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Unit 4: Living organisms and classification

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

5 min read 6 parts Lesson 6 of 8 3 quizzes

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

4.4 Using keys — HIA INTERNATIONAL notes: Use a dichotomous key to identify an organism, in question style and in pairs-of-statements style.Identifying organisms — biologists can look at pictures in a reference book or on the internet, but this does not always workKey — a set of …

  • Identifying the dragonfly
  • Pair of statements
  • Dichotomous key — a key that branches into two at each step, because dichotomous means ‘branching into two’
  • Choose the organism you want to identify
  • Starting at the top of the key, answer the first question: yes or no
  • Follow the line to the next question

Part 1 of 4What 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’

Part 2 of 4Using a key

1
Choose the organism you want to identify.
2
Starting at the top of the key, answer the first question: yes or no.
3
Follow the line to the next question.
4
Keep going until you arrive at the name of the organism.

Part 3 of 4Key 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

Part 4 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

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
Saying a dichotomous key has three choices at each step — it always has two
2
Starting in the middle of the key — always start at the top with the first question
3
Choosing the answer by guessing — look at the actual feature of the organism
4
Skipping questions — follow each line to the next question until the name is reached

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