CHAPTER 2 BIOLOGICAL CLASSIFICATION PREPARED BY DR KANAK

CHAPTER -2 BIOLOGICAL CLASSIFICATION PREPARED BY: DR. KANAK LATA CLASS: XI

• Who was the first person to attempt a more scientific basis of classification and what was his basis? 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. He also divided animals into two groups on the basis of presence or absence of red blood cells.

• Who gave two kingdom system of classification? Linnaeus gave two kingdom system of classification into Plantae and Animalia. Demerits of Linnaeus classification: This system did not distinguish between eukaryotes and prokaryotes, unicellular and multicellular organisms and photosynthetic (green algae) and non photosynthetic (Fungi) organisms.

R. H. Whittakar (1969) proposed a five kingdom classification namely Monera, Protista, Fungi, Plantae and Animalia. • What were the main criteria for Whittakar’s classification? The main criteria for Whittakar’s classifications were: • Cell structure. • Thallus organization. • Mode of nutrition. • Reproduction. • Phylogenetic relationships (Evolutionary relationships)

Kingdom Monera: • Sole members of this kingdom are bacteria. • Prokaryotes. • May be phosynthetic autotrophic or chemosynthetic autotrophic but mostly heterotrophs. • Present everywhere (omnipresent). • Wide range of habitat such as hot springs, deserts snow, deep oceans etc. • It shows extensive metabolic diversity. • Some are parasites. Structure is simple but behaviour is complex.

Classification of bacteria on the basis of their shapes: • Spherical: Coccus (Cocci) • Rod shaped: Bacillus (Bacilli) • Comma shaped: Vibrium (Vibrio) • Spiral: Spirillum (Spirilla)

Archaebacteria: • Archaebacteria are special because they live in most harsh habitats such as extreme salty water areas (halophiles), hot springs (thermoacidophiles) and marshy areas (methanogenes). • These bacteria have different cell wall structure which enables them to cope up extreme harsh condition. • Methanogenes are present in the guts of several ruminants like cow and buffaloes and hence responsible for production of methane gas from dung of these animals.

Eubacteria: • These are the true bacteria. Characterized by a rigid cell wall and presence of flagellum if motile. a)Cyanobacteria: • Called blue green algae. • They have chlorophyll ‘a’ similar to green plants that is why called photosynthetic autotrophs. • Cyanobacteria are unicellular, colonial or filamentous, marine or terrestrial algae. • The colonies are generally surrounded by mucilaginous (gelatinous) sheath. • Some of these organisms have capability to fix atmospheric nitrogen in specialized cells called heterocyst. Examples: Nostoc, Anabaena.

c) Chemosynthetic autotrophic bacteria: • It oxidizes various inorganic substances such as nitrites and ammonia and use the released energy for their ATP production. • They play great role in recycling nutrients like nitrogen, phosphorus, iron and sulphur d)Heterotrophic bacteria: • Most abundant in nature. • Mostly decomposers. • They are also helpful in making curd from milk, production of antibiotics, fixing nitrogen in legume root nodules. • Some causes severe diseases in human beings ( cholera, typhoid, tetanus) and plants (citrus canker)

e)Mycoplasma: • Lack of cell wall. • Smallest living cells known and can survive without oxygen. • Many are pathogenic in plants and animals. Reproduction in Bacteria: • Mainly by fission. • During unfavourable situation reproduces by spores. • They also reproduce by a sort of sexual reproduction by adopting a primitive type of DNA transfer from one bacterium to the other by conjugation tube.

Kingdom Protista: • Single celled eukaryotes so a well defined nucleus and membrane bound organelles are present. • Primarily aquatic. • This kingdom forms a link with the others dealing with plants, animals and fungi. • Presence of cilia or flagella. • Reproduces asexually and sexually by a process involving cell fusion and zygote formation.

v. Chrysophytes: Includes diatoms and golden algae (desmids) Present in fresh water as well as marine environments. Microscopic and plankton. Mostly photosynthetic. In diatoms the cell wall form two thin overlapping shells, that fit together as is shop box. The walls are embedded with silica and thus the walls are indestructible. It leave large amount of cell deposits in their habitat. Chief producers in the oceans. Diatomaceous earth: Deposits of silica on the earth of diatoms habitat is called diatomaceous earth. It is used in polishing, filtration of oils and syrups.

v. Dianoflagellates: Mostly marine and photosynthetic Yellow, green, brown, blue or red in colour depending on the main pigments present in their cells. The Cell wall has outer surface of cellulose. Most of them have two flagella: one lies longitudinally and the other transversely in a furrow between the wall plates. Due to the excessive growth of red dianoflagellates (Gonyaulax) the sea appear red (red tides). Toxic released by them may even kill marine fishes.

v. Euglenoids: • Majority of them are fresh water found in stagnant water. • Instead of a cell wall, they have a protein rich layer called pellicle which makes their body flexible. • Presence of two unequal size flagella. • Photosynthetic but sunlight is not present, they behaves as heterotrophs by predating on other smaller organisms. Example: Euglena.

v. Slime moulds: • Saprophytic protists. • Under suitable conditions, they form an aggregation called plasmodium which may grow and spread over several feet. • During unfavourable conditions, the plasmodium differentiates and forms fruiting bodies bearing spores at their tips. • These spores are resistant and survive for many years. The spores are dispersed by air currents.

v. Protozoans: • Heterotrophs and live as predators or parasites. • Regarded as primitive relatives of animals. i) Amoeboid protozoans: • Present in fresh water, sea water or moist soil. • They move and capture their prey with the help of pseudopodia (Amoeba). • Marine forms have silica shells on their structure. • Entamoeba is parasite.

ii)Flagellated protozoans: • Either free living or parasite. • Presence of flagella. • Parasitic form causes diseases like sleeping sickness. Example: Trypanosoma. iii)Ciliated Protozoans: • Aquatic. • Presence of cilia. • Presence of cavity (gullet) that opens to the outside of the cell surface. • Beating action of cilia causes the water laden with food to be entered into the gullet. Example: Paramecium.

iii)Sporozoans: • Have infectious spore like stage in their life cycle. • Example: Plasmodium (Malarial parasite) that causes malaria.

Kingdom fungi: • Heterotrophs. • Great diversity in morphology and habitat. • Fungi are cosmopolitan and occur in air, water, soil and on animals and plants. • Prefer to grow in warm and humid places. • Except yeast all are filamentous. • Cell wall is composed of chitin and polysaccharides. • They may be saprophytes (on dead), parasites (on or in living), symbionts (association with algae) or micorrhiza (with roots of higher plants). • Reproduction by vegetative means (fragmentation, fission, budding). • Asexual reproduction by spores called conidia or sporangiospores or zoospores. • Sexual reproduction by oospores, ascospores and basidiospores. • The various spores are produced in distinct structure called fruiting body.

Steps of sexual reproduction: • Fusion of protoplasm between two motile or non-motile gametes called plasmogamy. • Fusion of two nuclei called karyogamy. • Meiosis in zygote resulting in haploid spores. Diakaryon and dikaryophase: In ascomycetes and basidiomycetes, an intervening dikaryotic stage (n+n) that is two nuclei per cell occurs. Such a condition is called a dikaryon and the phase is called dikaryophase of fungus.

Various classes of kingdom Fungi: ØPhycomycetes: • Found in aquatic habitats and on decaying wood in moist and damp places or as obligate parasites on plants. • Mycelium is aseptate and coenocytic (multinucleate). • Asexual reproduction takes place by zoospores (motile) or by aplanospores (non-motile). • These spores are endogenously produced in sporangium. • Zoospores are formed by fusion of two gametes which may be isogamous or anisogamous. (Oogamous). Example: Mucor, Rhizopus, Albugo

ØAscomycetes: • Called Sac fungi. • May be unicellular (Yeast, Sacharomyces) or multicellular (Penicillium). • Saprophytic, decomposers, parasitic or coprophilous (growing on dung). • Mycellium is branched and septate. • Asexual spores are conidia produced exogenously on conidiophores. • Sexual spores are ascosopres produced endogenously in sac like asci (ascus- singular). Asci are arranged in a fruiting body called ascocarps. • Examples: Aspergillus, Claviceps, Neurospora ( used in biochemical and genetic work) • Members like morels and baffles are edible.

ØBasidiomycetes: • Commonly known forms are mushrooms, bracket fungi or puffballs. • Grow in soil, on logs and tree stumps. • Some are parasites like Puccinia and Ustilago. • Mycellium is branched and septate. • Absence of asexual spores but reproduces by vegetative means by fragmentation. • The sex organs are absent but fusion of two vegetative cells of different strains takes place which results in the formation of basidium. Karyogamy and meiosis takes place in basidium resulting in the formation of four basidiospores which are exogenous. The basidia are arranged in fruiting bodies called basidiocarps. • Examples: Agaricus, Ustilago, Puccinia.

ØDeuteromycetes: • Called fungi Imperfecti due to presence of only asexual and vegetative phase. • Reproduces by asexual spores called conidia. • Mycellium is septate and branched. • They may be saprophytes, parasites or decomposers. • Examples: Alternaria, Colletotrichum, Trichoderma.

Kingdom plantae: • Includes all eukaryotes chlorophyll containing organisms. • Few are partially heterotrophs like insectivorous plants (Bladderwort, Venus Fly trap) or parasites (Cuscuta). • Cell wall mainly made up of cellulose. • It includes algae, bryophytes, pteridophytes, gymnosperms and angiosperms. • Life cycle consists of two distinct phases: the diploid sporophytic and haploid gametophytic phase. These two phases alternate each other which is called alternation of generation.

Kingdom Animalia: • Consists of heterotrophic eukaryotic organisms that are multicellular and lack cell wall. • Directly or indirectly depends on plant for their food • Mode of nutrition is holozoic. • Reserve food material is in the form of glycogen or fat • Definite shape and size. • Definite growth pattern. • Sexual reproduction is by copulation of male and female followed by embryological development.

Viruses, Viroids and Lichens: Viruses: • Viruses are not true living that is why did not find a place in classification. • The viruses are non-cellular organisms. • They are characterized by having an inert crystalline structure outside the living cell. • Smaller than bacteria they passed through bacteria- proof filters. • They are obligate parasites. • They are inert outside their specific host cell. • In addition to protein viruses may contain DNA or RNA as genetic material which is infectious.

• Viruses that infect the bacteria are called bacteriophages or bacterial viruses and they have DNA as genetic material. • The protein coat of virus is called capsid made up of small subunits called capsomeres that protects nucleic acid. Capsomeres are arranged in helical or polyhedral geometric forms. • Most common diseases caused by viruses are mumps, small pox, herpes, influenza, AIDS etc. • In plants the symptoms can be mosaic formation, leaf rolling and curling, yellowing and vein clearing, dwarfing and stunted growth.

Viroids: • Smaller than virus. • Lack of protein coat. • Only free RNA is present which is of low molecular weight. • Discovered by T. O. Diener in 1971 and caused potato spindle tuber disease. Lichens: • It is an association of algae and fungi in which both are mutually benefitted from each other. • The algal component is called phycobiont and fungal component is called mycobiont. • Algae prepare food for fungi and fungi provide shelter and absorb mineral nutrients and water for its partner. They are very good pollution indicators as they do not grow in polluted areas.