Revision Notes

1.7 Dichotomous Keys

Constructing & Using a Key

  • Keys are used to identify organisms based on a series of questions about their features
  • Dichotomous means ‘branching into two’ and it leads the user through to the name of the organism by giving two descriptions at a time and asking them to choose
  • Each choice leads the user onto another two descriptions
  • In order to successfully navigate a key, you need to pick a single organism to start with and follow the statements from the beginning until you find the name
  • You then pick another organism and start at the beginning of the key again, repeating until all organisms are named


Example of a dichotomous key #1, IGCSE & GCSE Biology revision notes

Example of a dichotomous key #1


Example of Dichotomous Key #2 (Part 1), IGCSE & GCSE Biology revision notesDichotomous Keys table, IGCSE & GCSE Biology revision notes

Example of a dichotomous key #2


Exam Tip

Simple dichotomous keys almost always come up in the multiple choice paper, so make sure you can use one.

Very occasionally they show up in the theory paper, and when they do you almost always have to use one instead of constructing one, so focus on this rather than spending hours learning to construct them yourself!

Author: Jenna

Jenna studied at Cardiff University before training to become a science teacher at the University of Bath specialising in Biology (although she loves teaching all three sciences at GCSE level!). Teaching is her passion, and with 10 years experience teaching across a wide range of specifications – from GCSE and A Level Biology in the UK to IGCSE and IB Biology internationally – she knows what is required to pass those Biology exams.

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