Characteristics and Classification of Living Organisms

Introduction

• Topic: Characteristics and Classification of Living Organisms
• Context: Cambridge IGCSE Biology

Characteristics of Living Organisms

• Biology: Study of living things (organisms)
• Seven Characteristics (Mnemonic: MRS GREN):
  • Movement: Action causing change in position/place
  • Respiration: Cellular chemical reactions breaking down nutrient molecules, releasing energy for metabolism
  • Sensitivity: Responding to changes in internal/external environment
  • Growth: Permanent increase in size and dry mass
  • Reproduction: Processes making more of the same kind
  • Excretion: Removal of metabolic waste products and excess substances
  • Nutrition: Intake of materials for energy, growth, and development

Classification Systems

• Species: Group of organisms that reproduce to produce fertile offspring
• Classification: Grouping species by shared features

Binomial System

• Binomial System: International two-part naming system showing genus and species
  • Genus: Group of related species
  • Species: Specific organism within the genus
  • Format: Italicized, genus capitalized, species lowercase (e.g., Homo sapiens)

Dichotomous Keys

• Dichotomous Keys: Series of questions to identify organisms, each providing two choices

Importance of Classification

• Purpose: Simplifies the study of living things, reflects evolutionary relationships
  • Traditional: Based on shared physical features
  • Modern: Uses DNA sequences to determine relatedness

Five Kingdoms of Living Organisms

1. Animals:
   • Multicellular, nucleus, no cell walls/chloroplasts, nutrition from eating
   • Cell Features: Nucleus, cell membrane, mitochondria, ribosomes, cytoplasm
2. Plants:
   • Multicellular, nucleus, chloroplasts, cell walls from cellulose, photosynthesis
   • Cell Features: Nucleus, cell wall, chloroplasts, similar to animal cells
3. Fungi:
   • Multicellular, nuclei, non-cellulose cell walls, saprophytic/parasitic nutrition
   • Cell Features: Nucleus, cell wall (non-cellulose)
4. Protists:
   • Mostly unicellular, some multicellular, nucleus, some with cell walls/chloroplasts
   • Nutrition: Photosynthesis or eating other organisms
   • Features: Vary in presence of cell walls and chloroplasts
5. Prokaryotes (e.g., bacteria):
   • Unicellular, non-cellulose cell walls, cytoplasm, no nucleus/mitochondria
   • Cell Features: DNA strands, plasmids

Animal Kingdom Subclassification

• Vertebrates and Invertebrates
  • Vertebrates: Backbone present
    • Classes: Mammals, Birds, Reptiles, Amphibians, Fish
  • Invertebrates: No backbone
    • Groups: Myriapods, Insects, Arachnids, Crustaceans

Vertebrates

1. Mammals: Fur/hair, milk from mammary glands, four-chambered heart, different types of teeth (e.g. cats, elephants)
2. Birds: Feathers, hard-shelled eggs, beak, wings (e.g. toucan, parrot)
3. Reptiles: Scaly skin, rubbery eggs (e.g. snakes, turtles)
4. Amphibians: Moist skin, water-laid eggs, larval gills, adult lungs (e.g. frogs)
5. Fish: Scales, gills, fins (e.g. all species except a few)

Invertebrates

• Arthropods: Jointed legs
  1. Myriapods: Many body segments, each with legs (e.g. centipedes)
  2. Insects: Three-part body, three leg pairs, two wing pairs (e.g. butterflies)
  3. Arachnids: Four leg pairs, book lungs (e.g. spiders)
  4. Crustaceans: More than four leg pairs, gills (e.g. crabs)

Plant Kingdom Subclassification

• Ferns: Fronds, spores for reproduction
• Flowering Plants: Flowers and seeds
  • Types: Monocotyledons (monocots) and Dicotyledons (dicots)
    • Monocots: Branching roots, parallel leaf veins, petals in multiples of three
    • Dicots: Taproot system, branching leaf veins, petals in multiples of four or five

Viruses

• Viruses: Not classified as living, cannot perform life processes independently
  • Structure: Genetic material, protein coat

Conclusion

• Main Points: Characteristics and classification of living organisms, importance of grouping organisms scientifically}