Major Divisions Of Life

Prokaryotic, unicellular organisms; three major types or forms, including spherical coccus, rod-shaped bacillus and spiral-shaped spirillum forms; many pathogenic as well as beneficial species; studied in bacteriology and microbiology courses; grow practically everywhere, including your mouth and digestive tract, the root nodules of legumes and the sun-baked boulders of arid deserts; the latter bacteria are responsible for microscopic layers of iron and manganese oxide on boulders known as desert varnish.

Nitrogen fixation is a remarkable prokaryotic skill in which inert atmospheric nitrogen gas is converted into ammonia. Through another bacterial process called nitrification, the ammonia is converted into nitrites and nitrates, thereby making the vital element nitrogen readily available to the roots of higher plants. Since this process commonly occurs in the root nodules of legumes, farmers often rotate their crops with leguminous species (such as alfalfa and clover). The economic importance of legumes and root nodules is astonishing. For example, the average annual crop of clover seed in Ohio (250,000 bushels) will plant approximately 3 million acres in clover. This acreage would yield about 4.5 million tons of hay (worth about $90 million). Because of nitrogen fixation in the root nodules of clover, about 273 million pounds of nitrogen is added to the soil (worth about $50 million annually). Nitrogen fixation is also accomplished by a number of species of microscopic cyanobacteria, some of which live symbiotically in nonleguminous plants, including the leaves of water fern (Azolla) and the roots of cycads. The actual sites of nitrogen fixation in the cyanobacteria are special cells called heterocysts. The roots of alder trees (Alnus), wax myrtle (Myrica) and California lilac (Ceanothus) contain nitrogen-fixing actinomycetes rather than eubacteria. Nodules of the actinomycete Frankia on alder roots greatly resemble the Rhizobium nodules of legumes.

The fowing explanation is from Jim Deacon of the Institute of Cell and Molecular Biology, The University of Edinburgh.

Two molecules of ammonia are produced from one molecule of nitrogen gas. The reaction requires 16 molecules of ATP and a supply of electrons and protons (hydrogen ions) plus the enzyme nitrogenase. Nitrogenase consists of two proteins, an iron protein and a molybdenum-iron protein. The reaction occurs while N2 is bound to the nitogenase enzyme complex. The Fe protein is first reduced by electrons donated by ferredoxin. Then the reduced Fe protein binds ATP and reduces the molybdenum-iron protein, which donates electrons to N2, producing HN=NH. In two futher cycles of this process (each requiring electrons donated by ferredoxin) HN=NH is reduced to H2N-NH2, and this in turn is reduced to 2 NH3. Depending on the type of microorganism, the reduced ferredoxin which supplies electrons for this process in generated by photosynthesis, respiration or fermentation.

Actinomycetes include a large group of filamentous, fungus-like soil bacteria. They form long, threadlike, branched filaments that resemble gray spiderwebs throughout compost piles. In fact, the characteristic earthy smell of compost and recently overturned rotten logs in a forest is caused by thriving populations of actinomycetes. Electron microscopy and other studies have shown unequivocally that these organisms are bacteria and not fungi. Some authors refer to actinomycetes as actinobacteria and place them in their own phylum.

Note: Although most of the bacteria in this division Eubacteriophyta are heterotrophic, there are some autotrophic species which produce ATP and glucose by oxidizing chemicals in their environment (chemosynthesis) or by utilizing light energy in thylakoid membranes (photosynthesis). Some of the photosynthetic species have pigments similar to chlorophyll a in higher plants, but they do not produce oxygen as a by-product of photosynthesis. The photosynthetic Eubacteriophyta include purple sulphur bacteria, purple nonsulphur bacteria, green sulphur bacteria and prochlorobacteria. The prochlorobacteria are quite distinct from other members of the Eubacteriophyta because they possess both chlorophylls a and b of higher plants. The prochlorobacteria also produce oxygen like the Division Cyanophyta, but unlike the cyanobacteria they do not have phycobilin accessary pigments. [It should be noted here that some biologists place the prochlorobacteria in the Division Cyanophyta.]

There are numerous pathogenic forms of bacteria that live parasitically inside a living host. They are spread by airborne spores, contaminated foods and body fluids. The sciences of bacteriology and microbiology are concerned with the study of these organisms. The following images show three serious infectious bacteria, anthrax, gonorrhea and syphilis. Anthrax (Bacillus anthacis) is one of the microorganisms used in biological warfare because strains have been developed that are extremely infectious through the skin and through inhalation. In addition, it forms highly resistant spores that can survive for long periods. Approximately one teaspoon or two grams of anthrax may contain up to 20 billion spores. With an average infection rate of 10,000 spores per person, this is theoretically enough spores to infect 2 million people with inhalation anthrax.

Gonorrhea and syphilis are venereal diseases that are spread through sexual contact. Gonorrhea is caused by the bacterium Neisseria gonorrhoeae. Although rarely fatal, gonorrhea is a potentially serious infection of the urogenital system. A sample of pus from the infection can be placed on a microscope slide and stained to reveal masses of white blood cells and minute diplococcus bacteria (resembling minute paired dots). Syphilis is caused by the spiral-shaped (spirochaete) bacterium Treponema pallidum. The disease has three main stages which are typically separated by latent (dormant) periods during which the infected person may think the disease has vanished. In the initial stage, an ulcerated sore (called a chancre) appears in the genital area. In the secondary stage, a rash appears all over the body, even on the palms of the hands and soles of the feet. During the tertiary stage, the bacteria invade other organs of the body, such as the heart, liver and nervous system, the effects of which are devastating to the host. Long term effects of tertiary syphilis may include blindness, difficulty walking, insanity and eventually death. If detected early, both gonorrhea and syphilis can be treated with antibiotics; however, as with other bacteria, new resistant strains are constantly developing.

Six other sexually transmitted diseases in humans are: (1) Chlamydia caused by the bacterium Chlamydia trachomatis; (2) Vaginitis caused by the flagellated protozoan Trichomonas vaginalis. Vaginitis may also be caused by increased populations of yeast fungus (Candida albicans) that comprise the vaginal flora; (3) Hepatitis B and C caused by hepatitis viral strains B and C. Hepatitis A is generally acquired from contaminated food but may be transmitted sexually; (4) Genital Herpes caused by the herpes simplex virus type 2. Herpes simplex virus type 1 causes cold sores and fever blisters; (5) Genital Warts caused by the human papillomaviruses (HPVs). Genital warts are associated with cancer of the cervix and other urogenital tumors; and (6) AIDS (Acquired Immunodeficiency Syndrome) caused by the human immunodeficiency virus (HIV).

Prokaryotic filaments or gelatinous colonies of photosynthetic cells; produce the blue phycocyanin and red phycoerythrin phycobilin pigments; not always blue-green as in the coloration of the Red Sea by Trichodesmium erythraeum; referred to as "blue-green algae" in some references; cyanobacteria live in some of the most bizarre places on earth, including the trunks of trees and the roots of cycads; they also form a thin, black layer on the limestone blocks of Maya pyramids in Central America; cyanobacteria include some of the oldest life forms on earth and produce stromatolite fossils in limestone over 2 billion years old.

Note: The photosynthetic cyanobacteria contain chlorophyll a in their thylakoid membranes. Chlorophyll a is also present in thylakoid membranes within chloroplasts of higher plants. These bacteria also produce oxygen as a by-product of photosynthesis. In fact, a photosynthetic cell from a cyanobacterium is reminescent of a chloroplast, and some biologists believe that chloroplasts may have evolved from photosynthetic bacterial cells. This tentative explanation for the origin of chloroplasts is known as the Endosymbiont Hypothesis. Cyanobacteria also contain blue phycocyanin and red phycoerythrin pigments. Phycocyanin and phycoerythrin are accessary pigments called phycobillins which are also found in the red algae (Division Rhodophyta). Except for the prochlorobacteria, other bacteria in the Division Eubacteriophyta capable of carrying on photosynthesis do not produce oxygen and they do not have chlorophyll a. The prochlorobacteria have both chlorophyll a and chlorophyll b of higher plants, but do not have the phycobilins of the cyanobacteria. Because of their chemistry cell structure, they are probably the best candidates for precursors of chloroplasts. These remarkable green bacteria were discovered on marine invertebrates called sea squirts (Phylum Chordata) by Dr. Ralph Lewin of Scripps Institute of Oceanography in La Jolla, California.

Prokaryotic cells that are genetically quite distinct from the eubacteria; include methanogens (methane-producers), extreme halophiles and extreme thermophiles; live in some of the most extreme and inhospitable places on earth; may also live on the surface of Mars.

Note: The halobacteria have a unique photosynthetic pigment in their membranes but they do not produce oxygen. Like photosynthetic plants, the halobacteria produce their own ATP; but unlike green plants, they utilize bacteriorhodopsin instead of chlorophyll. The exact mechanism of ATP production is complicated and beyond the scope of this article, but it involves a "proton pump" across their cell membrane similar to the chemiosmotic mechanism for ATP synthesis in the chloroplasts and mitochondria of eukaryotic cells in higher organisms. Positively-charged hydrogen ions (protons), forced to one side of the membrane, flow back through special channels (pores) in the membrane as ATP (adenosine triphosphate) is enzymatically produced from ADP (adenosine diphosphate) and P (phosphate). These bacteria are especially interesting because the chemiosmotic mechanism for generating ATP does not require an electron transport system as in other photosynthetic bacteria and higher plants. Strains of these amazing bacteria have also been shown to survive anaerobically without free atmospheric oxygen while deeply embedded in thick salt crust. Bacteriorhodopsin is remarkably similar to the light sensitive pigment (rhodopsin) in the rod cells of human eyes which enables us to see in dim light. Thus, when we enter a dimly lighted room, it takes about 30 minutes for our eyes to adjust fully as the rhodopsin gradually increases in concentration. Of course, a flash of light can instantaneously break down your rhodopsin level, much to the chagrin of star-gazers who have become accustomed to the darkness.

In recent years, the traditional 5-kingdom system of classification has been challenged by authorities. Data from DNA and RNA comparisons indicate that archaebacteria are so different that they should not even be called a type of bacteria. Systematists have devised a classification level higher than a kingdom, called a domain or "superkingdom," to accomodate the archaebacteria. These remarkable organisms are now placed in the domain Archaea. Other prokaryotes, including eubacteria and cyanobacteria, are placed in the domain Bacteria. All the kingdoms of eukaryotes, including Protista (Protoctista), Fungi, Plantae and Animalia, are placed in the domain Eukarya. The large molecular differences between the majority of prokaryotes in the kingdom Monera and the archaebacteria warrants a separation based on categories above the level of kingdom. In other words, the differences between the true bacteria and archaebacteria are more significant than the differences between kingdoms of eukaryotes. The 3-domain system of classification is shown in the following table:

The kingdom Protista includes a diverse array of organisms, from minute flagellated cells to macroscopic kelp. The smallest microscopic organisms are termed protists, consequently some biologists prefer to call this kingdom the Protoctista rather than Protista. All members of this vast phylum have nucleated cells and live in aquatic habitats (freshwater and marine). According to Lynn Margulis, K.V. Schwartz and M. Dolan (1994), the cells of all Protoctista originally formed by bacterial symbioses (symbiogenesis).

Members of the kingdom Protoctista are not animals, which develop from an embryo called a blastula; they are not plants, which develop from an embryo that is not a blastula but is retained in the mother's tissue; they are not fungi which develop from spores and lack cilia and flagella (called undulipodia) at all stages of development; they are not monerans, which have prokaryotic cells. Fossil protoctists, with thick-walled resting stages or cysts, can be extracted from shale treated with hydroflouric acid. One of the richest sources of bizarre fossil protoctists was discovered in southern Australia during the late 1950s. Known as the Ediacaran biota, these deposits date back 600 million years ago. Some of these ancient protoctists may have been ancestral to certain animal and plant phyla. In fact, some flattened protoctists discovered in the Ediacaran biota had characteristics resembling lichens. [Lichens are organisms resulting from genetic mergers betweeen protists and fungi.] All the Ediacaran biota became extinct by about 530 million years ago and were replaced be shelled Cambrian animals.

Some general biology textbook authors place the microscopic, unicellular green algae (Division Chlorophyta) in the Kingdom Protista, and place the larger, multicellular (macroscopic) green algae (Division Chlorophyta) in the Kingdom Plantae. They also place the macroscopic, multicellular brown algae (Division Phaeophyta) and red algae (Division Rhodophyta) in the Kingdom Plantae. In fact, some authors place all of the algae divisions in the Kingdom Plantae. Although the Kingdom Protista includes mostly unicellular organisms, the Wayne's Word staff feels that these algal divisions belong in the Kingdom Protista (Protoctista) rather than the Kingdom Plantae.

Many different forms including unicellular (non-motile and flagellate), filamentous, and macroscopic (sea lettuce); common in fresh water and marine environments; not always green in color, e.g. bright red snow algae (Chlamydomonas nivalis) and orange Trentepohlia on trunks of Monterey cypress; also includes extreme halophilic species (Dunaliella and Dangeardinella) and the most common photobiont (autotrophic symbiont) found in lichens (e.g. Trebouxia); unicellular green algae also grow inside the hollow hairs of polar bears, giving their fur a greenish tinge; the term zoochlorellae refer to several species of symbiotic green algae of the division Chlorophyta; along the Pacific coast of North America, zoochlorellae produce the pale greenish color in sea anemone tentacles.

Includes macroscopic seaweeds or kelps (e.g. Macrocystis, Pelagophycus and Laminaria); harvested for the natural polysaccharide gums algin and laminaran; contain the pigment fucoxanthin.

Flagellated cells with conspicuous transverse groove; occur in blooms causing red tide and bioluminescence in ocean water; a wide variety of marine invertebrates, including sponges, jellyfish, sea anemones, corals, gastropods and turbellarians harbor within them golden spherical cells termed zooxanthellae; the photosynthetic activity of these symbiotic algal cells is vital to the survival of the individual coral animals and to the entire reef ecosystem; the zooxanthellae include several species of unicellular algae in the order Zooxanthellales within the algal division Pyrrophyta (also spelled Pyrrhophyta).

Cells with ornamented silica valves which fit together like a microscopic Petri dish; along with the dinoflagellates an extremely important member of the ocean food chain and estimated to produce more than 70% of the earth's atmospheric oxygen.

Contain the red pigment phycoerythrin and able to photosynthesize in deep waters of the euphotic zone; many beautiful macroscopic species; do not have centrioles or flagella; some species form bulk of algal reefs.

No true cell wall; cells animal-like and classified as flagellate protozoan by some zoologists; some species contain contractile vacuoles to expel water and exhibit cell-engulfing (phagocytosis).

Interesting macroscopic algae with prominent sex organs; found in fresh water ponds throughout San Diego County, California; sometimes placed in the Division Chlorophyta along with the green algae.

Note: The following two divisions Myomycota (slime molds) and Oomycota (water molds) are now placed in the kingdom Protista (Protoctista), although they are classified with the kingdom Fungi in older references. These divisions all produce motile cells (including swarm cells and zoospores) during some stage of their life cycles. Another division called Acrasiomycota (cellular slime molds) is also placed in the Protista. True fungi typically do not have eukaryotic 9 + 2 flagella (called undulipodia) at any stage in their life cycles. These classification systems are constantly changing, especially with new information from comparative DNA studies.

Very unusual organisms characterized by a multinucleate mass (blob) of protoplasm that moves in amoeboid fashion on wet logs and the forest floor; at a certain phase in its life cycle the plasmodium forms spore-bearing fruiting bodies; on several occasions, slime molds grown by Dr. George Zabka in the Palomar College botany lab have actually crawled out of their culture dish.

Nonseptate, coenocytic hyphae with sexual phase quite different from black bread mold (Zygomycota); forming cottony filaments on various substrates in water, including the gills of unfortunate fish; major nuisance when cultivating duckweeds in containers of water; the Oomycota were once classified as fungi because of their filamentous growth and heterotrophic mode of nutrition; their cell wall is not composed of chitin, as in fungi, but is made up of a mixture of cellulosic compounds and glycan; the nuclei in their filaments are diploid, with two sets of genetic information (chromosomes), not haploid as in the fungi.

Some members of the Kingdom Fungi (in the fungal classes Ascomycetes and Basidiomycetes) are associated with algal cells of the Kingdom Protista (in the algal division Chlorophtya) and/or prokaryotic cyanobacteria of the Kingdom Monera. This complex symbiotic, mutualistic relationship is called lichen. Lichens are essentially lichenized fungi containing unicellular monerans and/or protists.

Coenocytic hyphae composed of multinucleate, nonseptate filaments; produces stalked sporangia which are very conspicuous in the ubiquitous black bread mold (Rhizopus nigricans).

Spores produced in a sac-like structure called an ascus; includes cup fungi, yeast, leaf-curl fungi and truffles; also includes many lichenized fungi called lichens.

Spores produced on a club-shaped structure called a basidium; includes smut fungi, mushrooms, toadstools, puffballs and bracket fungi; some species contain toxic and hallucinogenic alkaloids; the mycelia of many species form an intricate symbiotic, mycorrhizal relationship with the roots of forest trees.

This class contains fungal species in which the sexual cycle is not fully understood; therefore, it is difficult to place them in a definite fungal class. It includes many unusual and interesting species, including parasitic and carnivorous fungi, and the amazing subterranean fungus gardens that leaf-cutter ants feed upon. Traditionally, deuteromycetes have been called the "Fungi Imperfecti" because they do not form sexual structures; therefore they are not complete or perfect. This large group of fungi includes the antibiotic producer Penicillium; Aspergillus, the fermenter used in making soy sauce and also the fungus responsible for aspergillosis, a form of pneumonia; Candida albicans, the cause of a common vaginal infection; and Trichophyton, which lives in skin infected with athlete's foot and groins afflicted with jockstrap itch. Also in the class Deuteromycetes are the fungi responsible for cryptococcosis and histoplasmosis in immunosuppressed humans, and the dreaded Rhizocotonia, a soil-dwelling fungus causing root rot in plants.

Note: The genus Aspergillus belongs to the fungal division Ascomycota. Members of this division have a unique sexual cycle in which nonmotile ascospores are produced within a saclike structure called an ascus. Complete sexual cycles with ascospores have not been found in all Aspergillus species. For this reason, they were once placed in the artificial fungal division Deuteromycota. DNA analysis has shown that they belong to the monophyletic division Ascomycota and all trace back to a common ancestor.

• David Ellis, Stephen Davis, Helen Alexiou, Rosemary Handke, and Robyn Bartley. 2007. Descriptions of Medical Fungi (Second Edition). Mycology Unit. Woman and Children's Hospital. School of Molecular & Biomedical Science, University of Adelaide, Australia. Available As A PDF Online.

This group includes fungi containing symbiotic algal cells (usually Division Chlorophyta) and/or cyanobacteria (Division Cyanophyta). Since they are essentially lichenized fungi containing symbiotic algal or cyanobacteria cells, they are best treated within the fungal classes Ascomycetes and Basiodiomycetes. By far the greatest number of lichen species belong to orders and families within the Ascomycetes.

Many species in the Kingdom Fungi are very important to people. In addition to all the delectable mushrooms, truffles and morels, there are some economically important fungi that have played a major role in the treatment of diseases. The antibiotic penicillin was discovered by the British scientist Sir Alexander Fleming in 1929. He noticed that certain bacteria would not grow in the vicinity of cultures of Penicillium mold. The discovery and eventual isolation of the drug penicillin from this common blue mold has led to the treatment of many human diseases and has saved countless lives. Penicillium molds (including P. roqueforti and P. camemberti) are also used to produce "smelly" cheeses, such as the blue, Roquefort and Camembert cheeses on your salads and spaghetti.

Aspergillus is another genus of mold that is closely related to Penicillium. Both economically important genera belong to the widely distributed family Aspergillaceae (also listed as Eurotiaceae in some references). This family is often placed in the Ascomycetes, although many authors place them in the Deuteromycetes because their complete sexual cycle is not known. Species of Aspergillus mold produce gallic acid used in photographic developers, dyes, and indelible black ink. [Gallic acid was originally extracted from oak galls.] Other species produce artificial flavorings, perfumes, chlorine and alcohols, and are used in the manufacture of plastics, toothpaste and soap. One interesting species of Aspergillus oryzae is used to make soy sauce by fermenting soybeans with the fungus. It is also used in the fermentation of rice to make sake. A Japanese food paste called "miso" is made by fermenting soybeans, salt and rice with the same mold. Miso is used in a number of Japanese dishes, including miso soup. According to K.R. Stern (Plant Biology, Fifth Edition, 1991), more than one-half million tons of miso are consumed annually.

Another very important family of fungi is the Saccharomycetaceae which includes nutritional food yeast (Kluyveromyces marxianus), beer, wine and bread yeast (Saccharomyces cerevisiae), and sherry yeast (Torulaspora delbrueckii). These microscopic fungi play a major role in the beer, wine and baking industries. In the brewery, ethyl alcohol (ethanol) from the fermentation process is the primary industrial product; in the bakery, carbon dioxide released from the fermentation process causes the dough to rise.

Mosses have minute "leaves" and stalks bearing a terminal capsule (sporangium) containing spores; moss sex organs (male antheridia and female archegonia) are typically produced on the leafy gametophytes of separate male and female plants; liverworts have a dorsi-ventrally flattened thallus with tiny palmlike stalks bearing male and female sex organs; the gametophyte thallus of some species also bears small, cuplike structures called gemmae cups; the cups contain lens-shaped buds called gemmae which can grow asexually into new thallus plants; there are aquatic and terrestrial forms of mosses and liverworts, some of which have a flattened, thallus that superficially resembles certain forms of green algae; these fascinating little nonvascular embryophytes are often subdivided into two separate divisions.

Primitive leafless vascular plants bearing 3-lobed sporangia on branches; includes the unusual wisk fern (Psilotum nudum; plants such as this (including treelike forms as tall as telephone poles) were abundant in ancient swamplands 300 million years ago.

Minute "true" leaves superficially resembling a moss; terminal, stalked spore-bearing strobilus in Lycopodium; in Selaginella male and female sporangia are produced in the leaf axils; also includes the bizarre quillworts (Isoetes); many fossil forms (some tree-like) dating back 300 million years ago; Lycopodium spores used for dust explosion demonstrations, and were used for flash powder prior to flash bulbs and strobe lights.

Primitive vascular plant group of the Carboniferous Period (300 million years ago) with jointed stems, whorls of tiny scale-like leaves at the nodes, and a terminal spore cone (strobilus); some species with dense branches at nodes, apparently resembling a bushy horse's tail to some botanists; also called "scouring rushes" because the silica-impregnated stems were used to clean pots and pans; many fossils, including tree-like forms dating back 300 million years ago; the present-day genus Equisetum is a living fossil with several species that are the only living representatives of this ancient group of vascular plants.

Leaves (fronds) with sporangia clusters (sori) on the underside; fronds arising from subterranean, creeping rhizomes and from trunks of tree-like forms (called tree ferns); includes the orders Filicales (true ferns Adiantum, Pteridium, Dryopteris, Polypodium, Polystichum, Pellaea, etc.), Marsileales (clover-leaf ferns Marselia and pillworts Pillularia), Ophioglossales (adder's tongue fern Ophioglossum), and Salviniales (water ferns Azolla and Salvinia). Sometimes these latter "ferns" are called "fern allies" because they belong to different orders; i.e. they do not belong to the order Filicales (the order of true ferns).

Palm-like plants with large seed and pollen cones; flourished during the days of the dinosaurs and undoubtedly were a major food supply for herbivorous dinosaurs; cycads were so numerous in Mesozoic times that this era is often called the Age of Cycads and Dinosaurs; cycads are dioecious species with pollen cones and seed cones produced on separate male and female individuals; in some species, the enormous pollen and seed cones may reach 3 feet in length and may weigh up to 90 pounds, the largest of all living cone-bearing plants.

Seeds borne in pairs on dwarf shoots; leaves similar in shape to the maidenhair fern (Adiantum); a true living fossil dating back 185 million years; only one living representative Ginkgo biloba.

A remarkable plant division including Ephedra, Gnetum and Welwitschia; stems of Ephedra are jointed with small scale-like leaves at the nodes; the bizarre, shredded, wind-blown leaves of Welwitschia arise from a woody caudex on the desert floor; this division includes species with vessels and other characteristics typically found in flowering plants.

Seeds borne on the surface of woody scales, the overlapping scales forming a cone; includes pine (Pinus), fir (Abies), spruce (Picea), hemlock (Tsuga), larch (Larix), juniper (Juniperus), and cypress (Cupressus); also includes the tallest (redwood) and most massive (giant sequoia) living organisms; some species (especially pines) require fire for seed germination and regeneration.

Multicellular animals not usually included in botany courses; without cell walls and without photosynthetic pigments, forming diploid blastula; there are more than one million species of animals in at least 30 phyla, more species than all the other kingdoms combined; more than half of all animal species are insects (800,000 species), and beetles (300,000 species) comprise the largest order of insects (one fifth of all species based on a total of 1.5 million); if all the species of plants and animals on earth were lined up at random, every 5th species would be a beetle.