Title Biological Classification Class 11 Notes.pdf ✅

Biological Classification 3 Biological classification is the scientific procedure of arranging organisms into groups on the basis of their similarities and dissimilarities and placing the group in a hierarchy of categories. Groups are assigned to a fixed hierarchy of categories such as species, genus, family, order, class and division, the final arrangement constituting a system of classification. A proper system of classification is a must because it is not possible to study every organism. The study of one or two organisms of a group gives sufficient information about the essential features of the group. Without any system of classification organisms cannot be identified. Classification helps in knowing the relationships amongst different groups of organisms. Aristotle (350 BC) divided animals into two categories, enaima (with red blood) and anaima (without red blood). Aristotle also classified animals on the basis of their habitat – aquatic (e.g., fish, whale), terrestrial (e.g., reptiles, cattle) and aerial (e.g., birds, bats). Kingdoms of Classification For years, all living organisms were classified into two kingdoms, the animal kingdom and the plant kingdom. Different workers proposed different kingdoms of classification. MONERA Monera is a kingdom of prokaryotes. Therefore, it is also known as prokaryota. Monerans are basically unicellular, may be mycelial, colonial and filamentous. Cell wall is made up of peptidoglycan, polysaccharides and cellulose. They do not contain any organised nucleus with distinct membrane. DNA is naked, i.e., not associated with histone proteins. It is called nucleoid. All the membrane bound cell organelles are absent like mitochondria, lysosomes, Golgi bodies, plastids, etc. Single stranded flagella, composed of flagellin, is present. Ribosomes are of 70S type (subunit 30S and 50S). Reproduction is by binary fission or budding. Monerans are adapted to all types of habitats–ocean bottoms, below icebergs, hot springs, dry deserts, dust particles, inside and outside the body of other organisms. There are two major groups of monerans, archaebacteria (ancient bacteria) and eubacteria (true bacteria). Eubacteria is of further two types; bacteria and cyanobacteria. Some other groups of monerans are mycoplasma, rickettsiae and actinomycetes. Archaebacteria These are relatively small, ancient and primitive form of bacteria. They consist of three main phylogenetic CBSE Books for Class 11 - https://bit.ly/3GLIUCf
4 Quick Reference groups, methanogens, halophiles and thermoacidophiles. Methanogens are obligate anaerobes. In bio-gas fermenters, these bacteria produce methane, e.g., Methanobacterium, Methanococcus. Halophiles are “salt-loving bacteria” as they are found to live in environments with a very high salt concentration. Thermoacidophiles live in extremely acidic environments (pH less than 2) that have extremely high temperatures (upto 110°C). They are found in hot sulphur springs. Bacteria Bacteria are a group of prokaryotic organisms which are characterised by peptidoglycan (also known as murein or mucopeptide) present in the cell wall, a compacted but naked DNA with attached mesosome and reserve food made of glycogen and fat. Bacteria were discovered by Leeuwenhoek in 1676. Cyanobacteria are a group of Gram negative, photosynthetic bacteria which consists of chlorophyll a, c-phycocyanin (blue coloured) and c-phycoerythrin (red coloured) pigments in them. These pigments together impart characteristic blue green colour to these cells. The structures of the bacterial cell that are present external to the cell wall are glycocalyx or capsule, flagella, fimbriae and pilli. The structure internal to the cell wall include plasmamembrane, mesosome, cytoplasm etc. Bacteria possess various forms and shapes, and are of 4 different types – coccus, bacillus, vibrio and spirullum. Based on the nature of staining, bacteria may be Gram + ve (retains the blue stain) or Gram – ve (does not retain the stain). Table : Differences between Gram + ve and Gram – ve bacteria Gram + ve bacteria Gram – ve bacteria 1. Cell wall more thick, thickness varies from 25-30 nm. Cell wall thin.Thickness varies 10-15 nm. 2. Cell wall is single layered. Three layered. 3. Porins are absent. Porins or hydrophilic channels occur in outer membrane. 4. High content of peptido- glycan (20-80% of the dry weight of the cell). Less content of peptidoglycan (10-20% of the dry weight of the cell). 5. Teichoic acids may be present. Teichoic acids absent. Besides the nuclear DNA, there is some extranuclear or extrachromosomal DNA, which is known as plasmid. Bacteria show both autotrophic and heterotrophic nutrition. Autotrophic nutrition is of two types – chemosynthesis and photosynthesis. Heterotrophic bacteria may be saprophytic, parasitic or symbiotic. Saprophytic bacteria obtain their food from organic remains, e.g., animal excreta, fallen leaves, vegetables, etc. Symbiotic bacteria live in mutually beneficial association with other organisms. Enteric bacterium Escherichia coli, live as a symbiont in human intestine. Parasitic bacteria live in contact with other living beings for obtaining nourishment or special organic compounds required for growth (growth factors). Bacteria show 3 methods of reproduction – vegetative reproduction, asexual reproduction and sexual reproduction. Vegetative reproduction includes budding and binary fission. Asexual reproduction takes place by endospore formation, conidia and zoospores. Sexual reproduction occurs in the form of genetic recombination. There are three main methods of genetic recombination – transformation, transduction, conjugation. During transformation, genetic material of one bacterial cell goes into another bacterial cell by some unknown mechanism and it converts one type of bacterium into another type (non-capsulated to capsulated form). This was first studied by Griffith (1928) in Diplococcus pneumoniae and hence is known as Griffith effect. In transduction genetic material of one bacterial cell goes to other bacterial cell by agency of bacteriophages or phages (viruses, infecting bacteria). Transduction was first of all reported in Salmonella typhimeurium by Zinder and Lederberg (1952). Conjugation was first reported by Lederberg and Tatum (1946) in E. coli bacteria. Conjugation occurs between donor cell and recipient cell. Donor cell is having sex pili and F-factor whereas recipient cell is having both. Economic importance Saprotrophic bacteria causes decay and decomposition of dead bodies of plants and animals, thus act as nature’s scavengers. In dairy industry, lactic acid bacteria (Streptococcus lactis) convert milk sugar lactose into lactic acid. Lactic acid coagulates milk protein casein and converts milk into yoghurt, curd and cheese. Some filamentous cyanobacteria (e.g., Anabaena, Nostoc, Scytonema, Tolypothrix) have the capacity to fix atmospheric nitrogen. All such cyanobacteria are heterocystous and the heterocysts are the main sites of nitrogen fixation. CBSE Books for Class 11 - https://bit.ly/3GLIUCf
Biological Classification 5 Some bacteria causes diseases of plants (e.g., citrus canker caused by Xanthomonas citri), animals (e.g., anthrax by Bacillus anthrasis) and humans (e.g., cholera by Vibrio cholerae, plague by Pasteurella pestis, etc). Actinomycetes Actinomycetes are mycelial (aseptate branched filaments) bacteria which form radiating colonies in culture. A number of antibiotics are produced by actinomycetes, especially the genus Streptomyces (streptomycin, chloramphenicol, tetracyclines, terramycin, erythromycin, viomycin, novobiocin, nystatin). Mycoplasma (PPLO) Mycoplasmas or mollicutes are the simplest and the smallest of the free living prokaryotes. The organisms are often called MLOs (mycoplasma like organisms) or PPLOs (pleuropneumonia like organisms). A cell wall is absent. Due to the absence of cell wall the organisms can change their shape and are pleomorphic. They mostly produce pleuropneumonia in domestic animals, a typical pneumonia and mycoplasmal urethritis in humans, little leaf disease of brinjal and witches broom in plants. PROTISTA Kingdom protista was created by Haeckel (1866). It includes all unicellular and colonial eukaryotes except those of green and red algae. Protists were the first eukaryotes to evolve about 1000 million years back. Phylogenetically the kingdom protista acts as a connecting link between the prokaryotic kingdom monera on one hand and the complex multicellular kingdoms – fungi, plantae and animalia on the other hand. Protists are regarded as ancestors of multicellular eukaryotic organisms. They are mostly aquatic. A well defined nucleus is present. The cytoplasm contains besides ribosomes, a variety of organelles such as mitochondria, plastids (in photosynthetic protists), lysosomes, cytoskeleton, endoplasmic reticulum and Golgi bodies. Cytoplasm is always in motion. The phenomenon is called cytoplasmic streaming or cyclosis. Flagella and cilia, have 9 + 2 pattern of microtubular strands. Food reserve is starch, glycogen, paramylon, chrysolaminarin and fat. Asexual reproduction is quite common and occurs through budding, binary fission, multiple fission, plasmotomy, sporulation, cyst formation, etc. Sexual reproduction occurs with the help of non-jacketed gametangia. It involves meiosis and karyogamy. The kingdom protista has been broadly divided into three main groups: − Photosynthetic protists (protistan algae) − Consumer-decomposer protists (slime moulds) − Protozoan protists Photosynthetic protists (Protistan algae) Photosynthesis takes place in these protists. They include chrysophytes, dinoflagellates and euglenoids. Diatoms included in phylum chrysophyta of algae are also known by the name golden algae. Diatoms are microscopic, single celled forms. Cell is called as frustule or shell. Diatoms have cell walls containing silica, constructed in two overlapping halves, epitheca and hypotheca, which fit together like two parts of a soap box (pennate types) or pair of petridishes (centric types). Due to their silica impregnations, the walls of diatoms are indestructible. As a result diatomaceous earth formation has occurred due to remains of cell walls of diatoms in the form of fossils. The common mode of multiplication is by binary fission. They serve as excellent insulators as are not destroyed by high temperature. They are used as very fine abrasive in metal polishes. Dinoflagellates are next to diatoms as producers in ocean. The blooms of Gonyaulax, Noctiluca and Gymnodinium cause red tides since the cells are present in such a large quantity that they colour the water. Some dinoflagellates are bioluminescent emit light. They are single celled, most of them are surrounded by a shell made up of thick interlocking plates. They are motile with two flagella, one projecting from one end and other running in a transverse groove. Like diatoms they have fucoxanthin in addition to chlorophyll a and chlorophyll c. They are autotrophic and photosynthetic. Some species of dinoflagellates are poisonous to vertebrates and when these accumulate, large number of fish in that region of ocean may be killed. Dinoflagellates are covered with cellulose cell walls which are divided into plates. The plates give them armoured appearance. Method of reproduction is only asexual. Sexual reproduction is usually absent (except in Ceratium). Euglenoids are Euglena like unicellular flagellates which possess pellicle instead of cell wall. Unicellular Euglena and its relatives have both animal and plant characteristics. Euglenoids are characterised by absence of cell wall, but they do contain flexible pellicle made up of protein. All the euglenoids have two flagella, one long and one short CBSE Books for Class 11 - https://bit.ly/3GLIUCf
6 Quick Reference by means of which they can swim easily. Euglena bears a flagellum inserted at the anterior end in a cavity. They bear a red pigmented eye spot and a gullet near the base of the flagellum. The pigment in eye spot is astaxanthin. Some euglenoids are holophytic (photoautotrophic) like other plants, few are saprobic. Some capture and ingest the organisms like animals (holotrophic). Green forms have saprobic mode in addition to holophytic (i.e., myxotrophic). Euglenoids store carbohydrates in the form of paramylon or paramylum bodies. Slime Moulds The slime moulds are widely distributed, growing in damp and shady places. They are consumer decomposer protists (= protistan fungi = fungus-animals) which are characterized by absence of chlorophyll. Slime moulds have characters of plants (cellulose cell wall), animals (phagotrophic nutrition) and fungi (spores). They take part in both decomposition of organic matter. Slime moulds exist in two types, acellular and cellular. Acellular slime moulds (plasmodial slime moulds) are present as slime masses on decaying leaves and lumber (disused articles of timber - wood for building). They move with the help of pseudopodia like the amoebae. The spores germinate to produce biflagellate swarm cells which function as gametes. On germination, each spore produces 1 - 4 haploid cells, either myxamoebae or swarm cells. Cellular slime moulds are characterised by complete absence of flagelleted cells in their life cycle, presence of wall-less uninucleate myxamoebae and formation of pseudoplasmodium by the aggregation of myxamoebae. Protozoans All protozoans are heterotrophs and live as predators or parasites. There are four major groups of protozoans. Amoeboid protozoans : These organisms live in fresh water, sea water or moist soil. They move and capture their 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. Flagellated protozoans : The members of this group are either free-living or parasitic. They have flagella. The parasitic forms cause diaseases such as sleeping sickness. Example Trypanosoma. Ciliated 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 Paramoecium. Sporozoans : This includes diverse organisms that have an infectious spore-like stage in their life cycle. The most notorious is Plasmodium (malarial parasite) which causes malaria. FUNGI Fungi are eukaryotic organisms which feed on dead and decaying organic matter or parasitize living organisms. They are achlorophyllous, spore bearing, non-vascular organisms or plants, which reproduce both sexually and asexually and whose generally filamentous and much branched plant body (mycelium) is surrounded by cell wall made of chitin or fungal cellulose or both. Fungi are ubiquitous (diverse habitats). Most of them are terrestrial but a few are aquatic (Monoblepharis, Saprolegnia). Many grow on humus soils as saprophytes e.g., mushrooms. The filamentous thread like structures that make up the fungal body is called mycelium. Hyphae is the unit structure that make up the mycelium (Gk word hypha - web). Hyphae are of two types – aseptate or coenocytic (multinucleate) and septate (number of partitions or septa). Septa are of 3 types – complete septum, septum with simple pore and septum with dolipore e.g., basidiomycetes. When mycelium by interweaving forms a compact resting structure it is called sclerotium. The septum becomes barrel-shaped around a central pore called dolipore septum, it may be surrounded by pore cap. When mycelium is interwoven to form web like structure it is called plectenchyma. It is of two types – prosenchyma and pseudoparenchyma. Fungi shows heterotrophic mode of nutrition as chlorophyll is absent. It may be either parasitic or saprophytic. Fungi may be eucarpic (only a part forms reproductive body) or holocarpic (whole mycelium forms reproductive body). Fungi reproduce by three methods - vegetative, asexual and sexual. Vegetative reproduction takes place by fragmentation, budding, oidium formation, sclerotia, chlamydospores and gemmae. Asexual reproduction takes place during favourable conditions. Asexual reproduction in fungi takes place by : − Zoospores : Uninucleate, thin walled, formed in zoosporangia and may be uniflagellate, e.g., Synchytrium or biflagellate, e.g., Saprolegnia. − Aplanospores : Thin-walled, non-motile spores formed inside sporangium, which give rise to new mycelium, e.g., Rhizopus, Mucor. − Conidia : non-motile, thin-walled exogenously produced spores on a conidiophore and sometimes CBSE Books for Class 11 - https://bit.ly/3GLIUCf