Who opened single-celled organisms, You will learn from this article.

Who discovered single-celled organisms?

Unicellular organisms are organisms that have only one cell in their body, which has a nucleus. They are both a cell and an independent organism. These include unique and invisible to the naked eye protozoa and bacteria. Single-celled organisms range in size from 0.2 to 10 microns.

The study of protozoa began later than other groups of animals. This is due to their small size, so only the invention of the microscope moved everything forward.

Dutchman Anthony Leeuwenhoek in 1675 he examined a drop of water under a microscope and was the first to discover a large number of microscopic organisms, which were the simplest single-celled organisms.

This discovery aroused great interest in them. Back then they were called “liquor small animals.” In the 17th-18th centuries, knowledge about them was chaotic and uncertain, which gave rise to Carl Linnaeus, another scientist, in his “System of Nature”, united all single-celled organisms into one genus of protozoa, which he called “Chaos infusorium”.

He made a huge contribution to the development of single-celled, microscopic organisms Muller. In his essay, he described 377 of their species. The scientist proposed species and generic names in the system of protozoa.

In the XVIII and early 19th centuries the study of single-celled organisms acquired the opposite diametrical character. For example, Ehrenberg described single-celled organisms as complexly organized creatures that have various systems organs. Another scientist, Dujardin, on the contrary, argued that they do not have internal organization and their body is built on sarcode - a structureless semi-liquid living substance.

In 1845, scientists Kölliker and Siebold distinguished unicellular animals from the general group of microscopic animals.

We hope that from this article you learned who discovered single-celled organisms.

Evolution of cellular organisms

The appearance of the first cellular organisms: more than 4 billion years ago

The first simple unicellular organisms (prokaryotes) appeared more than 4 billion years ago.Recently, in the oldest Archean sedimentary rocks on Earth, found in southwestern Greenland, traces of complex cellular structures, which are at least 3.86 billion years old.

According to another theory, there was no common ancestor as such, and the first protozoa that lived at that time, with the help of horizontal gene transfer among themselves, constantly evolved. It is assumed that at the earliest stages of evolution there was a kind of common gene “communal economy”. The picture of evolutionary connections in the world of ancestral prokaryotes was not so much a tree as a kind of mycelium with an intertwined network of horizontal transfers in the most diverse and unexpected directions. As organisms became more complex and mechanisms of sexual reproduction and reproductive isolation developed, horizontal transfer became more a rare occurrence(Fig. 2). At the same time, thanks to bacteriophage viruses, bacteria also develop a simple immune system.

At the same time, symbiogenesis occurred - mitochondria and plastids in the form of independent ones that existed at that time cellular organisms became part of a larger cell endosymbionts. Gradually they lost the ability to exist independently and turned into organoids . R Developing together, the endosymbiont gradually honed one skill - synthesis ATP . The inner cell decreased in size and transferred some of its minor genes to the nucleus. So the mitochondria retained only that part of the original DNA that they needed to work as a “living power plant.”

This led to the appearance in the Paleoproterozoic era (more than 2 billion years ago) of the first eukaryotes possessing a nucleus and being the ancestors of modern animals, plants, protists and chromists.

For the next almost 1.5 billion years, single-celled organisms reigned impeccably on our planet, until the first multicellular creatures appeared in the Edicarian period, about 630 million years ago. Initially, the simplest choanoflagellates, which are believed to stand on the border between unicellularity and multicellularity, formed embryonic colonies only with the help of a bacterial lipid, which is obtained from eaten bacteria, were combined into multicellular structures. The next step was the appearance in the same period of the first true multicellular macroorganisms - these organisms appeared on Earth immediately after the Marinoan glaciation - one of the stages of global glaciation, when our planet was completely covered with ice for many millions of years. Such unusual forms will never appear in nature again. These are mainly soft-bodied organisms consisting of individual fractals. Their body sizes varied from one centimeter to one meter. They looked so unusual that for a long time Scientists argued about which kingdom - plants or animals - they could be attributed to.

About 480-460 million years ago in the Silurian period, the first plants appeared on land (according to other sources, this happened in the Upper Cambrian 499-488 million years ago), and 50 million years later in the Devonian period, after the plants, the first animals (although there is some evidence showing that the first land animals lived in the Silurian (Fig. 3) or even Vendian periods). After this, the rapid development of all kinds of living beings began, the descendants of which we are.

Classification division:

Empire: Alive organisms

What is life? Definition of life

Questions about the origin of life, patterns historical development in various geological eras have always interested humanity. The concept of life covers the totality of all living organisms on Earth and the conditions of their existence. The essence of life is that living organisms leave behind offspring. Hereditary information is passed on from generation to generation, organisms self-regulate and recover during the reproduction of offspring. Life is a special high-quality, highest form of matter, capable of self-reproduction, leaving offspring.

The concept of life was given different definitions in different historical periods. The first scientifically correct definition was given by F. Engels: " Life is a way of existence of protein bodies, and this way of existence consists essentially in the constant self-renewal of chemical components these bodies"When the process of metabolism between living organisms and environment proteins disintegrate and life disappears. Relying on modern achievements biological science, the Russian scientist M.V. Volkenshtein gave a new definition to the concept of life: " Living bodies existing on Earth are open, self-regulating and self-reproducing systems built from biopolymers - proteins and nucleic acids"This definition does not deny the presence of life on other planets outer space. Life is called open system, as indicated by the continuous process of exchange of substances and energy with the environment. Based on the latest scientific achievements of modern biological science, the following definition of life is given: " Life is an open self-regulating and self-reproducing system of aggregates of living organisms, built from complex biological polymers - proteins and nucleic acids ". The basis of all living things are considered to be nucleic acids and proteins, since they function in the cell, form complex connections, which are part of the structure of all living organisms.

Living organisms are different from inanimate nature their inherent properties. TO characteristic properties living organisms include: unity chemical composition, metabolism and energy, similarity of levels of organization. Living organisms are also characterized by reproduction, heredity, variability, growth and development, irritability, discreteness, self-regulation, rhythm, etc.

The appearance of living beings on Earth and their evolution

Rice. 1. Colony of cyanobacteria in the fumarole of the Dzendzur volcano. Kamchatka. (Photo ) More than 4 billion years ago, the first life appeared on Earth. During this time, life has gone through a long development path, starting from the simplest molecular living solutions that appeared long before the simplest organisms - caocervate drops and ending with modern mammals. In parallel with the evolution of living beings, there was an evolution of their constituent molecules, so the first proteins that entered living beings had a lower rate of folding.

The first living organisms that appeared on our planet had neither DNA nor even RNA and lived in the form of living solutions located in tiny cavities that are often found in minerals. The role of RNA in the first self-reproducing living inhabitants simultaneously being both a carrier of hereditary information and a means of its further reproduction performed by a peptide nucleic acid, the backbone of which was a chain formed by N-(2-aminoethyl) glycine (AEG) monomers. Subsequently, it became more complex, which led to the formation of RNA. After some time this pre-life had to acquire its own shells - to move from the pre-organism level to the organism. This “living solution” used caocervates consisting of liptides as shells.

Recently, traces of complex cellular structures dating back at least 3.86 billion years were discovered in the oldest Archean sedimentary rocks on Earth, found in southwestern Greenland.

According to one theory, about 4.1 - 3.6 billion years ago during the Eoarchean period, from the diversity of single-celled living beings (prokaryotes) that existed at that time (Fig. 1), our first common ancestor, who lived then, divided into several branches, which subsequently in turn, divided into the currently existing kingdoms (animals, plants, fungi, protists, chromists, bacteria, archaea and viruses). Over time, the rest of the inhabitants of that period could not stand the competition with them and disappeared from the face of the Earth.

Around this time, the first viruses appear (Fig. 3).

Rice. 3. Bacteriophages The next stage of evolution was the appearance in the Paleoproterozoic era (more than 2 billion years ago) of the first eukaryotes possessing a nucleus and being the ancestors of modern animals, plants, protists and chromists.

For the next almost 1.5 billion years, single-celled organisms reigned impeccably on our planet, until the first multicellular creatures appeared in the Edicarian period, about 630 million years ago. Such unusual forms will never appear in nature again. These are mainly soft-bodied organisms consisting of individual fractals. Their body sizes varied from one centimeter to one meter. They looked so unusual that for a long time scientists argued about which kingdom - plants or animals - they could be attributed to.

Rice. 4. Silurian shallow waters About 480-460 million years ago in the Silurian period, the first plants appeared on land (according to some data in the Upper Cambrian 499-488 million years ago), and 50 million years later in the Devonian period, after the plants, the first animals came to land (although there is some evidence showing that the first land animals lived in the Silurian (Fig. 4) or even Vendian periods). After this, the rapid development of all kinds of living creatures began, the descendants of which we are.

Diversity of species of living things

Now, according to the most accurate estimates, there are about 1.6 million living species. Of these, 860,000 are insects, 350,000 are plants, 8,600 are birds and only 3,200 are mammals. Most of the remaining species, about 300,000, belong to marine invertebrates. The total number - 1.5 million - includes only those species whose descriptions have been published by scientists. It is believed that several times more species have not yet been described. Some scientists estimate that there are currently about 8.7 million species of eukaryotic organisms (plus or minus 1.3 million). This number does not include extinct species known only from fossils. Based on the number of fossil species already described, total extinct - those who ever lived during more than three billion years of life on Earth, are estimated to range from 50 million to 4 billion.

According to scientists, there are 2.2 million species in the oceans, 6.5 million on land. There are only about 7.77 million species of animals on the planet, 611 thousand mushrooms, 300 thousand plants. Plants are the luckiest of all. : Of these, 72% of species are described, while animals - 12%, mushrooms - only 7%.

Habitat	Earth			Ocean
	Cataloged	Supposed	±	Cataloged	Supposed	±
Eukaryotes
Animals	953 434	7 770 000	958 000	171 082	2 150 000	145 000
Mushrooms	43 271	611 000	297 000	1 097	5 320	11 100
Plants	215 644	298 000	8 200	8 600	16 600	9 130
Protista	8 118	36 400	6 690	8 118	36 400	6 960
Total	1 233 500	8 740 000	1 300 000	193 756	2 210 000	182 000
Prokaryotes
Bacteria	10 358	9 680	3 470	652	1 320	436
Archaea	502	455	160	1	1	0
Total	10 860	10 100	3 630	653	1 321	436
Total	1 244 360	8 750 000	1 300 000	194 409	2 210 000	182 000

Table 1. Number of species living on our planet

Unicellular organisms

Unicellular organisms- non-systematic category of living organisms, the body of which consists of one (unlike multicellular) cells ( unicellularity). It can include both prokaryotes and eukaryotes. The term "unicellular" is also sometimes used as a synonym for protists. Protozoa, Protista).

Main groups

Main article: Groups

The main groups of unicellular organisms:

Ciliates (12 microns - 3 mm)...
Amoebas (up to 0.3 mm)
Ciliary
Euglena

Prokaryotes

Prokaryotes are predominantly unicellular, with the exception of some cyanobacteria and actinomycetes. Among eukaryotes unicellular structure have protozoa, a number of fungi, and some algae. Unicellular organisms can form colonies.

Emergence and evolution

It is believed that the first living organisms on Earth were single-celled. The most ancient of them are considered to be bacteria and archaea. Unicellular animals and prokaryotes were discovered by A. Leeuwenhoek.

Eukaryotes

Eukaryotes, or Nuclear (Latin Eucaryota from the Greek εύ- - good and κάρυον - core) - a domain (superkingdom) of living organisms, whose cells contain nuclei. All organisms except bacteria and archaea are nuclear (viruses and viroids are also not eukaryotes, but not all biologists consider them living organisms).

Animals, plants, fungi, as well as groups of organisms under common name Protists are all eukaryotic organisms. They can be unicellular or multicellular, but they all have a common cell structure. It is believed that all these so dissimilar organisms have common origin, therefore the nuclear group is considered to be the highest-ranking monophyletic taxon. According to the most common hypotheses, eukaryotes appeared 1.5-2 billion years ago. Important role In the evolution of eukaryotes, symbiogenesis played a role - a symbiosis between a eukaryotic cell, apparently already having a nucleus and capable of phagocytosis, and bacteria swallowed by this cell - the precursors of mitochondria and chloroplasts.

What were the first single-celled organisms called? Unicellular organisms