Year 6 Science · Classifying living things · Lesson 2.5

Year 6 Science: Using a classification key

Part of the Year 6 Science classifying living things chapter. Chapter overview · whole chapter on one page

2.5

Using a classification key

Year 6
LH2: give reasons for classifying plants and animals based on specific characteristics; use classification keys to identify living things

Story. A class has a bag of mystery creatures from the school field. Mr Patel gives them a key: a list of yes or no questions. “Answer each question, and follow the step,” he says. “The key will tell you the group.”

A classification key is a list of questions with only yes or no answers. Each answer sends you to the next step, until you reach the name of the group.

A key is useful because the questions are based on specific characteristics. Each question splits the living things into two smaller groups.

The key below starts with the backbone. Work down it, one step at a time.

Step	Question	If yes	If no
A	Does it have a backbone?	Go to step B.	Go to step I.
B	Does it have feathers?	It is a bird.	Go to step C.
C	Does it have fur or hair?	It is a mammal.	Go to step D.
D	Does it have fins and live in water?	It is a fish.	Go to step E.
E	Does it have dry, scaly skin?	It is a reptile.	It is an amphibian.
I	Does it have six legs?	It is an insect.	Go to step J.
J	Does it have eight legs?	It is a spider.	It is a worm.

Bar chart of 20 creatures sorted by a class: fish 3, amphibians 2, reptiles 2, birds 4, mammals 3, insects 3, spiders 2, worms 1.

The table below gives the characteristics of some organisms. Use it with the key.

Organism	backbone	feathers	fur or hair	scales	fins	legs
Salmon	yes	no	no	yes	yes	no
Frog	yes	no	no	no	no	yes
Lizard	yes	no	no	yes	no	yes
Robin	yes	yes	no	no	no	yes
Dog	yes	no	yes	no	no	yes
Earthworm	no	no	no	no	no	no
Ant	no	no	no	no	no	yes

Key ideas

A key is a list of yes or no questions that leads to a group.
Start with the first question, and follow the step that matches your answer.
Each question uses a specific characteristic, such as feathers or legs.
A new key question must split the group into two parts.

Worked example 2.5.1

Use the key in section 2.5. An animal has feathers. Which group is it in? Write the group.

Method. Start at step A, then go to step B.

Step A. The animal has a backbone, so go to step B.
backbone: yes
Step B. The animal has feathers, so it is a bird.
feathers: yes
Write the answer.
bird

Check. Feathers are a characteristic of birds only. ✓

Worked example 2.5.2

Use the key in section 2.5. An animal has a backbone, fur and no feathers. Which group is it in? Write the group.

Method. Work down the key.

Step A. It has a backbone, so go to step B.
backbone: yes
Step B. It has no feathers, so go to step C.
feathers: no
Step C. It has fur, so it is a mammal.
fur: yes
Write the answer.
mammal

Check. A dog follows the same path. ✓

Worked example 2.5.3

Use the key in section 2.5. An animal has six legs and no backbone. Which group is it in? Write the group.

Method. Start at the backbone question.

Step A. It has no backbone, so go to step I.
backbone: no
Step I. It has six legs, so it is an insect.
six legs: yes
Write the answer.
insect

Check. An ant has six legs and no backbone. ✓

Watch out. Check the first question carefully: a no answer to the backbone question takes you to a different part of the key.

Watch out

Watch out: a key only works if you answer every question honestly, and follow the step that matches your answer.

Exam tip

Exam tip. When you use a key, write down each question and your answer, so that you can check the route.

Try it (with your teacher, or a grown-up at home). Make a key with three yes or no questions to separate three objects in the classroom: for example, a pencil, a book and a cup. Give the key to a partner, and see whether they can name the objects. Keep the questions simple and about one characteristic at a time.