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Unit 4: Living organisms and classification

Writing Keys — HIA International - Grade 6 Revision Notes & Topical Questions

5 min read 8 parts Lesson 8 of 8 1 quiz

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

4.5 Constructing keys (writing a key) — HIA INTERNATIONAL notes: Write a dichotomous key in both styles and improve it using feedback.Identifying organisms — biologists can look at pictures in a reference book or on the internet, but this does not always workKey — a set of questi…

  • Good questions
  • Poor questions
  • Identifying the dragonfly
  • A good key
  • Pair of statements
  • Dichotomous key — a key that branches into two at each step, because dichotomous means ‘branching into two’

Section 1 of 8What a key is

Identifying organisms
  • Identifying organisms biologists can look at pictures in a reference book or on the internet, but this does not always work
Key
  • Key a set of questions about the organism, where the answer to each question takes you to another question until you reach the name of the organism
Dichotomous key
  • Dichotomous key a key that branches into two at each step, because dichotomous means ‘branching into two’

Section 2 of 8Constructing 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.

Section 3 of 8Features 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

Section 4 of 8Key in question style

QuestionYesNo
Does it have legs?go to: Does it have more than six legs?go to: Is its body made up of rings?
Does it have more than six legs?crabgo to: Does it have four wings?
Does it have four wings?dragonflyhousefly
Is its body made up of rings?earthwormslug

Section 5 of 8Key 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

Section 6 of 8Improving 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

Section 7 of 8Key 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.

Section 8 of 8Exam technique

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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