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 and produce viable, fertile offspring.
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 and produce viable, fertile offspring.
What the Cambridge 9700 syllabus says
Official 2025-2027 spec · A2 LevelThese are the exact learning outcomes Cambridge sets for this topic. The candidate is expected to be able to do each of these on the relevant paper.
- discuss the meaning of the term species, limited to the biological species concept, morphological species concept and ecological species concept
- describe the classification of organisms into three domains: Archaea, Bacteria and Eukarya
- state that Archaea and Bacteria are prokaryotes and that there are differences between them, limited to differences in membrane lipids, ribosomal RNA and composition of cell walls
- describe the classification of organisms in the Eukarya domain into the taxonomic hierarchy of kingdom, phylum, class, order, family, genus and species
- outline the characteristic features of the kingdoms Protoctista, Fungi, Plantae and Animalia
- outline how viruses are classified, limited to the type of nucleic acid (RNA or DNA) and whether this is single stranded or double 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
- › Memorize the three Domains: Bacteria, Archaea, and Eukarya. All other groupings like 'Fungi' or 'Plantae' are Kingdoms.
- › Keep all decimal places in your calculator for intermediate steps and only round the final answer to three significant figures.
- › The 'IUCN' assesses and categorises species on the 'Red List of Threatened Species'; 'CITES' is the body that regulates international trade.
What is the biological species concept?
The biological species concept defines a species as a group of organisms that can interbreed in nature and produce viable, fertile offspring.
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.
More 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
Start in Study Mode, attempt each card before flipping, then rate Hard, Okay or Easy. Cards you rate Hard come back within a day; cards you rate Easy push out to weeks. Your progress is saved in your browser, so come back daily for 5–10 minute reviews until every card reads Mastered.
Study Mode
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