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Unit 4: Living organisms and classification

Constructing keys — HIA International - Grade 6 Revision Notes & Topical Questions

5 min read 6 parts Lesson 7 of 8 3 quizzes

📚 HIA International - Grade 6 Hub / Topical Revision
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Lesson summary

4.5 Constructing keys — HIA INTERNATIONAL notes: Construct a dichotomous key to identify organisms and improve it using feedback.Good questions — use features that can be seen clearly and answered with yes or no, such as ‘Is the learner female?’Poor questions — avoid questions wi…

  • Identifying the dragonfly
  • A good key
  • Pair of statements
  • Think of a way to split the organisms into two groups, for example by sex or hair colour
  • Look at one group and think of a way to split it into two
  • Repeat until you have a way to identify each organism in turn

Part 1 of 4Features and questions to use

Features and questions to use
Good questions
  • Good questions use features that can be seen clearly and answered with yes or no, such as ‘Is the learner female?’
Poor questions
  • Poor questions avoid questions with unclear answers,
    • such as ‘Is the plant tall?’ or ‘Does the plant have dark green leaves?’ because different people will answer differently

Part 2 of 4Constructing a key

1
Think of a way to split the organisms into two groups, for example by sex or hair colour.
2
Look at one group and think of a way to split it into two.
3
Repeat until you have a way to identify each organism in turn.
4
Write the key as questions or as pairs of statements.

Part 3 of 4Key in pairs-of-statements style

Key in pairs-of-statements style
Style
  • Style the key starts with a pair of statements to choose from, and a number tells you which pair to go to next
Same key
  • 1a It has legs, go to 2; 1b It does not have legs, go to 3
  • 2a It has exactly six legs, go to 4; 2b It has more than six legs: crab.
  • 3a Its body is made up of rings: earthworm; 3b Its body is not made up of rings: slug.
  • 4a It has four wings: dragonfly; 4b It has two wings: housefly.
Identifying the dragonfly
  • Identifying the dragonfly work through steps 1a, 2a, 4a

Part 4 of 4Improving a key

Test
  • Test another person uses the key to identify the organisms
Feedback
  • Feedback use their suggestions to change the key so that it works better
A good key
  • A good key is made of pairs of statements that are easy to choose between, and works so that someone can identify every organism

Key terms

TermMeaning
KeyA set of questions used to identify an organism.
DichotomousBranching into two.
IdentifyTo find the name of an organism.
ClassifyTo put an organism into a group.
Pair of statementsTwo choices, a and b, at each numbered step of a key.

Avoid these mistakes

1
Using unclear features such as ‘tall’ or ‘dark green’ — use features everyone will answer in the same way
2
Using more than two choices in a step — each step splits the group in two
3
Stopping before each organism has its own name — keep splitting until every organism is identified
4
Not testing the key — ask someone else to use it and improve it

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