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Biology for Advanced Level Secondary Schools

Example 2: Bracketed dichotomous keys for seven animal species (Figure 2.2)
1a. Organism has a backbone……………………….2

1b. Organism does not have a backbone……………3

2a. Organism has wings…………………………….4
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2b. Organism does not have wings………………….5

3a. Organism has antennae ……………………….. Grasshopper
3b. Organism does not have antennae………………Spider

4a. Organism has feathers…………………………..Bird
4b. Organism has hair……………………………….Bat

5a. Organism has legs………………………………6

5b. Organism does not have legs……………………Snake
6a. Organism has a tail…………………………….Lizard

6b. Organism does not have a tail………………….Frog

(a) (b) (c)

(d) (e) (f) (g)

Figure 2.2: Animals (a) grasshopper, b) frog (c) turtle (d) spider (e) bird (f) bat, and (g) snake

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