In the modern system of the organic world, there are about 2 million species. This variety is studied in the framework of taxonomy. The key objective of this discipline is to structure the organic world system. Consider its features in more detail.
General information
As you know, Darwin's evolutionary theory is recognized as a priority in biology. The system of the organic world should most fully reflect the evolutionary relationships of organisms. In other words, it must be phylogenetic. Such a system covers all taxonomic levels: from species, subspecies to classes, departments, kingdoms.
General classification
The division of the organic world into animals and plants has existed since the time of Aristotle. C. Linnaeus gave them the Latin names Animalia and Vegetabilia, respectively. This classification is considered generally accepted and is included in almost all biology manuals. It must be said, however, that scientists have long felt the disadvantages of such a division. Biologists could identify all of its defects only by the middle of the 20th century.
Prokaryotes and Eukaryotes
A fundamental role in the research was the establishment of significant differences between bacteria and blue-green algae and other living things (fungi, incl.). These two phylogenetically related groups lack a true core. Genetic material (DNA) is freely located in their cells. It is immersed in the nucleoplasm, not separated by a nuclear membrane from the cytoplasm. They lack a mitotic spindle, microtubules and centrioles, plastids and mitochondria. If they have flagella, then their device is very simple, they have a fundamentally different structure than animals and plants. Such organisms are called prokaryotes - "pre-nuclear".
The remaining participants in the organic world system - both single and multicellular - have a true core that surrounds the nuclear membrane. Due to it, it is sharply demarcated from the cytoplasm. As for the genetic material, it is located on the chromosomes. Organisms have a mitotic spindle or its analogue, consisting of microtubules. In addition to a clearly detectable nucleus and cytoplasm, mitochondria are also found, and in many - complex flagella and plastids. These organisms are called "eukaryotes" (Eucaryota) - "nuclear".
Gradually, scientists began to conclude that the differences between prokaryotes and eukaryotes are much deeper than, say, between higher plants and animals. Both of them, by the way, belong to the Eucaryota group.
Prokaryotes form a sharply isolated, specific group, which in the system of the organic world is often recognized as a kingdom or supra-kingdom.
Kingdoms of plants and animals
The separation of prokaryotes and eukaryotes is completely justified and is beyond doubt. A little more difficult to implement a taxonomic division of nuclear. As a rule, they are divided into two kingdoms: Animals and Plants. In the system of the organic world, the taxonomic boundaries of the former are quite clear (not taking into account the position of some groups of flagellates, which some zoologists traditionally classify as simple). However, the distribution limits of plants are constantly being reviewed.
From this kingdom it is necessary to exclude all prokaryotes, cyanes (blue-green algae). Controversial remains the position of the mushrooms. In the system of the organic world, they traditionally belong to plants, despite the fact that in the first half of the 19th century E. Fries (Swedish mycologist) proposed to separate them into an independent kingdom. I must say that subsequently, many mycologists agreed with him.
Mushrooms in the organic world system
Currently, scientists have not reached a consensus on the taxonomic volume, origin, and systematic position of these organisms. Mushrooms are considered today the most mysterious group. The identification of their types in the system of the organic world is accompanied by significant difficulties.
It has long been believed that mushrooms, in the broadest sense of the term, are not a natural group and probably have a different origin. Some scientists, for example, do not include myxomycetes (mucus membranes, mucous fungi).
Many experts (H. Ya. Gobi, A. De Bari) believe that myxomycetes came from the simplest flagellates. Some authors speak in favor of their combined nature: different groups descended from different flagellated ancestors.
The question of a place in the system of the organic world has not been completely resolved. Scientists cannot agree on the question of which kingdom mushrooms belong to: Animals or Plants.
As early as 1874, Yu. Saks suggested that basidiomycetes and myxomycetes were descended from red parasitic algae; in 1881, De Bari proposed the hypothesis that their ancestors were ficomycetes. At present, both the first and second theory have supporters.
Some scientists, based on morphological data, suggest that basidiomycetes and ascomycetes came from red algae. However, most mycologists believe that the similarity of these two groups of organisms is a consequence of convergence. Therefore, they believe, true fungi come from myxomycetes, and already through them - from protozoa. The connection of animals and fungi is confirmed by the results of biochemical analysis. The similarity is revealed by the primary structure of transport RNA and cytochromes, by nitrogen exchange pathways.
Protista
In accordance with modern ideas about the system of the organic world, 4 large kingdoms are distinguished in its composition. Some scholars point to the existence of another fifth kingdom. Its structure includes the so-called protists (Protista). These include pyrophytic, euglena and golden algae, as well as all protozoa.
It should be noted that the allocation in the modern system of the organic world of the heterogeneous kingdom of protists is not very unambiguously assessed by the scientific community. Separation of this group creates significant problems. The fact is that at present we have a generally established system of the organic world, and the diversity of kingdoms can significantly complicate the classification.
The dominance of prenuclear
These organisms have a separate position in the system of the organic world, and the variety of prokaryotes is simply amazing.
In nuclear, there is no real nucleus and membrane, and genetic information is in the nucleoid. DNA, as a rule, forms one strand closed in a ring. It has no connection with RNA and is not a real chromosome (which has a more complex structure).
There is no typical sexual process. The exchange of genetic information is sometimes carried out in the course of other (parasexual) processes that are not accompanied by nucleoid fusion.
Nuclear donors lack centrioles, mitotic spindles, microtubules, mitochondria, and plastids. The glycopeptide murein acts as a supporting framework for the cell wall. In most prokaryotes, flagella are absent or have a relatively simple structure.
Many representatives of prenuclear have the ability to fix molecular nitrogen. Nutrition occurs through the absorption of substances through the cell wall (absorbent (saprotrophic or parasitic) or autotrophic method).
This group includes only 1 kingdom - Shotguns (Mychota or Mychotalia from the word "mihi", which means lumps of chromatin that does not have the ability to mitosis). Some authors use the not-so-good notation Monera. He was also proposed by Haeckel for Protamoeba (supposedly a non-nuclear genus, which later turned out to be only a fragment of an ordinary amoeba).
The kingdom of bacteria
These organisms have a heterotrophic or autotrophic (chemotrophic, less commonly fluorotrophic) food system. If chlorophyll is present, then it is represented by bacteriochlorophylls. Bacteria lack phycoerythrin and phycocyanin. During photosynthesis, molecular oxygen is not released. Simple flagella are often found.
In addition to true bacteria, spirochetes, myxobacteria, actinomycetes, rickettsia, mycoplasmas, chlamydia and, possibly, viruses are assigned to the kingdom. It should be noted that this link has not been sufficiently studied, and it is likely that in the future its significance in the system of the organic world and evolution may be revised.
Cyan
Organisms of this subdomain are distinguished by autotrophic (photosynthetic) nutrition. Chlorophyll is presented as chlorophyll a. Auxiliary photosynthetic elements are phycoerythrin and phycocyanin. The process of photosynthesis is accompanied by the release of molecular oxygen.
The kingdom includes blue-green algae, forming one department.
Nuclear Organisms: Description
Eukaryotes have a true nucleus surrounded by a membrane. Genetic information is found on chromosomes in which DNA binds to RNA (except for pyrophytic algae).
Eukaryotes are characterized by a typical sexual process (alternating fusion of nuclei, reduction fission that occurs during meiosis). In some nuclear cases, apomixis is observed, i.e., reproduction occurs without fertilization, but with the genitals.
Many representatives of the kingdom have centrioles; a more or less typical mitotic spindle (or its analog formed by microtubules), plastids, mitochondria, and a well-developed endoplasmic membrane system are found.
If there are cilia or flagella, then they differ in a complex structure. They contain 9 paired (tubular) fibrils located on the periphery of the cover, and two single (also tubular) fibrils.
Nuclear organisms do not have the ability to fix nitrogen from the atmosphere. As a rule, they are aerobes, secondary anaerobes are rare.
The nuclear power system is absorbent or autotrophic (Holozoic). In the first case, the intake of substances is carried out through absorption through the cell wall. Naked food involves ingesting food and digesting it inside the body.
In the supremacy of eukaryotes, 3 kingdoms are distinguished: Plants, Mushrooms and Animals. In each of them there are kingdoms.
Animals
Organisms primarily heterotrophic are collected in this kingdom. As a rule, they lack a dense cell wall. Nutrition is usually done by ingesting food and digesting it. In some animals, however, the system is absorbent. Spare carbohydrates are formed in the form of glycogen. Reproduction and resettlement of animals is carried out without spores (except for some protozoa of the class Sporozoa).
Protozoa
Animals are assigned to this kingdom, the organism of which consists of one single cell or several colonies of absolutely identical cells. In the system of the organic world, one type of Protozoa is usually distinguished. Sometimes it is divided into 2 or more independent types.
Multicellular
This sub kingdom includes animals, the body of which consists of many specialized, unequal cells.
Currently, 16 types of multicellular organisms are distinguished in the organic world system. Sometimes their number is adjusted to 20-23. Common types are:
- Sponges.
- Coelenterates.
- Grebneviki.
- Flatworms.
- Nemerthins.
- Cavity worms.
- Ringworms.
- Arthropods.
- Onychophors.
- Clams.
- Echinoderms.
- Tentacles.
- Pogonofory.
- Maxillary.
- Chordates.
- Semi-chord.
Characteristics of the kingdom of mushrooms
It consists of heterotrophic organisms. Cells have a dense wall (cellulosic or hatin). Sometimes it is represented by a membrane. The power system is absent-minded, rarely autotrophic.
Carbohydrate reserves are mainly represented as glycogen. Some representatives have flagellar cells. However, in most cases they are absent.
Reproduction is carried out using haploid spores. When they germinate, meiosis occurs. As a rule, fungi are attached organisms. They are divided into two groups. The difference between them is very significant. Moreover, their common origin has not yet been proven and therefore is in doubt among many scientists. Nevertheless, before the final resolution of issues concerning the interaction of these groups with each other and with other kingdoms, it is advisable to consider them in the structure of one kingdom.
Lower mushrooms
Their vegetative phase consists of a mobile multinucleated protoplasmic mass that does not have cell walls (plasmodium), or an aggregate of amoeboid naked cells that preserve individuality (pseudoplasmodium). Nutrition can be absorptive or holozoic.
If flagellated cells are present, then usually two different flagella are present in them. Sporangia and debate are usually numerous. As part of the kingdom, there is one type (department) - myxomycetes.
Higher mushrooms
These organisms lack pseudoplasmodium and plasmodium. The vegetative phase is represented by threads (hyphae) or cells with a pronounced wall. The food is extremely absorbent. If flagellar cells are present, then they have one or two flagella.
As part of the kingdom, there are departments:
- Zoospore (or mastigomycetes).
- Zygomycetes.
- Ascomycetes.
- Basidomycetes.
- Imperfect mushrooms (artificial department).
Plants
They are phototrophic (autotrophic) organisms. Sometimes secondary heterotrophs (parasites or saprophytes) are found.
Cells have a dense wall, which usually consists of cellulose (in rare cases, chitin). The carbohydrate supply is presented in the form of starch. In red algae, it forms in the form of rhodamilon, which is close to glycogen.
Lower plants
Their genitals (gametangia) and sporulation organs (sporangia) are either unicellular or completely absent. As a rule, the zygote does not transform into a multicellular typical embryo.
In lower plants, the epidermis, stomata, and conductive cylinder are absent. As part of the kingdom, only algae are present (except for blue-green). In various systems, they are divided into departments. The most recognized are algae:
- Cryptophytic.
- Euglena.
- Pyrophytic.
- Golden
- Brown.
- Greens.
- Reds.
The situation of the latter, however, is considered highly controversial. The difference between red algae and other departments is the complete absence of flagella. There are also some biochemical and morphological features.
Higher plants
Their sporangia and gametangia are multicellular. The zygote transforms into a typical fetus. Higher plants have an epidermis, stomata, and many have a conducting cylinder (stela).
The subdomain includes the following departments:
- Psilophytes (or rhiniform).
- Mossy.
- Lap-like.
- Psiloid.
- Gymnosperms.
- Angiosperms (flowering).
The role of man in the system of the organic world
Humans are an integral element of nature. Within the framework of biological science, man belongs to the kingdom Animals, type - Chordates, subtype - Vertebrates, class - Mammals, subclass - Placental, order - Primates, genus - People, mind - Homo sapiens.
There are ongoing discussions about the role of people in the system. Many assumptions are put forward. According to the scientific ideas of modern philosophers, man is a unity of an animal, biological and spiritual personality. With this approach to the problem, human behavior is explained by the laws of procreation and self-preservation, common to living beings.