Page 45 - Science Coursebook

3.1 Keys

Some keys are arranged differently. The idea is the same, but in this kind of key

you are given two statements, a and b. You choose which statement describes the
organism. Once you have made the choice, this leads you to another pair of choices.

1 a has legs ...................................... go to 2
b does not have legs ..................... go to 3
2 a has six legs ................................ go to 4
b has more than six legs ............... crab
3 a body is made up of rings .......... earthworm
b body is not made up of rings .... slug
4 a has four wings ........................... dragonfl y
b has two wings ............................ housefl y

For example, to identify the dragonfly, you would
work through these statements: 1a, 2a, 4a.
Constructing keys

Imagine you are going to write a key to identify these
four students.

Step 1: Think of a way that you can split the Deidre Ben
students into two groups. For example, you
could split them into male and female students.

So your first question could be:
Is the student male?

Step 2: Now take just one of these groups – say
both of the female students. Think of another
way to split them into two. For example, you
could use the colour of their hair. Anna Ari

Questions
A+I 1 Copy and complete this key. Your key should enable
(permit) someone else to identify the four students. Is the student male?
A+I 2 Write another key to identify the four students, but
this time use the style of key that has two statements,
a and b, to choose from. Yes No
You could use the same features as in the key you
wrote for Question 1, or you could set yourself a

challenge and use different pairs of features.

Summary
• A key is a method of identifying an unknown organism.
• A key has a series of questions or statements, which you work through
in sequence to find the name of the organism.

3 Variation and inheritance 43