Title Med-RM_Bot_SP-1_Ch-4_Biological Classification.pdf ✅

Aakash Educational Services Limited - Regd. Office : Aakash Tower, 8, Pusa Road, New Delhi-110005 Ph. 011-47623456 Chapter Contents Biological classification is the scientific procedure to classify the organisms into different groups on the basis of their similarities and dissimilarities and placing the groups in a hierarchy of categories. KINGDOM SYSTEMS OF CLASSIFICATION The earlier systems of classification of organisms were simple and based on one or two characters. First scientific attempt for classification was performed by Aristotle in following manner : Living Organisms Plants Shrubs Herbs Trees Anaima Animals without RBCs  Enaima Animals having RBCs  Animals 1. Two Kingdom Classification: Linnaeus classified all living organisms into two kingdoms – Plantae and Animalia, on the basis of following criteria. Criteria Kingdom Plantae Kingdom Animalia Cell wall Locomotion Mode of nutrition Response to external stimulus Contractile system Organisms Present Absent Do not eat Slow Absent Bacteria, algae, fungi, bryophytes, pteridophytes, gymnosperms, angiosperms 1. 2. 3. 4. 5. 6. Absent Present Eat Fast Present Protozoa, vertebrates, invertebrates This two kingdom classification system does not distinguish between– (i) Unicellular and multicellular organisms, (ii) Eukaryotes and prokaryotes and (iii) Photosynthetic (green algae) and non- photosynthetic (fungi) organisms. Kingdom Systems of Classification Kingdom : Monera Kingdom : Protista Kingdom : Fungi Kingdom : Plantae Kingdom : Animalia Viruses Lichens Chapter 4 Biological Classification
96 Biological Classification NEET Aakash Educational Services Limited - Regd. Office : Aakash Tower, 8, Pusa Road, New Delhi-110005 Ph.011-47623456 There are few organisms like Chlamydomonas, Euglena and the slime moulds which share the characteristics of both animals and plants. Since there are certain organisms that do not fall naturally into either plant or animal kingdom, it was proposed that a new kingdom is to be established to accommodate such organisms. 2. Three kingdom classification : Haeckel, suggested that a third kingdom Protista should be created to include all unicellular microorganisms. This includes a wide variety of unicellular, mostly aquatic eukaryotes. Example - Fungi, Protozoa, Algae, Bacteria and Slime moulds. Thus, he proposed three kingdoms, namely - Plantae, Protista and Animalia. 3. Four kingdom classification : Copeland gave four kingdom of classification and included Monera as fourth kingdom. This kingdom includes all the prokaryotic organisms i.e. eubacteria (including cyanobacteria or blue-green algae) and archaebacteria. 4. R.H. Whittaker proposed Five kingdom classification system. This system divided organisms into kingdom Monera, Protista, Fungi, Plantae and Animalia, on the basis of following criteria : 1. Cell structure (either prokaryotic or eukaryotic) 2. Thallus organisation (body differentiated or not) 3. Mode of nutrition (autotrophic or heterotrophic) 4. Reproduction 5. Phylogenetic (or evolutionary) relationship Table : Characteristics of the Five Kingdoms Characters Five Kingdoms Monera Protista Fungi Plantae Animalia Prokaryotic Non-cellulosic (Polysaccharide + amino acid) Absent Cellular Autotrophic (chemosynthetic and photosynthetic) and Heterotrophic (saprophytic/parasite) Eukaryotic Present in some Present Cellular Autotrophic (Photosynthetic) and Heterotrophic Eukaryotic Present (without cellulose) with chitin Present Multicellular/ loose tissue Heterotrophic (Saprophytic/ Parasitic) Cell type Cell wall Nuclear membrane Body organisation Mode of nutrition Eukaryotic Present (cellulose) Present Tissue/organ Autotrophic (Photosynthetic) Eukaryotic Absent Present Tissue/organ/ organ system Heterotrophic (Holozoic etc.) Earlier classification systems included bacteria, blue green algae, fungi, mosses, ferns, gymnosperms and the angiosperms under ‘Plants’, due to presence of cell wall. This placed together groups which widely differed in other characteristics. It brought together the prokaryotic bacteria and the blue green algae (cyanobacteria) with other groups which were eukaryotic. It also grouped together the unicellular organisms and the multicellular ones. Chlamydomonas and Spirogyra were placed together under algae. The classification did not differentiate between the heterotrophic group – fungi and the autotrophic green plants, though they also showed a characteristic difference in their walls composition – the fungi had chitin in their wall while the green plants had a cellulosic cell wall. When such characteristics were considered, the fungi were placed in a separate kingdom – Kingdom Fungi.
NEET Biological Classification 97 Aakash Educational Services Limited - Regd. Office : Aakash Tower, 8, Pusa Road, New Delhi-110005 Ph.011-47623456 All prokaryotic organisms were grouped together under kingdom Monera and the unicellular eukaryotic organisms were placed in kingdom Protista. Kingdom Protista has brought together Chlamydomonas, Chlorella (earlier placed in Algae within plants and both having cell walls) with Paramoecium and Amoeba (earlier placed in the animal kingdom as they lack cell wall). It has put together organisms which, in earlier classifications, were placed in different kingdoms. This happened because the criteria for classification changed. Such kind of changes will take place in future also. This will depend on the improvement in our understanding of characteristics and evolutionary relationship. 5. Six kingdom classification : Carl Woese proposed six kingdom classification. These six kingdoms are Kingdom-Archaebacteria, Kingdom-Eubacteria, Kingdom-Protista, Kingdom-Fungi, Kingdom-Plantae and Kingdom-Animalia. He separated the archaebacteria from eubacteria on the basis of some major differences such as the absence of peptidoglycan in the cell walls of the former and the occurrence of branched chain lipids (a monolayer instead of a phospholipid bilayer) in the membrane. Based on the sequence of 16S ribosomal RNA genes, Woese found that the six kingdoms naturally cluster into three main categories. He called these categories as domains of life. These domains are Bacteria, Archaea and Eukarya and are believed to have originated from common ancestor called progenote. KINGDOM : MONERA Kingdom Monera includes the most ancient, the smallest, the simplest and the most abundant micro-organisms. They were the first inhabitants of the earth, and they still continue to flourish. Bacteria are the sole members of this kingdom. They occur almost everywhere. 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. Characters of Monera 1. They are unicellular, colonial or filamentous, prokaryotic organisms without nuclear membrane, nucleolus, chromatin and histone proteins. 2. Nucleoid or incipient nucleus is composed of naked DNA, RNA and non-histone proteins. DNA is circular and double stranded. 3. Cell wall is made up of peptidoglycan (Amino acids + Sugar) except in Archaebacteria and Mycoplasma. 4. Membrane bound cell organelles are absent. 5. Ribosomes are of 70S type. 6. Some of the bacteria are autotrophic but vast majority are heterotrophic. 7. Respiratory enzymes are found associated with plasma membrane. 8. Reproduction is asexual type. On the basis of their shape, bacteria are grouped under four categories : 1. The spherical Coccus (pl.: Cocci), 2. The rod-shaped Bacillus (pl.: Bacilli), 3. The comma-shaped Vibrium (pl.: Vibrio), and
98 Biological Classification NEET Aakash Educational Services Limited - Regd. Office : Aakash Tower, 8, Pusa Road, New Delhi-110005 Ph.011-47623456 4. The spiral Spirillum (pl.: Spirilla) Cocci Spore Bacilli Spirilla Flagellum Vibrio Fig. : Bacteria of different shapes Bacterial Life Processes Discussion of bacterial life processes revolves around the study of the prominent metabolic activities like respiration and nutrition. A. Respiration: On the basis of mode of respiration, the bacteria are divided into two main groups : i.e., aerobes and anaerobes. Each group is further of two types i.e. strict or obligate and facultative. (i) Obligate Aerobes : Can perform only aerobic respiration. e.g., Bacillus subtilis. (ii) Obligate Anaerobes : Can perform only anaerobic respiration. e.g., Clostridium botulinum. (iii) Facultative Aerobes : Anaerobic forms but can live in the presence of O2. e.g., Chlorobium. (iv) Facultative Anaerobes : Aerobic forms but can live anaerobically also. e.g., Pseudomonas. B. Nutrition : Bacteria is placed in a particular nutritional class based on their primary source of carbon, energy and electron. I. Autotrophic Bacteria (i) Photoautotrophic bacteria These bacteria are capable of entrapping solar energy and utilizing it for the synthesis of complex food materials due to the presence of pigments like bacteriochlorophyll (bacteriopurpurin) and bacterioviridin. In bacterial photosynthesis water is not the source of electron that acts as reducing power to convert CO2 into glucose. The bacteria obtain reducing power from various compounds such as hydrogen sulphide, thiosulphate or even some organic compounds. No oxygen is evolved (Anoxygenic) as it does not involve splitting of water. Hydrogen released by various compounds mentioned above is picked up by NAD+ which gets reduced to NADH2 acting as reducing power. NADH2 alongwith ATP, produced generally by entrapping solar energy are used to reduce CO2 to glucose. Simple equation for anoxygenic photosynthesis may be written as follows : Solar energy 2 2 enzymes (or any other compound acting as e donor ) CO H S    Sugar + (Sulphur or other oxidised compound) + H2O (ii) Chemoautotrophic bacteria These bacteria obtain energy for the synthesis of food by oxidising certain inorganic substances like ammonia, nitrates, nitrites, ferrous ions, etc. Thus, they do not utilise light as energy source. The chemical energy thus obtained, is trapped in ATP molecules. This energy is then used in carbon assimilation with the help of hydrogen from some source other than water. They play a great role in recycling nutrients like nitrogen, phosphorous, iron, sulphur.