Classification
Cambridge A-Level Biology (9700) · Unit 18: Classification, biodiversity and conservation · 8 flashcards
Classification is topic 18.1 in the Cambridge A-Level Biology (9700) syllabus , positioned in Unit 18 — Classification, biodiversity and conservation , alongside Biodiversity and Conservation. In one line: The biological species concept defines a species as a group of organisms that can interbreed in nature to produce fertile offspring, and are reproductively isolated from other species.
Marked as A2 Level: examined at A Level in Paper 4 (A Level Structured Questions) and Paper 5 (Planning, Analysis and Evaluation). It is not tested on the AS-only papers (Papers 1, 2 and 3).
The deck below contains 8 flashcards — 2 definitions and 6 key concepts — covering the precise wording mark schemes reward. Use the 2 definition cards to lock down command-word answers (define, state), then move on to the concept and calculation cards to handle explain, describe, calculate and compare questions.
The biological species concept
The biological species concept defines a species as a group of organisms that can interbreed in nature to produce fertile offspring, and are reproductively isolated from other species.
What the Cambridge 9700 syllabus says
2025-2027 syllabus, in our words · A2 LevelWhat the syllabus expects you to be able to do in this topic, in plain English. For the exact wording, see the official syllabus (PDF).
- Discuss what the term species means, limited to three concepts: the biological, morphological and ecological species concepts.
- Describe how organisms are classified into the three domains Eukarya, Bacteria and Archaea.
- State that both Archaea and Bacteria are prokaryotes but that they differ, limited to differences in ribosomal RNA, membrane lipids and cell wall composition.
- Describe how organisms in the domain Eukarya are classified into a taxonomic hierarchy, running from species up through genus, family, order, class and phylum to kingdom.
- Outline the features characteristic of the kingdoms Animalia, Plantae, Fungi and Protoctista.
- Outline the classification of viruses, limited to whether their nucleic acid is DNA or RNA and whether it is double or single stranded.
Cambridge syllabus keywords to use in your answers
These are the official Cambridge 9700 terms tagged to this section. Mark schemes credit responses that use the exact term — weave them into your answers verbatim rather than paraphrasing.
Tips to avoid common mistakes in Classification
- › Fungi, Plantae, Animalia and Protoctista are kingdoms within the domain Eukarya, not domains.
What is the biological species concept?
The biological species concept defines a species as a group of organisms that can interbreed in nature to produce fertile offspring, and are reproductively isolated from other species.
What are the key differences between Archaea and Bacteria?
Archaea and Bacteria differ in membrane lipids (Archaea have branched isoprene chains, Bacteria have fatty acids), ribosomal RNA (different sequences), and cell wall composition (Archaea lack peptidoglycan, Bacteria have peptidoglycan). Both are prokaryotes.
List the taxonomic hierarchy from kingdom to species.
The taxonomic hierarchy is: Kingdom, Phylum, Class, Order, Family, Genus, and Species. This system organizes organisms into increasingly specific groups based on evolutionary relationships.
Outline two characteristic features of the Kingdom Protoctista.
Protoctista are eukaryotic, mostly unicellular organisms. They exhibit a wide range of nutritional modes, including autotrophic (photosynthetic) and heterotrophic.
Describe the classification of viruses based on nucleic acid.
Viruses are classified based on their nucleic acid type: either DNA or RNA, and whether this nucleic acid is single-stranded (ss) or double-stranded (ds). Examples include ssRNA (
Outline two characteristic features of the Kingdom Fungi.
Fungi are eukaryotic, heterotrophic organisms with cell walls made of chitin. They obtain nutrients through absorption, often acting as decomposers or parasites.
Outline two characteristic features of the Kingdom Plantae.
Plantae are eukaryotic, multicellular organisms that are autotrophic (photosynthetic) and possess cell walls made of cellulose. They are primary producers in many ecosystems.
Outline two characteristic features of the Kingdom Animalia.
Animalia are eukaryotic, multicellular, heterotrophic organisms that lack cell walls. They obtain nutrients through ingestion and have complex organ systems.
Review the material
Read full revision notes on Classification — definitions, equations, common mistakes, and exam tips.
Read NotesMore topics in Unit 18 — Classification, biodiversity and conservation
Classification sits alongside these A-Level Biology decks in the same syllabus unit. Each uses the same spaced-repetition system, so progress in one informs the next.
Key terms covered in this Classification deck
Every term below is defined in the flashcards above. Use the list as a quick recall test before your exam — if you can't define one of these in your own words, flip back to that card.
How to study this Classification deck
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