Chapter 2: Biological Classification

Introduction to Biological Classification

• Classification of living organisms has evolved over time.
• Early classifications were instinctive, based on utility for food, shelter, clothing.
• Aristotle: Classified plants (trees, shrubs, herbs) & animals (red blood vs. no red blood).
• Linnaeus: Two Kingdom system (Plantae & Animalia) which lacked distinctions among cell types and nutritional modes.
• Need for more criteria: cell structure, nutrition, reproduction, evolutionary relationships.

Whittaker's Five Kingdom Classification (1969)

• Kingdoms: Monera, Protista, Fungi, Plantae, Animalia.
• Criteria: cell structure, body organization, mode of nutrition, reproduction, phylogenetic relationships.
• Led to better distinction between prokaryotes and eukaryotes, unicellular and multicellular organisms.

Kingdom Monera

• Comprises bacteria, most abundant microorganisms, found everywhere including extreme environments.
• Bacteria shapes: Coccus, Bacillus, Vibrio, Spirillum.
• Metabolism: Autotrophic (photosynthetic/chemosynthetic) or heterotrophic.

Archaebacteria

• Survive in harsh environments (halophiles, thermoacidophiles, methanogens).
• Unique cell wall structure aiding survival in extremes.

Eubacteria

• True bacteria with rigid cell wall and sometimes flagella.
• Cyanobacteria: Photosynthetic, can fix nitrogen.
• Heterotrophic bacteria: Decomposers, some are pathogens.

Kingdom Protista

• Single-celled eukaryotes, primarily aquatic.
• Includes Chrysophytes, Dinoflagellates, Euglenoids, Slime Moulds, Protozoans.

Chrysophytes

• Includes diatoms, golden algae; found in water, photosynthetic, form diatomaceous earth.

Dinoflagellates

• Marine, photosynthetic, can cause red tides, some produce toxins.

Euglenoids

• Freshwater, flexible pellicle instead of cell wall, can photosynthesize and ingest food.

Slime Moulds

• Saprophytic, form plasmodium, resistant spores.

Protozoans

• Heterotrophic, include amoeboid, flagellated, ciliated, and sporozoans.

Kingdom Fungi

• Heterotrophic, diverse habitats, important decomposers.
• Reproduce via spores, both asexual and sexual.

Classes of Fungi

• Phycomycetes: Aquatic/moist environments, aseptate hyphae.
• Ascomycetes: Sac fungi, multicellular (Penicillium), unicellular (yeast).
• Basidiomycetes: Mushrooms, rusts, smuts, produce basidiospores.
• Deuteromycetes: Known as imperfect fungi, reproduce asexually.

Kingdom Plantae

• Chlorophyll-containing eukaryotes, include algae, bryophytes, gymnosperms, angiosperms.
• Exhibit alternation of generations (sporophytic and gametophytic phases).

Kingdom Animalia

• Multicellular, heterotrophic, lack cell walls, diverse modes of nutrition.
• Reproduce sexually, exhibit growth into defined adult forms.

Viruses, Viroids, Prions, and Lichens

• Viruses: Non-cellular, require host cells for replication, cause diseases.
• Viroids: Infectious RNA particles, lack protein coat.
• Prions: Infectious proteins causing neurological diseases.
• Lichens: Symbiotic relationship between algae and fungi.

Summary

• Historical development of classification systems.
• Whittaker’s Five Kingdom classification improved understanding of life forms.
• Detailed characteristics of Monera, Protista, Fungi, Plantae, and Animalia.
• Introduction to viruses, viroids, prions, and lichens outside traditional classification.

Exercises

1. Discuss evolution of classification systems.
2. Economic importance of bacteria and archaebacteria.
3. Nature of diatom cell walls.
4. Significance of algal blooms and red tides.
5. Differences between viroids and viruses.
6. Overview of Protozoa groups.
7. Examples of partially heterotrophic plants.
8. Significance of phycobiont and mycobiont in lichens.
9. Comparative account of fungi classes.
10. Characteristics of Euglenoids.
11. Structure of viruses and common viral diseases.
12. Debate on whether viruses are living or non-living.