Dichotomous Key Explanation For Kids

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The phrase dichotomous key might not be instantly familiar, but we're betting as a parent, you've seen them before.

A dichotomous key is an important tool used by biologists to identify a given species or organism, and crop up in the GCSE biology syllabus. Dichotomous keys look like flow charts, and feature a series of images and text with two choices branching off at each step: you choose the one that fits the organism you want to identify.

At each stage, you're presented with a choice of characteristics, and answer 'yes' or 'no', until you make an identification of an organism, or species.

The word 'dichotomous' means two; they're sometimes also called a 'branching tree'. A dichotomous key is used to order information, and as a classification key, plus they're a tool for teaching younger nature-lovers about similar species.

When out exploring nature in a field, take a dichotomous key, to identify and learn characteristics of any organisms you discover.

What Is An Example of A Dichotomous Key?

Dichotomous keys help you identify characteristics and features, and order information. As you can see below, you ask specific questions where the answer is 'yes' or 'no'.

Example of a dichotomous key.
Image © Wikihow under a creative commons licence.

Vertebrates Dichotomous Key

Rabbit sitting on the grass.

Below are the classifications of vertebrates you can use your dichotomous key to discover.

Mammals: You might ask 'Does it have fur?'. If the answer is 'yes', it leads to 'mammal'.

Birds: If you said 'no', next maybe 'Does it have feathers'? If you say 'yes,' you've identified a bird.

Reptiles: If you choose 'no', you may ask if your organism has dry or moist skin. If you say 'dry', you've identified a reptile.

Fish: If you say 'moist', you might ask if your organism has scales or smooth skin. If 'scales', you've identified a fish.

Amphibians: If your organism has smooth, moist skin, it's an amphibian, like a frog.

Invertebrates

A pretty patterned butterfly on a leaf.

A similar biological key can be used to help you identify invertebrates (animals without backbones), which divide into one of various examples.

Worms: If your organism has no legs, or shell, but is segmented, it may be a worm.

Molluscs: If it has no legs, but a shell, it might be a mollusc.

Arachnids: If your specimen has eight legs, it's probably a spider (but could be a tick or mite).

If if it has six legs, you might ask, 'does it have wings'?

Lepidoptera: If the species has wings, it could be a moth or butterfly.

Insects: If it has no wings, it could be an insect or crustacean. If the body has three sections, it might be an insect-like an ant.  

Crustacean: If two sections, it might be a crustacean, like a crayfish.

There's a vast number of invertebrates, but based on the set of examples and features you've seen, a dichotomous key can help you make choices to simplify and discover which species it might be, and help you name it.

Plants

Little girl playing in a sunflower field, holding a sunflower and smiling.

Dichotomous keys are an important tool for budding botanists. A dichotomous key can be useful in helping you name species, and recognise organisms' characteristics. You can use a dichotomous key during any field trip.

Typical Dichotomous Keys Ask:

Does your plant grow seeds? If 'yes', you might ask if it has flowers.

Dicot: If 'yes', (it grows seeds and flowers) and it has leaves with net-like veins, it's a dicot, like a sunflower.

Monocot: If 'yes', (it has seeds and flowers) and it has leaves with long veins, it's a monocot, like a grass.

Conifer: If it has seeds, but no flowers, does it have needle-like leaves? If 'yes', it's a conifer.

Fern: If your plant has no seeds, but 'does have stems and leaves, it's a fern.

Moss: If it has no seeds, stems or leaves, it's moss or algae.

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