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Detailed notes on Characteristics and Classification of Living Organisms for Cambridge IGCSE Biology, covering key concepts, explanations, examples, and exam-focused revision points.
MRS GREN — the seven life processes shared by every living thing. Memorise the definitions verbatim; Cambridge mark schemes credit precise wording.
Mapped to the Cambridge IGCSE 0610 syllabus (2026-2028).
Mnemonic for the seven characteristics every living organism shows.
MRS GREN.
| Letter | Process | Cambridge definition |
|---|---|---|
| M | Movement | An action by an organism or part of it causing a change of position or place |
| R | Respiration | Chemical reactions in cells that break down nutrient molecules and release energy |
| S | Sensitivity | Ability to detect and respond to changes in the environment |
| G | Growth | Permanent increase in size and dry mass |
| R | Reproduction | Processes that produce more of the same kind of organism |
| E | Excretion | Removal of metabolic waste, toxic materials and substances in excess |
| N | Nutrition | Taking in of materials for energy, growth and development |
Memorise the wording exactly. Cambridge mark schemes are strict — they look for specific phrases (e.g. "chemical reactions in cells" for respiration, "dry mass" for growth, "metabolic waste" for excretion).
Worked qualitative. Why is a virus NOT considered a fully living organism by most biologists? Outside a host cell, viruses don't carry out respiration, growth, sensitivity, or excretion. They reproduce ONLY by hijacking a host cell. They miss several MRS GREN characteristics.
Two definitions Cambridge marks zealously — get them right.
Respiration vs breathing.
Worked qualitative. A plant doesn't have lungs but it still respires. Where? In every cell — at the mitochondria. The plant doesn't 'breathe' in the lung sense.
Excretion vs egestion.
Worked qualitative. A student says "we excrete faeces". Correct them: faeces are EGESTED. They contain undigested food, dead gut cells, gut bacteria — not metabolic waste.
Wet mass can fluctuate. Dry mass shows real growth.
Growth is a PERMANENT increase in size AND dry mass.
Why dry mass?
Plants vs animals.
Cell division. Growth involves making more cells (mitosis) AND existing cells getting larger.
Worked qualitative. A student weighs a seedling daily. Wet mass goes up by 5g in 3 days. Dry mass stays the same. What does this mean? The seedling has absorbed water but hasn't actually grown — no new cellular material has been made.
Cambridge tip. Always include "dry mass" in growth definitions for full marks.
All seven processes apply to plants and microbes too — examples for each.
Plants show all seven:
Single-celled organisms (bacteria, amoeba, paramecium) also show all seven — at the cellular scale.
Cambridge tip. When asked "give an example of MRS GREN process X in a plant", be specific: "phototropism" beats "moving"; "photosynthesis" beats "eating".
Verbatim phrases and definitions Cambridge mark schemes credit.
Characteristics of living organisms appears every Paper 4 (3-5 marks): define a process, distinguish respiration from breathing, distinguish excretion from egestion. Examiner reports flag the respiration/breathing confusion as the recurring lost mark.
Sources: Cambridge IGCSE Biology 0610 syllabus 2026-2028 (1.1); 0610/42 Oct/Nov 2024 — Q1 (MRS GREN definitions); 0610 Examiner Reports 2022-2024. Last reviewed 2026-05-07.
Step-by-step solutions to past-paper-style questions on characteristics of living organisms, written exactly the way a tutor would explain them at the board.
Question
List the seven characteristics shared by all living organisms and give a one-line description for each.
Step-by-step solution
Step 1
Movement: an action by an organism or part of it causing a change of position or place. Plants and microbes move too — not just animals.
Step 2
Respiration: chemical reactions in cells that break down nutrient molecules and release energy. NOT the same as breathing.
Step 3
Sensitivity: the ability to detect and respond to changes in the internal or external environment.
Step 4
Growth: a permanent increase in size and dry mass.
Step 5
Reproduction: the processes that produce more of the same kind of organism.
Step 6
Excretion: removal of metabolic waste, toxic materials and excess substances from organisms.
Step 7
Nutrition: taking in materials for energy, growth and development.
Answer
MRS GREN: Movement, Respiration, Sensitivity, Growth, Reproduction, Excretion, Nutrition.
Examiner tip
Cambridge expects the FULL definition of each — "breathing" is not respiration. "Excretion" is metabolic waste, NOT undigested food (that's egestion).
Question
For each observation, name the characteristic of living organisms it illustrates: (a) a sunflower head turns to face the Sun; (b) a person produces urea in the liver and removes it in urine; (c) a seedling becomes taller and heavier over two weeks; (d) a leaf takes in carbon dioxide and water to make glucose.
Step-by-step solution
Step 1
(a) Detecting and responding to a stimulus (light) is sensitivity.
Step 2
(b) Urea is a waste product made inside cells (from breaking down excess amino acids), so removing it is excretion.
Step 3
(c) A permanent increase in size and dry mass is growth.
Step 4
(d) Taking in raw materials to make food (here, by photosynthesis) is nutrition.
Answer
(a) Sensitivity; (b) Excretion; (c) Growth; (d) Nutrition.
Examiner tip
In matching questions, the trap is (b): students write 'egestion'. Urea is metabolic waste made in cells, so it is EXCRETION.
Question
A student writes that 'respiration is breathing in and out'. Correct the answer using Cambridge wording.
Step-by-step solution
Step 1
Breathing (or ventilation) is the muscular movement of air into and out of the lungs.
Step 2
Respiration is the CHEMICAL REACTIONS in CELLS that break down nutrient molecules to release ENERGY for processes like protein synthesis, active transport, contraction, and growth.
Step 3
All living cells respire. Many organisms (single-celled, plants, fungi) don't breathe at all but still respire.
Answer
Respiration = chemical reactions in cells breaking down nutrient molecules to release energy. Breathing = the air movements that supply oxygen to or remove CO₂ from the body. Different processes.
Examiner tip
This is the single most-marked confusion in Paper 4 examiner reports. Cambridge wants the cellular definition of respiration.
Question
A student claims a candle flame is alive because it moves, gives out heat (like respiration), grows, and 'reproduces' by lighting other candles. Explain why a flame is NOT a living organism.
Step-by-step solution
Step 1
A living organism must show all seven characteristics and be made of cells — a flame is not made of cells.
Step 2
It does not respire: the heat comes from combustion, not enzyme-controlled reactions inside cells releasing energy from nutrient molecules.
Step 3
It does not truly grow (it does not add to its own organised structure by making new cells), shows no sensitivity, carries out no nutrition (it consumes wax and oxygen but does not take in materials for growth and development), and the gases it gives off are combustion products, not metabolic excretory waste.
Answer
A flame only mimics a few features superficially. It is not made of cells, does not respire (it combusts), and does not show genuine growth, sensitivity, nutrition or excretion — so it fails the test of being a living organism.
Examiner tip
The mark is for linking each apparent 'life feature' to why it is NOT the biological process — especially heat = combustion, not respiration.
Question
When the leaves of a Mimosa pudica plant are touched, they rapidly fold inwards within a second, then slowly re-open after a few minutes. Identify the two characteristics of living organisms this behaviour demonstrates, and explain how the example shows these characteristics are not limited to animals.
Step-by-step solution
Step 1
Detecting the touch stimulus and reacting to it is sensitivity — the ability to detect and respond to changes in the environment.
Step 2
The folding of the leaves is a change of position of part of the organism, so it is also movement.
Step 3
This matters because students often assume only animals move and respond. The plant detects a stimulus and moves a part of itself, showing that sensitivity and movement are characteristics of all living organisms, including plants.
Step 4
The re-opening shows the response is reversible and controlled by the plant — it is a genuine biological response, not the leaf simply being knocked aside.
Answer
The behaviour shows sensitivity (detecting and responding to touch) and movement (the leaves change position). Because a plant performs both, the example proves these characteristics apply to all living organisms, not just animals.
Examiner tip
Top answers name BOTH characteristics and use the example to make the general point that MRS GREN applies to plants too.
Question
Some biologists argue that viruses are not living organisms. Using the seven characteristics of living organisms, evaluate this view.
Step-by-step solution
Step 1
For 'living': a virus contains genetic material (DNA or RNA) and can 'reproduce' — but only by hijacking a host cell's machinery, so it cannot reproduce on its own.
Step 2
Against 'living': outside a host, a virus shows none of MRS GREN. It does not respire (no cellular reactions of its own), does not carry out nutrition, does not grow, does not excrete metabolic waste, and shows no independent movement or sensitivity.
Step 3
A virus is not made of a cell — it has no cytoplasm, no membrane-controlled metabolism, and no organelles.
Step 4
Judgement: because a virus carries out 'life-like' activity only inside a host cell and not independently, most biologists classify it as a non-living infectious agent rather than a true living organism.
Answer
A virus reproduces and carries genetic material, which looks life-like, but on its own it shows none of the seven characteristics, is not made of a cell, and can only replicate by taking over a host. On balance it is best described as non-living, because it cannot independently carry out the life processes.
Examiner tip
A strong evaluation gives evidence on BOTH sides (reproduction vs lack of independent metabolism/cell structure) before reaching a clear judgement.
High-scoring sample answers for characteristics of living organisms on the Cambridge IGCSE 0610 paper, with examiner-style notes mapping each response to the mark scheme and assessment objectives.
State what is meant by the term excretion. (1 mark)
Model answer
Excretion is the removal from organisms of the waste products of metabolism (the chemical reactions in cells), together with toxic materials and substances in excess of requirements.
Why this scores
One mark for the idea of removing metabolic/waste/excess substances. Naming 'metabolism' or 'made in cells' secures the mark and separates it from egestion.
State two ways in which excretion is different from egestion. (2 marks)
Model answer
First, excretion removes waste produced inside the cells of the body (the waste products of metabolism, such as carbon dioxide and urea), whereas egestion removes undigested food (faeces) that has never been absorbed into the body's cells. Second, excreted substances have taken part in the organism's chemical reactions, while egested material has only passed through the gut.
Why this scores
Two clear contrasts. The key idea is origin: excretion = metabolic waste from cells; egestion = undigested food that never entered cells.
Explain the difference between respiration and breathing. (3 marks)
Model answer
Respiration is the series of chemical reactions in cells that break down nutrient molecules, such as glucose, to release energy for the cell's processes. Breathing (ventilation) is the muscular movement of the chest that moves air into and out of the lungs. The two are linked but different: breathing supplies the oxygen used in aerobic respiration and removes the carbon dioxide produced, but respiration itself happens in every living cell, including the cells of organisms that do not breathe, such as plants and bacteria.
Why this scores
Three marks: (1) respiration = energy release in cells from nutrients; (2) breathing = air movement in/out of lungs; (3) a correct linking or distinguishing point (e.g. respiration occurs in all cells / breathing supplies O₂ for respiration).
A car can move and uses fuel to release energy. Using the characteristics of living organisms, explain why a car is not a living organism. (4 marks)
Model answer
A living organism must show all seven characteristics and be made of cells, and a car fails this test in several ways. First, a car is not made of cells and so cannot carry out the cellular processes of life. Second, although it moves, it does so only when a person drives it, and although it releases energy from fuel this is combustion in an engine, not respiration controlled by enzymes in cells. Third, a car cannot grow by making new material of its own, cannot reproduce to make more cars, and shows no sensitivity of its own — any 'response' comes from the driver. Fourth, the exhaust gases are combustion products, not the metabolic waste of excretion. Because it cannot carry out genuine respiration, growth, reproduction, sensitivity, nutrition or excretion, a car is not living.
Why this scores
Four developed points, each contrasting an apparent feature with the true biological process. Naming 'not made of cells' and 'combustion, not respiration' are the highest-value points.
Describe how a flowering plant shows five of the seven characteristics of living organisms. (5 marks)
Model answer
A flowering plant shows all seven life processes, including the following five. Nutrition: it makes its own food by photosynthesis, taking in carbon dioxide and water and using light energy to produce glucose. Respiration: its cells break down glucose to release energy for processes such as growth and active transport, day and night. Growth: it permanently increases in size and dry mass as it produces new cells and tissues, for example growing taller and producing more leaves. Sensitivity: it detects and responds to stimuli, for instance shoots growing towards light (phototropism) and roots growing towards gravity. Excretion: it removes the waste products of metabolism, such as the carbon dioxide produced by respiration and the oxygen produced by photosynthesis.
Why this scores
One mark per characteristic correctly named AND illustrated with a plant example. Listing the characteristics without a plant-specific example would not gain full credit.
A gardener plants mustard seeds, which germinate and grow into seedlings. Explain how each of the seven characteristics of living organisms contributes to the survival and development of a mustard seedling. (6 marks)
Model answer
All seven life processes work together to keep the seedling alive and allow it to develop. Nutrition lets the seedling obtain food: once its leaves appear it photosynthesises, taking in carbon dioxide and water to produce glucose for energy and building materials. Respiration breaks down this glucose in every cell to release the energy needed for the seedling's activities, both day and night. Movement is shown as the shoot pushes upward and the leaves change position to face the light, helping it capture more sunlight. Sensitivity allows the seedling to detect stimuli and respond — the shoot grows towards light and the root grows downwards towards gravity, so it is correctly oriented. Growth is the permanent increase in size and dry mass as new cells are made, turning the tiny seedling into a larger plant. Excretion removes the waste products of metabolism, such as excess carbon dioxide, preventing harmful build-up. Finally, when mature the plant will carry out reproduction, producing flowers and seeds so that more mustard plants of the same kind are made. Together these processes allow the seedling to obtain energy, respond to its surroundings, grow and eventually reproduce.
Why this scores
All seven characteristics named and each linked to a seedling-specific function. For 6 marks the examiner looks for correct biology AND relevance to the seedling — generic definitions alone cap the mark.
Definitions to memorise and the exact keywords mark schemes credit for characteristics of living organisms answers — sharpened from recent examiner reports for the 2026 0610 sitting.
An action by an organism or part of an organism causing a change of position or place.
The chemical reactions in cells that break down nutrient molecules and release energy for metabolism.
Example
Glucose → CO₂ + water + energy (aerobic respiration in mitochondria).
The ability to detect and respond to changes in the internal or external environment.
Example
A plant root growing toward gravity (geotropism); a pupil constricting in bright light.
A permanent increase in size and dry mass.
Example
A seedling growing taller and heavier as cell numbers and mass increase.
The processes that produce more of the same kind of organism.
The removal from organisms of toxic materials, the waste products of metabolism (chemical reactions in cells), and substances in excess of requirements.
Example
Urea (from protein breakdown) excreted by kidneys; CO₂ excreted by lungs.
Taking in of materials for energy, growth and development.
Example
Photosynthesis in plants; eating and digesting food in animals.
An individual living thing made up of one or more cells.
The traps other students keep falling into on characteristics of living organisms questions — taken from recent Cambridge IGCSE 0610 examiner reports and mark schemes — and how to avoid them.
0610 Examiner Reports 2022-2024 (recurring)
Why it happens
In everyday English, 'respiration' often means breathing. In biology it specifically means cellular energy release.
How to avoid it
Learn the Cambridge wording: 'chemical reactions in cells that break down nutrient molecules and release energy'. Mention CELLS and ENERGY.
Why it happens
Both involve waste leaving the body, so it's easy to muddle.
How to avoid it
Excretion = waste produced INSIDE cells (metabolic waste, e.g. CO₂, urea). Egestion = removing undigested food that never crossed into the body (faeces). Different origin → different word.
Why it happens
Increase in size is the obvious feature.
How to avoid it
Cambridge wants 'permanent increase in size AND DRY MASS'. Wet mass can change just by drinking water — that's not growth.
Why it happens
Animals are the most familiar example.
How to avoid it
Plants move too: stems bend toward light (phototropism), petals open and close, parts grow. All seven characteristics apply to ALL living organisms.
The things students keep getting wrong in this sub-topic, answered.