Topic 1 of IGCSE Biology (Cambridge 0610) is characteristics and classification of living organisms. Examiners expect you to define the seven characteristics of life (MRS GREN), name and describe the five kingdoms, use and construct dichotomous keys, and write binomial names correctly. This revision guide walks you through each of these with clear definitions, examples, and exam-style tips so you can answer “state”, “describe”, “explain”, and “use/construct a key” questions for full marks.

---

The seven characteristics of life (MRS GREN)

Living organisms share seven characteristics. The acronym MRS GREN helps you remember them: Movement, Respiration, Sensitivity, Growth, Reproduction, Excretion, Nutrition. You must be able to define each and give at least one example for an organism.

Movement is a change in position of the whole organism or part of it. Animals move to find food, escape predators, or find mates; plants move slowly (e.g. roots towards water, shoots towards light). Respiration is the chemical process that releases energy from food (usually glucose) inside cells. It is not the same as breathing: breathing is gas exchange (taking in oxygen, releasing carbon dioxide); respiration is the release of energy. Sensitivity is the ability to detect changes in the environment (stimuli). Response is the reaction to that change (e.g. moving towards light). In exams, keep “sensitivity” as detecting and “response” as reacting.

Growth is a permanent increase in size and/or number of cells. Reproduction is the production of offspring so that the species continues. Excretion is the removal of waste products of metabolism (e.g. urea, carbon dioxide) from the body. It is not the same as egestion (removal of faeces; undigested food). Nutrition is taking in nutrients (food) for energy, growth, and repair. Plants make their own food by photosynthesis; animals take in food by eating.

In “explain” questions, link the characteristic to survival (e.g. “Excretion removes toxic waste so it does not build up and harm the organism.”).

---

Classification: putting organisms into groups

Classification is grouping organisms based on shared features. Large groups are split into smaller groups: Kingdom → Phylum → Class → Order → Family → Genus → Species. The more levels two organisms share, the more closely related they are. At IGCSE you need to know the five kingdoms and one or two key features of each.

Kingdom Animalia: multicellular; no cell walls; heterotrophic (feed on other organisms); often able to move. Examples: insects, fish, mammals. Kingdom Plantae: multicellular; cell walls made of cellulose; autotrophic (make food by photosynthesis); contain chlorophyll. Examples: flowering plants, ferns, mosses. Kingdom Fungus: multicellular (e.g. mushrooms) or unicellular (e.g. yeast); cell walls (not cellulose); heterotrophic; feed by absorption (often saprophytic or parasitic). Kingdom Protoctista: mostly unicellular; have a nucleus; diverse (e.g. Amoeba, Euglena, algae). Kingdom Prokaryotae (or Prokaryota): unicellular; no nucleus; DNA in cytoplasm; e.g. bacteria.

In exams you may be asked to state which kingdom an organism belongs to from a description, or to give one feature of a kingdom.

---

Binomial naming (Genus and species)

Every species has a scientific name made of two parts: the Genus (with a capital letter) and the species (lowercase). The name is usually italic or underlined (e.g. Homo sapiens or Homo sapiens). This system is binomial (“two names”) and is used worldwide so that the same organism has the same name in every country. For example, humans are Homo sapiens; the dog is Canis familiaris.

Common mistakes: writing both words with a capital letter (only Genus has a capital); not italicising or underlining; writing the species name first (Genus always comes first).

---

Dichotomous keys: using a key

A dichotomous key is a set of paired statements (or questions) that you follow step by step to identify an organism. At each step you choose one of two options (e.g. “has wings” / “no wings”); your choice leads you to the next step or to the name of the organism. To use a key: start at step 1; read both options; choose the one that matches your organism; follow the instruction (next step or name); repeat until you reach a name. Write the organism name exactly as given in the key.

Practise with past-paper keys so you get used to following steps in order and not skipping.

---

Dichotomous keys: constructing a key

To construct a key for a small set of organisms (e.g. 4–5), use visible, clear features that differ between them. Each step should have two contrasting options about the same type of feature (e.g. “has wings” vs “no wings”, not “has wings” vs “is green”). Avoid vague or overlapping choices (e.g. “big” vs “small” with no clear divide). Work through the organisms and split them into two groups at each step until each organism is identified.

Example for four insects: Step 1 – Has wings? Yes → go to 2. No → Insect A. Step 2 – Has spots? Yes → Insect B. No → go to 3. Step 3 – Has stripes? Yes → Insect C. No → Insect D.

---

Exam tips and command words

• State / Name: Give the characteristic or group (e.g. “respiration”, “Kingdom Animalia”).
• Describe: Say what the feature is or what happens (e.g. “Movement is a change in position by the organism or part of it.”).
• Explain: Link the characteristic to survival (e.g. “Excretion removes toxic waste so it does not build up.”).
• Use the key: Follow each step in order; write the organism name exactly as in the key.
• Construct a key: Use clear, visible features; one feature per step; same type of feature in each pair; no vague or overlapping choices.

---

Common mistakes to avoid

• Confusing respiration (release of energy from food) with breathing (gas exchange).
• Mixing up sensitivity (detecting changes) and response (reacting); or using them interchangeably.
• Writing binomial names with both words capitalised, or not italicising/underlining.
• In keys: using vague or overlapping choices (e.g. “big” vs “small” without a clear divide).

---

Revision checklist

• List and define all seven characteristics of life (MRS GREN) with an example each.
• Name the five kingdoms and state one feature of each.
• Use a dichotomous key to identify an organism from a list of features.
• Construct a simple dichotomous key from 4–5 organisms using clear, contrasting features.
• Write a binomial name correctly (Genus with capital; species lowercase; italic or underline).

---

Next steps

Book a free trial with an IGCSE Biology tutor to practise classification and key-construction under exam conditions, or explore Tutopiya’s learning portal for more revision resources.