Class 11 Biology Chapter 2 Notes (Biological Classification)

Biological classification is the scientific process of grouping organisms based on their similarities and differences. It involves arranging organisms into a hierarchical system of categories, from broad groups like kingdoms to specific groups like species. This classification helps us understand the evolutionary relationships between organisms and their place in the natural world. Here you can find the easy and short Class 11 Biology Chapter 2 Notes on Biological Classification for your NEET preparation.

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Class 11 Biology Chapter 2 Notes

Chapter 2: Introduction to Biological Classification    (Click here for Chapter 2 Notes)

Early Classification:

Ø  Aristotle: Classified organisms based on simple morphology into plants (trees, shrubs, herbs) and animals (with or without red blood).

Two Kingdom Classification (Linnaeus):

Ø  Divided organisms into Plantae and Animalia.

Limitations:

Ø  Did not distinguish between prokaryotes (e.g., bacteria) and eukaryotes (e.g., algae).

Ø  Overlooked unicellular and multicellular differences.

Ø  Grouped photosynthetic (green algae) with non-photosynthetic organisms (fungi).

Five Kingdom Classification (R.H. Whittaker, 1969):

Ø  Kingdoms: Monera, Protista, Fungi, Plantae, Animalia.

Ø  Basis: Cell structure, body organization, mode of nutrition, reproduction, phylogenetic relationships.

Kingdom Monera

Characteristics:

Ø  Prokaryotic, unicellular organisms.

Ø  Lack a true nucleus and membrane-bound organelles.

Ø  Found in diverse habitats (soil, hot springs, deserts, oceans).

Ø  Four bacterial shapes: Coccus (spherical), Bacillus (rod-shaped), Vibrio (comma-shaped), Spirillum (spiral).

Nutrition:

Autotrophic:

Ø  Photosynthetic autotrophs: Synthesize food using sunlight (e.g., cyanobacteria like Nostoc, Anabaena).

Ø  Chemosynthetic autotrophs: Oxidize inorganic substances (e.g., nitrates) for energy.

Heterotrophic:

Ø  Depend on organic matter (saprophytic or parasitic).

Archaebacteria:

Ø  Survive in extreme environments.

Ø  Examples: Halophiles (salty habitats), thermoacidophiles (hot springs), methanogens (anaerobic conditions, produce methane in ruminants’ guts).

Eubacteria:

Ø  True bacteria with a rigid cell wall and, if motile, flagella.

Ø  Cyanobacteria (blue-green algae) are photosynthetic and can fix nitrogen (e.g., Nostoc).

Ø  Play roles in nutrient recycling (e.g., nitrogen, sulfur).

Ø  Pathogens: Cause diseases like cholera, typhoid, tetanus.

Mycoplasma:

Ø  Lack a cell wall, smallest living organisms, pathogenic in plants and animals.

Kingdom Protista

Ø  Eukaryotic, unicellular organisms, primarily aquatic.

Ø  Act as a bridge between plants, animals, and fungi.

Groups:

Chrysophytes: Includes diatoms and golden algae (desmids).

Ø  Found in freshwater/marine habitats; photosynthetic.

Ø  Diatom walls are silica-based, forming “diatomaceous earth” (used in polishing, filtration).

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Dinoflagellates: Marine, photosynthetic organisms.

Ø  Appear in various colors (yellow, red, brown) due to pigments.

Ø  Cause red tides (e.g., Gonyaulax), releasing toxins harmful to marine life.

Euglenoids: Freshwater, flexible due to pellicle.

Ø  Photosynthetic in light; heterotrophic in darkness (e.g., Euglena).

Slime Moulds: Saprophytic protists.

Ø  Form a large plasmodium that produces spores in adverse conditions.

Protozoans: Heterotrophic protists.

Amoeboid: Move using pseudopodia (e.g., Amoeba).

Flagellated: Have flagella (e.g., Trypanosoma).

Ciliated: Use cilia for movement and feeding (e.g., Paramoecium).

Sporozoans: Parasitic with infectious spores (e.g., Plasmodium causes malaria).

Kingdom Fungi

Characteristics:

Ø  Eukaryotic, heterotrophic organisms.

Ø  Found in diverse habitats (air, water, soil, decaying matter).

Ø  Body structure: Hyphae form a mycelium.

Ø  Cell walls made of chitin and polysaccharides.

Ø  Nutrition: Saprophytic (decomposers), parasitic, or symbiotic (e.g., lichens, mycorrhizae).

Reproduction:

Ø  Vegetative: Fragmentation, budding.

Ø  Asexual: Spores like conidia, sporangiospores.

Ø  Sexual: Involves plasmogamy, karyogamy, and meiosis.

Classes:

Ø  Phycomycetes: Aseptate, coenocytic hyphae. Examples: Rhizopus, Mucor.

Ø  Ascomycetes: Sac fungi, septate hyphae. Examples: Penicillium, Neurospora.

Ø  Basidiomycetes: Mushrooms, rusts. Examples: Agaricus, Puccinia.

Ø  Deuteromycetes: Known as imperfect fungi (e.g., Alternaria).

Kingdom Plantae

Characteristics:

Ø  Eukaryotic, chlorophyll-containing organisms (autotrophic).

Ø  Examples: Algae, bryophytes, pteridophytes, gymnosperms, angiosperms.

Ø  Alternation of generations:

Ø  Sporophytic (diploid) phase alternates with gametophytic (haploid) phase.

Kingdom Animalia

Characteristics:

Ø  Multicellular, eukaryotic, heterotrophic organisms.

Ø  Lack cell walls, digest food internally, store energy as glycogen or fat.

Ø  Show complex neuromotor mechanisms and locomotion.

Ø  Reproduction primarily sexual.

Viruses, Viroids, Prions, and Lichens

Viruses:

Ø  Non-cellular, inert outside the host.

Ø  Structure: Capsid (protein coat) and genetic material (RNA or DNA).

Ø  Examples: Influenza, AIDS, plant mosaic viruses.

Viroids:

Ø  Smaller than viruses, consist of RNA, no protein coat.

Ø  Cause diseases like potato spindle tuber.

Prions:

Ø  Infectious proteins causing neurological diseases (e.g., mad cow disease, Creutzfeldt-Jakob disease).

Lichens:

Ø  Symbiotic association between algae (phycobiont) and fungi (mycobiont).

Ø  Indicators of air pollution (do not grow in polluted areas).

Summary

Biological classification organizes organisms into hierarchical categories based on similarities and differences, ranging from broad groups like kingdoms to specific groups like species. Early systems, such as Aristotle’s and Linnaeus’ two-kingdom classification, had limitations in distinguishing features like cellular structure and modes of nutrition. Modern systems, like Whittaker’s five-kingdom classification, address these gaps by considering aspects like cell type, body organization, and evolutionary relationships. Additional topics include unique organisms like archaebacteria, protists, fungi, viruses, and lichens, which highlight the diversity of life and their roles in ecosystems and human health.

Exercises

1. Discuss how classification systems have undergone several changes over a period of time?

Classification systems have evolved over time to reflect increasing knowledge of organismal diversity and relationships. Early systems like Aristotle’s morphology-based grouping and Linnaeus’ two-kingdom system were simplistic. Modern classifications, such as Whittaker’s five-kingdom system, consider advanced criteria like cellular organization, modes of nutrition, and evolutionary relationships. Molecular studies and phylogenetic data continue to refine these systems.

2. State two economically important uses of: (a) heterotrophic bacteria; (b) archaebacteria

(a) Heterotrophic bacteria: They aid in decomposition and nutrient recycling (e.g., nitrogen fixation by Rhizobium) and are used in industries (e.g., lactic acid bacteria in yogurt production).

(b) Archaebacteria: Methanogens produce methane used as biogas, and extremophiles like Thermus aquaticus provide enzymes for industrial and scientific applications (e.g., Taq polymerase for PCR).

3. What is the nature of cell-walls in diatoms?

Diatoms’ cell walls are made of silica, forming a rigid, glass-like structure called a frustule, which contributes to “diatomaceous earth” deposits.

4. Find out what do the terms ‘algal bloom’ and ‘red-tides’ signify

Algal blooms refer to rapid algae growth in water bodies due to nutrient enrichment, often leading to oxygen depletion. Red tides are caused by dinoflagellate blooms, which may release toxins harmful to marine life and humans.

5. How are viroids different from viruses?

Viroids consist only of RNA and lack a protein coat, whereas viruses have a protein capsid surrounding their genetic material, which may be RNA or DNA.

6. Describe briefly the four major groups of Protozoa

Amoeboids: Move with pseudopodia (e.g., Amoeba).

Flagellates: Use flagella for locomotion (e.g., Trypanosoma).

Ciliates: Have cilia for movement and feeding (e.g., Paramecium).

Sporozoans: Parasitic, producing infectious spores (e.g., Plasmodium).

7. Plants are autotrophic. Can you think of some plants that are partially heterotrophic?

8. What do the terms phycobiont and mycobiont signify?

Phycobiont refers to the algal partner in lichens, which performs photosynthesis, while mycobiont refers to the fungal partner, providing structure and moisture.

9. Give a comparative account of the classes of Kingdom Fungi under the following: (i) mode of nutrition (ii) mode of reproduction

Comparative account of Kingdom Fungi classes:

(i) Mode of nutrition:

Phycomycetes: Saprophytic or parasitic.

Ascomycetes: Saprophytic, parasitic, or symbiotic.

Basidiomycetes: Decomposers or symbiotic.

Deuteromycetes: Saprophytic or parasitic.

(ii) Mode of reproduction:

Phycomycetes: Asexual spores (zoospores), sexual by zygospores.

Ascomycetes: Asexual spores (conidia), sexual by ascospores.

Basidiomycetes: Sexual reproduction by basidiospores, no asexual spores.

Deuteromycetes: Asexual spores only (conidia).

10. What are the characteristic features of Euglenoids?

Euglenoids are freshwater, unicellular organisms with a protein-rich pellicle for flexibility. They are photosynthetic in light but can switch to heterotrophy in darkness (e.g., Euglena).

11. Give a brief account of viruses with respect to their structure and nature of genetic material. Also name four common viral diseases.

Viruses are non-cellular entities with a protein coat (capsid) and genetic material, either RNA or DNA. Examples of viral diseases include influenza, AIDS, polio, and dengue.

12. Organise a discussion in your class on the topic – Are viruses living or nonliving?

In a discussion on whether viruses are living or non-living, arguments for living include their ability to reproduce inside host cells and adapt through mutations. Arguments for non-living include their inertness outside hosts and lack of cellular structure.

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