In the modern system of the organic world, there are about 2 million species. This variety is studied within the framework of systematics. The key task of this discipline is the structuring of the system of the organic world. 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 connections of organisms. In other words, it must be phylogenetic. Such a system covers all taxonomic levels: from species, subspecies to classes, divisions, kingdoms.
General classification
The division of the organic world into animals and plants has existed since the time of Aristotle. K. Linnaeus gave them the Latin names Animalia and Vegetabilia, respectively. This classification is considered generally accepted and is included in almost all biology textbooks. However, it must be said that scientists have long felt the shortcomings of such a division. Biologists were able to identify all its defects only in the middle20th century.
Prokaryotes and eukaryotes
The fundamental role in the research was the establishment of significant differences between bacteria and blue-green algae and other living beings (including fungi). These two phylogenetically related groups lack a true nucleus. The genetic material (DNA) resides freely in their cells. It is immersed in the nucleoplasm, not separated by a nuclear membrane from the cytoplasm. They lack the 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 that of animals and plants. Such organisms are called prokaryotes - "pre-nuclear".
The rest of the members of the organic world system - both unicellular and multicellular - have a true nucleus, which is surrounded by a nuclear membrane. Due to it, it is sharply delimited from the cytoplasm. As for the genetic material, it is located in the chromosomes. Organisms have a mitotic spindle or its analogue, consisting of microtubules. In addition to the clearly visible 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 come to the conclusion that the differences between prokaryotes and eukaryotes are much deeper than, say, between higher plants and animals. Both, by the way, belong to the Eucaryota group.
Prokaryotes forma 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 quite justified and beyond doubt. It is somewhat more difficult to carry out a taxonomic subdivision 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 certain groups of flagellates, which some zoologists traditionally refer to as protozoa). However, plant distribution limits are constantly being revised.
From this kingdom it is necessary to exclude all prokaryotes, cyanides (blue-green algae). The position of mushrooms remains controversial. In the system of the organic world, they traditionally belong to plants, despite the fact that back in the first half of the 19th century, E. Fries (a Swedish mycologist) proposed to separate them into an independent kingdom. I must say that many mycologists later agreed with him.
Mushrooms in the organic world system
Currently, scientists have not come to a consensus regarding the taxonomic scope, origin and systematic position of these organisms. Mushrooms are considered today the most mysterious group. The selection of their types in the system of the organic world is accompanied by significant difficulties.
It has long been believed that mushrooms in the broad sense of the term are not a natural group and probably have different origins. Some scholars, for example, do notto them myxomycetes (mucus molds, slimy fungi).
Many experts (H. Ya. Gobi, A. De Bari) believe that myxomycetes originated from the protozoan flagellates. Some authors speak in favor of their combined character: different groups descended from different flagellated ancestors.
The question of the place in the system of the organic world has not been fully resolved either. Scientists cannot agree on the question of which kingdom fungi belong to: Animals or Plants.
Even in 1874 J. Sachs suggested that basidiomycetes and myxomycetes originated from red parasitic algae, in 1881 De Bari proposed the hypothesis that their ancestors were phycomycetes. Currently, both the first and second theories have supporters.
Some scientists, based on morphological data, suggest that Basidiomycetes and Ascomycetes originated 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 through them - from protozoa. The connection between animals and fungi is confirmed by the results of biochemical analysis. The similarity is revealed by the primary structure of transport RNA and cytochromes, the pathways of nitrogen metabolism.
Protists
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. In hiscomposition included the so-called protists (Protista). These include pyrrhophytes, euglenoids and golden algae, as well as all protozoa.
It should be noted that the allocation of a heterogeneous kingdom of protists in the modern system of the organic world is not unambiguously assessed by the scientific community. The isolation 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.
Pre-Nuclear Kingdom
These organisms have a separate position in the system of the organic world, and the diversity of prokaryotes is simply amazing.
Pre-nuclear lacks a true nucleus and membrane, and the genetic information is located in the nucleoid. DNA, as a rule, forms a single strand closed in a ring. It has no connection to RNA and is not a true chromosome (which is more complex).
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 the fusion of nucleoids.
Prenuclear lacks centrioles, mitotic spindle, microtubules, mitochondria and plastids. The glycopeptide murein acts as a supporting scaffold for the cell wall. Most prokaryotes have no flagella or have a relatively simple structure.
Many pre-nuclear species have the ability to fix molecular nitrogen. Power going onthrough the absorption of substances through the cell wall (absorptive (saprotrophic or parasitic) or autotrophic method).
This group includes only 1 kingdom - Drobyanki (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 entirely successful Monera designation. It was proposed by Haeckel for Protamoeba (supposedly a nuclear-free genus, which later turned out to be only a fragment of an ordinary amoeba).
The sub-kingdom of bacteria
These organisms have a heterotrophic or autotrophic (chemotrophic, less often fluorotrophic) nutrition 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 subkingdom. It should be noted that this link has not yet 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.
Cyaneas
Organisms of this sub-kingdom are distinguished by autotrophic (photosynthetic) nutrition. Chlorophyll is present in the form of chlorophyll a. Auxiliary photosynthetic elements are phycoerythrin and phycocyanin. The process of photosynthesis is accompanied by the release of molecular oxygen.
The sub-kingdom includes blue-green algae forming one department.
Nuclear Organisms: Description
Eukaryotes have a true nucleus surrounded by a membrane. Genetic information is contained in chromosomes in which DNA is linked to RNA (except for pyrrhophytes).
Eukaryotes are characterized by a typical sexual process (alternating fusion of nuclei, reduction division occurring during meiosis). In some nuclear ones, apomixis is observed, i.e. reproduction occurs without fertilization, but with the genitals.
Many members of the superkingdom have centrioles; a more or less typical mitotic spindle (or its analogue formed by microtubules), plastids, mitochondria, and a well-developed endoplasmic membrane system are found.
If there are cilia or flagella, they have a complex structure. They contain 9 paired (tubular) fibrils located on the periphery of the sheath, 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 rarely found.
The nuclear nutrition system is absorptive or autotrophic (holozoic). In the first case, the intake of substances is carried out by absorption through the cell wall. Holozoic nutrition involves swallowing food and digesting it inside the body.
In the super-kingdom of eukaryotes, 3 kingdoms are distinguished: Plants, Fungi and Animals. Each of them has sub-kingdoms.
Animals
This kingdom contains primarily heterotrophic organisms. As a rule, they do not have a dense wallcells. Nutrition is usually carried out by swallowing food and digestion. In some animals, however, the system is absorptive. Reserve carbohydrates are formed in the form of glycogen. Reproduction and resettlement of animals is carried out without spores (except for some protozoa of the Sporozoa class).
Protozoa
This subkingdom includes animals whose organism consists of a single cell or of 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 whose body consists of many specialized, unequal cells.
Currently, 16 types of multicellular organisms have been identified in the system of the organic world. Sometimes their number is adjusted to 20-23. Common types are:
- Sponges.
- Celiac.
- Comb jelly.
- Flatworms.
- Nemertines.
- Initial worms.
- Anned worms.
- Arthropods.
- Onychophora.
- Shellfish.
- Echinoderm.
- Tentacled.
- Pogonophores.
- Setojaws.
- Chordates.
- Semichordal.
Characteristics of the mushroom kingdom
It consists of heterotrophic organisms. Cells have a dense wall (cellulose or khatin). Sometimes it is represented by a membrane. The food system is absobtive, rarely autotrophic.
Carbohydrate stores are predominantly in the form of glycogen. Atsome representatives present flagellar cells. However, in most cases they are missing.
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. At the same time, their common origin has not yet been proven and therefore raises doubts among many scientists. Nevertheless, until the final solution of issues related to the interaction of these groups with each other and with other sub-kingdoms, it is advisable to consider them in the structure of one kingdom.
Inferior mushrooms
Their vegetative phase consists of a mobile multinuclear protoplasmic mass that does not have cell walls (plasmodium), or an aggregate of amoeboid naked cells that retain their individuality (pseudoplasmodium). Nutrition can be both absorptive and holozoic.
If there are flagellar cells, then they usually have two different flagella. Sporangia and spores are usually numerous. The subkingdom contains 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. Nutrition is extremely absorbent. If flagellated cells are present, then they contain one or two flagella.
Departments are distinguished in the sub-kingdom:
- Zoospores (or mastigomycetes).
- Zygomycetes.
- Ascomycetes.
- Basidomycetes.
- Imperfect mushrooms (artificial department).
Plants
They are phototrophic (autotrophic) organisms. Sometimes there are secondary heterotrophs (parasites or saprophytes).
Cells have a dense wall, which usually consists of cellulose (in rare cases, chitin). The supply of carbohydrates is in the form of starch. In red algae, it is formed in the form of rhodamylon, close to glycogen.
Inferior plants
Their reproductive organs (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 there is no epidermis, stomata and conductive cylinder. The sub-kingdom contains only algae (except for blue-green ones). In various systems, they are divided into departments. Algae are considered the most recognized:
- Cryptophytes.
- Euglenaceae.
- Pyrrhophytic.
- Golden.
- Brown.
- Greens.
- Red.
The position of the latter, however, is considered highly controversial. The difference between red algae and other divisions is the complete absence of flagella. There are also some biochemical and morphological features.
Higher plants
Their sporangia and gametangia are multicellular. The zygote develops into a typical embryo. Higher plants have epidermis, stomata, many have a conducting cylinder (stele).
The sub-kingdom includes departments:
- Psilophytes (or rhineous).
- Mossy.
- Lycopterids.
- Psiloid.
- Gymnosperms.
- Angiosperms (flowering).
The role of man in the system of the organic world
People are an essential element of nature. Within the framework of biological science, a person belongs to the kingdom Animals, type - Chordates, subtype - Vertebrates, class - Mammals, subclass - Placentals, order - Primates, genus - Humans, species - Homo sapiens.
There is constant debate about the role of humans in the system. Many assumptions are put forward. According to the scientific ideas of modern philosophers, a person is a unity of animal, biological and spiritual personality. With this approach to the problem, people's behavior is explained by the laws of procreation and self-preservation common to living beings.
