All living things can be grouped into five categories. This is called the five kingdom proposal and was introduced by Robert Whittaker in 1968 as a way to categorise all organisms.
Living organisms are divided into five kingdoms:
- Prokaryotae
- Protoctista
- Fungi
- Plantae
- Animalia
Prokaryotae
- Unicellular and Microscopic.
- Non-membrane bound (no nuclear membrane, no ER, no mitochondia).
- Cell wall made of murein.
- Examples: Bacteria or Cyanobacteria (photosynthesising bacteria).
Protoctista
- Mainly small eukaryotic organisms.
- Many live in aquatic environments.
- This is usually the kingdom where organisms which aren’t animals, plants or fungi go.
- Examples: Algae, slime moulds and the malaria causing Plasmodium.
Fungi
- Eukaryotic
- Multicellular
- Cell wall made of chitin.
- The members of this kingdom don’t possess photosynthetic pigments and are therefore heterotrophic.
- Examples: Mushroom, Mold, Puffball
Plantae
- Eukaryotic
- Multicellular
- Cell wall made of cellulose.
- Members of the plantae group contain photosynthetic pigment and gain their energy through it and are therefore autotrophic.
Animalia
- Eukaryotic
- Multicellular
- Heterotropic
- The members of this kingdom can be split into two groups, vertebrates and invertebrates. The diagram below shows the different subsections of the animalia
| Kingdom | Number of Cells | Type of Cells | How they gain their energy? | Do they move? | Examples |
|---|---|---|---|---|---|
| Prokaryotae | Unicellular | Prokaryotic | Some Heterotrophic, Some Autotrophic | Some | Bacteria, Cyanobacteria |
| Protoctista | Mainly Unicellular | Eukaryotic | Some Heterotrophic, Some Autotrophic | Some | Amoeba |
| Fungi | Multicellular | Eukaryotic | Heterotrophic | Mainly not | Mushroom, Mold, Puffball |
| Plantae | Multicellular | Eukaryotic | Autotrophic | No | Trees, Flowering Plants |
| Animalia | Multicellular | Eukaryotic | Heterotrophic | Yes | Bird, Human, Cow |
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The Three Domain System, developed by Carl Woese in 1990, is a system for classifying biological organisms.
Before Woese's discovery of archaea as distinct from bacteria in 1977, scientists believed there were only two types of life: eukarya and bacteria.
The highest ranking previously used had been "kingdom," based on the Five Kingdom system adopted in the late 1960s. This classification system model is based on principles developed by Swedish scientist Carolus Linnaeus, whose hierarchical system groups organisms based on common physical characteristics.
The Current System
As scientists learn more about organisms, classification systems change. Genetic sequencing has given researchers a whole new way of analyzing relationships between organisms.
Under this system, organisms are classified into three domains and six kingdoms. The domains are
- Archaea
- Bacteria
- Eukarya
The kingdoms are
- Archaebacteria (ancient bacteria)
- Eubacteria (true bacteria)
- Protista
- Fungi
- Plantae
- Animalia
Archaea Domain
Like bacteria, archaea are prokaryotic organisms and do not have a membrane-bound nucleus. They also lack internal cell organelles and many are about the same size as and similar in shape to bacteria. Archaea reproduce by binary fission, have one circular chromosome, and use flagella to move around in their environment as do bacteria.
Archaea are extreme organisms that live under some of the most extreme environmental conditions. This includes within hydrothermal vents, acidic springs, and under Arctic ice. Archaea are divided into three main phyla: Crenarchaeota, Euryarchaeota, and Korarchaeota.
- Crenarchaeota include many organisms that are hyperthermophiles and thermoacidophiles. These archaea thrive in environments with great temperature extremes (hyperthermophiles) and in extremely hot and acidic environments (thermoacidophiles.)
- Archaea known as methanogens are of the Euryarchaeota phylum. They produce methane as a byproduct of metabolism and require an oxygen-free environment.
- Little is known about Korarchaeota archaea as few species have been found living in places such as hot springs, hydrothermal vents, and obsidian pools.
Bacteria Domain
Bacteria are classified under the Bacteria Domain. These organisms are generally feared because some are pathogenic and capable of causing disease.
However, bacteria are essential to life as some are part of the human microbiota. These bacteria preform vital functions, such as enabling us to properly digest and absorb nutrients from the foods we eat. Bacteria that live on the skin prevent pathogenic microbes from colonizing the area and also aid in the activation of the immune system.
Bacteria are also important for the recycling of nutrients in the global ecosystem as they are primary decomposers.
Bacteria have a unique cell wall composition and rRNA type. They are grouped into five main categories:
- Proteobacteria: This phylum contains the largest group of bacteria and includes E.coli, Salmonella, Heliobacter pylori, and Vibrio. bacteria.
- Cyanobacteria: These bacteria are capable of photosynthesis. They are also known as blue-green algae because of their color.
- Firmicutes: These gram-positive bacteria include Clostridium, Bacillus, and mycoplasmas (bacteria without cell walls.)
- Chlamydiae: These parasitic bacteria reproduce inside their host's cells. Organisms include Chlamydia trachomatis (causes chlamydia STD) and Chlamydophila pneumoniae (causes pneumonia.)
- Spirochetes: These corkscrew-shaped bacteria exhibit a unique twisting motion. Examples include Borrelia burgdorferi (cause Lyme disease) and Treponema pallidum (cause syphilis.)
Eukarya Domain
The Eukarya domain includes eukaryotes or organisms that have a membrane-bound nucleus.
This domain is further subdivided into the kingdoms
- Protista
- Fungi
- Plantae
- Animalia
Eukaryotes have rRNA that is distinct from bacteria and archaeans. Plant and fungiorganisms contain cell walls that are different in composition than bacteria. Eukaryotic cells are typically resistant to antibacterial antibiotics.
Organisms in this domain include protists, fungi, plants, and animals. Examples include algae, amoeba, fungi, molds, yeast, ferns, mosses, flowering plants, sponges, insects, and mammals.
Comparison of Classification Systems
Systems for classifying organisms change with new discoveries made over time. The earliest systems recognized only two kingdoms (plant and animal.) The current Three Domain System is the best organizational system we have now, but as new information is gained, a different system for classifying organisms may later be developed.
Here is how the Five Kingdom System compares to the Three Domain System, which has six kingdoms:
Five Kingdom System:
- Monera
- Protista
- Fungi
- Plantae
- Animalia
| Archaea Domain | Bacteria Domain | Eukarya Domain |
| Archaebacteria Kingdom | Eubacteria Kingdom | Protista Kingdom |
| Fungi Kingdom | ||
| Plantae Kingdom | ||
| Animalia Kingdom |
The Five Kingdoms Of Life
The Amazing Diversity Of Living Systems
Living organisms are subdivided into 5 major kingdoms, including the Monera, the Protista (Protoctista), the Fungi, the Plantae, and the Animalia. Each kingdom is further subdivided into separate phyla or divisions. Generally "animals" are subdivided into phyla, while "plants" are subdivided into divisions. These subdivisions are analogous to subdirectories or folders on your hard drive. The basic characteristics of each kingdom and approximate number of species are summarized in the following table:
1. Kingdom Monera [10,000 species]: Unicellular and colonial--including the true bacteria (eubacteria) and cyanobacteria (blue-green algae). 2. Kingdom Protista (Protoctista) [250,000 species]: Unicellular protozoans and unicellular & multicellular (macroscopic) algae with 9 + 2 cilia and flagella (called undulipodia). 3. Kingdom Fungi [100,000 species]: Haploid and dikaryotic (binucleate) cells, multicellular, generally heterotrophic, without cilia and eukaryotic (9 + 2) flagella (undulipodia). 4. Kingdom Plantae [250,000 species]: Haplo-diploid life cycles, mostly autotrophic, retaining embryo within female sex organ on parent plant. 5. Kingdom Animalia [1,000,000 species]: Multicellular animals, without cell walls and without photosynthetic pigments, forming diploid blastula. |
| 1. The five-kingdom system of classification for living organisms, including the prokaryotic Monera and the eukaryotic Protista, Fungi, Plantae and Animalia is complicated by the discovery of archaebacteria. The prokaryotic Monera include three major divisions: The regular bacteria or eubacteria; the cyanobacteria (also called blue-green algae); and the archaebacteria. Lipids of archaebacterial cell membranes differ considerably from those of both prokaryotic and eukaryotic cells, as do the composition of their cell walls and the sequence of their ribosomal RNA subunits. In addition, recent studies have shown that archaebacterial RNA polymerases resemble the eukaryotic enzymes, not the eubacterial RNA polymerase.Archaebacteria also have introns in some genes, an advanced eukaryotic characteristic that was previously unknown among prokaryotes. In eukaryotic cells, the initial messenger RNA (M-RNA) transcribed from the DNA (gene) is modified (shortened) before it leaves the nucleus. Sections of the M-RNA strand called introns are removed, and the remaining portions called exons are spliced together to form a shortened (edited) strand of mature M-RNA that leaves the nucleus and travels to the ribosome for translation into protein. This process is known as "gene editing." Some authorities hypothesize that eukaryotic organisms may have evolved from ancient archaebacteria (archae = ancient) rather than from the common and cosmopolitan eubacteria. The archaebacteria could have flourished more than 3 billion years ago under conditions previously thought to be uninhabitable to all known life forms. Although many conservative references place the archaebacteria in a separate division within the kingdom Monera, most authorities now recognize them as a 6th kingdom--The kingdom Archaebacteria. In fact, data from DNA and RNA comparisons indicate that archaebacteria are so different that they should not even be classified with 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. Guillaume Lecointre and Hervé Le Guyader (2006) have published a remarkable book entitled The Tree of Life: A Phylogenetic Classification. The book includes the three major domains which are in turn subdivided into numerous branches (clades). An oversimplified 3-domain system of classification is shown in the following table. The number of subdivisions listed by G. Lecointre and H.L. Guyader for each domain are shown in parentheses.
5. There are more than one million species of animals (Kingdom Animalia), more 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--using a total of 1.5 million). In fact, if all the species of plants and animals on earth were lined up at random, every 5th species would be a beetle.
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The most morphologically and biochemically diverse, non-animal kingdom is the Plantae or Plant Kingdom. It is subdivided into the following 10 phyla or divisions. Note: These names vary considerably, depending on which botany reference you are using.
Categories Within The Kingdom Plantae
 Pteridophytes: Spores but no seeds
3. Division Lycophyta (club mosses). 4. Division Sphenophyta (horsetails). 5. Division Pterophyta (ferns). Spermatophytes: Seed Plants
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Each of the plant divisions in the above table are further subdivided into successively smaller and smaller subcategories. The complete hierarchal breakdown is Kingdom-Phylum (Division)-Class-Order-Family-Genus-Species. To remember this sequence, the following mnemonic device is often helpful:
Biological Organization
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Military Organization
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| Kingdom (one or more phyla) | Brigade (two or more regiments) |
| Phylum (one or more classes) | Regiment (two or more battalions) |
| Class (one or more orders) | Battalion (two or more companies) |
| Order (one or more families) | Company (two or more platoons) |
| Family (one or more genera) | Platoon (two or more squads) |
| Genus (one or more species) | Squad (a group of 12 soldiers) |
| Species (a distinct kind or unit) | Soldier (a distinct kind or unit) |
The following table compares the complete taxonomic hierarchy of a marine lichen of the rocky Pacific coast Verrucaria maura with the minute aquatic flowering plant Wolffia borealis:
| Kingdom | Fungi | Plantae |
| Phylum | Eumycota | Tracheophyta |
| Class | Ascomycetes | Angiospermae |
| Order | Pyrenulales | Arales |
| Family | Verrucariaceae | Lemnaceae |
| Genus | Verrucaria | Wolffia |
| Species | maura | borealis |
The plant kingdom includes nonvascular and vascular plants. Nonvascular plants lack a water-conducting system of tubular cells (called xylem tissue), and do not have true roots, stems and leaves. Like algae and fungi, the plant body of some nonvascular plants is often called a thallus. Nonvascular plants are all placed in the Division Bryophyta, including the mosses and liverworts. The vast majority of the plant kingdom are vascular, with tubular, water-conducting cells called xylem tissue. Like a microscopic pipeline system, they are arranged end-to-end from the roots to the leaves. Unlike nonvascular plants, they have true roots, stems and leaves. Some references place all the vascular plants in a separate phylum or division called the Tracheophyta. Most botanists now subdivide vascular plants into 9 divisions. More primitive vascular plants that reproduce by spores, but without seeds, are called pteridophytes, and include the 4 divisions Psilophyta (whisk ferns), Lycophyta (club mosses), Sphenophyta (horsetails), and Pterophyta (ferns). Seed-bearing vascular plants are called spermatophytes and include the primitive gymnosperms (with immature seeds or ovules naked and exposed directly to pollen) and the more advanced angiosperms (with ovules enclosed in an ovary that ripens into a fruit). Gymnosperms include the 4 divisions Cycadophyta (cycads), Ginkgophyta (maidenhair tree), Gnetophyta (mormon tea & the bizarre South African Welwitschia), and the Coniferophyta (conifers). The angiosperms are placed in the single division Anthophyta which includes all the flowering plants and 90 percent of all the plant kingdom.
See Diversity In Flowering Plants |
Twenty of the more than 100 species of Pinus on earth. All of these pines are native to the state of California, USA. 1. Monterey Pine (P. radiata), 2. Bishop Pine (P. muricata), 3. Santa Cruz Island Pine (P. remorata), 4. Whitebark Pine (P. albicaulis), 5. Limber Pine (P. flexilis), 6. Beach Pine (P. contorta), 7. Lodgepole Pine (P. murrayana), 8. Western White Pine (P. monticola), 9. Knobcone Pine (P. attenuata), 10. Bristlecone Pine (P. longaeva), 11. Foxtail Pine (P. balfouriana), 12. Four-Leaf Pinyon (P. quadrifolia), 13. Two-Leaf Pinyon (P. edulis), 14. One-Leaf Pinyon (P. monophylla), 15. Ponderosa Pine (P. ponderosa), 16. Coulter Pine (P. coulteri), 17. Digger Pine (P. sabiniana), 18. Torrey Pine (P. torreyana), 19. Jeffrey Pine (P. jeffreyi), 20. Sugar Pine (P. lambertiana).
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| According to R.M. Lanner (Conifers of California, 1999), there may be other significant changes in the pines of California. Allozyme studies in two-leaf pinyons (Pinus edulis) of the New York Mountains indicate that these populations are biochemically (and genetically) consistent with nearby one-leaf pinyon (Pinus monophylla), and that P. edulis may not occur in California. The unusual New York Mountains population appears to be a 2-needle variant of P. monophylla. The four-leaf or Parry pinyon of San Diego County (P. quadrifolia) may be a hybrid between P. monophylla and Sierra Juárez pinyon (P. juarezensis) of northern Baja California. According to Lanner, the latter species has five needles per fascicle and occurs in San Diego County. The hybrid hypothesis might explain the perplexing variation in needle number for P. quadrifolia, with clusters of three, four and five. |
| Foxtail pines (Pinus balfouriana) on the 11,000 ft (3353 m) slopes of Alta Peak. The 13,000 ft. (3962 m) crest of the Great Western Divide of the Sierra Nevada can be seen in the distance. |
Selection & Genetic Drift In California Cypress
Millions of years ago, cypress woodlands containing one or more ancestral species of the cone-bearing genus Cupressus once dominated vast areas of California. During the past 20 million years, as mountains were uplifted and the climate became increasingly more arid, most of these extensive cypress woodlands vanished from the landscape. In some areas, the cypress were probably unable to compete with more drought resistant, aggressive species, such as impenetrable chaparral shrubs and desert scrub. Although cypress are fire-adapted with serotinous seed cones that open after a fire, they are vulnerable if the fire interval occurs too frequently, before the trees are old enough to produce a sufficient cone crop. Chaparral shrubs quickly resprout after a fast-moving brush fire from well-established subterranean lignotubers. This may explain why some cypress groves occur in very rocky, sterile sites with poor soils where the chaparral shrubs can't compete as well.
Today this fascinating genus is represented by 10 species (or 8 species and 2 subspecies), confined to isolated groves scattered throughout the coastal and inland mountains, from the Mexican border to Oregon. Because some of these populations became isolated into "arboreal islands," gradual genetic changes over millions of years resulted in the present-day species and subspecies. This is somewhat analogous to the evolution of Darwin's finches on the Galapagos Islands. It is quite likely that natural selection played a role in cypress speciation. Cypress of arid inland mountains and valleys (such as Piute cypress, Macnab cypress, Cuyamaca cypress, and Arizona cypress) have glandular (resinous) foliage and are more drought resistant. Coastal species (such as Monterey cypress, Gowen cypress, Santa Cruz cypress and Mendocino cypress) are generally nonglandular without resin glands on the leaf surfaces. Some phenotypic variability, particularly between different isolated groves of the same species may be due (in part) to genetic drift. These differences include slight variations in foliage, bark characteristics (exfoliating vs. persistent), and the general shape of seed cones. These differences attributed to genetic drift are analogous to racial differences in people, such as different blood type percentages and facial characteristics.
The relatively short period of isolation for Cupressus (cypress) species may be one of the reasons taxonomists disagree on the total number of species native to North America. In 1948, Carl B. Wolf published his "Taxonomic and Distributional Studies of the New World Cypresses" (El Aliso 1: 1-250). Dr. Wolf listed a total of 15 species, one in Baja California, one on Guadalupe Island off the coast of Baja California, one in Mexico and Central America, two in Arizona, and 10 in California. In 1953, the number of U.S. species was reduced to six by Dr. Elbert Little, Jr. in his Check List of Native and Naturalized Trees of the United States (USDA Agriculture Handbook No. 41). These numbers have fluctuated greatly in subsequent publications. In addition, the nursery trade has added several cultivated varieties, including at least four different cultivars for the Arizona cypress.
New evidence from DNA sequencing has further complicated the number of cypress species, including the transfer of other conifer genera into the genus Cupressus. For example, the Jepson Manual of California Plants lists ten species; however, two of these C. nootkatensis (Alaska cedar) and C. lawsoniana (Port Orford cedar) were formerly placed in the genus Chamaecyparis. It is possible that some of the isolated species of Cupressus in California and Arizona have not been isolated long enough to warrant the status of a species. In fact, this is why most modern floras have consolidated four species into subspecies of the Arizona cypress (C. arizonica). These species have been isolated long enough for genetic drift to occur, but perhaps not long enough for the development of distinct species populations.
| Left: Seed cones of cypress (Cupressus) from groves in southern California. A. Tecate cypress (C. forbesii), B. Sargent cypress (C. sargentii), C. Piute cypress (C. nevadensis) [Syn. C. arizonica ssp. nevadensis], D. Cuyamaca cypress (C. stephensonii) [Syn. C. arizonica spp. stephensonii], E. Smooth-bark Arizona cypress (C. glabra) [Syn. C. arizonica ssp. glabra], F. Rough-bark Arizona cypress (C. arizonica) [Syn. C. arizonica ssp. arizonica]. Right: Seed cones of cypress from groves in central and northern California. G. Monterey cypress (C. macrocarpa), H. Gowen cypress (C. goveniana) [Syn. C. goveniana ssp. goveniana], I. Santa Cruz cypress (C. abramsiana), J. Sargent cypress (C. sargentii), K. Mendocino cypress (C. pygmaea) [Syn. C. goveniana ssp. pigmaea], L. Macnab cypress (C. macnabiana), M. Modoc cypress (C. bakeri). |
| Male (pollen) cones of the Piute cypress (Cupressus nevadensis) [syn. C. arizonica ssp. nevadensis). Each scalelike leaf bears a dorsal gland that exudes a resin droplet (red arrow). Interior cypress species such as this one typically have glaucous, resinous foliage, presumably an adaptation to dry, arid habitats. |
| A. Foliage and pollen cones of the Smooth-bark Arizona cypress (Cupressus glabra) [Syn. C. arizonica ssp. glabra]. B. Foliage of the Tecate cypress (C. forbesii). The scalelike leaves of Arizona cypress are glaucous and very glandular (sticky). The scalelike leaves of Tecate cypress are green and without dorsal resin glands. |
| Left: Monterey cypress (Cupressus macrocarpa) in Point Lobos State Park on the coast of central California. Right: Grove of Piute cypress (C. nevadensis) in the Piute Mountains, with Lake Isabella and the snow-covered Sierra Nevada in the distance. The Piute cypress are more drought resistant, with gray (glaucous), glandular (resinous) foliage similar to the Arizona cypress. In fact, some botanists now consider the Piute cypress to be a subspecies of the Arizona cypress and have named it C. arizonicassp. nevadensis. |
| A grove of Sargent cypress (Cupressus sargentii) in the San Rafael Mountains of Santa Barbara County, California. This species typically grows on outcrops of serpentine in the Coast Ranges of central and northern California. Serpentine is a shiny rock with a waxy luster and feel. It varies in color from creamy white and shades of green to black. In California, many species of rare and endangered plants are endemic to serpentine outcrops. Genetic drift has undoubtedly occured in isolated cypress groves such as this one, which are often referred to as "arboreal islands." |
Other Members Of The Division Coniferophyta
| Podocarpus gracilior, a member of the Podocarpaceae native to eastern Africa. Although it is sometimes called "fern pine" it does not belong to the genus (Pinus); however, like pines and other cone-bearing species, it does belong to the Division Coniferophyta. Minute female cones are composed of 2-4 reduced scales, but usually only one scale bears an ovule that matures into a seed. There is little resemblance to a cone in the mature seed. The seed has a hard coat surrounded by a fleshy outer layer (aril). The drupelike seed often sits on a fleshy red or purple base or cone axis that is called an aril in some references. The seeds are similar to the California nutmeg (Torreya californica) and Pacific yew (Taxus brevifolia), members of the closely-related Yew Family (Taxaceae). In the latter species, the naked seed sits partially exposed in a red, cup-shaped aril. Podocarpus seeds are often referred to as fleshy fruits called drupes, but this is incorrect because drupes develop from the ovaries of flowering plants. Another group of conifers with fleshy seed-bearing structures are the junipers (Juniperus) in the Cypress Family (Cupressaceae). Junipers actually produce small cones with fleshy, fused scales bearing one-several seeds. Podocarpus is a dioecious species, with separate male and female trees in the population. Podocarpus has an ancient lineage dating back to distant relatives that lived during the Jurassic Period 170 million years ago. |
| California nutmeg (Torreya californica), a member of the Division Coniferophyta, Order Taxales, Family Taxaceae. Like Podocarpus, the "naked" seed is enclosed in a fleshy, outer layer (called an aril) which superficially resembles a one-seeded fruit of an angiosperm. The name "nutmeg" is derived from its superficial resemblance to the fruit of the true nutmeg (Myristica fragrans). |
| Pacific yew (Taxus brevifolia), another member of the Division Coniferophyta, Order Taxales, Family Taxaceae that occurs in northern California, Oregon and Washington. Unlike the California nutmeg, the naked seed is not completely enclosed by the fleshy aril. Instead, the seed sits in a cup-shaped aril. Since this species is native to regions of the Pacific northwestern United States containing the timber tree Douglas fir (Pseudotsuga menziesii), it was once considered a weedy species when areas of the forest were logged. Luckily, the Pacific yew still survives because it is now considered to be an exceedingly valuable species. An extract from the bark (and needles) called taxol has been found to be a very effective treatment for ovarian and breast cancers. It is very important to preserve natural, old growth forests with a diversity of species, some of which may prove to be valuable medicines for the treatment of diseases. |
Santa Lucia Fir (Abies bracteata)
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| The Santa Lucia or bristlecone fir (Abies bracteata) has a tall, slender, steeple-like crown. Seed cones are produced near the top of the slender spire, and they are some of the most unusual cones of all cone-bearing trees on earth. Long, spine-like bracts extend outwardly from between the cone scales, and resemble the antennae of a space satellite. This uncommon and remarkable fir tree is endemic to steep, rocky slopes in the Santa Lucia Range of California's Coast Ranges. |
Santa Lucia fir (Abies bracteata), a remarkable California endemic.
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Using fossil evidence and computerized cladistic analyses, it is generally concluded that evolution in the plant kingdom proceeded from nonvascular, spore-bearing ancestors to vascular, seed-bearing, flowering plants, as more and more advanced morphological and biochemical traits gradually appeared along the geologic time scale. This is somewhat analogous to the evolution of Microsoft; however, unlike Microsoft, the phenomenal success of flowering plants is based on natural selection rather than timely, strategic decisions by brilliant top level executives such as Bill Gates.
References
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Scientific Classification
Biological Classification is the way scientists use to categorize and organize all of life. It can help to distinguish how similar or different living organisms are to each other. | An example of Classification Biological classification works a bit like the library does. Inside the library, books are divided up into certain areas: the kids books in one section, the adult books in another, and the teen books in another section. Within each of those sections, there will be more divisions like fiction, non-fiction. Within those sections there will be even more divisions such as mystery, science fiction, and romance novels in the fiction section. Finally you will get down to a single book. Biological classification works the same way. At the top there are the kingdoms. This is sort of like the adult section vs. the kids' section. The kingdoms divide up life into big groups like plants and animals. Under the kingdoms are more divisions which would be like fiction, non-fiction, mystery, etc. Finally, you get to the species, which is sort of like getting to the book in the library. 7 Major Levels of Classification There are seven major levels of classification: Kingdom, Phylum, Class, Order, Family, Genus, and Species. The two main kingdoms we think about are plants and animals. Scientists also list four other kingdoms including bacteria, archaebacteria, fungi, and protozoa. Sometimes an eighth level above the Kingdom called the Domain is used. Classification for Humans Here is an example of how humans are classified. You will see that our species is homo sapiens. Kingdom: Animalia Phylum: Chordata Class: Mammalia Order: Primates Family: Hominidae Genus: Homo Species: Homo sapiens |  |
Fun ways to Remember Biological Classification
A good way to remember lists is to make up a sentence using the first letters in a list. In this case we want to remember Kingdom, Phylum, Class, Order, Family, Genus, and Species: K, P, C, O, F, G, S
Here are some sentences:
- Kids Prefer Cheese Over Fried Green Spinach.
- Koalas Prefer Chocolate Or Fruit, Generally Speaking
- King Philip Came Over For Good Spaghetti
- Keeping Precious Creatures Organized For Grumpy Scientists
- Although the system of classification continues to be modified, Carolus Linnaeus, a Swedish plant scientist, is generally credited with inventing the current system.
- Animals with exoskeletons like insects and crabs are part of the Phylum Arthropoda and are often called arthropods.
- Under the Phylum Chordata we get the classes of animals many are familiar with such as mammals, amphibians, reptiles, fish and birds.
- A species is usually defined as individuals that can reproduce (have kids).
Cavalier-Smith's new classification scheme retained the plant, animal and fungal kingdoms from the traditional five kingdom model. It also split the kingdom Monera into the two groups, eubacteria and archaebacteria, as proposed by Woese and Fox.
Many protozoan’s are asymmetrical because they are not divisible into equivalent parts; a few show spherical symmetry.
The cnidarians and adult echinodems are usually radially symmetrical around a median axis through the mouth; planes through this axis will divide the animal into radial sectors (antimeres).
Members of most other phyla are bilaterally symmetrical; a lengthwise vertical (sagital) plane divides the animal into equal and opposite halves.
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In such animals the part that moves forward (and usually contains the mouth) is termed anterior; and the opposite end is posterioer; the back or upper surface is termed dorsal, and he under surface (usually toward the ground) is termed ventral (1.venter, belly). Structures on or toward the central longitudinal axis are termed medial, and those toward the sides are said to be lateral.
2. Segmentation:
In the annelids, arthropods, and chordates there is a linear repetition of body parts known as segmentation (metamerism); each repeated unit is a somite (metamere). In earth-worms the successive somites are essentially alike, but they are unlike in different body regions of a crayfish or insect. Metamerism is conspicuous both externally and internally in annelids, is mostly external with arthropods, and mainly internal in man and other chordates (vertebrae, body muscles, some blood vessels, and nerves).
3. Appendages:
Protruding parts that serve in locomotion, feeding, and other ways are termed appendages; examples are the tentacle of sea anemones, minute setae of earthworms, antennae and legs of arthropods, and the fins, legs, and wings of vertebrates.
4. Skeleton:
Most land dwellers and many aquatic animals have a skeleton for support or protection; it may be internal (frog, man, etc.) or external (coral, crab, insect) and may be of either inorganic or material.
5. Sex:
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An animal containing both female and male sex organs in one individual is termed monoecious (also hermaphroditic); members of most higher phyla are dicoecious, each individual being either male or female.
6. Embryonic development:
Cleavage of the egg is complete or holoblastic in many invertebrates, amphioxus, amphibians, and mammals. In eggs with much yolk, cleavage is incomplete or meroblastic, confined to a limited part as in squids, insects, many fishes, reptiles, and birds.
7. Larvae:
The young stages known as larvae often provide important information on relationships not evident in adult animals. Many have features obviously adapted to particular environments such as cilia for swimming. Their basic structure, however, is usually characteristic for each phylum or class. Barnacles and tunicates, for example, were first properly classified by study of their larvae.
Many aquatic invertebrates in the protostome line have a common type of larva- minute, transparent, and free-swimming. Often it is top shaped, and encircled by two lines of cilia that beat so as to suggest a rotating wheel, hence the name trochophore (Gr. Trochos, wheel + phoros, bear). The upper end has a plate with a tuft of cilia and a sense organ. With various modifications this is the early larva of many marine flatworms, nemerteans, mollusks, and some annelids.
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Cavalier-Smith's first major classification system was the division of all organisms into eight kingdoms. In 1981, he proposed that by completely revising Robert Whittaker's Five Kingdom system, there could be eight kingdoms: Bacteria, Eufungi, Ciliofungi, Animalia, Biliphyta, Viridiplantae, Cryptophyta, and Euglenozoa.[6]
In 1993, he revised his system particularly in the light of the general acceptance of Archaebacteria as separate group from Bacteria. In addition, some protists lacking mitochondria were discovered.[7] As mitochondria were known to be the result of the endosymbiosis of a proteobacterium, it was thought that these amitochondriate eukaryotes were primitively so, marking an important step in eukaryogenesis. As a result, these amitochondriate protists were separated from the protist kingdom, giving rise to the, at the same time, superkingdom and kingdom Archezoa. This was known as the Archezoa hypothesis. The eight kingdoms became: Eubacteria, Archaebacteria, Archezoa, Protozoa, Chromista, Plantae, Fungi, and Animalia.[8]
However, kingdom Archezoa is now defunct.[9] He now assigns former members of the kingdom Archezoa to the phylum Amoebozoa.[10]
Six kingdoms models
By 1998, Cavalier-Smith had reduced the total number of kingdoms from eight to six: Animalia, Protozoa, Fungi, Plantae (including Glaucophyte, red and green algae), Chromista and Bacteria.[11] Nevertheless, he had already presented this simplified scheme for the first time on his 1981 paper[6] and endorsed it in 1983.[12]
Table 11 From Eukaryote kingdoms: seven or nine?
Five of Cavalier-Smith's kingdoms are classified as eukaryotes as shown in the following scheme:
- Eubacteria
- Neomura
- Archaebacteria
- Eukaryotes
- Kingdom Protozoa
- Unikonts (heterotrophs)
- Kingdom Animalia
- Kingdom Fungi
- Bikonts (primarily photosynthetic)
- Kingdom Plantae (including red and green algae)
- Kingdom Chromista
The kingdom Animalia was divided into four subkingdoms: Radiata (phyla Porifera, Cnidaria, Placozoa, and Ctenophora), Myxozoa, Mesozoa, and Bilateria (all other animal phyla).
He created three new animal phyla: Acanthognatha (rotifers, acanthocephalans, gastrotrichs, and gnathostomulids), Brachiozoa (brachiopodsand phoronids), and Lobopoda (onychophorans and tardigrades) and recognised a total of 23 animal phyla.[11]
Cavalier-Smith's 2003 classification scheme:[13]
- Unikonts
- protozoan phylum Amoebozoa (ancestrally uniciliate)
- opisthokonts
- Bikonts
- protozoan infrakingdom Rhizaria
- phylum Cercozoa
- phylum Retaria (Radiozoa and Foraminifera)
- protozoan infrakingdom Excavata
- phylum Loukozoa
- phylum Metamonada
- phylum Euglenozoa
- phylum Percolozoa
- protozoan phylum Apusozoa (Thecomonadea and Diphylleida)
- the chromalveolate clade
- kingdom Chromista (Cryptista, Heterokonta, and Haptophyta)
- protozoan infrakingdom Alveolata
- phylum Ciliophora
- phylum Miozoa (Protalveolata, Dinozoa, and Apicomplexa)
- kingdom Plantae (Viridaeplantae, Rhodophyta and Glaucophyta)
- protozoan infrakingdom Rhizaria
Seven kingdoms model
Cavalier-Smith and his collaborators revised the classification in 2015, and published it in PLOS ONE. In this scheme they reintroduced the division of prokaryotes into two kingdoms, Bacteria (=Eubacteria) and Archaea (=Archebacteria). This is based on the consensus in the Taxonomic Outline of Bacteria and Archaea (TOBA) and the Catalogue of Life.[14]