Biological Classification Class 11 Notes for NEET

CBSE board is the central board that conducts board exams for classes 10th and 12th as these exams are conducted by central board authorities in the month of march and April. The Central Board of Secondary Education (CBSE) is one of the most prestigious and oldest educational boards in India. CBSE Board syllabus is mainly based on NCERT textbooks, as they set question papers by taking reference to NCERT textbooks. And this is the reason each competitive exam follows NCERT for setting their question paper.

Class 11 Biology Chapter 2 Notes created by MTG’s experienced subject matter experts vividly explain the various aspects of biological classification. Biological Classification class 11 notes cover all the important topics and concepts useful for the exam. It is certainly one of the most reliable study aids that you can place your hands on for building the foundation of Class 11 biology.

Importance of Biology Revision Notes

Biology Revision Notes for Class 11 CBSE – Quick revision notes for class 11 Biology are extremely useful for revising the entire syllabus during exam days. The revision notes cover all of the chapter’s important formulas and concepts. Even if you just want a quick overview of a chapter, quick revision notes are here to help. These notes will undoubtedly save you time on stressful exam days.

Biology is a fascinating subject, and the MTG Biology revision notes will help you prepare for your Class 11 CBSE exams. MTG’s expert-created Class 11 Biology NCERT notes cover the most recent CBSE curriculum, and these are well-researched CBSE notes that help students understand the topic clearly.

If you haven’t checked: The Living World Class 11 Notes

Topics Covered in Biological Classification Class 11 Notes

Notes prepared by MTG for biology chapter Biological Classification cover following topics

1. Class 11 Biological Classification Overview
2. Kingdoms of Classification
3. Kingdom MONERA
4. Kingdom PROTISTA
5. Kingdom Fungi
6. VIRUS, Viroids, lichens

Biological Classification Class 11 Notes for NEET

Class 11 Biological Classification Overview

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

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.

Kingdom 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

Important: The Living World Class 11 Important Question and Answers for CBSE PDF

Archaebacteria

These are relatively small, ancient and primitive form of bacteria. They consist of three main phylogenetic 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

S.no	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 peptidoglycan (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.

Biological Classification Class 11 Notes pdf 

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.
• 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 mycoplasma urethritis in humans, little leaf disease of brinjal, and witches broom in plants.

Kingdom 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 a 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 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.

You can check: 9 Amazing Biology Facts You Should Know

Kingdom 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 arranged in chains upon the conidiophore, e.g., Aspergillus and Penicillium or singly in Pythium, Phytophthora.
• There are three distinct phases in the process of sexual reproduction which occur in sequence of plasmogamy. (fusion of two protoplasts), karyogamy (fusion two haploid nuclei) and meiosis. If the fusing gametes differ in size and structure, they are called heterogametes and the process is called heterogamous.
• Heterogamous type of sexual reproduction is of two types : anisogamous and oogamous. Anisogamy consists of fusion of two morphologically similar gametes which differ in size. In oogamy, the gametes are produced inside the morphologically differentiated gametangia, antheridium and oogonium. The different methods by which compatible nuclei are brought together through plasmogamy are gametangial contact, gametangial copulation, spermatization and somatogamy.
• In gametangial contact the two gametangia come close to each other, but do not fuse. The male gametangium sends a tubular outgrowth, called fertilization tube, through which the non-motile male gamete or male nucleus migrates into the female gametangium. E.g., Phytophthora, Albugo. In gametangial copulation two gametangia fuse with each other and lose their identity in the sexual act resulting in the formation of zygospore. E.g., Mucor, Rhizopus.
• In spermatization some fungi produce numerous, minute, uninucleate, spore-like bodies called spermatia. These are transferred through various agencies to receptive hyphae or trichogyne of female gametangium. Finally, the contents of spermatium is transferred into receptive hypha through a pore. E.g., Puccinia graminis.
• In somatogamy, the sex organs are not formed and the fusion occurs between two vegetative or somatic cells resulting in dikaryotization. E.g., Agaricus.
• Fungi are divided into 4-classes according to the separation of mycelium and on the basis of characteristic features of reproduction:- phycomycetes, ascomycetes, basidiomycetes, deuteromycetes.

Table: Classification of fungi

Features	Phycomycetes	Ascomycetes	Basidiomycetes	Deuteromycetes
Common name	Algae like fungi	Sac fungi	Club fungi	Fungi imperfecti
Mycelium	Aseptate, coenocytic	Septate, branched unicellular	Secondary, mycelium, dikaryotic	Branched, septate mycelium
Asexual reproduction	Zoospores, aplanospores, chlamydospores, sporangiospore	Conidia, budding	Oidia, basidiospores	Conidia
Sexual reproduction	Isogamy, oogamy	Fusion of compatible nuclei. Ascospores formed in ascus	Somatogamy, Basidiospores formed on sterigmata	Absent or not known
Fruiting body	Zygospore	Ascocarp (cleistothecium, perithecium, apothecium)	Basidiocarp	Absent

Economic importance

Useful activities

• The fructifications of certain fungi are used as nutritious and delicious foods, e.g., Agaricus bisporus and A. campestris (mushrooms).
• Fungi especially yeasts (Saccharomyces cerevisiae), are utilised for the production of alcoholic beverages, such as beer, wine, whisky, rum and gin.
• Penicillium roqueforti and P. camemberti, are used for the production of cheese.
• Fungi have explored new field in medicine by producing antibiotics like :
  − Penicillin – Penicillium notatum and P. chrysogenum
  − Ergotine – Claviceps purpurea given after childbirth
  − Griseofulvin – Pencillium griseofulvum in skin diseases
  − Flavicin – Aspergillus flavus and A. fumigatus
• Fungi are responsible for the cause of a number of plant, animal (e.g., athlete foot : Tinea rubrum) and human diseases (e.g., ring worm : Trichophyton, Microsporum).
• Some important plant diseases are as follows :
  − Late blight of potato: Phytophthora infestans. (Famous famine of Ireland (1845) is associated with this disease which caused death of lakhs of people).
  − Early blight of potato: Alternaria solani.
  − Powdery mildews Erysiphe sps.
  − Loose smut of wheat: Ustilago tritici.
  − Black rust of wheat: Puccinia graminis-tritici.

You might also like: Board Exam Writing Skills – 5 Tips to Write Perfect Answers

Mycorrhiza

Mycorrhiza is the mutually beneficial or symbiotic association of a fungus with the root of higher plant. In a mycorrhizal association, the fungus may colonize the roots of a host plant either intracellularly or intracellularly. This mutualistic association provides the fungus with a renewable source of food through access to fixed carbon (sugars) from the plant photosynthate. In return, the plant gains the use of the mycelium’s tremendous surface area to absorb mineral nutrients from the soil especially phosphates.

VIRUS

• Virus (L. Poisonous fluid) is a group of ultramicroscopic, non-cellular, highly infectious agents that multiply only intracellularly inside the living host cells without involving growth and division. Outside the host cells, they are inert particles.
• Viruses are made up of nucleic acid (either RNA or DNA), envelope, capsid and enzymes.
• Envelope is the outer loose covering present in certain viruses like HIV and made of protein of viral origin, lipid and carbohydrates of host. Envelope proteins have subunits called peplomers. A virus without envelope is naked virus.
• Capsid is a protein covering around the genetic material. Capsid have protein subunits called capsomeres. TMV has 2130 capsomeres. They are arranged helically or in geometric forms. Capsid has antigenic properties.
• The nucleic acid present in the virus is called nucleoid. It is the infective part of virus which utilizes the metabolic machinery of the host cell for synthesis and assembly of viral components.
• The genetic material of viruses are of 4 types – double stranded DNA (ds DNA) e.g., Pox virus, Hepatitis-B virus; single stranded DNA (ss DNA) e.g., Coliphage f ×174 (cyclic); double stranded RNA (ds RNA) e.g., reo virus, wound tumour virus; single stranded RNA (ssRNA) e.g., tobacco mosaic virus, influenza virus, foot and mouth virus, polio virus, retroviruses (e.g., HIV) etc.
• Some common viral diseases are – influenza, polio, measles, chicken pox, hepatitis, AIDS, bird flu, SARS (severe acute respiratory syndrome) etc. In plants the symptoms can be mosaic formation, leaf rolling and curling, yellowing and vein clearing, dwarfing and stunted growth.
• Viruses are regarded as intermediate between non-living entities and living organisms. It is very difficult to ascertain whether they are living or nonliving.

Viroids

The term viroid has recently been introduced by T. O. Diener (1971) to describe the causal agent of the “potato spindle tuber disease”. Viroids are the smallest known agents of infectious disease. They consist of only of naked strand of nucleic acid without a protein coat. The nucleic acid of all viroids discovered so far has been shown to consists of single-stranded linear or circular RNA molecules. All viroids discovered so far cause several important diseases of cultivated plants like potato spindle tuber, citrus exocortis, chrysanthemum stunt and cucumber pale fruit.

lichens

• A lichen is a composite organism consisting of a fungus living in intimate association with one or more photosynthetic partners, that may be either a green alga or a cyanobacterium. The fungal member of the lichen is called mycobiont and the photosynthetic partner (algae or cyanobacterium) is called photobiont.
• Apparently, the alga or cyanobacterium provides the fungus with food, particularly carbohydrates produced by photosynthesis, and possibly with vitamins. The fungus probably absorbs, stores, and supplies water and minerals required by the alga or cyanobacterium. The lichens are considered to be “pioneer” organisms because they may make a region suitable for other plants through the weathering of rocks and the accumulation of organic debris. Decrease in lichen population of an area is indicative of air pollution.