Biological Classification PDF

Aristotle was the earliest to attempt a more scientific basis for classification of organisms. He classified plants into trees, shrubs & herbs and animals into 2 groups, those which had red blood and those that did not. Aristotle...

Aristotle was the earliest to attempt a more scientific basis for classification of organisms. He classified plants into trees, shrubs & herbs and animals into 2 groups, those which had red blood and those that did not. Aristotle It is proposed by Linnaeus (1758). This system classifies organisms into Two Kingdoms- Plantae & Animalia. Carl Linnaeus  Prokaryotes, {Bacteria & Cyanobacteria}, & eukaryotes {fungi, mosses, ferns, gymnosperms & angiosperms} were included under “plants”. It is based on the presence of cell wall, but prokaryotes & eukaryotes are widely different in other features It included unicellular & multicellular organisms in the same group Example: Chlamydomonas & spirogyra were placed under algae It did not differentiate between heterotrophic Fungai & autotrophic green plants. Fungi have chitinous cell wall while the green plants have cellulosic cell wall It is proposed by R.H. Whittaker (1969). It includes Monera, Protista, Fungi, Plantae & Animalia. This classification is based on cell structure, thallus organisation, mode of nutrition, reproduction & phylogenetic relationships. R.H. Whittaker Characters Monera Protista Fungi Plantae Animalia Cell type Prokaryotic Eukaryotic Eukaryotic Eukaryotic Eukaryotic Non-cellular Present Present Cell wall (polysaccharide + Present in some (without Absent (cellulose) amino acid) cellulose) Nuclear Absent Present Present Present Present membrane Body Multicellular, Tissue/organ/ Cellular Cellular Tissue/organ organization loose tissue organ system Autotrophic (photosynthetic & Autotrophic Heterotrophic Heterotrophic Mode of chemosynthetic) (photosynthetic) Autotrophic (saprophytic (holozoic, nutrition and heterotrophic and (photosynthetic) or parasitic) saprophytic etc) (saprophyte/ heterotrophic parasite) Bacteria are the most abundant microorganisms. Hundreds of bacteria are present in a handful of soil. They also live in extreme habitats such as hot springs, deserts, snow & deep oceans. Many are parasites. Bacterial structure is very simple but they are complex in behaviour and show metabolic diversity. Some bacteria are autotrophic (synthesize food from inorganic substrates). Majority are heterotrophs (they do not synthesize the food but depend on other organisms or on dead organic matter for food). They live in harshest habitats such as extreme salty areas (halophiles), hot springs (thermoacidophiles) and marshy areas (methanogens). Archaebacteria have a different cell wall structure for their survival in extreme conditions. Methanogens are present in the guts of ruminant animals (cows, buffaloes etc). They produce methane (biogas) from the dung of these animals. They have a rigid cell wall and a flagellum (if motile). They include Autotrophs (photosynthetic & chemosynthetic) and Heterotrophs.  They have chlorophyll a similar to that of green plants. Cyanobacteria (blue-green algae) Unicellular, colonial or filamentous, marine or terrestrial algae. They often form blooms in polluted water bodies. The colonies are generally surrounded by Some of them fix atmospheric N2 in specialized cells called gelatinous sheath. heterocysts. E.g. Nostoc & Anabaena. They oxidize inorganic substances such as nitrates, nitrites & ammonia and use the released energy for their ATP production. They play a great role in recycling nutrients like nitrogen, phosphorous, iron & sulphur. Most abundant in nature Majority are important decomposers They are used to make curd from milk. Production of antibiotics. Fixing nitrogen in legume roots etc. Some are pathogens causing damage to human beings, crops, farm animals and pets. E.g. Cholera, typhoid, tetanus, and citrus canker. Bacteria reproduce mainly by fission. 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 to the other. They are organisms without a cell wall. They are the smallest living cells known. They can survive without oxygen. Many are pathogenic in animals and plants. It includes single-celled eukaryotes. Protists are primarily aquatic. It forms a link with plants, animals and fungi. Cell contains well defined nucleus and other membrane-bound organelles. Some have flagella or cilia. Reproduce asexually and sexually by a process involving cell fusion & zygote formation. They are found in fresh water and marine environments. They are microscopic and float passively in water currents (plankton). Most of them are photosynthetic. It includes diatoms & golden algae (desmids). Diatoms They have siliceous cell walls forming two thin overlapping shells, which fit together as in a soap box. The cell wall deposit of diatoms over billions of years in their habitat is known as ‘diatomaceous earth’. This is used in polishing, filtration of oils and syrups. Diatoms are the chief ‘producers’ in the oceans. Mostly marine and photosynthetic. They appear yellow, green, brown, blue or red depending on the main pigments in cells. Cell wall has stiff cellulose plates on the outer surface. Most of them have 2 flagella; one lies longitudinally and the other transversely in a furrow between wall plates. Red dianoflagellates (E.g. Gonyaulax) undergo rapid multiplication so that the sea appears red (red tides). Toxins released by such large numbers can kill other marine animals such as fishes. Mainly fresh water organisms found in stagnant water. Instead of cell wall, they have a protein rich layer called pellicle. It makes their body flexible. They have 2 flagella, a short and a long one. They are photosynthetic in the presence of sunlight. When deprived of sunlight they behave like heterotrophs by predating on other smaller organisms. The pigments of euglenoids are identical to those of higher plants. E.g. Euglena. They are saprophytic protists. The body moves along decaying twigs and leaves engulfing organic material. 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. Spores possess true walls. They are extremely resistant and survive for many years. The spores are dispersed by air currents. They are heterotrophs (predators or parasites). They are believed to be primitive relatives of animals. Amoeboid Flagellated Ciliated Sporozoans Protozoans Protozoans Protozoans Live in fresh Free-living or Aquatic, actively infectious spore- water, sea water parasitic. move using cilia. like stage in their or moist soil. They have They have a life cycle. They move and flagella. cavity (gullet) E.g. Plasmodium capture prey by Parasitic forms that opens to (malarial putting out cause diseases outside. parasite). It pseudopodia (false feet). like sleeping Due to the causes malaria. E.g. Amoeba. sickness. movement of E.g. cilia, water with Marine forms have silica shells Trypanosoma food enters into on their surface. gullet. Some are E.g. Paramecium parasites. E.g. Entamoeba. It is a unique kingdom of heterotrophic organisms. Fungi are cosmopolitan and occur in air, water, soil and on animals and plants. They prefer to grow in warm and humid places. E.g. Bread Mould, Orange Rots, Mushroom, Toadstools etc. White spots on mustard leaves are due to a parasitic fungus Some fungi are the source of antibiotics, e.g., Penicillium. Some unicellular fungi (e.g. Yeast) are used to make bread and beer. Other fungi cause diseases in plants and animals. E.g. wheat rust-causing Puccinia. Penicillium Yeast Puccinia Except yeasts, fungi are filamentous. Their bodies consist of long, slender thread-like structures called hyphae. The network of hyphae is known as mycelium. Some hyphae are continuous tubes filled with multinucleated cytoplasm. These are called coenocytic hyphae. Others have septae or cross walls in hyphae. Fungal cell wall is made of chitin & polysaccharides Most fungi are saprophytes (absorb soluble organic matter from dead substrates). Some are parasites. Some live as symbionts – in association with algae as lichens and with roots of higher plants as mycorrhiza The sexual cycle involves 3 steps: Plasmogamy: Fusion of protoplasm between two motile or non-motile gametes. Karyogamy: Fusion of two nuclei. Meiosis: Occurs in zygote resulting in haploid spores. Based on the morphology of mycelium, mode of spore formation and fruiting bodies, Fungi are classified into various classes.  Sexual reproduction :- Zygospores Asexual reproduction Takes place by zoospores are formed by fusion of two (motile) or by aplanospores (non-motile). gametes. These are produced in sporangium. These gametes are isogamous (similar) or anisogamous or oogamous (dissimilar). Unicellular (e.g. yeast, Sacharomyces) or multicellular (e.g. Penicillium). They are saprophytic, decomposers, parasitic or coprophilous (growing on dung). Mycelium is branched and septate. Asexual reproduction By conidia produced exogenously on the special mycelium called conidiophores. Conidia germinate to produce mycelium. Sexual reproduction By ascospores produced endogenously in sac like asci (sing. ascus). Asci are arranged to form ascocarps (fruiting bodies). Examples Aspergillus, Claviceps & Neurospora. Neurospora is used in biochemical and genetic work. Many members like morels & buffles are edible and are delicacies. Includes mushrooms, bracket fungi or puffballs. They grow in soil, on logs and tree stumps and in living plant bodies as parasites (e.g. rusts & smuts). Mycelium is branched & septate. The asexual spores are generally not found, but vegetative reproduction by fragmentation is common. Sex organs are absent, but plasmogamy occurs by fusion of two vegetative or somatic cells of different strains or genotypes. The resultant structure is dikaryotic. It gives rise to basidium. Karyogamy & meiosis occur in basidium producing 4 basidiospores exogenously. Basidia are arranged in fruiting bodies called basidiocarps. E.g. Agaricus (mushroom), Ustilago (smut) and Puccinia (rust fungus). Sex organs are absent, but plasmogamy occurs by fusion of two vegetative or somatic cells of different strains or genotypes. The resultant structure is dikaryotic. It gives rise to basidium. Karyogamy & meiosis occur in basidium producing 4 basidiospores exogenously. Basidia are arranged in fruiting bodies called basidiocarps. E.g. Agaricus (mushroom), Ustilago (smut) and Puccinia (rust fungus). Deuteromycetes reproduce only by asexual spores (conidia). Mycelium is septate and branched. Some are saprophytes or parasites. Majority are decomposers of litter and help in mineral cycling. E.g. Alternaria, Colletotrichum and Trichoderma.  It includes all plants (eukaryotic chlorophyll- containing organisms with cellulosic cell wall). Some are partially heterotrophic such as the insectivorous plants (e.g. Bladderwort and Venus fly trap) or parasites (e.g. Cuscuta). Plantae includes algae, bryophytes, pteridophytes, gymnosperms & angiosperms. Life cycle of plants has two distinct phases – the diploid sporophytic & the haploid gametophytic – that alternate with each other. The lengths of the haploid 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. They are multicellular, heterotrophic,eukaryotic organisms without cell wall They directrly or indirectly depend on plants for food. They digest food in an internal cavity and store food reserves as glycogen or fat. Mode of nutrition is holozoic {ingestion of food} They have a definite growth and pattern and grow into adults that have a definite shape and size Higher forms show sensory and neuromotor mechanism Most of them are capablkeof locomotion Sexual reproduction is by copulation of male and female followed by embryological development  In five-kingdom classification, acellular organisms (viruses & viroids) and lichens are not mentioned. Viruses are non-cellular and not truly ‘living’. So they are not included in five-kingdom classification. Viruses have an inert crystalline structure outside the living cell. Viruses are obligate parasites. When they infect a cell they take over the machinery of host cell to replicate themselves, killing the host. Louis Pasteur : Gave the name ‘virus’ {means venom or poisonous fluid} D.J Ivanowsky : Discovered virus. He recognised certain microbes that cause mosaic disease of tobacco. They were smaller than bacteria because they passed through bacteria – proof filters M.W. Beijernick : Demonstrated that the extract of the infected plants of tobacco could cause infection in healthy plants and called the fluid as ‘Contagium vivium fluidum’ {infectious living fluid} W.M. Stanley : Showed that viruses could be crystallized and crystals consist largely of proteins A virus is a nucleoprotein, i.e, it has a protein coat (capsid) & genetic material (RNA or DNA). No virus contains both RNA & DNA. The genetic material is infectious. Generally, viruses that infect plants have single stranded RNA. Viruses that infect animals have either single or double stranded RNA or double stranded DNA. Bacteriophages (viruses that infect bacteria) usually have double stranded DNA. The protein coat (capsid) made of small subunits (capsomeres) protects nucleic acid. Capsomeres are arranged in helical or polyhedral geometric forms. Polyhedral geometric Viruses cause diseases like mumps, small pox, herpes, influenza & AIDS. Helical In plants, the symptoms can be mosaic formation, leaf rolling & curling, yellowing & vein clearing, dwarfing & stunted growth. Viroid: It is an infectious agent with a free low molecular weight RNA and no protein coat. These are smaller than viruses. It is discovered by T.O. Diener (1971). He found that it caused potato spindle tuber disease. Lichens: Lichens are symbiotic associations (mutually useful associations) between algae & fungi. The algal component is called phycobiont (autotrophic) and fungal component is mycobiont T.O. Diener (heterotrophic). Algae prepare food for fungi and fungi provide shelter and absorb mineral nutrients and water for its partner. Lichens are very good Pollution indicators. They do not grow in polluted areas. Potato spindle tuber disease