Using a Key

 

KEYS

  • A key is used to identify an organism.
  • A key consists of pairs (or small groups) of statements
  • In each pair or group of statements only one of those statements will be true

Think of each group of statements as a clue

When using a key follow these rules:

  1. Always start at clue number 1. This will have 2 or more statements in it.
  2. Look for the correct statement . This may give you the name of the organism.
    If it doesn’t you must go to the clue it directs you to.
  3. Repeat rule 2 until you have the name of the organism you are trying to identify.

 

Example 1

snailUse the key below to find the group that the animal above belongs to

1. Has an internal skeleton (vertebrate)) ………………………………. Goto 5
   Has no internal skeleton (invertebrate) ……………………………… Goto 2    

2. Has an exoskeleton (a hard outside skin) ……………………………… Goto 3
Has no exoskeleton (a soft skin)…………………………………….. Goto 4

3.   six legs ………………………………………………………Goto 8
eight legs……………………………………………………..Arachnid
more than eight, less than twenty legs ……………………………Crustacean
more than twenty………………………………………………..Goto 6

4. Body divided into segments…………………………………………Goto 7
No segments. Smooth skin………….. …………………………….Mollusc

5. Has fur or hair. Is warm blooded……………………………………Mammal
Has a dry, scaly skin. Breaths using lungs ………………………….Reptile
Has moist, smooth skin. Often lives near water ………………………Amphibian
Has a wet, scaly skin. lives in water. Breaths using gills ……………Fish
Has feathers and two legs. Is warm blooded…………………………..Bird

6. Has one pair of legs on each segment………………………………..Centipede
Has two pairs of legs on each segment ……………………………..Millipede

7. Pinkish brown. Slender body. Body has small bristles on each segment……Earthworm
Small squat body, (1 to 3 cm), pale yellow in colour. No proper legs…..Insect larva

8. Body divided into 3 parts, often has 2 pairs of wings…………………Insect
1 to 3 cm long, soft, cylindrical body …………………………….Insect larva

How to answer the question:
We can tell by looking at it that this is a snail and hence a mollusc, but how do  we use the key?

Start at rule 1.
This animal has no internal skeleton so we go to clue 2

It has a soft skin so we go to clue 4

It has no segments which tells us that it is a mollusc

Example 2
The key shown below shows three woodlice.
The key is used to identify them.
(Woodlouse 3 has already been done for you)

Pick one of the three woodlice and use the key to find out its name
Remember.. start at clue 1

Woodlouse 1
Woodlouse 1
Description
When threatened this woodlouse rolls up into a tight ball (with no gap).
It has a dull in appearance.
It can be up to 1.5cm (15mm) long.

Woodlouse 2
Woodlouse

This woodlouse cannot roll into a ball and is shiny.
It is around 1cm (10mm) long but can be slightly bigger

Woodlouse 3
Common striped Woodlouse
Woodlouse 3
Clue 1
Can roll into a ball ……………. Go to 2
Cannot roll into a ball  ……….. Go to 3

Clue 2.
Rolls up completely leaving no gap….. Common Pill Woodlouse
When it rolls up there is a gap ……… Armadillium Nasatum

Clue 3
.Does it have a clear dark stripe down its back?
Yes …………………. Common Striped Woodlouse
No …………………. Go to 4

4. Is it shiny?
Yes ……………… go to 5
No Common Rough woodlouse

5. Is it longer than 5mm?
Yes …………… Common Shiny Woodlouse
No …………… Common Pygmy Woodlouse

 

Woodlouse 1 = Answer shown here

Woodlouse 2 = Answer shown here