Biological Classification

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Biological Classification Class 11 Notes
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Biological Classification

[PREMIUM NCERT MODULE • DIVERSITY IN LIVING WORLD]

I. Evolution of Classification

Classification is the scientific procedure of grouping organisms into categories based on similarities and differences.

  • Aristotle: Used simple morphological characters. Plants (Trees, Shrubs, Herbs); Animals (with/without red blood).
  • Linnaeus: Two-Kingdom system (Plantae and Animalia). Failed to distinguish between Prokaryotes/Eukaryotes and Unicellular/Multicellular.
  • R.H. Whittaker (1969): Five-Kingdom Classification (Monera, Protista, Fungi, Plantae, Animalia).
[i] Criteria for 5 Kingdoms: Cell structure, Body Organisation, Mode of Nutrition, Reproduction, and Phylogenetic relationships.
II. Kingdom Monera (Bacteria)

Sole members are Bacteria. Prokaryotic and unicellular.

  • Archaebacteria: Live in extreme habitats. Halophiles (salty), Thermoacidophiles (hot springs), Methanogens (marshy/rumen of cattle).
  • Eubacteria (True Bacteria): Have rigid cell wall and motile flagella.
  • Cyanobacteria: Photosynthetic autotrophs (Blue-green algae). Have Heterocysts for N2 fixation (e.g., Nostoc, Anabaena).
  • Mycoplasma: Smallest living cells; Lack cell wall; survive without oxygen; pathogenic.
III. Kingdom Protista

Includes all single-celled eukaryotes. Primarily aquatic.

  • Chrysophytes: Diatoms and Desmids. Diatoms are "Chief Producers" in oceans; silica cell walls form "Diatomaceous earth".
  • Dinoflagellates: Marine/photosynthetic. *Gonyaulax* causes Red Tides.
  • Euglenoids: Fresh water. Have a protein-rich layer called Pellicle. Mixotrophic (Photosynthetic in light, heterotrophic in dark).
  • Slime Moulds: Saprophytic. Form aggregation called Plasmodium.
  • Protozoans: Amoeboid, Flagellated, Ciliated, and Sporozoans (e.g., Plasmodium - malarial parasite).
IV. Kingdom Fungi

Achromophyllous, heterotrophic organisms. Cell wall made of Chitin.

  • Phycomycetes: Aquatic habitats and decaying wood. Coenocytic mycelium. (e.g., Mucor, Rhizopus).
  • Ascomycetes (Sac-fungi): Multicellular (*Penicillium*) or Unicellular (*Yeast*). Branched/septate. (e.g., Aspergillus, Neurospora).
  • Basidiomycetes: Mushrooms, bracket fungi. Dikaryophase is prominent. (e.g., Agaricus, Puccinia).
  • Deuteromycetes (Fungi Imperfecti): Only asexual/vegetative phases are known. (e.g., Alternaria, Trichoderma).
V. Viruses, Viroids, Prions and Lichens

Wait, they are not included in Whittaker's classification system.

  • Viruses: Non-cellular. Genetic material (DNA or RNA) + Protein coat (Capsid). Obligate parasites.
  • Viroids: Smaller than viruses; lacks protein coat (*Potato spindle tuber disease*).
  • Prions: Abnormally folded protein causing BSE (Mad Cow) and Cr-Jacob disease.
  • Lichens: Symbiotic association between Algae (Phycobiont) and Fungi (Mycobiont). Pollution indicators (don't grow in SO2 areas).

Biological Classification HOTS

[ DIVERSITY & EVOLUTIONARY LOGIC ]

[Q] Why are Bacteria considered the most abundant organisms on Earth?
[A] Explanation:

Bacteria possess extreme metabolic diversity. They can survive in almost every possible habitat—from deep oceans and hot springs to human gut and frozen glaciers. Their rapid reproduction rate and diverse nutritional modes (autotrophic, heterotrophic, chemosynthetic) allow them to dominate every ecosystem.

[Q] "Diatoms are the chief producers in the ocean." Justify this statement.
[A] Explanation:

Diatoms are photosynthetic protists that contribute significantly to the total primary productivity of the oceans. Their silica-based cell walls (frustules) are indestructible, and their sheer population size forms the base of the marine food chain.

[Q] Why is Kingdom Protista often called a "Biological Dumping Ground"?
[A] Explanation:

Protista lacks well-defined boundaries. Any single-celled eukaryotic organism that doesn't fit perfectly into Fungi, Plantae, or Animalia is placed here. It includes plant-like (algae), animal-like (protozoa), and fungi-like (slime moulds) organisms, making it highly heterogeneous.

[Q] Differentiate between Virus and Viroid with respect to structure.
[A] Explanation:

A Virus consists of genetic material (DNA or RNA) enclosed in a protein coat called a capsid. A Viroid consists only of a low molecular weight free RNA molecule and completely lacks a protein coat.

[Q] Why are Lichens used as bioindicators of air pollution?
[A] Explanation:

Lichens are extremely sensitive to Sulfur Dioxide (SO2). They obtain their nutrients from the air and have no way to excrete toxins. In polluted areas, they absorb SO2 which destroys their chlorophyll, leading to their death. Thus, their absence in a city is a sign of high air pollution.

[Q6] Heterocyst function in Cyanobacteria.

Specialized cells for atmospheric Nitrogen fixation.

[Q7] Why is Mycoplasma unique?

Smallest living cell, lacks cell wall, survives without O2.

[Q8] Role of Methanogens in Cattle.

Present in Rumen; help in digestion of cellulose and produce Methane (Biogas).

[Q9] Pellicle in Euglena significance.

Protein-rich layer instead of cell wall; makes body flexible.

[Q10] Coenocytic mycelium definition.

Multinucleated cytoplasm without septa (cross-walls).

[Q11] Why are Deuteromycetes "Imperfect"?

Sexual phase is unknown; only asexual/vegetative reproduction seen.

[Q12] Red Tides caused by?

Rapid multiplication of Dinoflagellates like Gonyaulax.

[Q13] Slime mould aggregation name?

Plasmodium.

[Q14] Whittaker's 5th kingdom basis?

Phylogenetic relationships (evolutionary history).

[Q15] Archaebacteria vs Eubacteria wall?

Archaebacteria lack peptidoglycan; have branched chain lipids.

[Q16] Flagellar arrangement in Dinoflagellates.

Two flagella; one longitudinal and one transverse (in a furrow).

[Q17] Dikaryophase in Fungi.

Two nuclei per cell (n+n) before fusion. Seen in Ascomycetes/Basidiomycetes.

[Q18] Bacteriophage structure.

Viruses that infect bacteria; usually have Double Stranded DNA.

[Q19] Prions vs Virioids.

Prions are proteins; Viroids are RNA.

[Q20] Who gave the term Virus?

Pasteur (Beijerinck called it Contagium vivum fluidum).

Classification - 50 Premium Facts

Classification: 50 Mastery Facts

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01
Aristotle: Classified plants into herbs, shrubs, and trees.
02
Linnaeus: Proposed the Two-Kingdom Classification System.
03
Whittaker: Proposed the Five-Kingdom Classification in 1969.
04
Monera: Sole members are Bacteria; all are prokaryotic.
05
Bacteria shapes: Coccus (spherical), Bacillus (rod), Vibrio (comma).
06
Archaebacteria: Differ from eubacteria in their cell wall structure.
07
Methanogens: Present in the gut of ruminant animals (cows/buffaloes).
08
Cyanobacteria: Unicellular colonial algae with Chlorophyll-a.
09
Heterocysts: Specialized cells for N2 fixation in Nostoc.
10
Chemosynthetic bacteria: Oxidize inorganic substances like nitrates.
11
Binary Fission: Main mode of reproduction in bacteria.
12
Mycoplasmas: Completely lack a cell wall; smallest known lving cells.
13
Protista: Single-celled eukaryotes; boundaries are not well-defined.
14
Chrysophytes: Include diatoms and golden algae (desmids).
15
Diatomaceous Earth: Accumulated silica shells of diatoms over time.
16
Dinoflagellates: Possess two flagella; one transverse and one longitudinal.
17
Euglena: Has a protein layer called Pellicle instead of cell wall.
18
Slime Moulds: Aggregation called Plasmodium during favorable conditions.
19
Amoeboid protozoans: Move using pseudopodia (e.g., Entamoeba).
20
Trypanosoma: A flagellated protozoan that causes sleeping sickness.
21
Paramecium: A ciliated protozoan with a gullet and two nuclei.
22
Sporozoans: Includes Plasmodium, the infectious malarial parasite.
23
Kingdom Fungi: Heterotrophic, saprophytic, or parasitic multicellular organisms.
24
Chitin: The chemical component of fungal cell walls.
25
Saccharomyces: Also known as Yeast; a unicellular fungus.
26
Hyphae: Thread-like structures; network is called Mycelium.
27
Plasmogamy: Fusion of two motile or non-motile gamete protoplasms.
28
Phycomycetes: Mycelium is aseptate and coenocytic (e.g., Albugo).
29
Ascomycetes: Known as sac-fungi; spores are ascospores (endogenous).
30
Basidiomycetes: Bracket fungi/mushrooms; produce basidiospores (exogenous).
31
Deuteromycetes: Imperfect fungi; sexual phase not yet discovered.
32
Plantae: Multicellular eukaryotes with cellulose cell wall.
33
Animalia: Heterotrophic eukaryotes lacking cell walls.
34
Viruses: Genetic material (DNA/RNA) + Protein coat (Capsid).
35
D.J. Ivanowsky: Recognized causal organism of Mosaic disease (1892).
36
Beijerinck: Coined "Contagium vivum fluidum" (Infectious living fluid).
37
W.M. Stanley: Showed viruses could be crystallized (1935).
38
Capsomeres: Subunits that make up the viral capsid.
39
AIDS: Caused by Human Immunodeficiency Virus (HIV).
40
Viroids: Discovered by T.O. Diener (1971); free RNA without protein coat.
41
Prions: Infectious protein particles; abnormally folded (e.g., Mad Cow).
42
Lichens: Mutual association between algae and fungi.
43
Phycobiont: The algal component of a lichen (autotrophic).
44
Mycobiont: The fungal component of a lichen (heterotrophic).
45
Pollution indicators: Lichens do not grow in polluted areas.
46
Nostoc: Terrestrial cyanobacterium capable of fixing nitrogen.
47
Capsid: Protein shell protecting viral nucleic acid.
48
Flagellated protists: Protozoans like Trypanosoma with flagella.
49
Zoospores: Asexual motile spores produced by Phycomycetes.
50
Phylogeny: Classification based on evolutionary history.
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