IGCSE Biology: Characteristics and Classification of Living Organisms

Overview

• Biology: The study of living things (organisms)
• Characteristics of Living Organisms: Identified using the mnemonic MRS GREN:
  • M: Movement
  • R: Respiration
  • S: Sensitivity
  • G: Growth
  • R: Reproduction
  • E: Excretion
  • N: Nutrition

Characteristics of Living Things

• Movement: Change of position or place
• Respiration: Chemical reactions in cells that release energy
• Sensitivity: Ability to detect and respond to environmental changes
• Growth: Permanent increase in size and mass
• Reproduction: Production of offspring
• Excretion: Removal of metabolic waste
• Nutrition: Intake of materials for energy, growth, and development

Classification Systems

• Species: Group of organisms that produce fertile offspring
• Binomial System:
  • International system
  • Scientific names: Genus (capitalized) and species (lowercase) in italics
  • Example: Homo sapiens
• Dichotomous Keys:
  • Identify organisms through a series of yes/no questions
  • Example: Differentiating organisms based on body cover and features

Classification

• Purpose: Simplify study by grouping organisms
• Traditional Classification: Based on shared features
• Modern Classification: Utilizes DNA sequencing

Five Kingdoms of Life

1. Animals
   • Multicellular, no cell walls or chloroplasts
   • Obtain nutrients by consuming others
   • Examples: Cats, elephants
2. Plants
   • Multicellular, have cell walls and chloroplasts
   • Photosynthesize for nutrition
   • Examples: Trees, flowers
3. Fungi
   • Multicellular, cell walls (not cellulose)
   • Feed on decaying material or live as parasites
   • Example: Mushrooms
4. Protists
   • Mostly unicellular, some multicellular
   • May have chloroplasts; nutrition varies
   • Example: Algae
5. Prokaryotes
   • Unicellular, no nucleus
   • Example: Bacteria

Animal Kingdom Classification

• Vertebrates (backbone)
  • Mammals: Fur, milk for young, example: humans
  • Birds: Feathers, lay eggs, example: parrot
  • Reptiles: Scaly skin, example: snake
  • Amphibians: Moist skin, live in water and land, example: frog
  • Fish: Live in water, example: goldfish
• Invertebrates (no backbone)
  • Arthropods: Jointed legs
    • Myriapods: Many legs, example: centipede
    • Insects: Three body parts, example: butterfly
    • Arachnids: Eight legs, example: spider
    • Crustaceans: Many legs, gills, example: crab

Plant Kingdom Classification

• Ferns: Reproduce via spores
• Flowering Plants: Reproduce via seeds
  • Monocotyledons: Parallel veins, example: grasses
  • Dicotyledons: Branching veins, example: roses

Viruses

• Not Living: Cannot perform life processes independently
• Structure: Genetic material in a protein coat

• Note: This summary captures key points for studying IGCSE Biology, focusing on the characteristics and classification of living organisms. For further detail, refer to specific study materials and textbooks.