Biological Classification Notes: Class 11 Biology Chapter 2
Class 11 Biology Chapter 2 Biological Classification covers the historical systems of classification, RH Whittaker's Five Kingdom Classification (Monera, Protista, Fungi, Plantae, Animalia), characteristics of prokaryotes and eukaryotes, reproduction in fungi, and non-cellular acellular entities like Viruses, Viroids, Prions, and Lichens.
Overview of Topics & Subtopics (Click to Jump)
1. Systems of Classification & Kingdom Monera
Short Note:
• Five Kingdom Classification (R.H. Whittaker, 1969): Based on cell structure, body organisation, mode of nutrition, reproduction, and phylogenetic relationships. Kingdoms: Monera, Protista, Fungi, Plantae, Animalia.
• Kingdom Monera (Prokaryotes):
- Sole members are Bacteria. Lack membrane-bound organelles and a true nucleus.
- Archaebacteria: Live in extreme conditions—Halophiles (extreme salty areas), Thermoacidophiles (hot springs), Methanogens (marshy areas and gut of ruminants, produce methane gas).
- Eubacteria (True Bacteria): Possess rigid cell wall. Includes Cyanobacteria (Blue-green algae with chlorophyll 'a', perform nitrogen fixation via specialized cells called heterocysts e.g., Nostoc, Anabaena).
- Mycoplasma: Organisms that completely lack a cell wall. Smallest living cells, can survive without oxygen, pathogenic in animals and plants.
2. Kingdom Protista
Short Note:
• Includes all single-celled unicellular eukaryotes. Primarily aquatic.
• Chrysophytes: Diatoms and golden algae (desmids). Cell walls form two thin overlapping shells fitting like a soap box, embedded with silica forming Diatomaceous Earth (used in polishing, filtration of oils/syrups). Diatoms are chief producers in oceans.
• Dinoflagellates: Mostly marine, photosynthetic. Possess 2 flagella. Rapid multiplication of red dinoflagellates (e.g., Gonyaulax) causes red tides and releases toxins killing marine life.
• Euglenoids: Freshwater organisms lacking cell wall, instead have a protein-rich layer called pellicle making body flexible (e.g., Euglena). Mixotrophic nutrition.
• Slime Moulds: Saprophytic protists. Form an aggregation called plasmodium under suitable conditions.
• Protozoans: Heterotrophs (predators or parasites). Types: Amoeboid (Amoeba, Entamoeba), Flagellated (Trypanosoma - causes sleeping sickness), Ciliated (Paramecium), Sporozoans (Plasmodium - malaria parasite).
3. Kingdom Fungi
Short Note:
• Heterotrophic multicellular organisms (except unicellular Yeast). Cell wall composed of chitin and polysaccharides. Body consists of long, slender thread-like structures called hyphae; network of hyphae forms mycelium.
• Phycomycetes: Aseptate and coenocytic mycelium. Asexual spores: Zoospores (motile) or Aplanospores (non-motile). Examples: Mucor, Rhizopus (bread mould), Albugo (parasitic on mustard).
• Ascomycetes (Sac-fungi): Mostly multicellular, saprophytic/decomposers. Asexual spores are Conidia. Sexual spores are Ascospores produced inside sac-like asci. Examples: Penicillium, Aspergillus, Claviceps, Neurospora, Yeast.
• Basidiomycetes (Club-fungi): Mushrooms, bracket fungi, or puffballs. Sex organs absent; plasmogamy occurs by fusion of vegetative cells leading to basidiospores. Examples: Agaricus (mushroom), Ustilago (smut), Puccinia (rust fungus).
• Deuteromycetes (Fungi Imperfecti): Perfect (sexual) stage is absent or unknown. Reproduce only by asexual spores (conidia). Examples: Alternaria, Colletotrichum, Trichoderma.
4. Viruses, Viroids, Prions & Lichens
Short Note:
• Viruses: Non-cellular obligate parasites not included in Whittaker's 5 kingdom system. Consist of genetic material (ssRNA, dsRNA, or dsDNA) enclosed in a protein coat called a capsid (made of capsomeres). Dmitri Ivanowsky discovered Tobacco Mosaic Virus (TMV); MW Beijerinck called fluid Contagium vivum fluidum.
• Viroids: Discovered by T.O. Diener (1971). Free RNA without a protein coat, smaller than viruses. Causes Potato Spindle Tuber Disease.
• Prions: Abnormally folded proteinaceous infectious agents causing neurological diseases like Bovine Spongiform Encephalopathy (BSE / Mad Cow Disease) and Cr-Jacob disease (CJD) in humans.
• Lichens: Symbiotic association between an Alga (Phycobiont - autotrophic, prepares food) and a Fungus (Mycobiont - heterotrophic, provides shelter and absorbs mineral nutrients/water). Excellent pollution indicators (do not grow in SO2 polluted areas).
Intext & Conceptual Questions
R.H. Whittaker proposed the Five Kingdom Classification in 1969. The main criteria used by him for classification were:
1. Cell structure complexity: Prokaryotic vs. Eukaryotic.
2. Body organisation: Unicellular vs. Multicellular / Tissue / Organ level.
3. Mode of nutrition: Autotrophic (photosynthetic/chemosynthetic) vs. Heterotrophic (saprophytic/holozoic/parasitic).
4. Reproduction & Phylogenetic relationships: Evolutionary history and lineage.
The Five Kingdoms are:
• Kingdom Monera
• Kingdom Protista
• Kingdom Fungi
• Kingdom Plantae
• Kingdom Animalia
Textbook Chapter End Exercise Questions
(a) Economic uses of Heterotrophic Bacteria:
1. Dairy & Food Industry: Used in making curd from milk (Lactobacillus) and production of cheese.
2. Medicine & Agriculture: Used in manufacturing antibiotics (e.g., Streptomyces) and nitrogen fixation in legume roots (Rhizobium).
(b) Economic uses of Archaebacteria:
1. Biogas Production: Methanogens present in the gut of ruminants (cows and buffaloes) convert dung into biogas (methane).
2. Biotechnology: Enzymes isolated from thermoacidophilic archaebacteria (e.g., Taq polymerase from Thermus aquaticus) are widely used in PCR (Polymerase Chain Reaction).
Structure and Genetic Material of Viruses:
1. Viruses are non-cellular, obligate intracellular parasites consisting of a nucleic acid core surrounded by a protective protein coat called a capsid, made of subunit protein blocks called capsomeres.
2. A single virus contains either RNA or DNA, never both.
3. Generally, viruses that infect plants have single-stranded RNA (ssRNA). Viruses that infect animals have either single or double-stranded RNA or double-stranded DNA. Bacteriophages (viruses that infect bacteria) usually possess double-stranded DNA (dsDNA).
Reason for Exclusion from Five Kingdom Classification:
Whittaker's classification is strictly based on cellular organization and metabolic machinery. Viruses are acellular and do not display metabolic activity outside a host cell. They behave as non-living crystalline structures outside host cells and only become active upon entering a living host, using the host's machinery to replicate.