Classifying Organisms | Cambridge (CIE) O Level Biology Revision Notes 2021

How Organisms are Classified

• Species: Group of organisms that can reproduce to produce fertile offspring
• Classification based on shared features:
  • Example: Mammals have hair, feed young from mammary glands, have external ears

The Binomial System

• Developed by Linnaeus
• Subdivides organisms into smaller groups with more shared features:
  • Hierarchy: Kingdom, Phylum, Class, Order, Family, Genus, Species
• Binomial Names:
  • Latin, two parts: Genus (capitalized) and species (lowercase)
  • Example: Homo sapiens
  • Always in italics when typed

Classification System Diagram

• Visual representation showing the hierarchy from Kingdom to Species

Dichotomous Keys

• Used to identify organisms based on features
• Dichotomous: Branching into two, guiding user to organism name
• Steps:
  1. Start with one organism
  2. Follow statements to identify
  3. Repeat for next organism

Dichotomous Key Example

• Includes visual diagram showing branching decisions

Tips

• Exams often require using keys, not constructing them
• Focus on understanding how to navigate them

Additional Notes

• Mnemonic for Classification Order: KING PHILIP CAME OVER FOR GRANS SPAGHETTI
• Encouragement to join the Save My Exams community for more resources and support

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