Concept & Uses of Classification Systems - 1 | Biology for GCSE/IGCSE - Year 11 PDF Download

How Organisms are Classified

• There are millions of species of organisms on Earth
• A species is a group of organisms capable of reproducing to produce fertile offspring
• Organisms can be grouped based on shared characteristics; for instance, all mammals have bodies covered in hair, nourish their young from mammary glands, and possess external ears (pinnas)

The Binomial System

• Organisms were initially grouped by a Swedish scientist named Linnaeus, who devised a method to categorize living beings into smaller, more specialized clusters.
• The species within these clusters share increasingly similar characteristics as they are further subdivided.
• Linnaeus used the binomial system to assign Latin names to organisms. Each scientific name consists of two parts: the genus (always capitalized) and the species (beginning in lowercase).
• When written, binomial names are italicized to indicate their Latin origin, for instance, Homo sapiens.
• The hierarchy of classification follows this sequence: Kingdom, Phylum, Class, Order, Family, Genus, Species.

Dichotomous Keys

Dichotomous keys are tools used to identify organisms based on specific characteristics.

• Keys guide users through a series of questions about an organism's features.
• Each step in a key presents two descriptions, leading to the identification of the organism.
• Users make choices based on the descriptions provided.
• To navigate a key successfully:
  • Begin by selecting a single organism, or use an unfamiliar one provided in an exam question.
  • Follow the statements or questions from the start, using the information or images given in the question.
  • Continue until there are no more statements or questions, and you have identified the organism.
  • Repeat the process with another organism, starting from the beginning of the key each time, until all organisms are identified.