A student finds two beetles in a garden. Beetle A and Beetle B look very similar but a scientist says they belong to different species. Explain what is meant by the term 'species' and describe how scientists use observable features and DNA evidence to decide whether two organisms belong to the same species or different species.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Two beetles are found in the same garden. They look almost identical in colour and size, but genetic analysis reveals significant differences in their DNA sequences.
Model answer (5 marks)
A species is a group of organisms that can interbreed and produce fertile offspring.
Scientists first look at observable features – the morphology of the beetles. If the two beetles share many similar physical traits, they are likely to belong to the same or closely related species.
They then compare DNA sequences. Significant differences in the DNA show that the beetles are genetically distinct. The greater the DNA difference, the less closely related the organisms are, indicating they belong to different species.
Because the beetles have many similar observable features but also show large DNA differences, scientists classify them as separate species.
Scientists first look at observable features – the morphology of the beetles. If the two beetles share many similar physical traits, they are likely to belong to the same or closely related species.
They then compare DNA sequences. Significant differences in the DNA show that the beetles are genetically distinct. The greater the DNA difference, the less closely related the organisms are, indicating they belong to different species.
Because the beetles have many similar observable features but also show large DNA differences, scientists classify them as separate species.
Examiner tips
- Use the definition of species first; link morphology and DNA evidence; explain that DNA differences confirm species separation; keep answer concise and to the point.
Common mistakes
- Confusing ‘similar morphology’ with ‘same species’ without mentioning DNA; not stating that DNA differences indicate different species; using vague terms like ‘different’ instead of ‘different species’.
Mark scheme (5 marks)
- A species is a group of organisms that can interbreed / reproduce sexually to produce fertile offspring
- Scientists observe similarities and differences in the physical / observable features (morphology) of organisms to classify them
- If two organisms share many similar observable features they are likely to be in the same / closely related species or group
- Scientists compare DNA sequences between the two organisms
- Greater differences in DNA sequences indicate the organisms are from different species / less closely related, so the beetles are classified as different species
Key terms in this question
Related
- All Pearson Edexcel A-Level Biology A (9BI0) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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