# Explain how morphological and molecular evidence are each used to classify organisms into taxa, and outline one limitation of using morphological evidence alone.

> IB DP Biology Standard Level (2023 syllabus) — A3.1 Diversity of organisms · Explain · 4 marks

## Mark scheme (4 marks)

1. Morphological evidence involves comparing observable physical features (such as body structures, anatomy, or form) to group organisms that share similar characteristics into the same taxon.
2. Molecular evidence involves comparing DNA sequences (or amino acid/protein sequences) to determine evolutionary relationships; organisms with more similar sequences are considered more closely related and are placed in the same or closer taxa.
3. One limitation of morphological evidence alone: organisms can share similar structures due to convergent evolution rather than common ancestry, leading to incorrect classification.
4. A further limitation: morphological features can vary within a species (due to age, sex, or environment / phenotypic plasticity), making it difficult to consistently assign organisms to the correct taxon using appearance alone.

## Key terms

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

## 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)
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Source: [GradeNine](https://www.gradenine.co.uk/q/explain-how-morphological-and-molecular-evidence-e305bfc7) · Published by Druglandscape Ltd.