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You are building a dichotomous key for six leaf specimens. How many choices should each step offer?
AExactly three branching choices
BExactly two contrasting choices
COne choice for each specimen
DAs many choices as features seen
Answer & Solution
Correct answer: B. Exactly two contrasting choices
1. The word dichotomous means divided into two.
2. So each step of the key offers exactly two contrasting statements about a feature.
3. Choosing the true one halves the remaining possibilities and leads to the next numbered step.
4. Repeating that halving narrows six specimens down quickly and unambiguously.
5. Offering three or more choices at a step makes it a branched key rather than a dichotomous one, which the marking treats as incorrect.
_Source: NECTA ACSEE 2022 Biology 133/1, Question 2: Principles of Classification_