2.1 KingdomMonera 2.2 Kingdom Protisia 2.3: Kingdom Fungt 24 Kingdom Plantae 25 26 Viruses, Viroids ‘Kingdom Animalia and Lichens Crsrrer 2 Bioxocicat Cuassirication Since the dawn of elvilisation, there have been many attempts to classify living organisms. It was done instinctively not using criteria that were sclentific 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 dlassily plants into trees, shrubs and herbs, He also divided animals ‘nfo two groups, those which had red blood and those that did not. “Th Linnaeus’ time a Two Kingdom system of classification with Plantae and Animalia kingdoms was developed that included all plants and animals respectively. This system did not distinguish between fhe eukaryotes and prokaryotes, unicellularand multicellular organisms and photosynthetic (green algae) and non-photosynthetic (fungi) iganismis, Classiiication of organisms into plants and animals was easily done and was easy to understand, but, a large number of organisms did not fall into either category. Hence the two kingdom classification sed for a long time was found Inadequate, Besides, gross morphology anced was also felt for mchuding other characteristics like cell structure, Mature of wall, mode of nutrition, habitat, methods of reproduction, evolutionary relationships, etc. Classification systems for the living organisms have hence, undergone several changes over the time. ‘Though plant and animal kingdoms have been a constant under all diferent systems, the understanding of what groups/organisms be included under these kingdoms have been changing; the number and nature of other kingdoms have also been understood differently by different sctentists over the time 202021BioLocical. CLAssiFicaTIOn 17 ‘Taste 2.1 Characteristics of the Five Kingdoms Five Kingdoms Characters Monera Protista Fungi Plantae Animalia Cell type Prokaryotie Eukaryotic Eukaryotic Eukaryotle Eukaryotic Cell wall Noncellulosic Present in Present Present (Polysaccharide some with ebitin (cellulose) Absent + ammo acid) Nuclear een Present Present Present Present membrane Body Cellular Cellular Multiceullar/ Tissue/ _‘Tissuie/organ/ organisation loose tissue organ organ. system {iomogn: — Autotrophie Heterotrophte autotrophie Heterotrophte thetic and (Photosyn- (Saprophytic/ (Photosyn- (Holozolc/ Mode of , thetic) and Parasitic) thettc} Saprophytic photosynthetic) nutrition end Fielero. Hetero- ete) trophic (sapro- Tophic phytic/para- sitie) RH, Whittaker (1969) proposed a Five Kingdom Classification. The kingdoms defined by him were named Monera, Protista, Fungi, Plantae and Animalia, The main criterla for classification used by him include cell structure, body organisation, mode of nutrition, reproduction and Phylogenetic relationships. Table 2.1 gives a comparative account of different ‘characteristics of the five kingdoms. ‘The three-domain system has also been proposed that divides the Kingdom Monera into two domains, leaving the remaining eukaryotic kingdoms in the third domain and thereby a shx kingdom classification, You will learn about system in detail at higher classes. Let us look at this five kingdom classification to understand the issues and considerations that influenced the classification system, Earlier classification systems included bacteria, blue green algae, fungl, mosses, ferns, gymnosperms and the angiosperms under ‘Plants’. The character that unified this whole kingdom was that all the organisms included had a cell wall in their cells, This placed together groups which widely differed in ‘blue green algae (cyanobacteria) with oer groups WHICH Were eURARVOUC ITalso grouped together the unfoellular organisms and the mullicellular ‘ones, say. Tor example, CRlamgdomonas and Spirogyra were placed together (EETaoe The ceeatication ‘did not differentiate between the heterotrophic ‘@oup- fungi, and the autotrophic green plants, though they also showed a characteristic difference in their walls composition ~ the fumg\ had chitin 202021 yom Ope archos | Eubocle™ \§ ain # yo18 FF & Brotocy in thetr walls while the green plants had a cellulosic cell wall. When such characteristics were considered, the fung! were placed in a separate kingdom — Kingdom Fungi. All prokaryotic organisms were grouped together under Kingdom Monera and the unicellular eukaryotic organisms were placed in Kingdom Protista. Kingdom Protista has brought together (Chlamydomonas, Chlorella (earlier placed in Algae within Plants and both ‘cell walls) with Paramoectum and Amoeba (which were earlier placed in the animal kingdom which lack cell wall), It has put together organisms which, in earlter classifications, were placed in different kingdoms. ‘This happened because the criteria for classification changed. This kind of changes will take place n future too depending on the tmprovement tn our understanding of characteristics and evolutionary relationships. Over time, an attempt has been made to evolve a classification system which reflects not only the morphological, physiological and reproductive similarities, Dutis also phylogenetic, 1e., 1s based on_evolutionary relationshiy in this chapter we will study characteristics of Kingdoms Monera, Protista and Fungi of the Whittaker system of classification. ‘The Kingdoms Plantae and Animalia, commonly referred to as plant and animal kingdoms, respectively, will be dealt separately in chapters 3 and 4. 2.1 Kincpom Monzra Bacteria are the sole members of the Kingdom Monera. They are the most abundant micro-organisms. Bacteria occur almost everywhere. Hundreds ofbacteria are present ina handful of soll. They also live in extreme habitats Such as hot springs, deserts, snow and deep oceans where very few other life forms can survive. Many of them live in or on other organisms as parasites. Bacterfa are grouped under four categories based on their shape: the spherical Coceus (pl: cocci), the rod-shay 1: bacilli), the comma-shaped Vibrium (pl.: vibrio) and the spiral Spirillum (pl.: sory} (Figure 2.1). spore Flagelium Bacilli ~~ ‘Vibrio Figure 2.1 Bacteria of different shapesBIOLOGICAL CLASSIFICATION 19 ‘Though the bacterial structure ts very simple, they are very complex in behaviour. Compared to many other organisms, bacteria as a group Show the most extensive metabolic diversity. Some of the bacteria are ‘autotrophic, Le., they synthesise their own food from inorganic substrates, They may be photosynthetic autotrophic or chemosynthetic autotrophic. ‘The vast majority of bacteria are heterotrophs, Le., they depend on other organisms or on dead organic matter for food, 2.1.1 Archaebacteria ‘These bacteria are special since they live in some of the most harsh habitats such as extreme salty areas (halophiles), hot springs (thermoacidophiles) and marshy areas (methanogens). Archaebacteria differ from other bacteria in havinga different cell wall structure and this feature is responsible for thetr survival In extreme conditions, Methanogens are present in the gut of several ruminant animals such as cows and bullaloes and they are responsible for the production of methane (biogas) from the dung of these animals. 2.1.2 Eubacteria ‘There are thousands of different eubacteria or ‘true bacteria. They anecharactersed bythe presenceot'a rigid cell wall, and if motile, a flagellum. The cyanobacteria (also referred to as blue-green algae) have chlorophyll a similar to green plants and are at loon photosyathetic autotrophs (Figure 2.2). The, “9 ‘eria are unicellular, colontal or filamentous, cyano freshwater/marine or terrestiial algae. The colonies ‘are generally surrounded by gelatinous sheath. Th ‘fen form blooms in polluted water bodies: Some of these organisms can Tix atmospheric nitrogen in, specialised cells called heterocysts, ¢.g,, Nostocand Anabaena. Chemosynthetic autotrophic bacteria oxidise various inorganic substances such as nitrates, nitrites and ammonia and use the released, energy for their ATP production, They play a great role in recycling nutrients like nitrogen, phosphorous, iron and sulphur. Heterotrophic bacteria are most abundant in ature. The majority are important decomposers, Many of tem have a significant impact on human pgure 2.2 A filamentous bive-green affairs. They are helpful in making curd from milk, algae - Nostoc Mucilagenous sheath 20202120 Brotocy ‘ell wal Cell roots Cell wall membrane etc, Some are pathogens causing damage ‘to human beings, crops, farm animals and pets. Cholera, typhold, tetanus, citrus canker are well known diseases caused by different bacteria, Bacteria reproduce mainly by fission (Figure 2.3). Sometimes, under unfavourable conditions, they produce spores. They also reproduce by a sort of sexual reproduction by adopting a primitive type of DNA transfer from one bacterium, tothe other, Figure 2.9 A dividing bactertum ‘The Mycoplasma are organisms that completely lack a cell wall. They are the smallest living cells known and can survive without oxygen. Many mycoplasma are pathogenic In animals and plan Probis + Sin yee celle 2 euk lack well oe fined Allsingle-celled eukaryotes are placed under Protista, but the boundaries bound of this kingdom are not well defined. What may be ‘a photosynthetic d rotistan’ to one biologist may be ‘a plant’ to another. In this book we + Includes ch eplyles , Include Chrysophytes, Dinoflagellates, Euglenoids, Slime moulds and DinoPiagellakess Evglennd, Poaoans under Prosi. Members of Protsia are primarily aqua This kingdom forms a link with the others dealing with planis. anime Slime an » f774e222n and fungl. Beng eukaryotes, the protistan cell body contains a well defined + Pornany ayualic and iucleus and other membrane-bound organelles. Some have flagella or 2.2 Kinapom Protista Link with okey cilia, Protists reproduce asexually and sexually by a process Involving muthcetutar forms cell fusion and zygote formation. 2 Have well de fired 2.2.1 Chrysophytes Necleus, Membrane ry bound cetl ; This group Includes diatoms and golden algae (desmids). They are found ~ Lu in fresh water as well as in marine environments. They are microscopic as tell as Sexually’ and float passively in water currents (plankton). Most of them are Cheyso fe photosynthetic. In diatoms the cell walls form two thin overlapping shells, “which fit together as in a soap box. The walls are embedded with silica Includes Lalas & and thus the walls are indestructible. Thus, diatoms have left behind cles mid large amount of cell wall deposits in thetr habitat; this accumulation over s manne as well Billions of years ts referred to as ‘diatomaceous earth’. Being gritty this . ee float soll 1s used in polishing, filtration of olls and syrups. Diatoms are the fresh ta forms FI ‘hic producers’ in the oceans. eae Sy formtuo Hn over lappieg shets ft tygeter a4 @ Aoap box ~Goembecited with sit'ea(indespruchble) Y Diatomaceous arth beng EG Sed Im polishi' + Diakoms ave the ‘thief Plipabon of ors anol Syrups prekucer”in the Ocean: 202021Dino flaqettares - = MosbLy Marine and photosyntiehic appear blue, pe eer eh: based on pigment present i'n coer + SHA Celluteric platig of cet watt Biovocical CLassinicanion 21 wae paty of et pevbendocatar + Reol Linoflagetabe (Gonyautun) > Res te 2.2.2 DinoflagellateS Feo veleates info ) 4 ‘These organisms are mostly marine and photosynthetic. ‘They appear yellow, green, brown, blue or red depending on the main pigments present in their cells. The cell wall ‘has stiff cellulose plates on the outer surface. Most of ‘them have two flagella; one lies longitudinally and the other transversely in a furrow between the wall plates. Very often, red dinoflagellates (Example: Gonyaulax) undergo such rapid multiplication that they make the Sea appear red fred tes). Toxins released by such large numbers may even kill other marine animals such as fishes: Majority of them are fresh water organisms found in “Staghant water. Instead ofa cell wall, they have a protein rich layer called pellicle which makes their body flexible. ‘They have two flagella, a short and a long one. Though they are photos) In the presence of sunlight, when deprived of sunlight they behave like heterotrophs by predating on other smaller organisms. Interestingly, the ‘pigments of eugienoids are identical to those present in figher plants, Example: Euglena (Figure 2.4b).. 2.2.4 Slime Moulds ‘Slime moulds are saprophytic protists. The body moves along decaying twigs and Teaves engulfing organic materfal. Under suitable conditions, they form an aq Ge ‘aggregation called plasmodium which may grow and wrnm plasmoctium but Tn Atvers Spread over several feet. During unfavourable conditions, ¢ gyg:jior plasmecium form fretg the plasmodium differentiates and forms frultingbodies |), ge, beaning. Apores ot tip bearing spores at thelr ips. The spores possess true walls, ‘St as They are extremely resistant and survive for many years, Have (aie , @ven under adverse conditions. The spores are dispersed Peace cotton by air currents. Waivew Condom Ze 2.2.5 Protozoans s haponses 6 All protozoans are heterotrophs and live as predators or (a) Ay Curren é Parasites. They are believed to be primitive relatives of ‘animals, There are four major groups of protozoans, Figure 2.4 (a) Dinoflagellates = boul So eee (0) Bugiena “Amoeboid protozoans: These organisms live in fresh (0) Slime mould Le | water, sea water or moist soil. They move and capture (@) Paramoectum 20202122 Browocy ~ thetr prey by putting out pseudopodia (false feet) as in Amoeba. Marine forms have silica shells on their surface. Some of them such as Entamoeba are parasites, Plagellated protozoans: The members of this group are either free-living or parasitic, They have flagella. ‘The parasitic forms cause dlaseases such as sleeping sickness. Example: Trypanosoma. Ciltated protozoans: These are aquatic, actively moving organisms because of the presence of thousands of cilia. They have a cavity (gullet) that opens to the outside of the cell surface. The coordinated movement of rows of cilia causes the water laden with food to be steered into the gullet. Example: Paramoectum (Figure 2.4d). Sporozoans: This includes diverse organisms that have an infectious spore-like stage in their life cycle. The most notorious 1s Plasmodium (malarial parasite) which causes malaria, a disease which has a staggering effect on human population, Fung 2.3 Kinapom Foner Helereho pis with great Livevsity tm morplblegy ‘The fungt constitute a unique kingdom of heterotrophic organisms. They Pat show a great diversity in morphology and habitat. You must have seen and habitat (Cosme poles finan moist breul an rover Thecoramion mushroom yout Scewr in ai'y, walse , and toadstools are also fungl, White spots seen on mustard leaves are due Sm, On animals & toa parasitic fungus. Some unicellular fungl. €.g., yeast are used to make Plants bread and beer. Other fungl cause diseases in plants and animals; wheat . Tust-causing Puccinia is an important example. Some are the source of “Growin Warm 4 antibiotics, e.g,, Penicillium. Fung! are cosmopolitan and occur in alr, water, hum places - USueély soll and on antmals and plants. They prefer to grow In warm and humid Flamentous excep places. Have you ever wondered why we keep food in the refrigerator ? Yes, ' {UIST prevent food from going bad due to bacterial or fungal infections, Unieetluber yeast (erect With the exception of yeasts which are unicellular, fung! are Kb make bread Ad filamentous. Their bodies consist of long, slender thread-like structures beer) ‘called hyphae. The network of hyphae is known as mycelium, Some hyphae are continuous tubes filled with multinucleated cytoplasm - these are + Hyphae may be “Galle Coencytic hyphae, Others have septae oF croee walls tn thelr septate ey adepb2@ — byohae. The cell walls of fung! are composed of chitin and polysaccharides. (coenceyhie > mith Most funglare heterotrophic and absorb soluble organte matter from Pell wal is made up ~ deailsubstaies and hence ave called saprophytes, Those that depend "Ju, Ohltving plants and animals are called parasites. They can also ve as of chibn + Polypocthan ' symbionts — in association with algae as Hehens and with roots of higher May be saproplyrer, _Dlanisasmyeormitza bron Reproduction in fungi can take place by vegetative means — parnibes and symienl fragmentation, fission and budding. Asextal reproduction Is by spores chen mycorr bre Excepl Oomycepes (Celle lose coer wad) 202021Reproduchon > vegetative (ereqmentahor, a came oD) I “% called plasmogamy. ve 1a, oe oO Mucor RnB, Poospores (motte) or by aplanospores (non-motile). These '22bu4\ Spores are endogenously produced in sporangium. A zygospore 1s formed by fuston of two gametes. These @vead |gameies are similar im morphology (lsogamous) or oud © eget OLE spore tied (Cmeper) = sepuat(hs wes > Conih'a (Ex ogeVey nae Co Mer Sperengoapok, End penens) \ayeele > teanpores (Endeze nous t mamnie } g — Sexuat (bY Oorpgre, arcompore, barioboxpore) Spy BIoLocical CLASSIFICATION - Zs Pere rt 23 lane Shore + Spores proolucedt in Pru'hnd So; “ Peres Prebeg eles (Atco cant, Gasietvenrp) called conidia or sporanglospores or zoospores, and sexual reproduction 1s by oospores, ascospores and basidiospores. The various spores are produced In distinct structures called fruiting bodies. The sexual cycle involves the following three steps o < (Fusion of protoplasms between two motile or non-motile gametes. —[TS> GI (i) Fuston of two nuclet called karyogamy. () Metosis in zygote resulting in haploid spores. When a fungus reproduces sexually, two haploid hyphae of compatible mating types come together and fuse. In some fungi the fuston of two haploid cells immediately results in diploid cells (2n). However, in other fung! (ascomycetes and basidiomycetes), an intervening dikaryotic stage (n + n, L.e., two nucle per cell) occurs; such a condition is called-a ‘and the phase Is called dikaryophase of fungus. Later, the parental nuclei Tascandthe cells become diplotd, The fungi form fruiting pas P< bared bodies in which reduction division occurs, leading to formation of haploid spores. ‘The Morphology of the iaycelium, mode of spore formation and fruiting bodies form the basis for the Wision of the kingdom into various classes. 2.3.1 Phycomycetes “Members of phycomycetes are found in aquatic habitats and on decaying wood in moist and damp places or as obligate parasites on plants. The mycelium Is aseptate GaP ooenoaitio Reel Teproduction: takes place by ‘s Cissimilar (anisogamous or oogamous). Some common examples are Mucor (Figure 2.5a), Rhizopus (the bread ove mentioned ear) aA ugo (the parasitic fungi 2.3.2 Ascomycetes ‘Commonly known as sac-fung,, the ascomycetes are mostly, multicellular, e.g, Penicllum, or rarely unicellular e, yeast (Saccharomyces). They are saprophytic, decomposers, Figure 2.5 Fungi: (a) Mucor ‘parasitic or coprophilous (Growing on dung). Mycetiam (b) Aspergilias (¢) Agaricus L Emarples > Yeast (Saccharomyces) > Beer{ wine anct breny > fewerlitum (Anpbrefies fewerlie) > Clayreeps Sher ges > Neunsspers (Sroscphils =f plant reg dow)Fung > Haflonhe Lfe 7 24 fob. nerosis 24 Brotocy Examples © Aganices (mushroom © Pmanita( toad tee /) 1s branched and septate. The asexual spores are conidia produced Jexogenously on the special mycelium called conidiophores. Conidia on [germination produce mycelium, Sexual spores are called which are produced endogenously in sac like ascl (singular ascus). These asc! are arranged In different types of fruiting bodies called ascocarps. | Some examples are Aspergillus (Figure 2.56), Claviceps and Neurospora. Neurospora 1s used extensively in biochemical and genetic work. Many members like morels and is = are edible and are considered delicacies. EL be ® Pf bay @ B : 2.3.3 Basidiomycetes mont oijance & Commend best vecteet fa “t Commonly known forms of bastdiomycetes are mushrooms, bracket fund! focons— @® Pucernia Rest fen 5) -epulball _of puflballs. They grow In soll, on logs and tree stumps and in Wing pg "FE Diantboatesas parasites, -g. rusts and smuts, The myceltum is branched 2 Block rust vn okeat and seplate. The asexual spores are generally not found, but vegetative @ Ushi. Usblege (Smut Pong ) Teproduction by fragmentation 18 common. The sex organs are absent, but plasmogamy 1s brought about by fusion of two vegetative or somatic ‘cells of different strains or genotypes. The resultant structure is dikaryotle which ultimately gives rise to basidium, Karyogamy and meiosis take place in the basidium producing four basidiospores. The basidiospores aie exogenously produced on the basidium (pl: basidia). The basidia are arranged in fruiting bodies called basidiocarps. Some common members fe Agaricus (mushroom) (Figure 2.50), Ustitago (smut) and Puecinia (rust fungus). _1 “Toad stoot( Aman'ta) , 2.3.4 Deuteromycetes Commonly known as imperfect fungi because only the asexual or vegetative phases of these fing! are known, When the sexual forms of These fungi were discovered they were moved into classes they rightly belong to. It is also possible that the asexual and vegetative stage have been given one name (and placed under deuteromycetes) and the sexual stage another (and placed under another class). Later when the linkages were established, the fungt were correctly identified and moved out of deuteromycetes. Once perfect (sexual) stages of members of dueteromycetes were discovered they were often moved to ascomycetes and basidiomycetes. The deuteromycetes reproduce only by asexual spores known as conidia, The mycelium is septate and branched. Some members are saprophytes or parasites while a large number of them are decomposers of liter and help i mineral cycling, Some examples are Alternaria, Colletotrichum and Trichoderma. Ceat) Early blight of folae = «Red vet im Bieontvo) agent Siqarcan @ ¢ ee Fahong (cot 2020212.4 Kincpom Piantae Kingdom Plantae includes all eukaryotic chlorophyll-containing organisms commonly called plants. A few members are partially Teterotrophie such asthe insectivorous plats parasites. Bladdervort and Venus ly trap are examples of insectivorous planis and Cuscutais a chloroplasts and cell wall mainly made of cellulose. You will study the eukaryotic cell structure in detail in Chapter 8. Plantae mcludes algae, bryophytes, pteridophytes, gymnosperms and angiosperms. Life cycle of plants has two distinct phases - the diploid sporophytic and the haploid gametophytic - that alternate with each other. The lengths of the haplotd and diploid phases, and whether these phases are free living or dependent on others, vary among different groups in plants. ‘This phenomenon is called alternation of generation. Yow wil study further details of this kingdom in Chapter 3. 2.5 Kinepom Anmauia ‘This kingdom is characterised by heterotrophic eukaryotic organisms: that are multicellular and their cells lack cell walls. They directly or indirectly depend on plants for food. They digest their food In an internal cavity and store food reserves as glycogen or fat. Thetr mode of nutrition is holozoic — by ingestion of food. They follow a definite growth pattern and grow into adults that have a definite shape and size. Higher forms show elaborate sensory and neuromotor mechanism. Most of them are capable of locomotion. ‘The sexual reproduction ts by copulation of male and female followed by embryological development. Salient features of various phyla are described in Chapter 4, 2.6 Viruses, Virows, Prions anp LickEns: In the five kingdom classification of Whittaker there 1s no mention of lichens and some acellular organisms like viruses, virolds and prions. These are briefly mtroduced here, All of us who have suffered the ill effects of common cold or ‘fu’ know what effects viruses can have on us, even if we do not associate tt with our condition. Viruses did not find a place in classification since they are not considered truly living, ifwe understand living as those onganisms that have a cell structure. The viruses are non-cellular organisms that are characterised by having an inert crystalline structure outside the living cell. L's Vivion Cinerr) 9 Tnfecte inaide host( virus)26 Browocy ‘Tall fibres o Figure 2.6 (a) Tobacco Mosaic Virus (TMV), (b) Bacteriophage (Once they infect.a cell they take over the machinery of the host cellto replicate themselves, killing the host. Would you call viruses living or non-livin The name virus that means venom or poisonous fluid was given by Dmitri Ivanowsky (1892) recognised certain microbes as causal organism. of the mosate disease of tobacco (Figure 2.6a). These were found to be we smaller than bacteria because they passed through bacteria-proof filters. we MW. Beljerinek (1898) demonstrated that the extract of the infected plants of tobacco could cause infection in healthy plants and called the fluid as Contagium vivum fluidum (infectious living fluid). W.M. Stanley (1935) showed that viruses could be crystallised and crystals consist largely of ruses proteins. They are inert outside their specific host cell. Viruses are obligate parasites ebrous vuiclesp— In addition to proteins, viruses also contain genetic material, that could voter pavieees be elther RNA or DNA. No virus contains both RNAand DNA. A virus Is ° “anucleoprotein and the genetic material is infectious, In general, viruses how nebe that infect plants have single stranded RNA and viruses that infect animals wrapdapeltier DIVA *Y Thave-clther single or double siranded RNA or double siranded DNA. lon never both: Bacterial viruses or bacterlophages (viruses that infect the bacteria) are < ce cadbudy Usually double siranded DNA viruses (Figure 2.66). The protein coat + frotennces a (Hecate, Pelygonaf] 1's nucleic acid. These capsomeres are arranged in helical or polyhedral made up ‘Beveraf — seometric forms, Viruses cause diseases like mumps, small pox, herpes cap. f ‘and Influenza. AIDS in humans is also caused by a virus. In plants, the Sobsomeres Symptoms can be mosaic formation, leaf rolling and curling, yellowing Jakes over cellutey and vein clearing, dwarfing and stunted grow, SS wachinery of host cet/, wrustipty «Bd causes animar (AIDS, rmumbs, Flu, smabl pox, Herpes) ant Plant L'secse, Cleeg ve kb A cuvting > Yelloun'ne & Vein cleawieg , SranpnnAbyn Heel g roses LT mosaic Pormasos)BiowocicaL. CLASSIFICATION Viroids : In 1971, T.O. Diener discovered a new infectious agent that was smaller than viruses and caused potato spindle tuber disease. It was found to be a free RNA; it lacked the protein coat that ts found in viruses, hence the name virold. The RNA of the virold was of low molecular weight, Prions : In modern medicine certain infectious neurological diseases were found to be transmitted by an agent consisting of abnormally folded protein, The agent was simflar in size to viruses. These agents were called prions. The most notable diseases caused by prions are bovine spongiform encephalopathy (BSE) commonly called mad cow disease in cattle and its analogous variant Cr-Jacob disease (CJD) in humans. Lichens ; Lichens are symbiotic associations ‘.e, mutually useful associations, between algae and fungi, The algal component ts known as phycobiont and fungal component as myeobiont, which are autotrophic and heterotrophic, respectively. Algae prepare food for fung! and fungt provide shelter and absorb mineral nutrients and water for its partner. So close ts thelr 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, ve Biological classification of plants and animalswas first proposed by Aristotle on the basis of simple morphological characters, Linnaeus later classified all living organisms into two kingdoms ~ Plantae and Antmalfa. Whittaker proposed an elaborate five kingdom classification - Monera, Protista, Fungi, Plantae and Animalia, The main criteria of the five kingdom classification were cell structure, body organisation, ‘mode of nutrition and reproduction, and phylogenetic relationships. In the five kingdom classification, bacteria are included in Kingdom Monera. Bacteria are cosmopolitan in distribution. These organisms show the most extensive metabolic diversity. Bacteria may be autotrophic or heterotrophic in their mode of nutrition, Kingdom Protista Includes all single-celled eukaryotes such as Chrysophytes, Dinoflagellates, Euglenotds, Slime-moulds and Protazoans. Protists have defined nucleus and other membrane bound organelles. They reproduce both asexually and sexually, Members of Kingdom Fungl show a great diversity in structures and habitat, Most fung! are saprophytic in their mode of nutrition. ‘They show asexual and sexual reproduction. Phycomycetes, Ascomycetes, Basidiomycetes and Deuteromycetes are the four classes under this kingdom. ‘The plantae includes all eukaryotic chlorophyll-containing organisms. Algae, bryophytes, pteridophytes, gymnosperms and angiosperms are included in this group. The life cycle of plants exhibit alternation of generations — gametophytic and sporophytic generations. The heterotrophic eukaryotic, multicellular organisms lacking a cell wall are inchuded in the Kingdom Animalia, The mode of nutrition of these organisms ts holozolc. They reproduce mostly by the sexual mode, Some acellular organisms like viruses and viroids as well as the lichens are not included in the five kingdom system of classification. 202021 27Nope ye 2 10. 12, EXERCISES Discuss how classification systems have undergone several changes over a period of time? State two economically Important uses of: (a) heterotrophic bacteria () archaebacteria What fs the nature of cell-walls tn diatoms? Find out what do the terms ‘algal bloom’ and ‘red-tides' signify. How are virotds different from viruses? Desertbe briefly the four major groups of Protozoa. Plants are autotrophic. Can you think of some plants that are partially heterotrophic? What do the terms phycobtont and mycobiont signify? Give a comparative account of the classes of Kingdom Fungl under the following: () mode of nutrition (t) mode of reproduction What are the characteristic features of Euglenotds? Give a brief account of viruses with respect to their structure and nature of genetic material, Also name four common viral diseases, Organise a discussion in your class on the topic ~ Are viruses living or non- living?