Biology editorial review is supported by the
named review panel.
Reviewer participation may vary by guide. Checked against Cambridge IGCSE Biology 0610 (2026–2028); last reviewed August 2026.
Key concept
Living organisms are classified into five kingdoms: Animals, Plants, Fungi, Protoctists (Protists) and Prokaryotes, based on cell structure, nutrition method and body organisation.
Classification organises the diversity of life into manageable groups. The five-kingdom system is the classification model required by the Cambridge 0610 syllabus. Each kingdom is defined by shared features such as cell type, cell wall composition, and nutrition method. This guide covers the defining characteristics, key examples, and the exam questions you will face.
Defining Features of Each Kingdom
Kingdom
Cell type
Cell wall
Nutrition
Examples
Animals
Eukaryotic
No cell wall
Heterotrophic (ingest food)
Insects, fish, humans
Plants
Eukaryotic
Cellulose cell wall
Autotrophic (photosynthesis)
Ferns, mosses, flowering plants
Fungi
Eukaryotic
Chitin cell wall
Saprophytic (digest externally, absorb)
Mushrooms, yeast, Mucor
Protoctists
Eukaryotic
Varies
Some autotrophic, some heterotrophic
Amoeba, Chlorella, Plasmodium
Prokaryotes
Prokaryotic (no true nucleus)
Peptidoglycan cell wall
Varies
Lactobacillus, E. Coli
Key distinction: Eukaryotic cells have a membrane-bound nucleus; prokaryotic cells have DNA free in the cytoplasm (no nuclear envelope).
Fungi Are Not Plants
A common misconception is that fungi are plants. They differ in three critical ways:
No chlorophyll: fungi cannot photosynthesise.
Chitin cell walls: plants have cellulose cell walls.
Saprophytic nutrition: fungi secrete enzymes onto dead organic matter and absorb the digested products. Plants make their own food via photosynthesis.
Mucor is the named fungus in the syllabus. It is a bread mould that reproduces asexually by producing spores from sporangia. Its body consists of thread-like hyphae.
Protoctists: The "Leftovers" Kingdom
Protoctists are eukaryotic organisms that do not fit neatly into the animal, plant or fungi kingdoms. They are mostly unicellular but some are multicellular (e.g. Seaweed).
Amoeba: a heterotrophic protoctist that moves using pseudopodia and feeds by engulfing food particles (phagocytosis).
Chlorella: contains chloroplasts and photosynthesises like a plant, but is unicellular.
Plasmodium: the pathogen that causes malaria. It is a parasitic protoctist transmitted by female Anopheles mosquitoes.
When the examiner describes an organism as "eukaryotic, unicellular, and photosynthetic", it belongs in the protoctist kingdom, not the plant kingdom.
Try a focused question (3 marks)
Yeast is a single-celled organism with a cell wall made of chitin. It feeds by absorbing nutrients from its surroundings. To which kingdom does yeast belong? Explain your answer. (3 marks)
Show the answer and marking guidance
Yeast belongs to the Fungi kingdom.
It has a cell wall made of chitin (not cellulose).
It feeds saprophytically / by absorbing nutrients externally digested, which is characteristic of fungi.
Original Cambridge-style practice written for this site. It is not an official Cambridge past-paper question.
Common mix-ups to avoid
Check these points against your own answer before moving on.
Classifying fungi as plants because they do not move.
Forgetting that prokaryotes lack a membrane-bound nucleus: this is their defining feature.
Confusing protoctists with bacteria: protoctists are eukaryotic, bacteria are prokaryotic.