Biological Classification PDF

02 Biological Classification 01. INTRODUCTION There have been many attempts to classify living organisms. It was done instinctively not using criteria that were scientific but borne out of a need to use organisms for o...

02 Biological Classification 01. INTRODUCTION There have been many attempts to classify living organisms. It was done instinctively not using criteria that were scientific but borne out of a need to use organisms for our own use for food, shelter and clothing. Initial classifications were done instinctively not using scientific but borne out of a need to use organisms for own use. Classification systems for living organisms have hence undergone several changes over time. Though plant and animal kingdoms have been a constant under all different systems of classifications. The understanding of what groups/organisms be included under these kingdoms have been changing. The numbers and nature of other kingdoms have also been understood differently by different scientists. NCERT Question : Discuss how classification systems have undergone several changes over a period of time? 02. HISTORY OF TAXONOMY (A) ARISTOTLE : 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. Aristotle also divided animals into two groups, those which had red blood and those that did not. www.allen.in [ 37 ]  NEET : Biology Plants (On the basis of Morphology) Trees Shrubs Herbs Animals Anaima Enaima (Invertebrates with no red blood) (Vertebrates with red blood) (B) THEOPHRASTUS : He wrote first book of Botany i.e. “Historia Plantarum”. He is known as father of botany and father of ancient plant taxonomy also. Theophrastus classified plants into four groups on the basis of growth forms. (i) Herbs (ii) Shrubs (iii) Undershrub (iv) Trees (C) CAROLUS LINNAEUS (TWO KINGDOM CLASSIFICATION) : He is known as father of taxonomy, father of plant Life forms taxonomy and father of animal taxonomy. Linnaeus gave the two-kingdom system classification. He grouped plants and animals into kingdom Plantae and kingdom Animalia respectively Plantae cell wall Animalia on the basis of cell wall only. present cell wall absent He gave plant nomenclature in his book “Species Plantarum”. Linnaeus gave plant classification in his book “Genera Plantarum”. He used mainly the character of male reproductive organ i.e. stamen (androecium) and made 24 classes of plant. [ 38 ] www.allen.in Biological Classification Demerits of two kingdom classification : In two kingdom classification prokaryotes (bacteria, blue green algae) and eukaryotes (fungi, mosses/bryophytes, fern/pteridophytes, gymnosperm and angiosperm) are placed in same kingdom. In two kingdom system unicellular organism (Chlamydomonas and Chlorella) and multicellular organism (Spirogyra) are placed together under algae in plant kingdom, because they have cell wall. This classification did not differentiate between the heterotrophic fungi and autotrophic green plants, though they also showed a characteristic difference in their cell wall composition - the fungi had chitin in their walls while the green plants had a cellulosic cell wall. Hence the two kingdom classification used for a long time was found inadequate. Besides, gross morphology a need was also felt for including other characteristics like cell structure, nature 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 different 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 scientists over the time. Therefor three kingdom classification (Haeckel), four kingdom classification (Copeland) also came into existence. (D) GEORGE BENTHAM AND JOSEPH DALTON HOOKER : (i) Both Bentham and Hooker are related to Royal botanical garden. (ii) In this book, Bentham and Hooker gave the biggest and natural classification of spermatophyta (seeded plants) Division – Spermatophyta (202 families) 3 Classes Dicotyledonae Gymnospermae Monocotyledonae (165 families) (3 families) (34 families) www.allen.in [ 39 ]  NEET : Biology Merits of Bentham and Hooker classification :- The classification of Bentham and Hooker was mainly based on the floral characters. The classification of Bentham and Hooker was natural. It is the simplest classification because this classification is based on actual observations. Demerits of Bentham and Hooker :- In this classification the phylogeny of plants is not considered, because in it, gymnosperms are placed in between dicots and monocots. The sequence of evolution is as follows :- Phylogeny = Gymnosperm → Dicots → Monocots. (E) R. H. WHITTAKER : R.H. Whittaker (1969) proposed a five-kingdom classification. The kingdoms defined by him were named as Monera, Protista, Fungi, Plantae and Animalia. The main criteria used by him for making classification are: (i) Cell structure (Complexity of cell) (ii) Thallus organisation (complexity of organism)/Body organization (iii) Mode of nutrition (iv) Reproduction/Life style (v) Phylogenetic relationship [ 40 ] www.allen.in Biological Classification TABLE 2.1 Characteristics of the Five Kingdoms Five Kingdoms Characters Monera Protista Fungi Plantae Animalia Cell type Prokaryotic Eukaryotic Eukaryotic Eukaryotic Eukaryotic Noncellulosic Present Present Cell wall (Polysaccharide + Present in some (without Absent (cellulose) amino acid cellulose) Nuclear Absent Present Present Present Present membrane Body Multicellular/ Tissue/ Tissue/organ/ Cellular Cellular organisation loose tissue organ organ system Autotrophic Autotrophic Heterotrophic (chemosynthetic and Heterotrophic Mode of (Photosynthetic) Autotrophic (Holozoic/ photosynthetic) and (Saprophytic nutrition and Photosynthetic Saprophytic Heterotrophic /Parasitic) Heterotrophic etc.) (saprophyte/parasite FIVE KINGDOM (i) Monera : All the prokaryotes (Eubacteria, Rickettsia, Actinomycetes, BGA, Archaebacteria, Mycoplasma) (ii) Protista : All the Unicellular eukaryotes (Dinoflagellates, Diatoms, Euglenoids, Slime moulds (false fungi) and Protozoans) (iii) Fungi : True fungi (iv) Plantae : All the multicellular plants – Algae, Bryophyta, Pteridophyta, Gymnosperms, Angiosperms. (v) Animalia : All the multicellular animals Note : (a) In five kingdom classification virus, viroids, prions and lichens are not mentioned. (b) According to five kingdom classification. Chlamydomonas and Chlorella are placed in kingdom protista. www.allen.in [ 41 ]  NEET : Biology Species is smallest taxonomic category and basic unit of classification. Each rank or taxon in fact represents a unit of classification. These taxonomic groups/categories are distinct biological entities and are not merely morphological aggregates. Each genus may have one or more than one specific epithets representing different organisms, but having morphological similarities. Genus comprises a group of related species which has more characters in common in comparison to species of other genera. In museum insects are preserved in insect box after collecting, killing and pinning. Keys are generally analytical in nature. Classification proposed by Bentham and Hooker is natural non-phylogenetic. Whittaker gave the five kingdom (Monera, Protista, Fungi, Plantae and Animalia) Classification. BEGINNER’S BOX-1 TAXONOMIC CATEGORIES TO CARL WOESE 1. Family is placed between :- (1) Genus and species (2) Order and class (3) Class and genus (4) Order and genus 2. Chemosynthesis is mode of nutrition is found in kingdom :- (1) Monera (2) Protista (3) Fungi (4) Plantae 3. Which of the following is not mention in five kingdom classification :- (1) Bacteria (2) Virus (3) Amoeba (4) Fungi 4. Smallest unit of classification is :- (1) Genus (2) Species (3) Order (4) Kingdom 5. Biological concept of species is based on :- (1) Morphology (2) Interbreeding (3) Physiology (4) All 6. According to five kingdom classification, multicellular heterotrophs are included in : (1) Three kingdom (2) One kingdom (3) Two kingdom (4) Three domain 7. According to five kingdom classification, archaebacteria belong to :- (1) Archaea (2) Protista (3) Plantae (4) Monera [ 42 ] www.allen.in Biological Classification 8. According to R.H. Whittaker which kingdom includes producer, decomposer and consumer is: (1) Plantae (2) Fungi (3) Protista (4) Animalia 9. Basis of two kingdom system was :- (1) Cell wall (2) Nucleus (3) Cell membrane (4) Pigments 10. Two kingdom classification was given by :- (1) Linnaeus (2) Bentham and Hooker (3) Theophrastus (4) Carl Woese 11. Consider the following statements with respect to characteristic features of the kingdom. (i) In animalia, the mode of nutrition is autotrophic. (ii) In monera, the nuclear membrane is present. (iii) In protista, the cell type is prokaryotic. (iv) In plantae, the cell wall is present. Of the above statements, which one is correct ? (1) (i) only (2) (ii) only (3) (iii) only (4) (iv) only 12. Analyse the following statements and identify the correct options given below I. Two kingdom system of classification did not distinguish between the eukaryotes and prokaryotes, unicellular and multicellular organism and green algae and fungi. II. The two kingdom classification used for a long time was found inadequate. Options And Answer(s) (1) I a true, but II is false (2) I is false, II is true (3) I and II are true (4) I and II are false 13. Match the kingdom listed under column I with the characteristics give under column II choose the answer which give the correct combination. Column I Column II Kingdom haracteristics (A) Animalia (P) Unicellular prokaryote (B) Plantae (Q) Multicellular heterotroph (C) Protista (R) Multicellular autotroph (D) Monera (S) Unicellular eukaryote (1) A–S, B–Q, C–R, D–P (2) A–Q, B–R, C–S, D–P (3) A–S, B–R, C–Q, D–P (4) A–R, B–Q, C–S, D–P www.allen.in [ 43 ]  NEET : Biology 03. KINGDOM – MONERA Bacteria are the sole members of the Kingdom Monera. They are the most abundant micro-organisms. Bacteria occur almost everywhere. Hundreds of bacteria are present in a handful of soil. 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. Main characteristic of prokaryotes: (a) Cell wall: Cell wall of prokaryotes is made up of peptidoglycan or murein which is a type of mucopeptide. Peptidoglycan is made of polysaccharides and amino acids. (b) Cell membrane: Like eukaryotes the cell membrane of prokaryotes is made up of lipoprotein [lipid + protein] The space between cell wall and cell membrane is known as periplasmic space. This space, is analogous to lysosome because in this space the digestion of complex substance is done. Cell wall Cell membrane Periplasmic space Cytoplasm 70S type ribosomes Genophore/Nucleoid (c) Cytoplasm: The cytoplasm of prokaryotes lacks membrane bound cell organelles. In Prokaryotic cell, the nucleus is indistinct. The nucleus of prokaryotes is also known as incipient nucleus, genophore, nucleoid or fibrillar nucleus. Nuclear membrane is absent around nucleus. It also lacks nucleolus. Prokaryotes also lack the true chromosome. Instead of it, a false chromosome is present, which is made up of ds circular naked DNA + Non-histone protein like polyamines. This false chromosome coils and forms the chromosomal region, which is known as nucleoid. In prokaryotes ribosomes are of 70s type. Ribosomes are the site of protein synthesis [ 44 ] www.allen.in Biological Classification (A) EUBACTERIA : (i) Shape of Bacteria : Bacteria are grouped under four categories based on their shape: (a) The spherical Coccus (pl.: cocci) e.g. Streptococcus (b) The rod-shaped Bacillus (pl.: bacilli) e.g. Escherichia coli (c) The comma-shaped Vibrium (pl.: vibrio) e.g. Vibrio cholerae (d) The spiral Spirillum (pl.: spirilla) e.g. Spirillum Spore Flagellum Cocci Spirilla Bacilli Vibrio Figure 2.1 Bacteria of different shapes (ii) Motility in Bacteria : Bacteria are motile as well as non-motile. Movement in bacteria takes place by means of flagella. Number and arrangement of flagella is called flagellation. Peritrichous – When flagella are found on the whole body of bacterium e.g. E.coli., Salmonella typhi (iii) Pili (Sing. Pilus) : Bacterial cell wall is covered by numerous hair like structures called pili. Pili are smaller than the flagella. They are of two types (A) Longer pili, (B) Shorter pili. Longer pili are also known as 'F' pili or 'sex' pili. Longer pili occur in only donor (F+ or male) bacteria and help in conjugation. These are absent in recipient bacteria or female. The shorter pili take part in attachment to rocks in streams and to the host tissue. These are also known as 'infective' pili or Fimbriae. These are found only in pathogenic bacteria. www.allen.in [ 45 ]  NEET : Biology (iv) Structure of prokaryotic cell or a typical bacterial cell : Though the bacterial structure is very simple, they are very complex in behaviour Bacterial cell has a chemically complex cell envelope. The cell envelope consists of a tightly bound three layered structure. (a) Glycocalyx (b) Cell wall (c) Cell membrane Although each layer of the envelope performs distinct function they act together as a single protective unit. (a) Glycocalyx Capsule - Thick, nonsticky, regular and smooth layer. Slime layer - Thin, sticky, irregular and rough layer. When bacteria are surrounded by capsule, called capsulated bacteria. Formation of capsule is performed by cell membrane. Capsulated bacteria are mostly pathogenic. Capsule is made up of polysaccharides and polypeptides. When the molecules of polysaccharides are very loosely arranged they form a thin and sticky layer, known as slime layer. Glycocalyx protects the bacteria from W.B.C. and also helps in colony formation. (b) Cell Wall – Bacterial cell wall is rigid and made up of mainly peptidoglycan or murein which is a type of muco-peptide. Gram (+) and Gram (-) bacteria: In Gram (+) bacteria cell wall is single layered and thick. It is made up of peptidoglycan. Lipids are also present but in less quantity. [ 46 ] www.allen.in Biological Classification While in Gram (-) bacteria cell wall is double layered. Inner layer is thin and composed of peptidoglycan while outer layer is thick and made up of lipopolysaccharide. Some quantity of lipoproteins and phospholipids are also present in outer layer. (c) Cell membrane or Plasmalemma or Plasma membrane This is the inner most layer. Bacterial cell membrane is made up of lipoprotein like the eukaryotic membrane. (d) Cytoplasm – In bacterial cytoplasm membrane bound cell organelles viz. Mitochondria, Chloroplast E.R., Lysosome, Golgi body, Microbodies are absent. Bacterial cytoplasm does not show streaming or cyclosis. (e) Cytoplasmic Structures – Mesosomes – Mesosome was discovered by F. James. Mesosome is a special membranous structure formed by the extension or infoldings or invaginations of plasma membrane into the cell. These extensions are in the form of vesicles, tubules and lamellae. These are functionally mitochondria like structures. Oxidative enzyme are found in mesosome. Functions They help in cell respiration and cell wall secretion processes to increase surface area of the plasma membrane and enzymatic content. Help in DNA replication and distribution to daughter cells during cell division. Storage granules/Inclusion bodies – Glycogen granules –They store carbohydrate Volutin granules – These are also known as metachromatic granules or phosphate granule. Chromatin material (Nucleoid) – Nucleus of bacterial cell is called Nucleoid or Genophore or Incipient nucleus or fibrilar nucleus. Nuclear membrane and nucleolus are absent. True chromosomes are also absent in bacterial cells. Instead of true chromosome they contain a single false chromosome or prochromosome. It consists of a double stranded circular naked DNA (without histone) + Non-histone proteins. Non-histone proteins are polyamines. Nucleoid is connected to mesosome. www.allen.in [ 47 ]  NEET : Biology Beside this DNA another small and circular DNA is also present in bacterial cell, which is called Plasmid. It is also known as extra chromosomal or extranuclear or extra genomic genetic material. (The term 'plasmid' was given by Lederberg). Plasmids have the ability to replicate independently. Plasmids are of many types on the basis of their function or phenotypic character F-plasmid (fertility factor) – On the basis of presence or absence of 'F' plasmid, there are two types of bacteria. (a) F+ – Cells, carrying 'F' plasmid, act as donor and are called F+ or male. (b) F– – Cells, lacking 'F' plasmid, act as recipient and are called F– or female. When 'F" plasmid is attached with main DNA, it is designated as Episome and this type of cell is known as HFR cell. (HFR – Highly frequent recombinant cell) Plasmid Plasmid (Episome) FF++or or Donor Donor Hfr or Hfr or Donor Donor FF–- or or Recipient Recipient Plasmid Plasmid (Episome) – + F or Recipient F or Donor Hfr or Donor [ 48 ] www.allen.in Biological Classification R-factor - Resistance to certain antibiotics. Antibiotic Antibiotic Degraded Degraded Antibiotic Antibiotic Enzyme R-Plasmid R-Plasmid Enzyme (v) Staining of Bacteria : Gram Staining technique : (a) First of all H.C. Gram differentiated bacteria on the basis of staining. (b) In the first step of this method bacteria are stained with Crystal violet or gentian violet and then KI solution. (c) After staining, bacteria are washed with Acetone or Ethyl alcohol. After washing some bacteria retain the stain and some bacteria are decolourised. (d) Bacteria which retain stain (violet or purple) are called Gram(+) and bacteria which decolourise are known as Gram(–). Gram(–) bacteria are counter stained by saffranine. Crystal Violet KI-I Solution Destain with ethanol Safranine Gram Negative Gram Positive www.allen.in [ 49 ]  NEET : Biology (vi) Bacterial Nutrition : Bacteria as a group show the most extensive metabolic diversity. Most of the bacteria are heterotrophic but some are autotrophic. On the basis of nutrition bacteria are classified into following three categories. Nutrition Nutrition Autotrophic Autotrophic Heterotrophic Heterotrophic Symbiotic Symbiotic CO22 += HH22OO Sugar Sugar (a) Autotrophs : These bacteria use light or chemical energy for their own food synthesis. On the basis of source of energy autotrophs are of following two types (i) Photosynthetic autotrophs = Photoautotrophs = Phototrophs These bacteria use light energy for food synthesis. In bacterial photosynthesis H-donor is not water, so they do not release oxygen during photosynthesis hence this is called Non-oxygenic photosynthesis e.g.- Rhodospirillum. Photosynthetic structure – Some eubacteria (purple bacteria and green sulphur bacteria) have capacity of photosynthesis. In bacterial cytoplasm many photosynthetic pigments are scattered. Pigments – In purple bacteria (sulphur and non-sulphur) – Bacteriochlorophyll 'a' & 'b'. In green sulphur bacteria – Bacteriochlorophyll 'a', Chlorobium chlorophyll or Bacterioviridin. Autotrophic Photosynthetic Chemosynthetic Source of energy: Light Source of energy: Chemical [ 50 ] www.allen.in Biological Classification (ii) Chemosynthetic autotrophs = Chemoautotrophs = Chemotrophs These are non-photosynthetic autotrophs i.e.; photosynthetic pigments are absent. They use chemical energy instead of light energy for food synthesis. These bacteria oxidise some chemical compounds and release energy which is used for food synthesis. e.g. Nitrifying bacteria – They oxidise nitrogenous compounds and obtain energy. Nitrite bacteria – Convert ammonia into Nitrite (Nitrosomonas & Nitrococcus) Nitrate bacteria – Convert nitrite into nitrates (Nitrobacter) Note : Chemosynthetic bacteria play a great role in recycling nutrients like nitrogen, phosphorus, iron and sulphur. NCERT Question : State two economically important uses of heterotrophic bacteria (b) Heterotrophs : Most of the bacteria are heterotrophic i.e., they cannot manufacture their food. They receive their own food from dead organic matter or living organism. These are of following types (i) Saprotrophic bacteria – These bacteria obtain food from dead and decaying organic matter. e.g. Bacillus vulgaris, Clostridium botulinum, Pseudomonas (ii) Parasitic bacteria – They obtain their food from living organism. e.g. Mycobacterium leprae, Mycobacterium tuberculosis. (c) Symbiotic bacteria : They form symbiotic relation with other organisms. These bacteria convert atmospheric nitrogen into ammonia and then into nitrogenous compounds like Amino acids, NO3 or salts of ammonia. e.g. Rhizobium www.allen.in [ 51 ]  NEET : Biology (vii) Respiration : On the basis of respiration bacteria are of two types (1) Aerobic bacteria: They use oxygen in respiration. e.g. Azotobacter (2) Anaerobic bacteria: They do not use oxygen in respiration. e.g. Clostridium (viii) Reproduction : Reproduction leads to increase in number of individuals. Bacteria reproduce only by asexual reproduction but they also perform a primitive type of gene transfer from one bacterial cell to the other which is called genetic recombination. (a) Asexual Reproduction : Following methods of asexual reproduction are found in bacteria. (i) Binary fission: Cell wall Cell This is the most common method of bacterial reproduction. membrane DNA First of all, DNA replication takes place in bacterial cell. Under favourable conditions bacterial cell divides into two cells due to formation of a septum (partition) in the centre of the cell. Figure 2.3 A dividing bacterium Each daughter cell grows into a new bacterium. Thus, the bacterial cell divides by amitosis which is a faster process then mitosis or meiosis. Adequate Adequate Nutrients Nutrients Moisture Moisture Temperature Temperature (ii) By Endospore: Endospore formation occurs under unfavourable conditions. Spore Only one endospore is formed in a bacterial cell. It is a highly resistant structure. It is resistant to high temperature, radiations, antibiotics and chemicals. Endospore have maximum resistant power due to presence of Ca-dipicolinate in wall. [ 52 ] www.allen.in Biological Classification (b) Genetic Recombination : (i) Conjugation: Gene transfer by physical contact between two bacterial cells. Conjugation between F+ and F– (a) First of all, donor cell is attached to recipient cell with the help of sex pili. Sex pili help in formation of conjugation tube. (b) The 'F' factor now replicates and the replica moves to F–. through conjugation tube. (c) Both the cells are then separated. Due to transfer of 'F' factor F-cell now becomes F+ cell. + – F F F-factor Bacterial Recipient chromosome Conjugating cells – + F cell becomes F as it obtains copy of F factor + + + F cell Now both F cells F cell separate apart (ii) Transformation: Transfer of genetic material from one bacterium to another bacterium through surrounding is called transformation. Free DNA DNA integrates with genomic DNA www.allen.in [ 53 ]  NEET : Biology (iii) Transduction: When the gene transfer process between two different bacteria is carried out by virus (bacteriophage) called transduction. (B) ECONOMIC IMPORTANCE OF BACTERIA : Harmful Activities : (i) Disease in Human beings : Disease Bacterium Tuberculosis (T.B.) – Mycobacterium tuberculosis Leprosy – Mycobacterium leprae Tetanus – Clostridium tetani Typhoid – Salmonella typhi Cholera – Vibrio cholerae (ii) Disease in Animals – Anthrax – Bacillus anthracis (iii) Disease in plants Citrus canker – Xanthomonas citri Crown gall in many plants – Agrobacterium tumefaciens Note : Plant pathogenic bacteria are mostly gram negative and non-spore forming bacteria. (iv) Food poisoning – Botulism – Clostridium botulinum – It is most lethal type of food poisoning. These bacteria survive in absence of O2. These bacteria multiply in canned food. Their toxins damage the parasympathetic nervous system. It leads to paralysis of both smooth and striped muscles, resulting in immediate death. [ 54 ] www.allen.in Biological Classification Useful Activities : (i) Dairy products – Dairy products are formed with the help of bacterial fermentation. Lactobacillus (LAB) Milk ⎯⎯⎯⎯⎯⎯⎯⎯⎯ → Curd Note : Lactobacillus lactis (LAB/Lactic acid bacteria) increase vitamin B12 in curd. LAB also help in checking the disease causing microbes in stomach. (ii) Antibiotics – Many antibiotic medicines are obtained from the bacteria. For example, streptomycin is obtained from Streptomyces griseus (It is an actinomycetes) (iii) Pollution indicating bacteria: - Water in which E. coli bacteria are present known as polluted water. Quality of water depends on number of E. coli. If E. coli are very much in no. the water will be highly polluted. So, the E. coli is known as pollution indicating bacteria. (iv) Bacteria for genetic engineering - e.g. E. coli and Agrobacterium ⎯→ These are Gram (–) bacteria (C) ARCHAEBACTERIA (GROUP OF ANCIENT BACTERIA) : Evolutionary they are primitive. They were the first to be born on our planet and they are present now days with their primitive characters. They are the "Oldest living fossils". Mostly archaebacteria are anaerobes. Their cell wall is not made up of peptidoglycan like that of eubacteria. Their cell wall is made up of complex polysaccharides and complex polypeptide. Cell membrane of archaebacteria is highly complex because of branched lipid chain. Due to complex cell wall and cell membrane archaebacteria can survive in harsh habitat. www.allen.in [ 55 ]  NEET : Biology Cell wall Cell Membrane Prokaryotic cytoplasm Nucleoid-Circular ds DNA, Non-histone proteins Ribosome 70s Cell wall Branched fatty acid chain Cell Membrane NCERT Question : State two economically important uses of archaebacteria. Archaebacteria includes following bacteria : (i) Methanogens "Methane producing bacteria" (a) Methanogens are found in manshy area and gobar gas fermenter and produce methane. e.g. Methanobacterium, Methanococcus, Methanomicrobium (b) Methanogens is found in the rumen of cattle and responsible for the production of methane (biogas). Rumen [ 56 ] www.allen.in Biological Classification (ii) Halophiles (“Halo”- Salt and “Philos”- like) These archaebacteria are found in extreme salty areas. Some halophiles have bacteriorhodopsin in their cell membrane, which absorbs suitable light radiations and produces ATP e.g. Halobacterium. Found in extreme salty areas (20% w/v salt concentration). Bacteriorhodopsin Cell wall H+ ions ADP + Pi ATP Cell Membrane (iii) Thermoacidophiles These archaebacteria are found at those places where temperature is approx 80°C to 100°C and medium is acidic. [pH = 2] They are found in hot sulphur springs. Hot water sulphur springs are found in the Himalayan region. e.g. Thermophilus, Sulfolobus (D) CYANOBACTERIA (BLUE GREEN ALGAE) : They are included in Kingdom Monera, because blue green algae (B.G.A) are prokaryote. The name cyanobacteria was suggested by ICNB [International Code of Nomenclature for Bacteria] Cyanobacteria were the first organism that produced O2 on our earth. Cyanobacteria are photosynthetic prokaryotes; however, they are also found as symbiont with some plants. e.g. Cycas In cyanobacteria membranous extensions into the cytoplasm are found called chromatophores. They have pigments for photosynthesis: Chlorophyll 'a' – green, Carotenoids – yellow, C - Phycocyanin – blue, C - Phycoerythrin – red Different forms of BGA or Cyanobacteria : (a) Unicellular: Some B.G.A. are unicellular e.g. Spirulina (Spirulina is an edible B.G.A. because it has large amount of proteins. It can be grown artificially in water tanks. It is a fodder for cattle.) www.allen.in [ 57 ]  NEET : Biology (b) Colonial: Some B.G.A. are found in colony i.e. cell Heterocyst colonies. e.g. Anabaena, Microcystis Mucilagenous sheath (c) Filamentous: Some B.G.A. are filamentous. There are many cells arranged in a row to form a filamentous body. The filament of B.G.A. is known as trichome. Figure 2.2 A Filamentous B.G.A.-Nostoc e.g. Oscillatoria, Nostoc Structure of Cyanobacteria : Mucilaginous sheath Inclusion Bodies Outer Cell wall Gas Vacuole Inner layers -granule Cyanophycean Cell Membrane granule Nucleoid Polysome Chromatophore/ Photosynthetic lamellae (a) The structure of B.G.A. is similar to Gram (–ve) eubacteria. Because the cell wall of B.G.A. is bilayered. Outer layer is made up of lipopolysaccharides and the inner layer is made up of peptidoglycan. (b) B.G.A. are surrounded by a mucilaginous membrane or gelatinous sheath or envelope. This envelope is made up of mucopolysaccharides. (c) They do not produce flagellated structures in their life cycle. (d) Inclusion bodies : -granules and gas vacuoules. (e) In B.G.A. reserve food material is cyanophycean starch, which is not starch actually, it has similarities with glycogen. Cyanophycean starch is present is special granules known as cyanophycean granules (-granules). [ 58 ] www.allen.in Biological Classification (f) Gas vacuoles are found in B.G.A. and purple and green photosynthetic eubacteria. (g) Special type of cells are found for nitrogen fixation in Nostoc and Anabaena known as Heterocyst. Heterocyst is a thick walled, non-green cell. Note : Inclusion bodies are non-membranous structures. Nucleoid – ds circular naked DNA Ribosomes – 70s type Nitrogen fixation : (a) Some of the B.G.A., can perform nitrogen fixation. They convert atmospheric nitrogen in to ammonia and then nitrogenous compounds like amino acids, nitrates. These nitrates increase the fertility of soil. Hence B.G.A. improves the fertility of soil by nitrogen fixation. (b) B.G.A. fix nitrogen in two forms :- Symbiotic form and Asymbiotic or free living form Symbiotic form Free living form e.g. Anabaena & Nostoc e.g. Anabaena, Nostoc These B.G.A. form symbiotic Some B.G.A. are found free living in association with many plants and water and soil and perform nitrogen performs nitrogen fixation. fixation. e.g. :-  In the leaves of Azolla Aulosira → This.B.G.A. is found in  In the coralloid roots of Cycas plenty in paddy fields. This B.G.A. Azolla → If Azolla is grown with rice, performs nitrogen fixation due to than the production increases up to which the production of rice is 50% [because Anabaena are found in increased. the leaves of Azolla] Oscillatoria = also fix N2 in paddy fields. Note : Special type of cells are found for nitrogen fixation in Nostoc and Anabaena known as Heterocyst. Heterocyst is a thick walled, non-green cell. Heterocyst does not perform photosynthesis like other vegetative cells. www.allen.in [ 59 ]  NEET : Biology Reproduction : BGA reproduce by two methods: (1) Binary fission e.g. Spirulina (2) Fragmentation: e.g. Oscillatoria Fragment Fragmentation Fragment Fragment Useful activities: They provide fertility to soil by nitrogen fixation. Spirullina is a very good source of protein. Some BGA are used as green manure. Some species of Oscillatoria secrete toxins, which inhibits the growth of mosquito larva in water Water bloom Harmful activities: Water bloom BGA which grow in water tanks, they damage them also. (E) MYCOPLASMAS : In 1898, two French scientists E. Nocard and R. Roux while studying pleural fluids of cattle suffering from pleuropneumonia disease, discovered the organisms which are known as mycoplasma and were designated as PPLO (i.e. Pleuropneumonia like organism). Nowak (1929) put these organisms under the genus Mycoplasma. Mycoplasmas are unicellular, smallest prokaryotic organisms. The diameter of cell varies from 0.1mm to 0.3mm. Cell membrane is made up of lipoprotein. Both DNA (double stranded DNA, mainly circular) and RNA (ssRNA) are present. They are cell wall less hence, they exhibit pleomorphism and thus called "Joker of microbiology". [ 60 ] www.allen.in Biological Classification Osmotrophic mode of nutrition (absorption of nutrients by osmosis) is found in Mycoplasma. They are resistant to penicillin antibiotics, as penicillin acts on cell wall. They are sensitive to tetracycline & chloramphenicol that act on metabolic activities. Most of the species of Mycoplasma can survive without oxygen. Species of Mycoplasma are saprophyte or parasite. Shape and Structure Flagellum & Mesosome - absent Cell membrane Inclusion body Nucleoid Prokaryotic Polysome Cytoplasm Ribosome 70s Cell wall absent Reproduction in mycoplasma: Most common method of reproduction in Mycoplasma is Binary fission. Parent cell or Mother cell Daughter cells Diseases : Plant disease: Aster yellow disease of sunflower. Animal disease: Bovine pleuropneumonia Aster yellow of sunflower www.allen.in [ 61 ]  Primary Atypical Pneumonia NEET : Biology Bovine Pleuropneumonia Immune system Primary Atypical Pneumonia Bovine Pleuropneumonia The cytoplasm of prokaryotes lack membrane bounded cell organelles. Cyanobacteria are gram –ve, photosynthetic, oxygenic monera (prokaryotes). Though the bacterial structure is very simple, they are very complex in behaviour, because they are both autotroph (Phototroph and Chemotrophs) and heterotrophs. (Parasites, Saprophytes and Symbionts). As a group bacteria show most extensive metabolic diversity. Cell membrane of archaebacteria has branched lipid chain. In some bacteria their body is filament or fungi like (mycelium), so they are also called filamentous bacteria or actinomycetes or mycobacteria. These bacteria are very important for us, as they are used in making antibiotics. The cell wall of actinomycetes contains mycolic acid. e.g. Streptomyces, Mycobacterium, Beggiatoa, Frankia. Barophilic prokaryotes – Prokaryotes which grow and multiply in very deep marine ediments. The richest source of bacteria is soil. Hundreds of bacteria are present in a handful of soil. [ 62 ] www.allen.in Biological Classification BEGINNER’S BOX-2 KINGDOM MONERA 1. The bacteria which are associated with some plant roots and fix atmospheric nitrogen are :- (1) Azotobacter (2) E. coli (3) Rhizobium (4) Pseudomonos 2. In paddy field blue green algae are grown :- (1) For medicinal use (2) To increase soil fertility (3) To serve as food for fishes (4) To conserve water 3. The digestive tracts of ruminants contain :- (1) Halophilic bacteria (2) Methanogens (3) Thermoacidophile bacteria (4) Mycoplasma 4. Archaebacteria differ from eubacteria in one of the following respect :- (1) Their cell wall lack peptidoglycan (2) They tolerate extreme environment (3) They have unique cell membrane with branched lipid chain (4) All of these 5. Crown galls in plants is caused by a bacterium which is most widely used in genetic engineering is : (1) E. coli (2) Agrobacterium (3) Pseudomonas (4) Nitrosomonas 6. Which of the following may be used in the reclamation of soil :- (1) Mycoplasma (2) Methanogen (3) Nostoc (4) E. coli 7. Murein is found in the cell wall of :- (1) Diatoms (2) Cyanobacteria (3) Archaea (4) Mycoplasma 8. Which of the following is first oxygenic photosynthetic organism :- (1) Green algae (2) Red algae (3) Blue-green algae (4) Golden algae 9. Teichoic acid is present in :- (1) Gram +ve bacteria (2) Gram –ve bacteria (3) Mycoplasma (4) Blue green algae 10. Blue green algae can photosynthesize due to presence of :- (1) Heterocyst (2) Chloroplast (3) Chromatophore (4) Leghaemoglobin www.allen.in [ 63 ]  NEET : Biology 11. Which of the following group consists of only ingestive organisms ? (1) Monera (2) Protista (3) Fungi (4) Animalia 12. How many kingdoms were included in Domain Eukarya? (1) Two (2) One (3) Four (4) Six 13. Given below are two statements: one is labelled as Assertion (A) and the other is labelled as Reason (R). Assertion :- Mycoplasma show resistance against some antibiotics such as penicillin. Reason :- Cell membrane of mycoplasma is trilayered and made up of lipoprotein. In the light of the above statements, choose the correct answer from the options given below: (1) Both (A) and (R) are correct but (R) is not the correct explanation of (A) (2) (A) is correct but (R) is not correct (3) (A) is not correct but (R) is correct (4) Both (A) and (R) are correct and (R) is the correct explanation of (A) 14. Which of the following statements regarding Blue green algae are correct ? (i) Cyanobacteria have chlorophyll-a similar to green plants (ii) All BGA have heterocysts and can fix atmospheric nitrogen (iii) They form blooms in polluted water bodies (iv) Nostoc and Anabena are photoautotrophs (1) (i), (ii) & (iii) (2) Only (ii) (3) (i), (iii) & (iv) (4) (ii), (iii) & (iv) 15. Match the following column correctly :- Column-I Column-II (a) Mesosome (i) Protect the bacteria from WBC (b) Glycocalyx (ii) DNA replication & cell division (c) Nucleoid (iii) False chromosomal coiled region Phosphate (d) (iv) Storage reservoir for phosphate granules (1) a–ii, b–i, c–iii, d–iv (2) a–i, b–ii, c–iii, d–iv (3) a–ii, b–iii, c–iv, d-I (4) a–iv, b–i, c–iii, d–ii [ 64 ] www.allen.in Biological Classification 04. KINGDOM – PROTISTA Protista Euglenoids Protozoans Dinoflagellates Chrysophytes Slime mould All the organism included in Protista are unicellular eukaryotes. i.e. the structure of all protists is similar to eukaryotic cell. Members of Protista are primarily aquatic. Being eukaryotes, the protistan cell body contains a well-defined nucleus and other membrane- bound organelles. Some have flagella or cilia. The members of Protista have characters of plants, animals and fungi also hence the boundary lines of this kingdom are not well defined. Some protists have cell wall around them, which is made up of cellulose. Beneath cell wall, cell membrane is present. Cell membrane is made up of lipoprotein. e.g. Dinoflagellates, Diatoms Some protists do not have cell wall, they are surrounded by cell membrane, which surrounds all the cell organelles. e.g. Euglenoids, Slime moulds, Protozoa Nutrition : Mode of nutrition in protists is of different types (a) Holophytic or Photosynthetic: They prepare their own food by photosynthesis. (b) Holozoic: Some protists have holozoic mode of nutrition, which is similar to animals i.e. food is first ingested (intaken) and then digested. (c) Osmotrophic or Absorptive: Food is first digested and then ingested in this mode of nutrition. Some protists obtain their food from dead organic substances. These protists secrete some extracellular enzymes. www.allen.in [ 65 ]  NEET : Biology These enzymes convert the complex organic substances into simpler substances. Now these simple substances can be easily absorbed through the body surface. If food is absorbed from livings, it is parasitic and if from dead organic matter it is saprophytic mode of nutrition. (d) Mixotrophic: Some Protists have more than one type of nutrition e.g. Euglena. Reproduction : Protists reproduce asexually and sexually by a process involving cell fusion and zygote formation. Reproduction Sexual Asexual By fusion of gametes No fusion of gametes 1. Binary Fission e.g. Dinoflagellates, Meiosis Chrysophytes Euglenoids Zygote 2. Spore formation Syngamy (Diploid) e.g. Slime moulds New cells Gametes (Haploid) Progeny (A) CHRYSOPHYTES : This group includes diatoms and golden algae (desmids). They are found in fresh water as well as in marine environment. Diatoms are also known as pearls of oceans. e.g. Navicula Structure : Vacuole Plastid Chl. a & c, Fucoxanthin Cell Membrane Cell wall Nucleus Fat/Oil Lucosine Mitochondria (Diploid) [ 66 ] www.allen.in Biological Classification They are found in different shapes such as circular, rectangular, triangular, elongated and boat shaped. NCERT Question : What is the nature of cell-walls in diatoms? The cell wall(shell) of diatoms is made up of cellulose in which silica particles are embedded in at many places. Due to which the cell wall appears to be made up of silica. This silicated cell wall is called "shell" or "frustule". Their cell wall is made up of two halves, which are arranged like the lids of soap box. Their cell wall have silica in very large quantity. Due to this reason their cell wall is hard. The cell wall does not get destroyed after their death so at the bottom of sea, very huge rocks of dead diatoms are formed which are known as "diatomite" or "diatomaceous earth" or "keiselgurh". Diploid nucleus is present in Diatom. Diatoms have pigments Chlorophyll 'a', Chl 'c', and xanthophyll (fucoxanthin). Due to these pigments they appear golden coloured. They are chief, producers in the ocean due to very high number of them in oceans. (i) Stored food – Leucosin (Chrysolaminarin) & fats (Oil). (ii) Movement – They are immotile, because flagella are absent in them. They float passively on the surface of water (Plankton) due to low molecular weight stored fats. Reproduction : (a) Mainly asexual – binary fission. Binary Fission www.allen.in [ 67 ]  NEET : Biology (b) Sexual reproduction – Very rare - by gametic meiosis. Diplontic Life Cycle Diploid nucleus Diploid nucleus Meiosis I Haploid nucleus Meiosis II Haploid nucleus Syngamy (B) DINOFLAGELLATES : Division – Pyrophyta : Dinoflagellates are mainly marine. Dinoflagellates are haploid They are found on the surface of water. They appear yellow, green, brown blue or red depending on the main pigments present in their cells. In Dinoflagellates, the nutrition is mainly photosynthetic. e.g. Noctiluca, Gonyaulax Structure : Thecal plates Thecal Their cell wall is divided in to plates, which is made up of cellulose. Transverse Transverse furrow furrow Dinoflagellates have two flagella - one is Transverse Transverse transverse and other is longitudinal. Longitudinal Longitudinal flagellum flagellum furrow furrow Dinoflagellates show a special type of movement which is like whirling whips, Longitudinal Longitudinal flagellum flagellum therefore they are called "whirling whips". Figure 2.4 (a) Dinoflagellates Dinoflagellates are yellow-brown or golden brown in colour. These colours of Dinoflagellates are due to the pigments present in them - Chlorophyll 'a', Chl. 'c' and Xanthophylls. [ 68 ] www.allen.in Biological Classification They have starch as stored food. Reproduction : (a) Mainly Asexual – Binary fission. (b) Sexual reproduction is very rare in them. NCERT Question : Find out what do the terms ‘algal bloom’ and ‘red-tides’ signify. Some facts: (a) Dinoflagellates (e.g. - Noctiluca, Gonyaulax show 'bioluminescence' due to presence of photogenic Binary Fission granules in cytoplasm, so these dinoflagellates are also known as 'night light'. Also, knowns "fire algae" because they appear as glowing light due to bioluminescence. (b) Gonyaulax spreads on the surface of sea water, through rapid multiplication due to Division which the sea water appears red. It is called red tide. It is also responsible for water bloom. (c) Both Gymnodinium & Zygote(2n) Gonyaulax secrete toxins, Zygotic Meiosis and Germination which can cause paralysis in human beings. Humans acquire these toxins through food chain. These toxins also affect the marine animals. NCERT Question : What are the characteristic features of Euglenoids? www.allen.in [ 69 ]  NEET : Biology (C) EUGLENOIDS : Division – Euglenophyta : Previously euglenoids were placed in plant kingdom due to their photosynthetic ability. But due to the absence of cell wall and animals like nutrition some scientists placed them in animal kingdom. But now according to five kingdom classification they are included in Protista. Structure Structure Long Flagellum Long Flagellum Reservoir Reservoir Eye Eye Spot Spot Contractile Small Flagellum Small Flagellum Contractile vacuole vacuole Nucleus Nucleus Pellicle Pellicle Chloroplast Chloroplast Chl a, b Zeaxanthin Zeaxanthin e.g. Euglena Euglena Figure 2.4 (b) Euglena They are found as free-living organisms in fresh water lakes, ponds, etc. But sometimes they are also found in damp soil and brackish water. Though they are photosynthetic in presence of sun light, when deprived of sunlight they behave like heterotrophs by predating on other smaller organisms. e.g. Euglena Structure : They are unicellular, cell wall is absent around them. They are surrounded by a cell membrane which is made up of lipoprotein and this cell membrane is covered with pellicle. Pellicle is mainly made up of protein and it is elastic in nature. At the anterior end of Euglenoids, a cavity is present, which is known as reservoir. Flagellum is orginated from the base of reservoir. Euglenoids have only one functional flagellum and one non-functional flagellum. One eye spot is present at anterior position. They have a contractile vacuole. These contractile vacuoles help in osmoregulation. Euglenoids have a haploid nucleus and chloroplast. [ 70 ] www.allen.in Biological Classification Chloroplast has following pigments : Chl. 'a' , Chl. 'b' and Xanthophyll - These pigments are identical to higher plant Stored food - Paramylum and fat. Reproduction - Asexual reproduction by longitudinal binary fission. (D) SLIME MOULDS : These organisms develop a slimy mass at the time of their vegetative phase therefore they are called slime moulds. They are also called false fungi. Slime moulds are saprophytic found on decaying twigs and leaves engulfing organic material, so they also show phagotrophic mode of nutrition. Figure 2.4 (c) Slime Moulds Under suitable conditions they form an aggregation which may grow and spread over several feet called plasmodium. During unfavourable conditions plasmodium forms fruiting bodies, which bear spores at their tip. The spores posses true walls. They are extremely resistant and survive for many years, even under adverse conditions. The spores are dispersed by air current. e.g. Physarum Sporangium Sporangium Spore Spore Dispersal by Dispersal by air current air current Formation Formation of aggregate aggregate Plasmodium Plasmodium Spore germination Spore germination www.allen.in [ 71 ]  NEET : Biology (E) PROTOZOANS : In includes unicellular eukaryotes One celled body performs all the biological activities like multicellular animals. Microscopic : Mostly aquatic Free living Parasitic (Amoeba) (Plasmodium) Body level of organisation is protoplasmic level. Few show nuclear dimorphism. e.g. Paramoecium. Locomotory structures. (i) Finger-like (ii) Whip-like (iii) Hairy Cilia (iv) Absent in Pseudopodia Flagella e.g. Paramoecium sporozoan e.g. Amoeba e.g. Trypanosoma e.g. Plasmodium Digestion : Nutrition in Protozoans is mainly holozoic (Amoeba) and Parasitic (Plasmodium). Digestion is intra cellular takes place in food vacuole. Holozoic nutrition is the process of nutrition that takes place in organisms that take solid or liquid food inside their body. Amoeba follows holozoic nutrition. Steps of holozoic nutrition (i) Ingestion (ii) Digestion (iii) Absorption (iv) Assimilation (v) Egestion Respiration and excretion take place by general body surface. Some excretion may occur through contractile vacuole. Nitrogenous waste is Ammonia. Some fresh water protozoans get rid of excess water through contractile vacuole by the process known as Osmoregulation. [ 72 ] www.allen.in Biological Classification Reproduction : Reproduction Asexual Sexual Reproduction Reproduction Binary fission Multiple fission Syngamy Conjugation Simple e.g. Amoeba e.g. Plasmodium e.g. Plasmodium e.g. Paramoecium Transverse e.g. Paramoecium Longitudinal e.g. Trypanosoma Amoeboid protozoans : (i) Live in fresh water , sea water or moist soil (ii) Move and capture their prey by putting out pseudopodia (false feet) as in Amoeba (iii) Marine forms have silica shells on their surface. (iv) Some of them such as Entamoeba are parasites. Flagellated protozoans : (i) The members of this group are either free-living or parasitic. (ii) They have flagella. (iii) Example: Trypanosoma. (iv) The parasitic forms cause diseases like sleeping sickness. Ciliated protozoans : (i) These are aquatic, actively moving organisms because of the presence of thousands of cilia. (ii) 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 : (i) This includes diverse organisms that have an infectious spore-like stage in their life cycle. (ii) The most notorious is Plasmodium (malarial parasite) which causes malaria, a disease which has a staggering effect on human population. www.allen.in [ 73 ]  NEET : Biology 05. KINGDOM – FUNGI The fungi or mycota is a unique kingdom of heterotrophic organisms. Members of this kingdom are also called fungi. They show a great diversity in morphology and habitat. They can be seen in from of moulds on bread, butter, leather, pickle, rotten fruits (orange rotting) and vegetables or as parasites in plants (white spot on mustard leaves) and animals. Fungi prefer to grow in warm and humid places so we keep food in refrigerator, which prevent food from going bad due to bacterial or fungal infections. Fungi do not have chlorophyll and chloroplast. NCERT Question : Give a comparative account of the classes of Kingdom Fungi under the following : Mode of nutrition On the basis of source of food fungi are of two types : (a) Saprotrophic: These fungi obtain their food from dead organic matter such as bread, rottening fruit, vegetable and dung. (b) Parasitic: They obtain their food from living organism, such as plants, animals and human beings. Nutrition is absorptive in fungi. (c) Symbiontic– in association with algae as lichens and with roots of higher plants as mycorrhiza. A very few fungi are unicellular or non-mycelial e.g. Yeasts and most of the fungi are mycelial i.e. their body is made of mycelium. Which is composed of hyphae or filaments. [ 74 ] www.allen.in Biological Classification Cell wall of fungi is mainly made of chitin which is also called fungal cellulose but actually it is not cellulose. Cell wall also have some quantity of polysaccharides, proteins, lipid and cellulose. (i) Cell wall of the members of class-oomycetes is mainly made up of cellulose. (ii) In fungi the stored food is in the form of glycogen and oil. NCERT Question : Give a comparative account of the classes of Kingdom Fungi under the following: Mode of reproduction Reproduction : (a) Vegetative reproduction : It occurs by different processes. (i) Fragmentation - Sometimes the fungal filament (mycelium) breaks into small pieces due to any reason. Now these pieces form a new fungal filament and start working like normal filament. (ii) Budding – Some times a bud is formed in non-mycelial fungi. Now this bud, separates from the mother cell and functions as young fungi. At the time of separation of bud from its mother cell or fungi, the nucleus of mother cell divides mitotically into two parts. Out of these two nuclei, one remains with in the mother cell while the other e.g. e.g.Saccharomyes Saccharomyes(Yeast) migrates to the bud. (Yeast) e.g. Saccharomyces (Yeast) (iii) Fission - Sometimes the fungal cell divides into two parts. Its nucleus also divides into two parts. Daughter Each cell receives a nucleus and starts working as cells a new cell. e.g. Schizosaccharomyes (Yeast) e.g. Schizosaccharomyces (Yeast) (b) Asexual reproduction : Asexual reproduction takes place by the formation of different types of spores. Spores are of following types www.allen.in [ 75 ]  NEET : Biology (i) Sporangiospores - They are formed in sporangia. Sporangium is formed at the tip of fungal filament. The fungal filament on which sporangium is formed is called as sporangiophore. Numerous spores (sporangiospores) are present in the sporangium, they come out by rupturing of sporangia and germinate to form fungal filaments. These spores are endogenously produced in sporangium. Sporagium Sporangium Germinating Germinating Spores Spores Branching Branching in hypha in hypha Mycelium Mycelium Sporangiospores are of Two types : 1. Zoospore : When the sporangiospores formed in sporangia are flagellated and motile, then they are called as zoospores. In this condition the sporangia are called zoosporangia. 2. Aplanospore : When sporangiospores are non-flagellated and non-motile then they are called aplanospores. (ii) Conidia - The formation of conidia takes place exogenously. These conidia are formed at the tip of Mycelium. Conidium Chain of conidia Germination Mycelium [ 76 ] www.allen.in Biological Classification Sexual Reproduction : The cell in which gametes are formed is called gametangium. Sexual reproduction in fungi completes in three steps (i) Plasmogamy - This is the first stage of sexual reproduction. In this stage two sex cells fuse with each other but their nuclei do not fuse due to Germination which a single cell has two nuclei. In phycomycetes the fusion of two haploid cells Plasmogamy immediately result in diploid cells (2n). However, Dikaryon in other fungi (Ascomycetes and Spores Basidiomycetes), an intervening dikaryotic stage Karyogamy Synkaryon/ (n + n, i.e., two nuclei per cell) occurs. Such a Meiosis Zygote condition is called a dikaryon and phase is called Diploid dikaryophase of fungus. (ii) Karyogamy - In this stage the nuclei present in the cell fuse with each other to form a diploid nucleus which is known as synkaryon. (iii) Meiosis (Reduction division) - In this stage, meiosis takes place in the diploid nucleus due to which again haploid nuclei or haploid cells are formed. In fungi, Sexual Fusion is of Many Types : (A) Gametangial contact - (a) In this process, first of all male and female sex organs are formed on two different hypha of same mycelium. Male sex organ is called antheridium and female sex organ is called oogonium. (b) In mature antheridium & oogonium both have one – one nucleus. Antheridium and oogonium come close to each other and perform plasmogamy and karyagamy. Oogonium Antheridium Plasmogamy & Haploid Karyogamy Oospore (2n) Germination Sexual Mycelium Meiosis Spores www.allen.in [ 77 ]  NEET : Biology (B) Gametangial copulation :- (a) In this process, two identical gametangia directly fuse to perform plasmagamy and karyogamy resulting in formation of diploid zygospore. Gametangia (b) Now meiotic division takes place in Plasmogany and karyogamy zygospore, as a result of which haploid spores are formed. Now each spore germinates and gives rise to a new (2n) Zygote mycelium. (Zygospore) (C) Spermatization : Some fungi form Meiosis uninucleate thin walled non-motile spore like Haploid spores bodies. These spores are called spermatia or Germination Pycniospores (nonmotile male gametes). Mycelium (D) Somatogamy : In it sex organs are not formed only two hyphae come close to each other and get fused. Classification : True fungi are divided into following classes on the basis of morphology of mycelium, mode of spore formation and fruiting bodies during sexual reproduction – (A) Phycomycetes (B) Ascomycetes (C) Basidiomycetes (D) Deuteromycetes (A) PHYCOMYCETES : Habitat : All the fungi included in this class are called as lower fungi. Members of phycomycetes are found in aquatic habitat (members of this class known as algal fungi) and on decaying wood in moist and damp place or as obligate parasites on plants. Hypha [ 78 ] www.allen.in Biological Classification Mycelium : The fungal filament (mycelium) of the fungi included in this class are coenocytic, aseptate and branched. Asexual reproduction = by zoospores, aplanospores and conidia. Sexual reproduction = may be isogamous, anisogamous and oogamous. Phycomycetes includes further groups like oomycetes, zygomycetes Isogamous Anisogamous Oogamous Note : The mycelium of both oomycetes and zygomycetes is same in structure i.e. coenocytic & aseptate. But they are dissimilar in their method of sexual reproduction. (a) Oomycetes : Asexual reproduction :- Conidium By the formation of zoospores and conidia. sporangium Sexual reproduction :- By Gametangial contact Type of sexual reproduction Oogamous - All the members e.g.: - (i) Phytophthora infestans: - Causes late blight of potato. This disease is known as " Famine of Ireland" - 1845 (ii) Pythium species: - Causes "Damping off" disease in tobacco & "vegetable crops". (ii) Albugo candida or Cystopus candidus: - It causes "White rust or white spots disease" in the members of cruciferae family. www.allen.in [ 79 ]  NEET : Biology (b) Zygomycetes : Asexual reproduction: - By the formation of aplanospores. Rhizopus Sexual reproduction: - By Gametangial copulation. Types of sexual reproduction : Isogamous: - All the members e.g.: - (i) Pilobolus : - (ii) Rhizopus & Mucor :- These are known as bread mold. They prefer to grow on bread. Note : Rhizopus is common bread mold. The tip of mycelium of Rhizopus is black coloured. Therefore this fungus looks black coloured. Septum with simple pores (B) ASCOMYCETES : "The sac fungi" Members of this class are mostly multicellular rarely Uniucleated Hypha unicellular (e.g. yeast). Habitat : Members of Ascomycetes are saprophytic decomposers, parasitic or coprophilous (growing on dung) Mycelium : Septate and branched. Septa are found in mycelium of ascomycetes. Pores are present in septa. These pores allow cytoplasm to pass from one cell to other cell. Pores do not allow passing of nucleus. Asexual reproduction : By Conidia Sexual reproduction : By somatogamy and gametangial contact [ 80 ] www.allen.in Biological Classification Somatogamy : Ascospores are formed during sexual reproduction. On this basis they are named as Ascomycetes. (a) There are three stages in sexual reproduction of Ascomycetes Plasmogamy → Karyogamy → Meiosis. (b) In it two fungal hypha of mycelium come close to each other and their cells fuse to form dikaryon. (c) After this an outgrowth originates from dikaryon which is called ascogenous hypha. Ascogenous hypha develops and form a sac like structure which is called ascus (Plural - Asci). Due to this sac like ascus, ascomycetes are called as sac fungi. Ascogenous hypha Mycelia Plasmogamy Karyogamy Ascus Diploid Nucleus Meiosis Haploid Hypha Nuclei Hypha Division in nuclei Germination and karyokinesis Ascospore Fruiting Body (d) Now both the nuclei reach in ascus and fuse to form diploid nucleus. Now ascus is protected by some fungal filaments to form a fruiting body, called as ascocarp in which reductional division occurs leading to formation of haploid ascospores. Note : Minimum four ascospores are formed in one ascus but generally '8' ascospores are formed in one Ascus. www.allen.in [ 81 ]  NEET : Biology (e) By the rupturing of ascocarp & ascus, ascospores become free and each ascospore forms a new mycelium. e.g. (i) Penicillium : - Conidia ▪ Penicillin antibiotic was obtained from Penicillium Branched notatum. Conidiophore ▪ Alexander Fleming discovered penicillin while working on Staphylococcus bacteria. Penicillum (ii) Aspergillus : - ▪ Different species of Aspergillus are related to "aspergillosis" disease and secretion of "aflatoxins" (carcinogenic) substance. ▪ Aspergillus niger – Known as weed of laboratory and produce citric acid. Conidia Unbranched Conidiophore Aspergillus Figure 2.5 (b) (iii) Claviceps: - ▪ Claviceps purpurea – It causes "Ergot disease" of Bajra and Rye. ▪ "Ergotin" (drug) is obtained from it. ▪ Narcotic drug (LSD) is also obtained from it. ▪ LSD (Lysergic acid diethylamide) is a hallucinogenic drug. (iv) Morchella: - ▪ The edible species of Morchella are commonly called as morels. [ 82 ] www.allen.in Biological Classification (v) Neurospora: - ▪ Red or Pink mold "Drosophila of plant Kingdom". ▪ It is used for the study of genetics and biochemical studies in Plant kingdom. ▪ Beadle and Tatum proposed "One gene - one enzyme theory" in Genetics by experimenting on Neurospora. (vi) Truffles: - ▪ Some members of ascomycetes are known as Truffles. They are also edible. (vii) Yeast e.g. Saccharomyces, Schizosaccharomyces. ▪ Yeasts are unicellular fungi. ▪ Yeasts grow on ripened fruits like grapes, sugarcane, date palm and flowers. ▪ Mycelium is absent in yeasts. High sugar concentration Pseudomycelium (C) BASIDIOMYCETES (CLUB FUNGI) : Mycelium - Branched, Septate and uni or binucleate They grow in soil, on logs (thick wooden pieces), and tree stumps (thin wooden branches) and in living plant bodies as parasites. Main mycelium of basidiomycetes is dikaryotic and septate. In these fungi the monokaryotic mycelium is also found which is short living and soon converts into long living dikaryotic mycelium. The conversion of monokaryotic mycelium into dikaryotic mycelium is Dikaryotisation. Asexual spores are generally not found in basidiomycetes but vegetative reproduction by fragmentation. The sex organs are absent because they perform sexual reproduction by two methods i.e. Somatogamy and Spermatisation. www.allen.in [ 83 ]  NEET : Biology Most of the members are heterothallic so fusion is found between different strains or genotypes. Sexual reproduction : Sexual reproduction is performed by two methods (i) Somatogamy (ii) Spermatization (i) Somatogamy -This is the most common method of reproduction among the members of Basidiomycetes. e.g. Ustilago, Agaricus Secondary mycelium PLASMOGAMY Primary mycelium KARYOGAMY Haploid MEIOSIS Primary mycelium Dispersal and germination (a) First of all, the two-mycelium come close to each other. (b) Now their apical ends fuse with each other (Plasmogamy), as a result of which dikaryon is formed. (Dikaryon - The cell in which two nuclei are present) (c) Now a club shaped structure is formed on every cell, which is known as basidium. (d) Now both the nuclei of each cell fuse with each other (karyogamy) in basidium. Due to which each becomes diploid. (e) After that diploid nucleus of the basidium divides by meiosis, as a result of which four haploid spores are formed on basidium, which are known as basidiospores. (f) Now the Basidiospores become free from basidium and produce a new monokaryotic mycelium on germination. [ 84 ] www.allen.in Biological Classification Examples: (a) Bracket or Shelf fungi :– (b) Puff balls – e.g. Clavatia Bracket or Puff balls Figure 2.5 (c) Agaricus Shelf fungi (c) Mushrooms - It is a fleshy, spore bearing fruiting body of basidiomycetes fungi. Most delicious, edible mushroom - Agaricus bisporus World's most poisonous mushroom - Amanita muscaria (It is also hallucinogenic) (Poisonous mushrooms are known as Toad - stool) Note : Agaricus – It is called gill fungi. (d) Rust Fungi: - Puccinia graminis (black rust of wheat) (e) Smut fungi - They cause smut disease and Smut fungi produce black spores, which are known as smut spores. e.g. Ustilago nuda or Ustilago tritici - Loose smut of wheat. Note : Basidiomycetes - Also known as "Club fungi" because a club shaped basidium is formed in them. (D) DEUTEROMYCETES : It is also called "fungi Imperfecti", because perfect stage or sexual reproduction is absent in this class of fungi. Those fungi are included in this class in which sexual reproduction is absent or is not discovered at yet. When the sexual forms of this class of fungi were discovered they were moved into Branched, septate Hypha right class ascomycetes or basidiomycetes from deuteromycetes. Mycelium : Septate and branched Asexual reproduction : Takes place with the help of conidia. Some members are saprophytic or paras