Biological Classification

Transcription

1 Biological Classification Introduction: There have been many attempts to classify living organisms. It was done instinctively not using criteria that were scientific but borne out of a need to use organisms for our own use for food, shelter and clothing. Aristotle was the earliest to attempt a more scientific basis for classification. He used simple morphological characters to classify plants into trees, shrubs and herbs & divided animals into two groups, those which had red blood and those that did not. During Linnaeus' time a Two Kingdom system of classification with Plantae and Animalia kingdoms was developed that included all plants and animals respectively, which was used till very recently & did not distinguish between the eukaryotes and prokaryotes, unicellular and multicellular organisms and photosynthetic (green algae) and non-photosynthetic (fungi) organisms. Classification of organisms into plants and animals was easily done and was easy to understand, inspite, a large number of organisms did not fall into either category. Hence the two kingdom classification used for a long time was found inadequate. It was felt to include, other characteristics like cell structure, nature of wall, mode of nutrition, habitat, methods of reproduction, evolutionary relationships, etc. besides gross morphology, Hence classification systems for the living organisms have undergone several changes over time. In 1866, the German investigator Ernst Haeckel proposed a three-kingdom system of classification. Haeckel's three kingdoms were Animalia, Plantae, and Protista. Members of the kingdom Protista included the protozoa, fungi, bacteria, and other microorganisms. In 1956 Hebert F. Copeland, an American taxonomist, suggested that all prokaryotes, i.e. Bacteria, cyanobacteria etc be placed under the kingdom Monera ( Mychota). He named the four kingdoms as Monera ( Mycota), Protista, Plantae, and Animalia. Five Kingdom Classification: American Taxonomist R.H. Whittaker (1969) proposed the Five Kingdom Classification. He named them Monera, Protista, Fungi, Plantae and Animalia where the main criteria for classification used by him include cell structure, thallus organisation, mode of nutrition, reproduction and phylogenetic relationships. The classification of living organisms according to Whittaker into five kingdoms namely are as follows: KINGDOM: MONERA Monera consists of primitive organisms. The organisms are very small and single celled. They consists of prokarytotes which includes species like the bacteria, archaebacteria, cyanobacteria and mycoplasma. Example: bacteria, oscillatoria, nostoc, etc.

2 KINGDOM: PROTISTA Protista are single-celled eukaryotes and are mainlky aquatic. It includes diatoms, golden algae, euglena and protozoans like amoeba, paramoecium, plasmodium etc. They are mostly marine and photosynthetic. Example: paramecium KINGDOM: MYCOTA Kingdom Mycota or Kingdom Fungi consists of network of thread-like structures called as mycelium. The bodies consists of long, thread-like structures which are called hyphae. These organisms are mostly saprophytes or parasites and also symbionts. This kingdom of fungi also includes lichens, mycorrhiza, etc. Example: Aspergillus KINGDOM: METAPHYTA Kingdom Metaphyta or Kingdom Plantae are eukaryotic, mutlicellular plants, They contain chlororphyll pigment, which helps them prepare their own food by the process of photosynthesis. This kingdom includes all types of plants like herbs, shrubs, trees, flowering and non flowering plants. Example: rose plant, mango tree, algae, bryophytes, etc. KINGDOM: METAZOA Kingdom Animalia or Kingdom Metazoa are heterotrophic, eukaryotic, multicellular organisms. They lack cell wall. This kingdom includes all types of animals. Example: lion, peacock, etc.

3 Merits of Five Kingdom Classification: This system of classification is more scientific and natural. It is the most accepted system of modern classification as the different groups of animals are placed phylogenetically. The prokaryotes are placed in a separate kingdom as they differ from all other organisms in their organization. As the unicellular organisms are placed under the kingdom protista, it has solved many problem related to the position of organisms like euglena. The fungi totally differ from other primitive eukarytotes hence, placing the group fungi in a status of kingdom is justifiable. The kingdom Plantae and Animalia shows the phylogeny of different life styles, in the five kingdom classification, they are more homogeneous group than the two kingdom classification. This system of classification clearly indicates cellular organization and modes of nutrition, the character which have appeared very early in the evolution of life. Demerits of Five Kingdom Classification: This system of classification has drawbacks with reference to the lower forms of life. The Kingdom of Monerans and the Protists include diverse, heterogenous forms of life. In both the kingdoms there are autoptrophic and hetertrophic organisms. They also include organisms which have cells with cell wall and cells without cell wall. All the organisms of these three kingdoms do not originate from a single ancestor. Multicellular organisms have originated from protists several times. Organisms like the unicelluar green algae like volvox and chlamydomonas have not been included under the Kingdom Protista because of their resemblance to other greeen algae. The general organization of the slime moulds are completely different from the members of protists. In this system of classification viruses have not been given proper place. Kingdom Monera: Kingdom Monera - All the organisms of this kingdom are prokaryotes. Complex structure was the basis of classification of organisms, many centuries ago. According to R.H. Whittaker's five kingdom classification all the bacteria were placed under the Kingdom Monera. Monera are considered as the most primitive group of organisms. They include various types of bacteria and blue-green algae. Monerans are most abundant of all organisms, due to their versatility of their habitat. It is estimated that a single drop of water contains 50 billion bacteria. General characteristics of the kingdom Monera are as follows: They are primitive organisms. All organisms of the kingdom are prokaryotes. They are present in both living and non-living environment. They can survive in harsh and extreme climatic conditions like in hot springs, acidic soils etc. They are unicellular organisms. Membrane bound nucleus is absent.

4 DNA is in double stranded form, suspended in the cytoplasm of the organism,referred as nucleoid. A rigid cell wall is present. Membrane bound cellular organelles like mitochondria are absent. Habitat - Monerans are found everywhere in hot springs, under ice, in deep ocean floor, in deserts and on or inside the body of plants and animals. Nutrition - autotrophs - can prepare their own food, heterotrophs - depend on others for food, saprophytes - feed on dead and decaying matter, parasitic - live on other host cells for survival and cause, symbiotic - in mutual relation with other organisms, commensalism - it is where one organism is benefited and the other is not affected, mutualism - where both the organisms are benefited. Respiration - respiration in these organisms vary, they may be obligate aerobes - the organisms must have organisms for survival; obligate anaerobes - the organisms cannot survive in the presence of oxygen; facultative anaerobes - these organisms can survive with or without oxygen. Circulation - is through diffusion. Movement - is with the help of flagella. Reproduction is mostly asexual, sexual reproduction is also seen. Asexual reproduction is by binary fission, sexual reproduction is by conjugation, transformation and transduction. Classification of Kingdom Monera Kingdom Monera has been classified into two groups - Archaebacteria and Eubacteria. Archaebacteria are microbes that live in extreme and harsh conditions, they are known as extremophiles. These bacteria lack cell wall, their cell membrane is made up of different lipids, and their ribosomes are similar to that of eukaryotes. Archaebacteria are of three major groups of bacteria based on their habitat i.e., thermophiles, halophiles and methanogens. Some extremophiles live in boiling water like geysers of Yellowstone National Park and and in volcanoes. These are known as 'thermophiles'. Some extremophiles live in extremely salty water, the salt loving bacteria are known as 'halophiles'. Some bacteria are present in the guts of ruminants and are responsible for production of methane gas from their dung. These bacteria are known as 'methanogens'. Eubacteria are true bacteria. The characteristic feature is the presence of rigid cell wall and if

5 present a motile flagelllum that aids in locomotion.these organisms are characterized based on their nutrition and their shapes. Classification based on Shape Bacteria can be classified in four groups based on shape : Spherical or round shaped bacteria are called cocci, Rod-shaped are bacilli, Comma-shaped bacteria are vibrio and spiral shaped bacteria are spirilla. Classification Based on Mode of Nutrition Based on the mode of nutrition bacteria are broadly classified into Autotrophic and Heterotrophic. Autotrophic bacteria - Bacteria which prepare their own food are autotrophic. (Example Cyanobacteria) Heterotrophic bacteria - Bacteria which are dependent on other organisms for their food are heterotrophic.(example Escherichia coli) Autotrophic bacteria can be chemosynthetic or photosynthetic. Chemosynthetic bacteria are those which prepare their food with the help of inorganic substrates. Photosynthetic bacteria are autotrophic bacteria which prepare their own food by the process of photosynthesis. Cyanobacteria (Blue-green algae) - They have chlorophyll similar to plants and hence they are photosynthetic autotrophs. They may be unicellular, colonial or filamentous. The colonies are surrounded by gelatinous sheath. They can also fix atmospheric nitrogen. Cyanobacteria multiply by fragmentation, hormogones and akinetes. Hormogones are small trichome segments which separate naturally in filamentous forms due to death of an intervening cell or presence of heterocyst. Akinetes are thick-walled resting spores.

6 Some of these organisms can fix atmospheric nitrogen in specialised cells called heterocysts, e.g., Nostoc and Anabaena. Cyanobacteria protect the soil from erosion. They are also used in reclamation of saline & alkaline soil. Chemosynthetic autotrophs - these organisms oxidise substances like nitrites, nitrates, ammonia etc. The help in recycling substances like nitrogen, sulphur, iron etc. Heterotrophic bacteria are those which are dependent on other organism either directly or indirectly for their nutrition. They are most abundant and are important decomposers. Some are helpful in curdling milk, production of antibiotics, in nitrogen fixation and some are pathogens. Heterotrophic bacteria can be parasitic and saprophytic. Parasitic bacteria are those which depend on the host for nutrition and cause harm to the host. Saprophytic bacteria feed on dead and decaying matter. Mostly decomposer Helpful in making curd from milk Produce antibiotics Symbiotically associated with leguminous plant and fix nitrogen. Some are pathogen causing diseases like cholera, typhoid, and tetanus. Bacteria reproduce mainly by fission, also produce spore in unfavorable condition. Reproduce sexually by transfer of DNA form one bacteria to other, the process called conjugation. Symbiotic - it is a type where the bacteria are in mutual relation with other organisms. Symbiosis is of two types mutualism and commensalism. Mutualism is where the bacteria and the other organism are benefited due to the relationship. Commensalism is a relationship where the bacteria is benefited while the other organism is not affected by the relationship.

7 Classification based on Gram's staining Gram's staining is a test on cell walls developed by Hans Christian Gram. This method helps classifying bacteria into Gram positive bacteria and Gram negative bacteria. Gram Positive Bacteria - The bacteria's cell wall is made up of protein-sugar complex that takes on purple color during gram staining. Mycoplasma : They are tiny organisms found in soil and sewage water. Some are parasites. They are the smallest among living organisms (other than viruses) varying in size from to 0.150mm in diameter. They exhibit a great deal of variation in their shape and form. They are unicellular, gram negative, non-motile prokaryotes which lack a distinct cell wall. Some examples of mycoplasmas are pathogenic parasites in humans, animals and plants. The most familiar example is Mycoplasma pneumoniae which causes the disease pneumonia.

8 Kingdom Protista: All are unicellular and eukaryotic. Mostly aquatic, can live in moist places. Forms a link between plants, animals and fungi. The cell contain nucleus and membrane bound organelles. May be a photosynthetic protistan to one biologist may be a plant to another. Being eukaryotes, the protistan cell body contains a well defined nucleus and other membrane-bound organelles. Some have flagella or cilia. Protists reproduce asexually (binary fission, multiple fission, budding, sporulation & cyst formation) and sexually by a process involving cell fusion and zygote formation. Chrysophytes : Includes diatoms and golden algae (desmids) Found in freshwater or marine water. Mostly planktonic ( passive swimmer) Photosynthetic pigments are chlorophyll a & chlorophyll c and fucoxanthin rich carotenoids. Cell walls overlap to fit together like a soap box. Cell wall contains silica hence indestructible. Their accumulation forms Diatomaceous Earth. Reproduction is by binary fission. Size will decrease progressively with each generation which is restored by the formation of auxospore (rejuvenescent cells). Used in polishing, tooth pastes, filtration of oils and syrups. Diatomaceous earth enhances night visibility of paints. Diatoms are the chief producers in the oceans.

9 Dinoflagellates : Marine, photosynthetic. Cell wall has stiff cellulose plates. Appears yellow, green, brown, blue or red depending on the pigments. Have two flagella one longitudinal and other transversely in a furrow between wall plates. Red Dinoflagellates (Gonyaulax) form red tides. The common mode of multiplication is by binary fission which may be longitudinal, oblique or transverse. Spore, cysts & sexual reproduction also occur. Euglenoids : Unicellular flagellates Mostly fresh water form found in stagnant water. Instead of cell wall they have protein rich layer pellicle which makes body flexible. They have two flagella one short and one long Euglenoids show metaboly i.e. wriggling type of movement due to passage of contraction & expansion from one end to the other and also flagellar locomotion. Photosynthetic in presence of sunlight but become heterotrophs if they do not get sunlight. Sexual reproduction is not known. Multiplication commonly occurs through longitudinal binary fission. Cyst formation occurs during unfavourable conditions. e.g. Euglena

10 Slime Moulds : Saprophytic Protists Form aggregates to form plasmodium grow on decaying twigs and leaves. Plasmodium forms fruiting bodies bearing spores at their tips. Spores have true walls which are extremely resistant and survive for many years. Slime Mold: Physarum polycephalum Vomit Slime Mold: Fuligo septica Protozoans : All protozoans are heterotrophs and live as predators or parasites. Believed to be primitive relatives of animals. These are divided into four major groups on the basis of locomotery organelle they have. Amoeboid protozoans : Move and Catch prey using pseudopodia, e.g., Amoeba. Many forms have silica shells on their surface. Some of them are parasitic e.g. Entamoeba. Flagellated protozoans : Either free living or parasitic. They have flagella. Cause disease like sleeping sickness e.g., Trypanosome.

11 Ciliated protozoans : These are aquatic, actively moving organisms due to presence of thousands of cilia. e.g., Paramecium. They have a cavity called gullet that opens to outside the cell. Sporozoans : Lack any locomotery organelle. All members are parasitic. Have infective spore like stage in life cycle, e.g., Plasmodium which causes Malaria.

12 Kingdom Fungi: With the exception of yeasts which are unicellular all others are multicellular and filamentous. Consists of long slender thread like structure called hypha. Non chlorophyllous Network of hyphae called mycelium. Uninucleated or multinucleated (coenocytic) Cell wall made of complex polysaccharide called chitin. Grow in warm and humid places. Saprophytic, parasitic, symbiotic (Lichen) Reproduce asexually by spores conidia sporangiospores or zoospores. Sexual reproduction is by oospores, ascospores and basidiospores. Sexual cycle involves the following thee steps: Plasmogamy: fusion of protoplasms between two motile or non-motile gametes. Karyogamy: fusion of two nuclei Meiosis: zygote undergoes meiosis resulting haploid spores. When a fungus reproduces sexually, two haploid hyphae of compatible mating types come together and fuse. In some fungi the fusion of two haploid cells immediately results in diploid cells (2n). In other fungi (ascomycetes and basidiomycetes), an intervening dikaryotic stage (n + n i.e. two nuclei per cell) occurs; such a condition is called a dikaryon and the phase is called dikaryophase of fungus. Later, the parental nuclei fuse and the cells become diploid. The fungi form fruiting bodies in which reduction division occurs, leading to formation of haploid spores. The morphology of the mycelium, mode of spore formation and fruiting bodies form the basis for the division of the kingdom into various classes. Classification of Fungi: Fungi are classified based on (i) morphology of mycelium (ii) mode of spore formation (iii) fruiting bodies and (iv) presence or absence of sexual stage.

13 Phycomycetes : Found in aquatic habitat, on decaying wood in moist and damp places. Some of them are obligate parasite on plants. Mycelium is aseptate and coenocytic Asexual reproduction by zoospores (motile) or by aplanospores (nonmotile). Spores are produced endogenously in sporangium. Zygospore produced by fusion of gametes. e.g., Mucor, Rhizopus, Albugo. Ascomycetes : Commonly known as sac fungi. Unicellular (yeasts) or multicellular (e.g. Penicillium) Saprophytic, decomposers, parasitic or coprophilous. Mycelium branched and septate. Asexual spores are called conidia produced exogenously on the conidiophores. Conidia on germination produce mycelium. Sexual spores are called ascospores produced endogenously in ascus produced inside fruiting body called Ascocarp. e.g., Aspergillus, Neurospora

14 Basidiomycetes Common known forms called mushrooms, bracket fungi or puffballs. Mycelium septate and branched. Asexual spores generally are not found. Vegetative reproduction by fragmentation. Sexual reproduction by fusion of vegetative or somatic cells of different strains to form basidium produced in basidiocarp. Basidium produces four basidiospores after meiosis. e.g., Agaricus, Ustilago. Deuteromycetes : Called as Fungi Imperfecti as sexual form (perfect stage) is not known for them. Once sexual form is discovered the member is moved to Ascomycetes or Basidiomycetes. Mycelium is septate and branched. Are saprophytic, parasitic or decomposers. e.g., Alternaria, Colletotrichum.

15 Kingdom Plantae: Kingdom Metaphyta or Kingdom Plantae are eukaryotic, mutlicellular plants. They contain chlororphyll pigment, which helps them prepare their own food by the process of photosynthesis. This kingdom includes all types of plants like herbs, shrubs, trees, flowering and non flowering plants. Chlorophyll containing multcellular eukaryots. Cell wall made of cellulose. Life cycle shows alternation of generation having gametophytic (n) and sporophytic(2n) phase Kingdom Animalia: Heterotrophic multicellular eukaryots. Lack cell wall. Depend on plants directly or indirectly. Stores food reserves as fat or glycogen. Holozoic nutrition. Capable of locomotion. Follow a definite growth pattern. Reproduction is sexual.

16 Viruses, Viroids & Lichens: Viruses: They did not find a place in Whitaker classification. Take over the machinery of host cell on entering it but as such they have inert crystalline structure, due to which it is difficult to call them living or non-living. Pasteur gave the term Virus i.e., poisonous fluid. D. J. Ivanowsky (1892) found out that certain microbes caused Tobacco Mosaic Disease in tobacco plant. M. W. Beijerinek (1898) called fluid as Contagium vivum fluidum as extracts of infected plants of tobacco could cause infection in healthy plants. W. M. Stanely (1935) showed viruses could be crystallised to form crystals of protein which are inert outside their specific host. Structure of Virus: Its a nucleoprotein made up of protein called Capsid. Capsid is made up of capsomeres arranged in helical or polygeometric forms. Have either DNA or RNA as genetic material which may be single or double stranded. In general, viruses that infect plants have single stranded RNA and viruses that infect animals have either single or double stranded RNA or double stranded DNA. Bacterial viruses or bacteriophages have double stranded DNA. Viruses cause diseases like mumps, small pox, herpes and influenza. AIDS in humans is also caused by a virus. In plants, the symptoms can be mosaic formation, leaf rolling and curling, yellowing and vein clearing, dwarfing and stunted growth. Viriods: In 1971 T.O. Diener discovered a new infectious agent that was smaller than viruses and caused potato spindle tuber disease. Viroids are nucleic acid species of relatively low molecular weight and unique structure that cause several important diseases of cultivated plants. Similar nucleic acid species may be responsible for certain diseases of animals and humans. Viroids are the smallest known agents of infectious disease. Unlike viral nucleic acids, viroids are not encapsidated. Despite their small size, viroids replicate autonomously in cells of susceptible plant species.

17 Known viroids are single-stranded, covalently closed circular, as well as linear, RNA molecules with extensive regions of intramolecular complementarity; they exist in their native state as highly base-paired rods. Lichens: Lichens are symbiotic associations i.e. mutually useful associations, between algae and fungi. The algal component is known as phycobiont and fungal component as mycobiont, which are autotrophic and heterotrophic, respectively. Algae prepare food for fungi and fungi provide shelter and absorb mineral nutrients and water for its partner. So close is their association that if one saw a lichen in nature one would never imagine that they had two different organisms within them. Lichens are very good pollution indicators they do not grow in polluted areas. Crustose lichens The thallus forms a crust over the substrate and is firmly attached to it. There is an upper cortex, at least in early development, but no lower cortex and the medulla is in direct contact with the substrate and commonly grows into it to some extent. Consequently, the lichen normally cannot be collected intact without collecting a portion of the substrate along with it. There are various terms to describe the nature of the thallus surface (quite apart from sexual reproductive structures such as apotheciaor asexual reproductive structures such as soralia or isidia). The surface may be smooth or lumpy ('warted') and frequently the surface is areolate, i.e. composed of small, separate islands of thallus seated on an underlying prothallus or hypothallus. These areoles may be clearly separate ('dispersed') or be closely contiguous and often represent break-up of the thallus surface ('cracked-areolate'). If the surface is cracked but not broken up into discrete areoles, it is said to be 'rimose'. Sometimes the surface is pruinose.

18 Foliose lichens These are some of the largest and perhaps most complex lichens. The thallus generally forms flat, leaf-like lobes, with differentiated layers of tissue, the upper and lower cortices, forming the upper and lower surfaces. The lobes are commonly, but not always, appressed to the substrate surface, but can be lifted away. The lower cortex is often differently coloured, frequently brown or black and usually bears rhizines. In Peltigera the lower surface is ecorticate. In foliose lichens with multiple branches of the thallus that may stand away from the substrate, the differentiated lower cortex distinguishes them from fruticose lichens, e.g. Evernia prunastri, in which the thallus lobes are white beneath, and Pseudevernia furfuracea, in which the undersides are black when mature. Fruticose lichens The thallus is extended up into a tufted or pendant branched structure, the branches being covered by a single cortex. In fruticose lichens with flattened branches, e.g. Ramalina spp., the cortex extends round both surfaces of the branch. Consequently, they differ from foliose lichens with branched, aerial lobes such as Evernia.