prokaryoteIt is a kind of unicellular organism without nucleus, and there is no membrane in its cellsOrganelle。ProkaryoteBiology includesBacteria and“Blue-green algae”OfCyanobacteria, the simplest group of living creaturesMitogenesisTo reproduce.Prokaryotes were once the onlyLife formsThey have monopolized the earth for more than 2 billion years.Now they are still very prosperous, andNutrient saltsPlays an important role in the cycle of.The prokaryotic kingdom includes at least 4000 species of organisms.[1]
basic feature
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① No between nucleoplasm and cytoplasmnuclear membraneTherefore, there is no shaped nucleus（QuasinuclearOr nuclear like);
② Genetic material is different fromHistoneCombined annular double helixDeoxyribonucleic acid(DNA) filaments that do not form chromosomes (some prokaryotesgenomeIn addition, there are smaller ones that can enter and exit cellsplasmidDNA)；
③ With simplicityDichotomyMode reproduction, without mitosis or meiosis;
④ Without sexual behavior, some species sometimes combine, transform or transducePartial genomeQuasi sexual behavior of transferring from one cell to another (seeBacterial conjugation)；
⑤ No muscle ballActinIt forms a microfiber system, so the cytoplasm cannot flow and does not formPseudopodia, phagocytosis and other phenomena;
⑥FlagellumNot bymicrotubuleIt is composed of several helical or parallel protein filaments without "9+2" structure;
⑧ Unit membrane system in cellsCyanobacteriahave otherthylakoidThe outer part is generally formed by the inner fold of the cell membrane, including oxidative phosphorylatedElectron transfer chain(Cyanobacteria carry out photosynthesis in saclike bodies, othersPhotosynthetic bacteriaPhotosynthesis is carried out on the membrane system of cell membrane inner fold;ChemotrophicBacteriaCell membrane systemEnergy metabolism);
⑩ Most prokaryotes have unique composition and structurecell wallwait.In short, prokaryoticCellular structureThanEukaryoteIts cell structure is much simpler.[1]
Classified status
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The prokaryotic kingdom includes all cells lackingnuclear membraneMost of them are bacteria.
haveProkaryotic cellA large group of organisms with structures.It includesBacteriophyta(This also includesActinomycetes）、Cyanophyta、Prochlorophyta、Rickettsia, Mycoplasma andchlamydiaEtc.Among the above categories, Cyanophyta and Prochlorophyta are greenAutotrophThere are also a few bacteriaLight energyOr chemoautotrophic bacteria.But most bacteria and other types are heterotrophic,SaprophyticOr parasitic.Rickettsia is a kind of small specialized intracellular parasite between viruses and bacteria, spherical or rod-shaped.Mycoplasma is also called fungoidPlastidIt is an independent living microorganism between rickettsia and bacteria.It doesn'tcell wall, soft, changeable in shape, spherical or filamentous and branched in length.Chlamydia is an obligate parasite.Put all kinds ofprokaryoteThe prokaryotic kingdom was founded in 1969 by American biologistswhittaker (R · H · Whittaker).He divided biology into five kingdoms according to cell structure and nutrition type, namely prokaryotic kingdomprotista, the plant kingdom, the fungus kingdom, and the animal kingdom have gradually been accepted and approved by people.[1]
Evolutionary status
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In terms of evolution, prokaryotic organisms are the oldest;Today,prokaryoteIt is the largest category.From the biological point of view, the key factor of their success is undoubtedly theircell divisionFast speed, and metabolic diversity.Prokaryotes can survive in many environments that other organisms cannot tolerate, such as Antarctic ice, deep ocean, and even hot springs with nearly boiling points. Some species can survive in the absence ofFree oxygenIn the environment ofAnaerobic respirationTo get energy.[1]
Ecological characteristics
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From an ecological point of view, prokaryotes act as decomposers, decomposing animal and plant remains and releasing elements that can be used by plants.Prokaryotes inNitrogen fixationOn the other hand, it also plays an important role.Although the atmosphere is rich in nitrogen, eukaryotes cannot directly use the nitrogen in the airprokaryoteThe nitrogen fixation effect of some species in the gas phase can only be used after the gaseous nitrogen is converted into inorganic compounds such as ammonia or amine ions.
metabolize
Blue algae do not have chloroplasts, but have photosynthetic pigments (chlorophyll and phycocyanin) and enzymes related to photosynthesis, which can carry out photosynthesis.Photosynthetic bacteriaUnder anaerobic conditions, use light energy assimilationcarbon dioxideDifferent from green plants, photosynthetic bacteria do not produce oxygen during photosynthesis.in prokaryotes Aerobic bacteriaCarry out aerobic respiration, such as "in the discovery of exploring photosynthesis, Engelman used the characteristics of aerobic bacteria to attract oxygen and marked that oxygen is released by chloroplasts".
Prokaryotes have complex species, so their metabolic types are diverse, including autotrophic aerobic type, autotrophic anaerobic type, autotrophic facultative anaerobic type, heterotrophic aerobic type, heterotrophic anaerobic type, heterotrophic facultative anaerobic type.
Composition in ecosystem
Producers: common ones are cyanobacterianitrifying bacteria, can combine inorganic matter into organic matter, autotrophic.Consumers: commonShigellaandEscherichia coli, parasitic in the human digestive tract, heterotrophic.Decomposer: Prokaryote living in saprophytic life, such asBacillus subtilis。
Common types
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fromProkaryotic cellThe organisms formed are called prokaryotes, which include six categories: bacteria, cyanobacteria, actinomycetes, mycoplasma, chlamydiaRickettsia。
There are three basic forms of bacteria: cocci, bacilli, and spirochetes (including spirochetes and vibrio). Common forms include Escherichia coliBacillus anthracis, Bacillus subtilisDiplococcus pneumoniae、Vibrio cholerae、Mycobacterium tuberculosis, lactic acid bacteria, nitrogen fixing bacteria (rhizobia), sulfur bacteria, iron bacteria, nitrifying bacteria, etc.
The common cyanobacteria are colored coccobacteria, moniliflora, quivering algae and spirulina.[1]
Relationship with human beings
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Prokaryotes are closely related to humans.imageEscherichia coliMost of them are beneficial to human beings. For example, coliform bacteria in the intestines can produce a small amount of vitamins, lactic acid bacteria in the intestines can inhibit the propagation of harmful bacteria, and actinomycetes in the soil can extract vitamins.However, there are also some pathogenic microorganisms in prokaryotes, such as Bacillus anthracis (anthrax), Vibrio cholerae (cholera), tuberculosis bacillus (tuberculosis)Staphylococcus aureus（food poisoning）、Botulinum(Food poisoning), chlamydia (trachoma), etc. are harmful to human beings.[1]
