Keys…

Keys are a means of identifying objects by answering a series of yes/no questions. They are sometimes known as dichotomous keys because each question divides the possible answers into two groups. In biology, they are especially useful for identifying an unknown type of organism.

Some keys will come with pictures to help with the identification process – here are two examples.

A fungus key

A pond-life key

Keys can just be text based. I have designed one here to help identify six members of an alien race.

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Choose one of the aliens above and then answer the following questions to identify him.

Q1. Does your alien have spiral antennae? If YES go to Q2. If NO go to Q3.

Q2. Does your alien have brown hair? If YES he is Abe. If NO go to Q4.

Q3. Does your alien have grey hair? If YES he is Bob. If NO go to Q5.

Q4. Does you alien have blue eyes? If YES he is Caleb. If NO he is Dan.

Q5. Does your alien have brown eyes? If YES he is Eddy. If NO he is Prinz Friedrich, Lord High Inquisitor, Grand Mage of Darkness, Destroyer of Worlds and Master of Chaos. (Bad luck if you chose him – he is a bit of a trouble maker.)

Keys are very simple devices. When you make them yourself you must avoid questions that are impossible to answer such as “Is it quite big?” or “Can it see in the dark?” – in the first case you have no frame of reference and in the second case you would need to know what it was in order to answer the question. This is the only serious pitfall to avoid. The “if” then “go to” structure also lends itself really well to simple computer programs.

Design a key to distinguish between the following six pieces of laboratory equipment.

Just in case you aren’t sure, they are a test-tube, a beaker, a round-bottomed flask, a conical flask, a funnel and a flat-bottomed flask. You need to begin with a question that splits them into two roughly equally sized groups. You can use the comments below to leave your suggestions (you might want to work it out in a text editor beforehand then paste it into the comments box). You could email me a version and I will post it as a .pdf link. Or you might write a simple computer program to do the same thing. I have done that using Construct2 – try it here but only once you have thought about it a little for yourself.