Since ancient times, observing animals, people have noticed similarities and differences in their structure, behavior, and living conditions. Based on their observations, they divided animals into groups, which helped them understand the system of the living world. Today, man's desire to systematically understand the animal world has become the science of classifying living organisms - taxonomy.
Principles of taxonomy
The foundations of modern taxonomy were laid by the scientists Lamarck and Linnaeus.
Lamarck proposed the principle of relatedness as a basis for assigning animals to one group or another. Linnaeus introduced binary nomenclature, that is, a double name for the species.
Each type in the name has two parts:
- genus name;
- species name.
For example, pine marten. Marten is the name of a genus, which may include many species (stone marten, etc.).
Lesnaya is the name of a specific species.
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Linnaeus also proposed the main taxa, or groups, that we still use today.
View
The species is the initial element of classification.
Organisms are classified as one species according to a number of criteria:
- similar structure and behavior;
- identical set of genes;
- similar ecological living conditions;
- free interbreeding.
The species can be very similar in appearance. Previously, it was believed that the malaria mosquito was one species, but now it has been found that there are 6 species that differ in the structure of their eggs.
Genus
We usually name animals by gender: wolf, hare, swan, crocodile.
Each of these genera may contain many species. There are also genera containing only one species.
Rice. 1. Types of bears.
Differences between species of a genus can be obvious, as between a brown and a polar bear, and completely invisible, as between twin species.
Family
Genera are united into families. The family name may be derived from the generic name, e.g. mustelids or bearish.
Rice. 2. The cat family.
Also, the name of the family can indicate the structural features or lifestyle of animals:
- lamellar;
- bark beetles;
- cocoon worms;
- dung flies.
Related families are collected into groups.
Units
Rice. 3. Order Chiroptera.
For example, the order Carnivora includes animals that are different in structure and lifestyle, such as:
- weasel;
- polar bear;
- fox.
If there is a good harvest of berries and mushrooms, a brown bear from the order of carnivores may not hunt for a long time, while a hedgehog from the order of insectivores hunts almost every night.
Class
Classes are numerous groups of animals. For example, the class of Gastropods has about 93 thousand species, and the class of open-jawed insects has more than a million.
Moreover, new species of insects are discovered every year. According to some biologists, there may be from 2 to 3 million species in this class.
Phylums are the largest taxa. The most important of them:
- chordates;
- arthropods;
- shellfish;
- annelids;
- flatworms;
- roundworms;
- sponges;
- coelenterates.
The most voluminous taxa are kingdoms.
All animals are united in the animal kingdom.
We present the main systematic groups in the table “Classification of Animals”.
Discrepancies
Scientists have different views on the classification of the animal world. Therefore, textbooks often classify a certain group of animals as different taxa.
For example, single-celled animals are sometimes classified as the Kingdom of Protists, and are sometimes considered animals of the protozoan type.
Additional classification elements are often introduced with the prefixes over-, under-, infra-:
- subtype;
- superfamily;
- infraclass and others.
For example, crustaceans were previously considered a class in the phylum Arthropods. In the new books they are considered a subtype.
What have we learned?
The science of taxonomy deals with the classification of species of animals and other organisms. Having studied this topic in 7th grade biology, we learned the main and additional taxa into which lower-order taxa are grouped. Animals are classified according to certain characteristics. The higher the order of the taxon, the more general the characters will be.
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1. The basic and smallest unit of classification is view.
2. The largest unit of classification is kingdom.
3. Each type must be classified, that is, assigned to each of the specified categories.
4. Classify biological object means determining the degree of its similarity and difference from others by comparing it with them.
5. The more fully the various characteristics of organisms are taken into account, the greater the degree of similarity that appears will reflect the relatedness of the organisms.
6. Based on individual signs of similarity, the construction is based artificial systems. Artificial (formal ) systems - These are systems of organisms in which the classification of species is based only on the degree of their similarity and does not take into account the historical relationships of different taxa. Artificial systems are created due to a lack of data on the historical development, structure, and ecological characteristics of certain groups of organisms. For example, for a long time the Type Worms was distinguished, which included flat, round and annelid worms and some worm-like animals.
7. Natural systems take into account the degree of historical relationship of various taxa. Natural (phylogenetic) systems- these are systems of organisms in which the classification of species is based on their degree of similarity and reflects the phylogenetic relationship between systematic groups of organisms.
8. Used to classify living organisms double (binary ) nomenclature, which was introduced by C. Linnaeus. Binary nomenclature - double name of species, the first word of which indicates the genus, and the second - to the view. For example: domestic dog (Canis familiaris). The use of Latin facilitates mutual understanding between scientists from different countries and prevents misunderstandings that may arise if in the scientific works of each country animals and plants are named only in the language of their people. For a set of rules of biological nomenclature, there are special nomenclature codes. The main ones at the moment are the International Code of Botanical Nomenclature (ICBN), and the nomenclature of fungi historically refers to it, the International Code of Zoological Nomenclature (ICZN) and the International Code of Nomenclature of Bacteria (ICNB). There is also the International Code of Classification and Nomenclature of Viruses (ICVCN) and the International Code of Nomenclature of Cultivated Plants (ICNCP).
Rank - a concept used in taxonomy to denote the subordination of various groups of living organisms that differ from each other in the degree of relatedness. Taxonomic (systematic) categories of different levels or ranks (species, genus, family, etc.) are assigned to real isolated groups of organisms - taxa. Taxon - a group of organisms united on the basis of methods of classification, related to each other by varying degrees of relatedness, and sufficiently separated from other groups so that it can be assigned a specific taxonomic category of one rank or another. Unlike a taxonomic category, a taxon always designates specific biological objects. For example, the concepts of “ferns” or “vertebrates” designate groups of organisms that serve as objects of classification and are therefore taxa. Thus, the concept of “species”, “genus”, etc. are not taxa, but a specific species domestic dog (Canis familiaris) is a taxon.
For classification, the main taxonomic categories are used: Kingdom → Type(in zoology), Department (in botany) Class → Row(in zoology), Order(in botany) → Family → Genus → View. Used where necessary auxiliary rank (superkingdom, subkingdom, supertype, subtype, etc.).
Currently, the organic world of the Earth has about 1.5 million animal species, 0.5 million plant species, and about 10 million microorganisms. It is impossible to study such a diversity of organisms without systematizing and classifying them.
The Swedish naturalist Carl Linnaeus (1707-1778) made a great contribution to the creation of the taxonomy of living organisms. He based the classification of organisms on principle of hierarchy or subordination, and took as the smallest systematic unit view. For the name of the species it was proposed binary nomenclature, according to which each organism was identified (named) by its genus and species. It was proposed to give the names of systematic taxa in Latin. So, for example, the domestic cat has a systematic name Felis domestica. The foundations of Linnaean systematics have been preserved to the present day.
Modern classification reflects evolutionary relationships and family ties between organisms. The principle of hierarchy is preserved.
View- this is a collection of individuals that are similar in structure, have the same set of chromosomes and a common origin, freely interbreed and produce fertile offspring, adapted to similar living conditions and occupy a certain area.
Currently, nine main systematic categories are used in taxonomy: empire, superkingdom, kingdom, phylum, class, order, family, genus, species (Scheme 1, Table 4, Fig. 57).
Based on the presence of a designed kernel, everything cellular organisms are divided into two groups: prokaryotes and eukaryotes.
Prokaryotes(nuclear-free organisms) - primitive organisms that do not have a clearly defined nucleus. In such cells, only the nuclear zone containing the DNA molecule is distinguished. In addition, prokaryotic cells lack many organelles. They only have an outer cell membrane and ribosomes. Prokaryotes include bacteria.
Eukaryotes- truly nuclear organisms, have a clearly defined nucleus and all the main structural components of the cell. These include plants, animals, and fungi.
Table 4
Examples of classification of organisms
In addition to organisms that have a cellular structure, there are also non-cellular life forms - viruses And bacteriophages. These forms of life represent a kind of transitional group between living and inanimate nature.
Rice. 57. Modern biological system
* The column represents only some, but not all, existing systematic categories (phyla, classes, orders, families, genera, species).
Viruses were discovered in 1892 by Russian scientist D.I. Ivanovsky. Translated, the word “virus” means “poison”.
Viruses consist of DNA or RNA molecules covered with a protein shell, and sometimes additionally with a lipid membrane (Fig. 58).
Rice. 58. HIV virus (A) and bacteriophage (B)
Viruses can exist in the form of crystals. In this state, they do not reproduce, do not show any signs of being alive, and can persist for a long time. But when introduced into a living cell, the virus begins to multiply, suppressing and destroying all structures of the host cell.
Penetrating into a cell, the virus integrates its genetic apparatus (DNA or RNA) into the genetic apparatus of the host cell, and the synthesis of viral proteins and nucleic acids begins. Viral particles are assembled in the host cell. Outside a living cell, viruses are not capable of reproduction and protein synthesis.
Viruses cause various diseases of plants, animals, and humans. These include tobacco mosaic viruses, influenza, measles, smallpox, polio, human immunodeficiency virus (HIV), defiant AIDS disease.
The genetic material of the HIV virus is presented in the form of two RNA molecules and a specific reverse transcriptase enzyme, which catalyzes the reaction of viral DNA synthesis on the viral RNA matrix in human lymphocyte cells. Next, the viral DNA is integrated into the DNA of human cells. In this state it can remain for a long time without manifesting itself. Therefore, antibodies in the blood of an infected person are not immediately formed and it is difficult to detect the disease at this stage. During the process of blood cell division, the DNA of the virus is passed on to the daughter cells.
Under any conditions, the virus is activated and the synthesis of viral proteins begins, and antibodies appear in the blood. The virus primarily affects T-lymphocytes, which are responsible for producing immunity. Lymphocytes stop recognizing foreign bacteria and proteins and producing antibodies against them. As a result, the body stops fighting any infection, and a person may die from any infectious disease.
Bacteriophages are viruses that infect bacterial cells (bacteria eaters). The body of the bacteriophage (see Fig. 58) consists of a protein head, in the center of which there is viral DNA, and a tail. At the end of the tail there are tail processes that serve to attach to the surface of the bacterial cell and an enzyme that destroys the bacterial wall.
Through a channel in the tail, the DNA of the virus is injected into the bacterial cell and suppresses the synthesis of bacterial proteins, instead of which DNA and viral proteins are synthesized. In the cell, new viruses are assembled, which leave the dead bacterium and invade new cells. Bacteriophages can be used as medicines against pathogens of infectious diseases (cholera, typhoid fever).
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8. Diversity of the organic world§ 51. Bacteria. Mushrooms. Lichens
Taxonomy- a branch of biology that deals with the classification (grouping) of modern and fossil organisms based on similarity and relatedness.
The purpose of taxonomy is to describe, name, classify and construct an evolutionary ( phylogenetic ) a system of organisms that allows us to display family relationships between different classification groups of organisms, as well as the directions and paths of evolution of the organic world.
Systematic features- the most significant signs of external and internal structure, by which taxonomy establishes the similarity and relatedness of organisms.
When classifying living organisms, the following are taken into account:
■ features of their morphological and anatomical structure;
■ features of reproduction, embryonic development and life activity;
■ physiological and biochemical characteristics;
■ type of reserve nutrients;
■ the origin and historical development of a group of living organisms, determined from fossil remains;
■ distribution and habitat (ecological niche);
■ structure and chemical composition of cells;
■ number of chromosomes in the karyotype, etc.
The classification of organisms is based on the identification of certain systematic systems subordinate to each other ( taxonomic ) categories.
Taxonomic(or systematic) categories- These are designations for groups of organisms that differ in the degree of relatedness.
There are taxonomic categories of different levels (see below) assigned to specific groups of organisms - taxa .
Taxon- a group of related organisms that can be assigned a specific taxonomic category. Examples of taxa: chordates, mammals, domestic dog.
❖ Taxonomic categories (in decreasing order of subordination):
■ view,
■ gender,
■ family,
■ order (order - for plants),
■ class,
■ type (department - for plants),
■ kingdom,
■ supremacy.
There are also intermediate categories - subkingdom, subtype, superclass, subclass, etc. Within a species, subspecies, varieties, forms, etc. are distinguished.
Elementary systematic unit- view.
A species is a historically established set of populations, individuals of which are similar in morphological, physiological and biochemical characteristics, are adapted to certain living conditions, occupy a certain area in nature and are capable of interbreeding with each other to form fertile offspring.
Binary nomenclature of the form(introduced by C. Linnaeus in 1753): the name of each species is formed from two words, the first of which means the name of the genus to which the species belongs, and the second is the specific epithet (examples: Scots pine, magnolia grandiflora, brown bear). Next to the name of the organism (in Latin) in the scientific literature, the name of the scientist who first named or described this species is indicated in abbreviated form.
Currently, two superkingdoms and five kingdoms of organisms are distinguished (see table).
This system of organisms does not include viruses, which are non-cellular life forms.
Brief characteristics of prokaryotes and eukaryotes
Prokaryotes- organisms whose cells do not have a formed nucleus.
Prokaryotes include bacteria, cyanobacteria and some other organisms.
Prokaryotes lack, except for the nucleus, all organelles known in eukaryotes (mitochondria, chloroplasts, endoplasmic reticulum, lysosomes, Golgi complex); there are only numerous (up to 20 thousand) ribosomes and one large circular DNA molecule associated with a very small amount of protein. Most bacteria also contain small circular DNA molecules called plasmids.
The basis of the cell wall of all prokaryotes is murein- a polysaccharide with several amino acids attached.
In a number of bacterial species, the plasmalemma forms mesosomes- invaginations into the cytoplasm, on the folded membranes of which enzymes and photosynthetic pigments are located, due to which mesosomes are able to perform the functions of mitochondria, chloroplasts and other organelles.
Eukaryotes- organisms whose cells contain a formed nucleus surrounded by a nuclear envelope.
Eukaryotes include both unicellular (protists) and multicellular (fungi, plants and animals) organisms.
The genetic material of eukaryotes is localized in chromosomes, consisting of DNA and protein. In addition to the nucleus, eukaryotes have membrane-bound cellular organelles (sometimes with their own DNA) - mitochondria, endoplasmic reticulum, lysosomes, Golgi complex, and in plants there are also plastids and large vacuoles.
Kingdoms of organisms
Bacteria- single-celled prokaryotic organisms.
Protista- eukaryotic unicellular or colonial organisms with a cellular level of organization (examples: green euglena, volvox, common amoeba).
Mushrooms- immobile eukaryotic organisms, the body of which consists of thin intertwining threads that form mycelium (in some types of fungi there is no mycelium).
Plants- multicellular, eukaryotic, autotrophic organisms leading an attached lifestyle, capable of synthesizing organic substances from inorganic ones in the process of photosynthesis.
Animals- multicellular, eukaryotic, heterotrophic organisms, most species of which are capable of active movement.
Key words of the summary: diversity of living organisms, systematics, biological nomenclature, classification of organisms, biological classification, taxonomy.
Currently, more than 2.5 million species of living organisms have been described on Earth. To organize the diversity of living organisms, they serve taxonomy, classification And taxonomy.
Taxonomy - a branch of biology, the task of which is to describe and divide into groups (taxa) all existing and extinct organisms, establish family relationships between them, and clarify their general and particular properties and characteristics.
The branches of biological systematics are biological nomenclature And biological classification.
Biological nomenclature
Biological nomenclature is that each species receives a name consisting of a generic and specific name. The rules for assigning appropriate names to species are governed by international nomenclature codes.
For international species names it is used Latin language . The full name of the species also includes the name of the scientist who described the species, as well as the year the description was published. For example, international name house sparrow - Passer domesticus(Linnaeus, 1758), A tree sparrow - Passer montanus(Linnaeus, 1758). Typically, in printed text, species names are italicized, but the name of the describer and the year of the description are not.
The requirements of the codes apply only to international names of species. In Russian you can also write “ field sparrow " And " tree sparrow ».
Biological classification
Classification of organisms uses hierarchical taxa(systematic groups). Taxa have different ranks(levels). The ranks of taxa can be divided into two groups: obligatory (any classified organism belongs to taxa of these ranks) and additional (used to clarify the relative position of the main taxa). When systematizing different groups, a different set of additional taxon ranks is used.
Taxonomy- a section of taxonomy that develops the theoretical foundations of classification. Taxon a group of organisms artificially isolated by man, related by one degree or another of kinship, etc. at the same time, sufficiently isolated so that it can be assigned a certain taxonomic category of one rank or another.
In the modern classification there is the following taxon hierarchy: kingdom, division (type in the taxonomy of animals), class, order (order in the taxonomy of animals), family, genus, species. In addition, they highlight intermediate taxa : over- and subkingdoms, over- and subdivisions, over- and subclasses, etc.
Table “Diversity of living organisms”
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