At present, more than 2.5 million species of living organisms have been described on Earth. However, the actual number of species on Earth is several times greater, since many types of microorganisms, insects, etc. are not taken into account. In addition, it is believed that the modern species composition is only about 5% of the species diversity of life during its existence on Earth. Systematics, classification and taxonomy serve to streamline such a variety of living organisms.
Systematics is a branch of biology that deals with the description, designation and classification of existing and extinct organisms by taxa.
Classification – the distribution of the entire set of living organisms according to a certain system of hierarchically subordinate groups – taxa.
Taxonomy is a branch of systematics that develops the theoretical foundations of classification.
A taxon is a group of organisms artificially isolated by man, related by one degree or another of kinship, sufficiently isolated so that it can be assigned a certain taxonomic category of one or another rank. The smallest taxonomic unit is the species . In modern taxonomy of living organisms, there is the following hierarchy of taxa: kingdom, department ( type in animal taxonomy), class, order ( order in animal taxonomy), family, genus, species . In addition, intermediate taxa are distinguished: supra- and sub-kingdoms, supra- and subdivisions, etc. The taxonomy of living organisms is constantly changing and updating. The main major taxa of living organisms are listed below.
Cellular forms – the over-kingdom of Prokaryotes (non-nuclear) and the over-kingdom of Eukaryotes (with a formed nucleus)
Kingdom of Prokaryotes
Kingdom ARCHEBACTERIA (ANCIENT BACTERIA)
Kingdom EUBACTERIA (TRUE BACTERIA)
Kingdom PROKARYOTIC ALGAE: department Cyanobacteria , department Prochlorophytes
Superkingdom of Eukaryotes
– sub-kingdom of Slime molds: Department of Myxomycetes
– subkingdom Fungi: department Chytridiomycetes , department Oomycetes , department Zygomycetes , department Ascomycetes or Marsupials , department Basidiomycetes , department Deuteromycetes or Imperfect fungi
– subkingdom Bagryanka: department Red algae
– sub-kingdom True algae: department Green algae , department Golden algae , department Yellow – green algae , department Diatoms , department Brown algae , department Pyrophytic algae , department Euglena algae
– subkingdom Higher plants: department Bryophytes , department Rhynioid , department Lycopsoid , department Horsetail , department Ferns , department Gymnosperms , department Angiosperms (class Monocotyledonous, class Dicotyledonous)
– subkingdom Unicellular: type Sarcomastigophora (class Flagellates, class Sarcodaceae), type Sporoviki , type Ciliates
– sub-kingdom Multicellular: type Sponge , type Intestinal (classes Hydroid polyps, Scyphoid polyps, Coral polyps), type Ctenophores , type Flatworms (classes Monogenetic flukes, Trematodes, Tapeworms), type Roundworms (classes Nematodes, hairy, acanthocephalans, Rotifers ), phylum Annelids (classes Polychaete worms, oligochaete worms, Leeches), phylum Arthropods (classes Crustacea, horseshoe crabs, arachnids, centipedes, insects), phylum Mollusca (classes Gastropoda, Bivalves, Cephalopoda), phylum Echinodermata (classes Sea lilies, Sea stars, Sea urchins, Holothurians), Chordata type (subtype Tunicates, subtype Cranial and subtype Vertebrates, including classes – Cyclostomes, Cartilaginous fishes, Bony fishes, Amphibians, Reptiles, Birds, Mammals).
Types of nutrition of living organisms
All living organisms that live on Earth are open systems that depend on the supply of matter and energy from outside. The process of consuming matter and energy is called nutrition. Chemical substances are necessary for building the body, energy – for the implementation of vital processes.
There are two types of nutrition in living organisms: autotrophic and heterotrophic.
Autotrophs (autotrophic organisms) – organisms that use carbon dioxide as a source of carbon (plants and some bacteria). In other words, these are organisms capable of creating organic substances from inorganic substances – carbon dioxide, water, mineral salts. Depending on the source of energy, autotrophs are divided into photoautotrophs and chemoautotrophs. Phototrophs are organisms that use light energy for biosynthesis (plants, cyanobacteria). Chemotrophs – organisms that use the energy of chemical reactions of oxidation of inorganic compounds for biosynthesis (chemotrophic bacteria: hydrogen, nitrifying, iron bacteria, sulfur bacteria, etc.).
Heterotrophs (heterotrophic organisms) – organisms that use organic compounds (animals, fungi and most bacteria) as a carbon source. In other words, these are organisms that are not able to create organic substances from inorganic ones, but need ready-made organic substances. According to the method of obtaining food, heterotrophs are divided into phagotrophs (holozoans) and osmotrophs. Phagotrophs (hololozoa) swallow solid pieces of food (animals), osmotrophs absorb organic matter from solutions directly through cell walls (fungi, most bacteria). According to the state of the food source, heterotrophs are divided into biotrophs and saprotrophs.
Biotrophs feed on living organisms. These include zoophages (feeding on animals) and phytophages (feeding on plants), including parasites.
Saprotrophs use the organic matter of dead bodies or excretions (excrement) of animals as food. These include saprotrophic bacteria, saprotrophic fungi, saprotrophic plants (saprophytes), saprotrophic animals (saprophages). Among them there are detritophages (feeding on detritus), necrophages (feeding on animal corpses), coprophages (feeding on excrement), etc.
Catabolism (energy metabolism, dissimilation) is a set of reactions leading to the formation of simple substances from more complex ones (hydrolysis of polymers to monomers and the breakdown of the latter to low molecular weight compounds of carbon dioxide, water, ammonia, and other substances). Catabolic reactions usually go with the release of energy.
Anabolism (plastic metabolism, assimilation) is a concept opposite to catabolism: a set of reactions for the synthesis of complex substances from simpler ones (the formation of carbohydrates from carbon dioxide and water during photosynthesis, matrix synthesis reactions). Anabolic reactions require energy to proceed. The processes of plastic and energy exchange are inextricably linked. All synthetic (anabolic) processes require energy supplied during dissimilation reactions. The reactions of splitting (catabolism) themselves proceed only with the participation of enzymes synthesized in the process of assimilation.
In relation to free oxygen, organisms are divided into three groups: aerobes, anaerobes and facultative forms.
Aerobes (obligate aerobes) – organisms that can live only in an oxygen environment (animals, plants, some bacteria and fungi).
Anaerobes (obligate anaerobes) – organisms that are unable to live in an oxygen environment (some bacteria).
Facultative forms (facultative anaerobes) – organisms that can live both in the presence of oxygen and without it (some bacteria and fungi). In obligate aerobes and facultative anaerobes, in the presence of oxygen, catabolism proceeds in three stages: preparatory, oxygen-free, and oxygen. As a result, organic substances break down into inorganic compounds. In obligate anaerobes and facultative anaerobes, with a lack of oxygen, catabolism proceeds in the first two stages: preparatory and anoxic. As a result, intermediate organic compounds still rich in energy are formed.
Stages of energy metabolism (catabolism):
The first stage – preparatory – consists in the enzymatic splitting of complex organic compounds into simpler ones. Proteins are broken down into amino acids, fats into glycerol and fatty acids, polysaccharides into monosaccharides, nucleic acids into nucleotides. In multicellular organisms, this occurs in the gastrointestinal tract, in unicellular organisms, in lysosomes under the action of hydrolytic enzymes. The released energy is dissipated in the form of heat. The resulting organic compounds either undergo further oxidation or are used by the cell to synthesize its own organic compounds.
The second stage – incomplete oxidation (oxygen -free) – consists in the further breakdown of organic substances, is carried out in the cytoplasm of the cell without the participation of oxygen. Anoxic, incomplete oxidation of glucose is called glycolysis . As a result of glycolysis, two molecules of pyruvic acid (PVA) are formed from one glucose molecule, and two ATP molecules are synthesized. Further , in the absence of oxygen in the environment, PVC is processed either into ethyl alcohol – alcoholic fermentation (in yeast and plant cells with a lack of oxygen), or into lactic acid – lactic acid fermentation (in animal cells with a lack of oxygen). In the presence of oxygen in the environment, the products of glycolysis undergo further splitting to final products, that is, they are included in the third stage.
The third stage – complete oxidation (respiration) – is the oxidation of PVC to carbon dioxide and water, carried out in mitochondria, with the obligatory participation of oxygen.
The overall equation for the breakdown of glucose in the process of cellular respiration:
C 6 H 12 O 6 + 6O 2 + 38H 3 RO 4 + 38ADP → 6CO 2 + 44H 2 O + 38ATP
Thus, during glycolysis, 2 ATP molecules are formed, during cellular respiration – another 36 ATP, in general, with complete oxidation of glucose – 38 ATP.
Heterotrophic organisms build their own organic matter from organic food components. Heterotrophic assimilation essentially boils down to the rearrangement of molecules: food organic substances (proteins, fats, carbohydrates) → simple organic molecules (amino acids, fatty acids, monosaccharides) → body macromolecules (proteins, fats, carbohydrates). Autotrophic organisms are capable of completely independently synthesizing organic substances from inorganic molecules consumed from the external environment. In the process of photo- and chemosynthesis, simple organic compounds are formed, from which macromolecules are subsequently synthesized: inorganic substances (CO 2 , H 2 O) → simple organic molecules (amino acids, fatty acids, monosaccharides) → macromolecules of the body (proteins, fats, carbohydrates). Consider the most important, from the point of view of ecology, metabolic processes of plastic metabolism – photosynthesis and chemosynthesis.
Photosynthesis (photoautotrophy) is the synthesis of organic compounds from inorganic ones due to the energy of light.
The overall photosynthesis equation is:
6CO 2 + 6H 2 O → C 6 H 12 O 6 + 6O 2
Photosynthesis proceeds with the participation of photosynthetic pigments, which have the unique property of converting sunlight energy into chemical bond energy in the form of ATP. The process of photosynthesis consists of two phases: light and dark. In the process of photosynthesis, in addition to monosaccharides (glucose, etc.), monomers of other organic compounds are synthesized – amino acids, glycerol and fatty acids. Thus, thanks to photosynthesis, plants provide themselves and all life on Earth with the necessary organic substances and oxygen.
Chemosynthesis (chemoautotrophy) is the process of synthesis of organic compounds from inorganic (CO 2 , etc.) due to the chemical energy of the oxidation of inorganic substances (sulfur, hydrogen, hydrogen sulfide, iron, ammonia, nitrite, etc.). Only chemosynthetic bacteria are capable of chemosynthesis: nitrifying, hydrogen, iron bacteria, sulfur bacteria, etc. They oxidize compounds of nitrogen, iron, sulfur and other elements. All chemosynthetics are obligate aerobes, as they use atmospheric oxygen. Nitrifying bacteria oxidize nitrogen compounds, iron bacteria convert ferrous iron into oxide, sulfur bacteria oxidize sulfur compounds . The energy released during oxidation reactions is stored by bacteria in the form of ATP molecules and used for the synthesis of organic compounds. Chemosynthetic bacteria play a very important role in the biosphere. They are involved in wastewater treatment, contribute to the accumulation of minerals in the soil, and increase soil fertility.