosperms have a significant place.

1. What plants are classified as lower? What is their difference from the higher ones?
2. Which group of plants currently occupies a dominant position on our planet?

Methods for studying ancient plants. The world of modern plants is diverse (Fig. 83). But in the past, the plant world of the Earth was completely different. Paleontology helps us trace the picture of the historical development of life from its beginning to the present day (from the Greek words “palaios” - ancient, “he/ontos” - existing and “logos”) - the science of extinct organisms, their change in time and space .

Rice. 83. Approximate number of species of modern plants

One of the branches of paleontology - paleobotany - studies the fossil remains of ancient plants preserved in layers of geological sediments. It has been proven that over the centuries the species composition plant communities changed. Many plant species died out, others came to replace them. Sometimes plants found themselves in such conditions (in a swamp, under a layer of collapsed rock) that without access to oxygen they did not rot, but were saturated with minerals. Petrification occurred. Petrified trees are often found in coal mines. They are so well preserved that their internal structure can be studied. Sometimes imprints remain on hard rocks, from which one can judge the appearance of ancient fossil organisms (Fig. 84). Spores and pollen found in sedimentary rocks can tell scientists a lot. Using special methods, it is possible to determine the age of fossil plants and their species composition.

Rice. 84. Imprints of ancient plants

Change and development of the plant world. Fossil remains of plants indicate that in ancient times the plant world of our planet was completely different from what it is now.

In the most ancient layers of the earth's crust, it is not possible to find signs of living organisms. In later sediments, remains of primitive organisms are found. The younger the layer, the more often more complex organisms are found, which become increasingly similar to modern ones.

Many millions of years ago there was no life on Earth. Then the first primitive organisms appeared, which gradually changed and transformed, giving way to new, more complex ones.

In the process of long-term development, many plants on Earth disappeared without a trace, others changed beyond recognition. Therefore, it is very difficult to completely restore the history of the development of the plant world. But scientists have already proven that all modern plant species descended from more ancient forms.

Initial stages of development of the plant world. The study of the oldest layers of the earth's crust, imprints and fossils of previously living plants and animals, and many other studies have made it possible to establish that the Earth was formed more than 5 billion years ago.

The first living organisms appeared in water approximately 3.5-4 billion years ago. The simplest single-celled organisms were similar in structure to bacteria. They did not yet have a separate nucleus, but they had a metabolic system and the ability to reproduce. They used organic and mineral substances dissolved in the water of the primary ocean for food. Gradually, the supply of nutrients in the primary ocean began to deplete. A fight for food began between the cells. Under these conditions, some cells developed a green pigment - chlorophyll, and they adapted to the use of energy sunlight to convert water and carbon dioxide into food. This is how photosynthesis arose, that is, the process of formation of organic substances from inorganic ones using light energy. With the advent of photosynthesis, oxygen began to accumulate in the atmosphere. The composition of the air began to gradually approach the modern one, that is, it mainly includes nitrogen, oxygen and a small amount of carbon dioxide. This atmosphere contributed to the development of more perfect forms life.

The appearance of algae. Single-celled algae evolved from the ancient simplest unicellular organisms capable of photosynthesis. Single-celled algae are the ancestors of the plant kingdom. Along with floating forms, those attached to the bottom also appeared among the algae. This way of life led to the division of the body into parts: some of them serve for attachment to the substrate, others carry out photosynthesis. In some green algae, this was achieved thanks to a giant multinucleate cell, divided into leaf-shaped and root-shaped parts. However, the division of the multicellular body into parts that perform different functions turned out to be more promising.

Important for further development plants had the occurrence of sexual reproduction in algae. Sexual reproduction contributed to the variability of organisms and their acquisition of new properties that helped them adapt to new living conditions.

Exit of plants to land. The surface of continents and the ocean floor have changed over time. New continents rose and existing ones sank. Due to vibrations of the earth's crust, land appeared in place of the seas. The study of fossil remains shows that the plant world of the Earth also changed.

The transition of plants to a terrestrial lifestyle was apparently associated with the existence of land areas that were periodically flooded and cleared of water. The drainage of these areas occurred gradually. Some algae began to develop adaptations for living outside of water.

At this time, the globe had a humid and warm climate. The transition of some plants from an aquatic to a terrestrial lifestyle began. The structure of ancient multicellular algae gradually became more complex, and they gave rise to the first land plants (Fig. 85).

Rice. 85. The first sushi plants

One of the first terrestrial plants were rhiniophytes that grew along the banks of reservoirs, for example rhinia (Fig. 86). They existed 420-400 million years ago and then died out.

Figure 86. Rhiniophytes

The structure of rhinophytes still resembled the structure of multicellular algae: there were no true stems, leaves, roots, they reached a height of about 25 cm. The rhizoids, with the help of which they attached to the soil, absorbed water and mineral salts from it. Along with the similarity of roots, stems and primitive conducting systems, rhiniophytes had integumentary tissue that protected them from drying out. They reproduced by spores.

Origin of higher spore plants. From rhiniophyte-like plants came the ancient mosses, horsetails and ferns and, apparently, mosses, which already had stems, leaves, and roots (Fig. 87). These were typical spore plants; they reached their heyday about 300 million years ago, when the climate was warm and humid, which favored the growth and reproduction of ferns, horsetails and mosses. However, their emergence onto land and separation from the aquatic environment was not yet final. During sexual reproduction, spore plants require an aquatic environment for fertilization.

Rice. 87. Origin of higher plants

Development of seed plants. At the end of the Carboniferous period, the Earth's climate almost everywhere became drier and colder. Tree ferns, horsetails and mosses gradually died out. Primitive gymnosperms appeared - descendants of some ancient fern-like plants.

Living conditions continued to change. Where the climate became more severe, ancient gymnosperms gradually died out (Fig. 88). They were replaced by more advanced plants - pine, spruce, fir.

Plants that reproduced by seeds were better adapted to life on land than plants that reproduced by spores. This is due to the fact that the possibility of fertilization in them does not depend on the presence of water in the external environment. The superiority of seed plants over spore plants became especially clear when the climate became less humid.

Angiosperms appeared on Earth about 130 million years ago.

Angiosperms turned out to be the most adapted plants for life on land. Only angiosperms have flowers; their seeds develop inside the fruit and are protected by the pericarp. Angiosperms quickly spread throughout the Earth and occupied everything possible places a habitat. For more than 60 million years, angiosperms have dominated the Earth.

Adapted to different conditions existence, angiosperms created a diverse vegetation cover of the Earth from trees, shrubs and grasses.

New concepts

Paleontology. Paleobotany. Rhiniophytes

Questions

1. Based on what data can we say that the plant world developed and became more complex gradually?
2. Where did the first living organisms appear?
3. What was the significance of the advent of photosynthesis?
4. Under the influence of what conditions did ancient plants switch from an aquatic lifestyle to a terrestrial one?
5. Which ancient plants gave rise to ferns, and which to gymnosperms?
6. What is the advantage of seed plants over spore plants?
7. Compare gymnosperms and angiosperms. What structural features provided angiosperm plants with an advantage?

Quests for the curious

In summer, explore the steep banks of rivers, the slopes of deep ravines, quarries, pieces of coal, and limestone. Find fossilized ancient organisms or their imprints.

Sketch them. Try to determine what ancient organisms they belong to.

Do you know that...

The oldest imprint of plant flowers was found in Colorado (USA) in 1953. The plant looked like a palm tree. The imprint is 65 million years old.

Some forms of ancient angiosperms: poplars, oaks, willows, eucalyptus, palm trees - have survived to this day.

The Plant Kingdom is surprisingly diverse. It includes algae, mosses, mosses, horsetails, ferns, gymnosperms and angiosperms (flowering) plants.

Lower plants - algae - have a relatively simple structure. They can be unicellular or multicellular, but their body (thallus) is not divided into organs. There are green, brown and red algae. They produce huge amounts of oxygen, which not only dissolves in water, but is also released into the atmosphere.

Man uses seaweed in chemical industry. Iodine, potassium salts, cellulose, alcohol, acetic acid and other products are obtained from them. In many countries, seaweed is used to prepare a variety of dishes. They are very useful, as they contain a lot of carbohydrates, vitamins, and are rich in iodine.

Lichens consist of two organisms - a fungus and an algae, which are in complex interaction. Lichens play an important role in nature, being the first to settle in the most barren places. When they die, they form soil on which other plants can live.

Higher plants are called mosses, mosses, horsetails, ferns, gymnosperms and angiosperms. Their body is divided into organs, each of which performs specific functions.

Mosses, mosses, horsetails, and ferns reproduce by spores. They are classified as higher spore plants. Gymnosperms and angiosperms are higher seed plants.

Angiosperms have the highest organization. They are widespread in nature and are the dominant group of plants on our planet.

Almost all agricultural plants grown by humans are angiosperms. They provide people with food, raw materials for various industries, and are used in medicine.

The study of fossil remains proves the historical development of the plant world over many millions of years. The first to appear from plants were algae, which evolved from more simple organisms. They lived in the water of the seas and oceans. Ancient algae gave rise to the first land plants - rhiniophytes, from which came mosses, horsetails, mosses and ferns. Ferns reached their peak in Carboniferous period. With climate change, they were replaced first by gymnosperms and then by angiosperms. Angiosperms are the most numerous and highly organized group of plants. It has become dominant on Earth.