Biological classification class 11

Introduction to Biological Classification

• Historical Background

  • Early attempts to classify living organisms were instinctual, catering to human needs (food, shelter, clothing).

  • Aristotle first proposed a scientific system, classifying plants by morphology (trees, shrubs, herbs) and animals by blood types (red blood vs. non-red blood).

  • Linnaeus introduced a Two Kingdom system (Plantae and Animalia), which did not accommodate all organisms adequately.

Limitations of Early Classification Systems

• Simple classifications like Linnaeus' failed to distinguish between:

  • Eukaryotes and prokaryotes

  • Unicellular and multicellular organisms

  • Photosynthetic (green algae) and non-photosynthetic (fungi) organisms

• Many organisms did not fit into either kingdom, leading to inadequacies.

• Evolutionary relationships, cell structure, nutrition modes, and reproduction methods were also necessary for classification.

Modern Classification Systems

Five Kingdom Classification by R.H. Whittaker (1969)

• Proposed kingdoms:

  • Monera

  • Protista

  • Fungi

  • Plantae

  • Animalia

• Key classification criteria:

  • Cell structure

  • Body organization

  • Mode of nutrition

  • Reproduction

  • Phylogenetic relationships

Three-Domain System

• Proposed to further elaborate on Monera by dividing it into two domains, leading to a six kingdom classification (details in higher studies).

Characteristics of the Five Kingdoms

Kingdom Monera

• Bacteria: Sole members of Monera, abundant micro-organisms found in diverse habitats.

• Four categories based on shape:

  • Coccus: Spherical

  • Bacillus: Rod-shaped

  • Vibrio: Comma-shaped

  • Spirillum: Spiral-shaped

• Metabolic diversity:

  • Autotrophic (photosynthetic or chemosynthetic)

  • Heterotrophic (decomposers, pathogens)

Archaebacteria

• Thrive in harsh environments (halophiles, thermoacidophiles, methanogens).

• Unique cell wall structures aid survival.

Eubacteria

• Characterized by rigid cell walls; some are photosynthetic (cyanobacteria).

• Important nutrient recyclers and decomposers.

Kingdom Protista

• Comprises all single-celled eukaryotes; includes various groups based on characteristics.

• Chrysophytes (Diatoms, golden algae): Microscopic, mostly photosynthetic.

• Dinoflagellates: Marine, photosynthetic; can cause red tides due to rapid population increases.

• Euglenoids: Flexibility in the absence of sunlight; contain chlorophyll.

• Slime Moulds: Saprophytic, can form plasmodium under certain conditions.

• Protozoans: Heterotrophic, have various movement and feeding mechanisms.

Kingdom Fungi

• Diverse group of heterotrophic organisms with complex structures.

• Reproduction through:

  • Asexual (fragmentation, budding)

  • Sexual (with complex life stages).

Classifications in Fungi

• Phycomycetes: Aquatic, obligate parasites.

• Ascomycetes: Sac fungi, include yeast; important in biochemical processes.

• Basidiomycetes: Includes mushrooms; reproduce via basidiospores.

• Deuteromycetes: Imperfect fungi, classified based on observed reproduction.

Kingdom Plantae

• Encompasses all eukaryotic chlorophyll-containing organisms.

• Characters:

  • Eukaryotic structure

  • Cell wall mainly composed of cellulose

  • Exhibit alternation of generations (diploid sporophyte and haploid gametophyte).

Kingdom Animalia

• Composed of multicellular, heterotrophic organisms without cell walls.

• Holozoic nutrition via internal digestion; primarily develop through sexual reproduction.

Additional Organisms

Viruses

• Non-cellular entities, reliant on host cells for replication; causes various diseases.

Viroids

• Infectious agents composed solely of RNA; lacks protein coat.

Prions

• Infectious proteins linked to neurological diseases.

Lichens

• Symbiotic associations between algae and fungi; important indicators of environmental health.

Summary

• Overview of classification evolution from Aristotle to Whittaker's five kingdoms, emphasizing the need for distinguishing characteristics.

• Discussion on viruses and associated diseases, with acknowledgment of the complexities of the biological classification system.