IGCSE Biology: Characteristics and Classification of Living Organisms (Cambridge 0610)

This guide covers Topic 1 Characteristics and classification of living organisms, for Cambridge IGCSE Biology 0610, 2026–2028 series. Cambridge IGCSE Biology is tiered — Core content is examined at grades C–G, and Extended candidates (Core + Supplement) are assessed for grades A*–G — and this guide marks which outcomes belong to each tier.

Where this fits in 0610

Characteristics and classification of living organisms is the first of twenty-one topics in 0610. It sets out what counts as “living” in the first place, and how the diversity of life is organised into named groups — both ideas that the rest of the syllabus takes for granted, from the plant/animal cell comparisons in Topic 2 through to the five-kingdom groupings that reappear whenever a later topic asks candidates to classify an unfamiliar organism.

Syllabus coverage

CAMBRIDGE IGCSE BIOLOGY 0610 — TOPIC 1 CHARACTERISTICS AND CLASSIFICATION OF LIVING ORGANISMS

• 1.1 Characteristics of living organisms (Core) — describing the seven characteristics shared by all living organisms: movement, respiration, sensitivity, growth, reproduction, excretion and nutrition (often remembered by the mnemonic MRS GREN)
• 1.2 Concept and uses of classification systems (Core) — that organisms are classified into groups by shared features, that a species is a group of organisms able to reproduce to produce fertile offspring, the binomial system of naming species (genus + species), and constructing and using dichotomous keys based on identifiable features; (Supplement) that classification systems aim to reflect evolutionary relationships, and that the similarity of DNA base sequences between organisms is used as a means of classification — the more recently two groups shared a common ancestor, the more similar their DNA
• 1.3 Features of organisms (Core) — the main features used to place organisms into the animal and plant kingdoms, and into groups within the animal kingdom (vertebrates: mammals, birds, reptiles, amphibians, fish; arthropods: myriapods, insects, arachnids, crustaceans), and classifying organisms using those features; (Supplement) the main features used to place all organisms into one of five kingdoms — animal, plant, fungus, prokaryote and protoctist — the features used to place plants into ferns and flowering plants (dicotyledons and monocotyledons), and the features of viruses (a protein coat and genetic material)

The seven characteristics — MRS GREN

Letter	Characteristic	What it means
M	Movement	An action by an organism or part of an organism causing a change of position or place
R	Respiration	The chemical reactions in cells that break down nutrient molecules and release energy for metabolism
S	Sensitivity	The ability to detect and respond to changes in the internal or external environment
G	Growth	A permanent increase in size and dry mass
R	Reproduction	The processes that make more of the same kind of organism
E	Excretion	The removal of the waste products of metabolism and substances in excess of requirements
N	Nutrition	The taking in of materials for energy, growth and development

Two distinctions examiners specifically test: respiration is not breathing — respiration is the chemical release of energy inside cells, while breathing (or gas exchange) is the physical movement of gases in and out of the body. And excretion is not egestion — excretion removes waste made by the organism’s own metabolism (such as carbon dioxide or urea), while egestion is the removal of undigested food (faeces), which was never part of the organism’s chemistry.

Building and reading a dichotomous key

A dichotomous key identifies an organism through a series of paired statements, each offering exactly two contrasting options, leading the user step by step to a name:

1.  Has a backbone .......................... go to 2
    No backbone ............................. INVERTEBRATE

2.  Has feathers ............................. BIRD
    No feathers .............................. go to 3

3.  Has fur or hair .......................... MAMMAL
    No fur or hair ............................ go to 4

4.  Has fins ................................. FISH
    No fins ................................... go to 5

5.  Has scaly, dry skin ...................... REPTILE
    Has moist skin ............................ AMPHIBIAN

Each numbered pair must offer only two options, based on a feature that can actually be observed on the specimen in front of you — vague or overlapping criteria (such as “large” without a stated size) make a key impossible to use consistently between different people.

Groups within the animal kingdom (Core)

All candidates need the main features used to place animals in these groups (syllabus 1.3.2).

Vertebrate group	Main features
Mammals	Fur or hair; external ears (pinnae); mammary glands produce milk for the young
Birds	Feathers; a beak; wings (front limbs); lay eggs with hard shells
Reptiles	Dry, scaly skin; lay eggs with rubbery (leathery) shells, on land
Amphibians	Moist skin with no scales; lay eggs without shells in water
Fish	Scales; fins; gills for gas exchange

Arthropod group	Main features
Insects	Three body parts (head, thorax, abdomen); three pairs of legs; one pair of antennae; usually two pairs of wings
Arachnids	Two body parts; four pairs of legs; no antennae
Crustaceans	More than four pairs of legs; two pairs of antennae; a hard exoskeleton (often with calcium carbonate)
Myriapods	A long body with many segments; one or two pairs of legs on each segment; one pair of antennae

All arthropods have jointed legs, a segmented body and an exoskeleton. Exam questions often give a photo or description and ask which group an organism belongs to, so learn the features that tell the groups apart (e.g. counting legs and body parts).

The five kingdoms (Supplement)

Kingdom	Defining feature
Animal	Multicellular; no cell wall; feed by ingestion
Plant	Multicellular; cellulose cell wall; make food by photosynthesis
Fungus	Cell wall made of chitin (not cellulose); usually made of thread-like hyphae (yeast is single-celled); feed by secreting enzymes onto organic matter and absorbing the products
Prokaryote	No nucleus; genetic material free in the cytoplasm (e.g. bacteria)
Protoctist	Mostly single-celled; not clearly animal, plant or fungus

Viruses are not placed in any of the five kingdoms. The syllabus requires you to state that a virus consists only of a protein coat and genetic material — that is the examinable content, with the reasoning for why this excludes them from the five kingdoms as useful background rather than a required outcome in its own right.

How to approach it

Start with the MRS GREN characteristics, since exam questions often present an unfamiliar organism or process and ask candidates to identify which characteristic of life it demonstrates — precise definitions matter more here than they first appear to, particularly distinguishing respiration (a chemical process releasing energy) from breathing or gas exchange, which students frequently conflate. For classification, practise constructing and reading dichotomous keys directly, since this is a practical skill examined by giving candidates a set of organisms and asking them to build or follow a key, not just define one. All candidates need the features of the vertebrate and arthropod groups; Extended candidates also need the five kingdoms and the plant groups (ferns and flowering plants, with monocotyledons and dicotyledons) — these recur as short-answer identification questions across past papers, and partial recall (getting the kingdom right but the wrong subgroup) is a common source of dropped marks.

Official syllabus

Cambridge IGCSE Biology 0610 syllabus for 2026, 2027 and 2028 — cambridgeinternational.org.