# Explain how the five-kingdom classification system groups living organisms, and state one limitation of using only observable physical features to classify organisms.

> Pearson Edexcel A-Level Biology A (9BI0) — Topic 3 Classification and Biodiversity · Explain · 5 marks

> Scientists have used different classification systems over time. The five-kingdom system groups all known living organisms into five kingdoms: Prokaryotae, Protoctista, Fungi, Plantae, and Animalia.

## Mark scheme (5 marks)

1. The five kingdoms are distinguished by fundamental differences in cell structure and/or organisation (e.g. presence/absence of a nucleus)
2. Organisms are placed into smaller and smaller groups (e.g. kingdom → phylum → class → order → family → genus → species) based on shared characteristics
3. Correct identification of at least two kingdoms with a distinguishing feature for each (e.g. Plantae — multicellular, photosynthetic; Fungi — multicellular, saprophytic / cell walls made of chitin; Animalia — multicellular, no cell wall; Protoctista — mostly unicellular eukaryotes)
4. Using observable physical features alone can be misleading because organisms that look similar may not be closely related (convergent evolution / analogous structures)
5. Additional evidence such as DNA / genetic sequencing or biochemical analysis provides more accurate classification

## Key terms

- [five-kingdom classification system](https://www.gradenine.co.uk/glossary/five-kingdom-classification-system)
- [observable physical features](https://www.gradenine.co.uk/glossary/observable-physical-features)

## Related

- [Revision notes for Pearson Edexcel A-Level Biology A (9BI0)](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-five-kingdom-classification-system-108e43c3) · Published by Druglandscape Ltd.