# Explain how the classification of species can change over time as new evidence becomes available, using the relationship between morphological and molecular data as examples.

> IB DP Biology Standard Level (2023 syllabus) — A3.2 Classification and cladistics · Explain · 4 marks

## Mark scheme (4 marks)

1. Traditional classification was based on morphological (physical/structural) similarities between organisms
2. Molecular data (DNA/RNA sequences or amino acid sequences) can reveal evolutionary relationships not apparent from morphology alone
3. Convergent evolution can cause unrelated organisms to appear morphologically similar, leading to incorrect classification
4. When molecular evidence contradicts morphological groupings, taxa may be reclassified / classification is revised to reflect true evolutionary (phylogenetic) relationships

## Key terms

- [molecular data](https://www.gradenine.co.uk/glossary/molecular-data)

## Related

- [Revision notes for IB DP Biology Standard Level (2023 syllabus)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
- [Practice this with AI marking (free)](https://www.gradenine.co.uk/start)

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Source: [GradeNine](https://www.gradenine.co.uk/q/explain-how-the-classification-of-species-c382baff) · Published by Druglandscape Ltd.