IGCSE Biology Revision Notes: Characteristics and Classification of Living Organisms

Introduction

• Overview of IGCSE syllabus in Biology
• Focus on the characteristics and classification of living organisms

Characteristics of Living Organisms

• Definition: Biology is the study of living things (organisms).
• Seven Characteristics (Mrs Gren):
  • Movement: Action by organism/part causing a position change
  • Respiration: Chemical reactions breaking down nutrients to release energy for metabolism
  • Sensitivity: Ability to detect and respond to environmental changes
  • Growth: Permanent increase in size and dry mass
  • Reproduction: Processes making more of the same kind of organism
  • Excretion: Removal of waste products of metabolism and excess substances
  • Nutrition: Taking in materials for energy, growth, and development

Classification of Living Organisms

• Definition: Grouping organisms based on shared features
• Species: Group of organisms that can reproduce to produce fertile offspring
• Binomial System:
  • Internationally agreed naming system (Genus + Species)
  • Genus: Group of related species (Capitalized)
  • Species: Specific name (lowercase)
  • Example: Homo sapiens
  • Names are italicized when typed

Dichotomous Keys

• Definition: Tools to identify organisms using a series of questions
• Function: Provides two descriptions at a time leading to organism identification

Importance of Classification Systems

• Aims to reflect evolutionary relationships
• Traditional classification based on physical features, now enhanced by DNA sequence analysis
• Organisms classified into one of five kingdoms: Animals, Plants, Fungi, Protists, Prokaryotes

The Five Kingdoms

1. Animal Kingdom

• Multicellular, nucleated cells without cell walls
• Nutrition: Heterotrophic (eating other organisms)
• Sub-groups:
  • Vertebrates: Animals with backbones
    • Classes: Mammals, Birds, Reptiles, Amphibians, Fish
  • Invertebrates: Animals without backbones
    • Includes Arthropods: Myriapods, Insects, Arachnids, Crustaceans

2. Plant Kingdom

• Multicellular with nucleated cells and cell walls made of cellulose
• Nutrition: Autotrophic (photosynthesis)
• Sub-groups:
  • Ferns: Reproduce by spores
  • Flowering plants:
    • Divided into Monocotyledons and Dicotyledons
    • Key differences in root systems, leaf veins, and flower petal arrangements

3. Fungi

• Usually multicellular with nuclei and cell walls not made of cellulose
• Nutrition: Saprophytic (decaying material) or Parasitic (live material)

4. Protists

• Mostly unicellular, some multicellular, with a nucleus
• Nutritional modes vary (photosynthesis or heterotrophy)

5. Prokaryotes

• Unicellular organisms without a nucleus
• Cell walls not made of cellulose
• Example: Bacteria

Conclusion

• Viruses: Not classified as living organisms; do not carry out life processes independently
• Summary of key concepts in characteristics and classification of living organisms

Final Notes

• Encouragement to subscribe to IGCSE study buddy for more biology revision videos.