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15.9 Classification

GCSE Biology · AQA · Chapter 15: Genetics and Evolution

A free GCSE Biology lesson for AQA (8461) from OBA School: the Linnaean system of groups and the binomial system for naming living things. Watch the video, read the explanation and worked examples, then try the revision questions. You can work through the full lesson, with every video, practice quizzes and printable worksheets with mark schemes, in our free online course.

What you will learn

  • List the groups of the Linnaean system in order, from kingdom to species
  • Explain the basis on which Linnaeus classified organisms
  • Write and interpret binomial (two-part) scientific names
  • Use classification to judge how closely organisms are related
  • Explain why scientific names are more useful than common names

Key words

  • Classification: Sorting living things into groups based on their shared features.
  • Kingdom: The largest group in the Linnaean system, e.g. the animal kingdom or the plant kingdom.
  • Genus: A group of closely related species. It is the first part of a scientific name.
  • Species: The smallest group: organisms that can interbreed to produce fertile offspring.
  • Binomial system: Naming each species with two words: its genus and its species, e.g. Homo sapiens.

The Linnaean system

Carl Linnaeus, a Swedish scientist working in the 1700s, classified living things according to their structure and characteristics – what they looked like and how their bodies were built. He sorted organisms into a series of groups, each one inside the next:

Memory aid: Order of groups: Kingdom, Phylum, Class, Order, Family, Genus, Species. Try: “Keep Ponds Clean Or Frogs Get Sick”.

As you go down from kingdom to species, each group contains fewer organisms that are more similar to each other.

Naming living things: the binomial system

Linnaeus gave every species a two-part Latin name:

  • The first word is the genus. It starts with a capital letter.
  • The second word is the species. It starts with a small letter.
  • The name is written in italics when typed, or underlined when handwritten.
  • Lion; Scientific name Panthera leo; Genus Panthera; Species leo
  • Tiger; Scientific name Panthera tigris; Genus Panthera; Species tigris
  • Domestic cat; Scientific name Felis catus; Genus Felis; Species catus
  • Human; Scientific name Homo sapiens; Genus Homo; Species sapiens

Worked example: who is most closely related?

Lions and tigers share the genus Panthera. The domestic cat is in a different genus, Felis, but the same family (Felidae).
Organisms that share more groups – especially a genus – are more closely related.

Answer: the lion and tiger are more closely related to each other than either is to the cat

Why scientific names matter

  • The same organism can have many common names in different places and languages. A scientific name is the same worldwide.
  • One common name can refer to different species (a “robin” in Britain and in North America are different birds).
  • The name shows the genus, so it tells scientists something about relationships.

Linnaeus’ system was a huge step forward, but it was based only on what could be seen. In the next section you will see how new evidence has changed it.

Common mistakes

  • Writing the species name with a capital letter (Homo Sapiens) – only the genus has a capital.
  • Getting the order of the groups mixed up, especially order and family. Use a memory aid.
  • Thinking organisms in the same order are more closely related than organisms in the same genus. Lower groups mean closer relationships.
  • Giving only the genus as the scientific name. A species name needs both words.

Revision questions

Try these, then check your answers below each one.

Question 1. Which list shows the Linnaean groups in the correct order, from largest to smallest? (Choose from: Kingdom, phylum, class, order, family, genus, species, Kingdom, class, phylum, order, family, genus, species, Kingdom, phylum, class, family, order, genus, species, Species, genus, family, order, class, phylum, kingdom.)

Answer: Kingdom, phylum, class, order, family, genus, species

Working: Kingdom, phylum, class, order, family, genus, species.

Question 2. Which is the correct way to write the scientific name of humans? (Choose from: Homo sapiens, homo sapiens, Homo Sapiens, Sapiens homo.)

Answer: Homo sapiens

Working: Homo sapiens: genus capitalised, species lower case, written in italics.

Question 3. True or false? Linnaeus classified living things according to their structure and characteristics.

Answer: True

Working: True. He used observable features.

Related lessons

Continue in the full course

This lesson is section 15.9 (AGCBH1509) of our free GCSE Biology course for AQA. In the full course you get every video for this section, a self-marking practice quiz, a printable worksheet with a mark scheme, chapter tests, and your progress saved. Go to the full GCSE Biology course.

 

 

 

 

 

 

 

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