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IGCSE Biology: Characteristics and Classification of Living Organisms

Jul 22, 2024

IGCSE Biology: Characteristics and Classification of Living Organisms

Introduction

  • Biology: Study of living things (organisms)
  • This video summarizes Topic 1: Characteristics and classification of living organisms

Seven Characteristics of Living Things (MRS GREN)

  • Movement: Change of position or place
  • Respiration: Chemical reactions in cells breaking down nutrient molecules to release energy
  • Sensitivity: Ability to detect and respond to changes in the environment
  • Growth: Permanent increase in size and dry mass
  • Reproduction: Processes to produce more of the same kind of organism
  • Excretion: Removal of waste products of metabolism and substances in excess
  • Nutrition: Intake of materials for energy, growth, and development

Classification Systems

  • Species: Group of organisms that can reproduce to produce fertile offspring
  • Species are classified by shared features
  • Binomial System: International system to name species using genus and species
    • Genus: Group of related species
    • Format: Genus (capitalized) + species (lowercase), in italics (e.g., Homo sapiens)

Dichotomous Keys

  • Tool to identify organisms based on a series of questions
  • Dichotomous: Branching into two
  • Provides two descriptions at a time to narrow down to species

Purpose of Classification

  • Classification: Grouping organisms to simplify study
  • Reflects evolutionary relationships
  • Traditional classification was based on shared features; now also uses DNA sequences

Levels of Classification

  • Five Kingdoms: Animals, Plants, Fungi, Protists, Prokaryotes
    1. Animals: Multicellular, nuclei, no cell walls or chloroplasts, nutrition by eating
      • Animal Cell: Nucleus, cell membrane, mitochondria, ribosomes, cytoplasm
    2. Plants: Multicellular, nuclei, chloroplasts, cell walls (cellulose), photosynthesis
      • Plant Cell: Includes cell wall and chloroplasts
    3. Fungi: Multicellular (mainly), nuclei, cell walls not from cellulose, saprophytic/parasitic nutrition
      • Fungal Cell: Cell wall (not cellulose)
    4. Protists: Mostly unicellular, nuclei, some with cell walls/chloroplasts, various modes of nutrition
    5. Prokaryotes: Unicellular, cell walls (not cellulose), no nucleus/mitochondria
      • Bacterial Cell: DNA strands, plasmids, no nucleus

Animal Kingdom

  • Vertebrates: Backbone

    1. Mammals: Hair/fur, mammary glands, four-chambered heart, varied teeth (e.g., humans, cats)
    2. Birds: Feathers, hard-shelled eggs, beak, wings (e.g., toucan, parrot)
    3. Reptiles: Scaly skin, rubbery eggs (e.g., snakes, crocodiles)
    4. Amphibians: Moist skin, eggs in water, larvae with gills, adults with lungs (e.g., frogs)
    5. Fish: Scales, gills, fins (e.g., salmon)

  • Invertebrates: No backbone

    • Arthropods: Jointed legs; divided into myriapods, insects, arachnids, crustaceans
      1. Myriapods: Many segments, jointed legs (e.g., centipedes)
      2. Insects: Three body parts, 3 pairs of legs, 2 pairs of wings (e.g., butterflies)
      3. Arachnids: Four pairs of legs, book lungs (e.g., spiders)
      4. Crustaceans: More than 4 pairs of legs, gills (e.g., crabs)

Plant Kingdom

  • Ferns: Fronds, reproduce by spores
  • Flowering Plants: Reproduce by flowers and seeds
    • Monocotyledons: Branching root system, parallel veins, petals in multiples of three
    • Dicotyledons: Taproot system, broad leaves with branching veins, petals in multiples of 4 or 5

Viruses

  • Not considered living
  • Cannot carry out life processes independently
  • Consist of genetic material in a protein coat

Conclusion

  • Summary of classification and characteristics of living organisms.

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