To answer this question, it is necessary to establish when and where the first eukryotic cell came from, to determine the most primitive group of protozoa, to determine the most highly organized group of protozoa.

A eukaryotic cell could only come from a prokaryotic cell. the first eukryotic cell arose 1.5 billion years ago (the middle of the Archean era). There are a number of hypotheses that explain how from a prokaryotic cell with min. With a set of structures for life, a large, complex eukaryotic cell with a large number of structural organelles arises.

1 hypothesis– evolutionary, according to which a simple prokaryotic cell grew, became more complex and, through long evolution, acquired those components that are inherent in a eukaryotic cell.

2 hypothesis- symbiotic or symbiogenesis hypothesis, according to this hypothesis, several prokaryotic cells united. For example, a certain photosynthetic prokaryotic organism invaded a larger prokaryotic cell and after some time turned into a chloroplast. Another prokaryotic organism, heterotrophic, aerobic, has turned into mitochondria. Proof of this is the fact that chloroplasts and mitochondria have their own DNA, RNA molecules, ribosomes and are capable of division.

there are other theories that combine elements of hypothesis 1 and 2

Directions of evolution of protozoa.

1 . Increase in body size. It pays to be big. Large body sizes increase the independence of organisms from environmental factors, the security of a large animal is higher and the absolute speed is greater.

2. Increased movement speed. Greater opportunity to catch up with prey and less chance of being eaten

3. Complication of behavior.

The most highly organized and advanced group are ciliates.

During evolution, protozoa face a number of problems. As the size of the protozoa increases, the flagellum cannot cope with the function of moving a large cell. Accordingly, it is necessary to increase their number. (replace the flagellum with cilia). With an increase in size, complication of behavior and internal structure, a larger amount of hereditary material is required, i.e. more cores. This process of increasing the number of structures of the same name is called polymerization. Following polymerization, differentiation and specialization of organelles by function is possible. This division of labor is more efficient, so there is no great need large quantity organelles And after differentiation, polygomerization occurs (a decrease in their number). The next problem is with which protozoa encounter is an increase in cell size. It is impossible to increase the size of the cell indefinitely. A diffusion barrier stands in the way of such an increase. The diffusion barrier lies in the fact that as the size of the cell increases, V increases in proportion to the cube of R, and S is proportional to the square of R, and at some point the cell will cease to function as an open system, i.e. stops exchanging matter, energy and information with the environment. One way to solve this problem is to change the shape of the body. For example, in the ciliate trumpeter or infusoria suvoiki (attached forms). However, with such complex shapes body, movement is impossible or difficult. In addition, this is only a special case of solving the problem, which does not remove the diffusion barrier. Another more promising way to overcome the diffusion barrier is the transition to coloniality, the most important direction in the evolution of protozoa. Colonies are formed during multiple mitotic divisions without subsequent cell divergence, i.e. a colony is a descendant of the 1st cell. As the size of the colony increases, problems with reception, nutrition, and movement arise again. Accordingly, there is a need to divide functions between individual cells. Differentiation occurs. However, in colonies differentiation is always temporary, i.e. the cell can change its function. Thus, the evolution of colonies followed the path of increasing cell size and differentiation.

Unicellular organisms are organisms whose body consists of only one cell with a nucleus. They combine the properties of a cell and an independent organism.

Single-celled plants are the most common algae. Single-celled algae live in fresh water bodies, seas, and soil.

The spherical unicellular chlorella is widespread in nature. It is protected by a dense shell, under which there is a membrane. The cytoplasm contains a nucleus and one chloroplast, which in algae is called a chromatophore. It contains chlorophyll. Organic substances are formed in the chromatophore under the influence of solar energy, as in the chloroplasts of land plants.

The globular algae Chlorococcus (“green ball”) is similar to chlorella. Some types of chlorococcus also live on land. They give the trunks of old trees growing in humid conditions a greenish color.

Among unicellular algae there are also mobile forms, for example. The organ of its movement is flagella - thin outgrowths of the cytoplasm.

Unicellular fungi

Packets of yeast sold in stores are compressed single-cell yeast. A yeast cell has the typical structure of a fungal cell.

The single-celled late blight fungus infects living leaves and tubers of potatoes, leaves and fruits of tomatoes.

Unicellular animals

Like single-celled plants and fungi, there are animals in which the functions of the whole organism are performed by one cell. Scientists have united everyone into a large group - protozoa.

Despite the diversity of organisms in this group, their structure is based on one animal cell. Since it does not contain chloroplasts, protozoa are not able to produce organic substances, but consume them in finished form. They feed on bacteria. single-celled, pieces of decaying organisms. Among them there are many causative agents of serious diseases in humans and animals (dysentery, Giardia, malarial Plasmodium).

Protozoa that are widespread in fresh water bodies include the amoeba and the slipper ciliate. Their body consists of cytoplasm and one (amoeba) or two (slipper ciliates) nuclei. Digestive vacuoles are formed in the cytoplasm, where food is digested. Excess water and metabolic products are removed through contractile vacuoles. The outside of the body is covered with a permeable membrane. Oxygen and water enter through it, and various substances are released. Most protozoa have special organs of movement - flagella or cilia. The slipper ciliates cover their entire body with cilia; there are 10-15 thousand of them.

The movement of the amoeba occurs with the help of pseudopods - protrusions of the body. The presence of special organelles (organs of movement, contractile and digestive vacuoles) allows protozoan cells to perform the functions of a living organism.

Life on Earth appeared billions of years ago, and since then living organisms have become increasingly more complex and diverse. There is ample evidence that all life on our planet has a common origin. Although the mechanism of evolution is not yet fully understood by scientists, its very fact is beyond doubt. This post is about the path the development of life on Earth took from the simplest forms to humans, as our distant ancestors were many millions of years ago. So, from whom did man come?

The Earth arose 4.6 billion years ago from a cloud of gas and dust surrounding the Sun. In the initial period of the existence of our planet, the conditions on it were not very comfortable - in the environment outer space There was still a lot of debris flying around, constantly bombarding the Earth. It is believed that 4.5 billion years ago the Earth collided with another planet, resulting in the formation of the Moon. Initially, the Moon was very close to the Earth, but gradually moved away. Due to frequent collisions at this time, the Earth's surface was in a molten state, had a very dense atmosphere, and surface temperatures exceeded 200°C. After some time, the surface hardened, the earth's crust formed, and the first continents and oceans appeared. The oldest rocks studied are 4 billion years old.

1) The most ancient ancestor. Archaea.

Life on Earth appeared, according to modern ideas, 3.8-4.1 billion years ago (the earliest found traces of bacteria are 3.5 billion years old). How exactly life arose on Earth has not yet been reliably established. But probably already 3.5 billion years ago, there was a single-celled organism that had all the features inherent in all modern living organisms and was a common ancestor for all of them. From this organism, all its descendants inherited structural features (they all consist of cells surrounded by a membrane), a method of storing the genetic code (in DNA molecules twisted in a double helix), a method of storing energy (in ATP molecules), etc. From this common ancestor There were three main groups of single-celled organisms that still exist today. First, bacteria and archaea divided among themselves, and then eukaryotes evolved from archaea - organisms whose cells have a nucleus.

Archaea have hardly changed over billions of years of evolution; the most ancient ancestors of humans probably looked about the same

Although archaea gave rise to evolution, many of them have survived to this day almost unchanged. And this is not surprising - since ancient times, archaea have retained the ability to survive in the most extreme conditions - in the absence of oxygen and sunlight, in aggressive - acidic, salty and alkaline environments, in high (some species feel great even in boiling water) and low temperatures, at high pressures, they are also capable of feeding on a wide variety of organic and non-organic organic substances. Their distant, highly organized descendants cannot boast of this at all.

2) Eukaryotes. Flagellates.

For a long time, extreme conditions on the planet prevented the development of complex life forms, and bacteria and archaea reigned supreme. About 3 billion years ago, cyanobacteria appeared on Earth. They begin to use the process of photosynthesis to absorb carbon from the atmosphere, releasing oxygen in the process. The released oxygen is first consumed by the oxidation of rocks and iron in the ocean, and then begins to accumulate in the atmosphere. 2.4 billion years ago, an “oxygen catastrophe” occurs - a sharp increase in the oxygen content in the Earth’s atmosphere. This leads to big changes. For many organisms, oxygen turns out to be harmful, and they die out, being replaced by those that, on the contrary, use oxygen for respiration. The composition of the atmosphere and climate are changing, becoming much colder due to a drop in greenhouse gases, but an ozone layer appears, protecting the Earth from harmful ultraviolet radiation.

About 1.7 billion years ago, eukaryotes evolved from archaea - single-celled organisms whose cells had a more complex structure. Their cells, in particular, contained a nucleus. However, the emerging eukaryotes had more than one predecessor. For example, mitochondria, essential components of the cells of all complex living organisms, evolved from free-living bacteria captured by ancient eukaryotes.

There are many varieties of single-celled eukaryotes. It is believed that all animals, and therefore humans, descended from single-celled organisms that learned to move using a flagellum located at the back of the cell. The flagella also help filter water in search of food.

Choanoflagellates under a microscope, as scientists believe, it was from such creatures that all animals once descended

Some species of flagellates live united in colonies; it is believed that the first multicellular animals once arose from such colonies of protozoan flagellates.

3) Development of multicellular organisms. Bilateria.

Approximately 1.2 billion years ago, the first multicellular organisms appeared. But evolution is still progressing slowly, and in addition, the development of life is being hampered. Thus, 850 million years ago, global glaciation began. The planet is covered with ice and snow for more than 200 million years.

The exact details of the evolution of multicellular organisms are unfortunately unknown. But it is known that after some time the first multicellular animals divided into groups. Sponges and lamellar sponges that have survived to this day without any special changes do not have separate organs and tissues and filter nutrients from the water. The coelenterates are not much more complex, having only one cavity and a primitive nervous system. All other more developed animals, from worms to mammals, belong to the group of bilateria, and their distinguishing feature is the bilateral symmetry of the body. It is not known for certain when the first bilateria appeared; it probably happened shortly after the end of global glaciation. The formation of bilateral symmetry and the appearance of the first groups of bilateral animals probably occurred between 620 and 545 million years ago. Findings of fossil prints of the first bilateria date back to 558 million years ago.

Kimberella (imprint, appearance) - one of the first discovered species of bilateria

Soon after their emergence, bilateria are divided into protostomes and deuterostomes. Almost all invertebrate animals come from protostomes - worms, mollusks, arthropods, etc. The evolution of deuterostomes leads to the appearance of echinoderms (such as sea ​​urchins and stars), hemichordates and chordates (which includes humans).

Recently, the remains of creatures called Saccorhytus coronarius. They lived approximately 540 million years ago. By all indications, this small (only about 1 mm in size) creature was the ancestor of all deuterostome animals, and therefore of humans.

Saccorhytus coronarius

4) The appearance of chordates. The first fish.

540 million years ago the “Cambrian explosion” occurs - in a very short period of time a huge number of the most different types sea ​​animals. The fauna of this period has been well studied thanks to the Burgess Shale in Canada, where the remains of a huge number of organisms from this period have been preserved.

Some of the Cambrian animals whose remains were found in the Burgess Shale

Many amazing animals, unfortunately long extinct, were found in the shale. But one of the most interesting finds was the discovery of the remains of a small animal called pikaia. This animal is the earliest found representative of the chordate phylum.

Pikaya (remains, drawing)

Pikaia had gills, a simple intestine and circulatory system, as well as small tentacles near the mouth. This small animal, about 4 cm in size, resembles modern lancelets.

It didn't take long for the fish to appear. The first animal found that can be classified as a fish is considered to be the Haikouichthys. He was even smaller than Pikaiya (only 2.5 cm), but he already had eyes and a brain.

This is what Haykowihthys looked like

Pikaia and Haikouihthys appeared between 540 and 530 million years ago.

Following them, many larger fish soon appeared in the seas.

First fossil fish

5) Evolution of fish. Armored and early bony fishes.

The evolution of fish lasted quite a long time, and at first they were not at all the dominant group of living creatures in the seas, as they are today. On the contrary, they had to escape from such large predators as crustaceans. Fish appeared in which the head and part of the body were protected by a shell (it is believed that the skull subsequently developed from such a shell).

The first fish were jawless; they probably fed on small organisms and organic debris, sucking in and filtering water. Only about 430 million years ago the first fish with jaws appeared - placoderms, or armored fish. Their head and part of their torso were covered with a bone shell covered with skin.

Ancient shell fish

Some of the armored fish acquired large sizes and began to lead predatory image life, but a further step in evolution was made thanks to the appearance of bony fish. Presumably originated from armored fish common ancestor cartilaginous and bony fish inhabiting modern seas, and the armored fish themselves, the acanthodes that appeared at about the same time, as well as almost all jawless fish subsequently became extinct.

Entelognathus primordialis - a probable intermediate form between armored and bony fishes, lived 419 million years ago

The very first discovered bony fish, and therefore the ancestor of all land vertebrates, including humans, is considered to be Guiyu Oneiros, who lived 415 million years ago. Compared to predatory armored fish, which reached a length of 10 m, this fish was small - only 33 cm.

Guiyu Oneiros

6) The fish come to land.

While fish continued to evolve in the sea, plants and animals of other classes had already reached land (traces of the presence of lichens and arthropods on it were discovered as early as 480 million years ago). But in the end, fish also began to develop land. From the first bony fishes two classes arose - ray-finned and lobe-finned. The majority of modern fish are ray-finned, and they are perfectly adapted for life in water. Lobe-finned fish, on the contrary, have adapted to life in shallow waters and small freshwater bodies, as a result of which their fins have lengthened and their swim bladder has gradually turned into primitive lungs. As a result, these fish learned to breathe air and crawl on land.

Eusthenopteron ( ) is one of the fossil lobe-finned fishes, which is considered the ancestor of land vertebrates. These fish lived 385 million years ago and reached a length of 1.8 m.

Eusthenopteron (reconstruction)

- another lobe-finned fish, which is considered a likely intermediate form of the evolution of fish into amphibians. She could already breathe with her lungs and crawl onto land.

Panderichthys (reconstruction)

Tiktaalik, whose remains were found dating back to 375 million years ago, was even closer to amphibians. He had ribs and lungs, he could turn his head separately from his body.

Tiktaalik (reconstruction)

One of the first animals that were no longer classified as fish, but as amphibians, were ichthyostegas. They lived about 365 million years ago. These small animals, about a meter long, although they already had paws instead of fins, still could hardly move on land and led a semi-aquatic lifestyle.

Ichthyostega (reconstruction)

At the time of the emergence of vertebrates on land there was another mass extinction- Devonian. It began approximately 374 million years ago, and led to the extinction of almost all jawless fish, armored fish, many corals and other groups of living organisms. Nevertheless, the first amphibians survived, although it took them more than one million years to more or less adapt to life on land.

7) The first reptiles. Synapsids.

The Carboniferous period, which began approximately 360 million years ago and lasted 60 million years, was very favorable for amphibians. A significant part of the land was covered with swamps, the climate was warm and humid. Under such conditions, many amphibians continued to live in or near water. But approximately 340-330 million years ago, some of the amphibians decided to explore drier places. They developed stronger limbs, more developed lungs, and their skin, on the contrary, became dry so as not to lose moisture. But to really long time living far from water, another important change was necessary, because amphibians, like fish, spawned, and their offspring had to develop in an aquatic environment. And about 330 million years ago, the first amniotes appeared, that is, animals capable of laying eggs. The shell of the first eggs was still soft and not hard, however, they could already be laid on land, which means that the offspring could already appear outside the reservoir, bypassing the tadpole stage.

Scientists are still confused about the classification of amphibians from the Carboniferous period, and whether some fossil species should be considered early reptiles or still amphibians that acquired only some reptilian features. One way or another, these either the first reptiles or reptilian amphibians looked something like this:

Westlotiana is a small animal about 20 cm long, combining the features of reptiles and amphibians. Lived approximately 338 million years ago.

And then the early reptiles split, giving rise to three large groups of animals. Paleontologists distinguish these groups by the structure of the skull - by the number of holes through which muscles can pass. In the picture from top to bottom there are skulls anapsid, synapsid And diapsid:

At the same time, anapsids and diapsids are often combined into a group sauropsids. It would seem that the difference is completely insignificant, however, the further evolution of these groups took completely different paths.

Sauropsids gave rise to more advanced reptiles, including dinosaurs, and then birds. Synapsids gave rise to a branch of animal-like lizards, and then to mammals.

300 million years ago the Permian period began. The climate became drier and colder, and early synapsids began to dominate on land - pelycosaurs. One of the pelycosaurs was Dimetrodon, which was up to 4 meters long. He had a large “sail” on his back, which helped regulate body temperature: to quickly cool down when overheated or, conversely, to quickly warm up by exposing his back to the sun.

The huge Dimetrodon is believed to be the ancestor of all mammals, and therefore of humans.

8) Cynodonts. The first mammals.

In the middle of the Permian period, therapsids evolved from pelycosaurs, more similar to animals than to lizards. Therapsids looked something like this:

A typical therapsid of the Permian period

During the Permian period, many species of therapsids, large and small, arose. But 250 million years ago a powerful cataclysm occurs. Due to a sharp increase in volcanic activity, the temperature rises, the climate becomes very dry and hot, large areas of land are filled with lava, and the atmosphere is filled with harmful volcanic gases. The Great Permian Extinction occurs, the largest mass extinction of species in the history of the Earth, up to 95% of marine and about 70% of land species become extinct. Of all the therapsids, only one group survives - cynodonts.

Cynodonts were predominantly small animals, from a few centimeters to 1-2 meters. Among them were both predators and herbivores.

Cynognathus is a species of predatory cynodont that lived about 240 million years ago. It was about 1.2 meters long, one of the possible ancestors of mammals.

However, after the climate improved, the cynodonts were not destined to take over the planet. Diapsids seized the initiative - dinosaurs evolved from small reptiles, which soon took over the majority ecological niches. The cynodonts could not compete with them, they crushed them, they had to hide in holes and wait. It took a long time to get revenge.

However, the cynodonts survived as best they could and continued to evolve, becoming more and more similar to mammals:

Evolution of cynodonts

Finally, the first mammals evolved from cynodonts. They were small and presumably nocturnal. A dangerous existence among a large number of predators contributed to the strong development of all senses.

Megazostrodon is considered one of the first true mammals.

Megazostrodon lived approximately 200 million years ago. Its length was only about 10 cm. Megazostrodon fed on insects, worms and other small animals. Probably he or another similar animal was the ancestor of all modern mammals.

We will consider further evolution - from the first mammals to humans - in.

Animals consisting of a single cell with a nucleus are called unicellular organisms.

They combine characteristics cells and independent organism.

Unicellular animals

Animals of the subkingdom Unicellular or Protozoa live in liquid environments. Their external forms are varied - from amorphous individuals that do not have a definite outline, to representatives with complex geometric shapes.

There are about 40 thousand species of single-celled animals. The most famous include:

• amoeba;
• green euglena;
• ciliate-slipper.

Amoeba

It belongs to the rhizome class and is distinguished by its variable shape.

It consists of a membrane, cytoplasm, contractile vacuole and nucleus.

Assimilation nutrients carried out with the help of a digestive vacuole, and other protozoa, such as algae and etc., serve as food. For respiration, amoeba requires oxygen dissolved in water and penetrating through the surface of the body.

Green euglena

It has an elongated fan-shaped shape. It feeds by converting carbon dioxide and water into oxygen and food products thanks to light energy, as well as ready-made organic substances in the absence of light.

Belongs to the class Flagellates.

Ciliate slipper

A class of ciliates, its outline resembles a shoe.

Bacteria serve as food.

Unicellular fungi

Fungi are classified as lower non-chlorophyll eukaryotes. They differ in external digestion and chitin content in the cell wall. The body forms a mycelium consisting of hyphae.

Unicellular fungi are systematized into 4 main classes:

• deuteromycetes;
• chytridiomycetes;
• zygomycetes;
• ascomycetes.

A striking example of ascomycetes is yeast, which is widespread in nature. The speed of their growth and reproduction is high due to their special structure. Yeast consists of a single round cell that reproduces by budding.

Unicellular plants

A typical representative of lower unicellular plants often found in nature are algae:

• chlamydomonas;
• chlorella;
• spirogyra;
• chlorococcus;
• Volvox.

Chlamydomonas differs from all algae in its mobility and the presence of a light-sensitive eye, which determines the places of greatest accumulation of solar energy for photosynthesis.

Numerous chloroplasts are replaced by one large chromatophore. The role of pumps that pump out excess fluid is performed by contractile vacuoles. Movement is carried out using two flagella.

Green algae, Chlorella, unlike Chlamydomonas, have typical plant cells. A dense shell protects the membrane, and the cytoplasm contains the nucleus and chromatophore. The functions of the chromatophore are similar to the role of chloroplasts in land plants.

The spherical algae Chlorococcus is similar to Chlorella. Its habitat is not only water, but also land, tree trunks growing in a humid environment.

Who discovered single-celled organisms

The honor of discovering microorganisms belongs to the Dutch scientist A. Leeuwenhoek.

In 1675, he examined them through a microscope of his own making. The name ciliates was assigned to the smallest creatures, and since 1820 they began to be called the simplest animals.

Zoologists Kelleker and Siebold in 1845 classified unicellular organisms as a special type of the animal kingdom and divided them into two groups:

• rhizomes;
• ciliates.

What does a single cell animal cell look like?

The structure of single-celled organisms can only be studied using a microscope. The body of the simplest creatures consists of a single cell that acts as an independent organism.

The cell contains:

• cytoplasm;
• organoids;
• core.

Over time, as a result of adaptation to the environment, certain species of unicellular organisms developed special organelles for movement, excretion and nutrition.

Who are the protozoa?

Modern biology classifies protozoa as a paraphyletic group of animal-like protists. The presence of a nucleus in a cell, unlike bacteria, includes them in the list of eukaryotes.

Cellular structures differ from those of multicellular organisms. In the living system of protozoa, digestive and contractile vacuoles are present; some have organelles similar to the oral cavity and anus.

Protozoan classes

In the modern classification based on characteristics, there is no separate rank and significance of unicellular organisms.

Labyrinthula

They are usually divided into the following types:

• sarcomastigophores;
• apicomplexans;
• myxosporidium;
• ciliates;
• labyrinthula;
• Ascestosporadia.

An outdated classification is considered to be the division of protozoans into flagellates, sarcodes, ciliates and sporozoans.

In what environments do unicellular organisms live?

The habitat of the simplest unicellular organisms is any humid environment. Common amoeba, green euglena and slipper ciliates are typical inhabitants of polluted fresh water sources.

Science has long classified opalines as ciliates, due to the external similarity of flagella to cilia and the presence of two nuclei. As a result of careful research, the relationship was refuted. Sexual reproduction opaline occurs as a result of copulation, the nuclei are identical, and the ciliary apparatus is absent.

Conclusion

It is impossible to imagine a biological system without single-celled organisms, which are the source of nutrition for other animals.

The simplest organisms contribute to the formation of rocks, serve as indicators of pollution of water bodies, and participate in the carbon cycle. Microorganisms have found widespread use in biotechnology.

Lesson objectives:

1. familiarize students with the structural features of the eye and establish the relationship between its structure and its functions;
2. show the diversity of the organs of vision and the features of their structure;
3. show the fundamental unity of the natural sciences;
4. promote the development of skills in working with a textbook, additional literature, and a computer;
5. become familiar with the processes that ensure the perception of visual images, the most common visual defects – myopia and farsightedness;
6. protection of abstracts in electronic form.

Equipment: camera and its model, eye model, “Visual Analyzer” tables, computer, multimedia projector.

IN modern world you receive information in new ways: through a computer, the Internet. This information is absorbed better and is a complement to traditional methods. It is no coincidence that they say: “It is better to see once than to hear a hundred times.”

BIOLOGY TEACHER: We present to your attention the presentation “Visual analyzer of invertebrates” made by the first group.

We saw that the visual analyzer becomes more complex not only in unicellular organisms, but also in vertebrates. Even with the same structure of the eye, there are many differences associated with the ecological characteristics of the species.

BIOLOGY TEACHER: Thanks to the organ of vision, we see the whole palette of colors, admire nature, and all this because special light-sensitive cells of the eye, cones, provide color vision. The whole variety is made up of three colors: red, green and purple. Each of these colors absorbs different wavelengths and mixing them gives all the other colors. Presentation No. 3: “Color perception”.

PHYSICS TEACHER: In the modern world there are much more people with visual defects and these defects are acquired much faster than even 10 years ago. The reason for this is the computer, TV, game consoles, etc. So, you understand that the next presentation is “Vision defects” and how to prevent them.

PHYSICS TEACHER: Dalton said: “If you see a “lion” on a cage with a tiger, don’t believe your eyes!” Since “The mind knows how to look at the world not with the eye, but through the eye...” About optical illusions last message. Presentation No. 5: “Illusions”.

BIOLOGY TEACHER: It’s amazing, but people often do not appreciate what is given to them by nature. The messages made by your classmates once again prove that the eye is a very complex optical system, and it is not always perfect. It is violated by a mass of congenital, acquired and age-related changes that require timely correction and treatment. Vision is our wealth, which must be treated with care from early childhood.

References:

• Encyclopedia "Science", ROSMEN, 2000
• Biology, 9th grade, Batuev A.S., DROFA, 1996
• Visual analyzer: from single-celled organisms to humans, G.N. Tikhonova, N.Yu. Feoktistova, Library “First of September”, 2006
• Encyclopedia “Everything about everything” for children
• A book for reading on human anatomy, physiology and hygiene, I.D. Zverev, ENLIGHTENMENT, 1983
• Encyclopedia for children. Biology, vol. 2, AVANTA +, 1994
• Encyclopedia for children. Physics. AVANTA +, 1994
• Biology. Lesson plans based on the textbook by N.I. Sonina and M.R. Sapina, 8th grade, TEACHER, 2007