(7) Using keys to identify organisms

An identification key is based on a series of questions and descriptive statements to enable to identify a type of organism, and if detailed enough, a particular species of plant or animal.

Keys are useful in identifying organisms that you capture in some trapping techniques.

As you work your way down a key you gradually narrow the options as to what the organism may be.

A "Minibeast" is a term for a variety of arthropods and other invertebrates, including spiders, ants, butterflies, bees, wasps, flies, woodlice, and many others.

Part of a more complex key for minibeasts that you find on the ground, or in the air, in a garden or woodland.

Note: Centipedes can have between 15 and 177 pairs of legs depending on the species (average 35 pairs), and millipedes can have up to 200 pairs. The main difference is that centipedes have one pair of legs on each segment of their bodies and millipedes have two - I thought you would really like to know this!

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Key points on using identification keys for plants or animals

Based on the syllabus-specifications for students taking the UK AQA, Edexcel and OCR GCSE level biology examinations (~US grades 9-10 biology).

Revision notes on Using Identification Keys to Identify Organisms - a key practical skill for biology exams.

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What Is an Identification Key?

An identification key is a tool used by biologists to identify unknown organisms - whether they’re plants or animals - based on their observable features.

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Types of Keys

1. Dichotomous Key

• Most common type.

• Series of paired statements or questions that describe two contrasting characteristics.

• You choose the one that matches your organism and follow the instructions to the next step until the species is identified.

Example: 1a. Has feathers → go to 2
1b. Does not have feathers → go to 3
2a. Feathers are black and white → Magpie
2b. Feathers are all brown → Sparrow

2. Numbered or Flowchart Keys

• Can be arranged as a list or a branching diagram.

• Useful for visual learners — each decision point branches out like a family tree.

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How to Use a Key – Step by Step

1. Observe your specimen carefully. Focus on key features:

   • Number of legs

   • Leaf shape or vein pattern

   • Presence of wings, fur, spots, gills, etc.

2. Start at the first question in the key.

3. Choose the option that best matches the organism.

4. Follow the instructions — this might lead you to:

   • The next question

   • The name of the organism

5. Continue until the organism is identified.

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Common Features Used in Keys

Plants

• Leaf shape (rounded, serrated)

• Leaf arrangement (opposite, alternate)

• Type of stem (woody, soft)

• Flower color, number of petals

• Fruit type

Animals

• Number of limbs or legs

• Body symmetry (bilateral, radial)

• Presence of wings, antennae, shell

• External skeleton (e.g. insects vs. mammals)

• Type of covering (fur, feathers, scales)

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Why Are Keys Important in Ecology?

• Help students accurately name species during fieldwork.

• Reduce confusion from regional names (e.g. woodlouse vs. pillbug).

• Allow consistent, systematic identification, especially when sampling biodiversity.

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Exam Tips

• Practise using real dichotomous keys — many exam papers ask you to follow one to identify a specimen.

• Read each statement carefully; a single misread can lead to the wrong organism.

• Pay close attention to observable features, not assumptions (e.g., don’t assume all green plants are the same).

• Try constructing your own simple keys to get the hang of the logic — it’s a fantastic revision technique.

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Keywords, phrases and learning objectives for this part on ecological surveying and biodiversity

Know how to use a key to identify a plant or animal species of keys to identify plant or animal organisms.

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