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Cambridge IGCSE · Biology 0610

Characteristics of living organisms

Recognise and distinguish the seven life processes used as evidence that an organism is living: movement, respiration, sensitivity, growth, reproduction, excretion and nutrition. This original practice pack is limited to Cambridge IGCSE Biology 0610 section 1.1. Classification systems, cell structure, transport processes and the detailed mechanisms taught in later topics are excluded.

2026 / 2027 / 2028 · Academic review not recorded · Published 2026-09-08

AI-assisted practice — not independently academically reviewed. Answers may contain errors; check important results against your course materials.

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Lesson contents · 18 sections

What you will learn

  • Recall the seven shared characteristics of living organisms and use their scientific names accurately.
  • Recognise movement by a whole organism or one of its parts, even when no change of location occurs.
  • Distinguish cellular respiration, which releases usable energy from nutrients, from breathing and gas exchange.
  • Identify sensitivity from evidence that an organism detects a change and produces a response.
  • Distinguish permanent growth in size and dry mass from temporary changes caused by water uptake or movement.
  • Recognise reproduction as the production of new organisms of the same kind and explain its importance to continuity of a species.
  • Distinguish excretion of metabolic wastes and excess substances from egestion of undigested food.
  • Recognise nutrition as obtaining materials needed for energy, growth and development.
  • Apply the seven characteristics to unfamiliar organisms, observations and short data sets without assuming that one observation alone proves life.

Explanation

Seven processes provide a biological checklist

Biologists describe living organisms through seven linked processes: movement, respiration, sensitivity, growth, reproduction, excretion and nutrition. The initials are sometimes remembered as MRS GREN, but the words matter more than the mnemonic. Each characteristic has a precise biological meaning, so a familiar word such as growth or respiration must not be interpreted only by its everyday meaning.

A single process is rarely enough to decide whether an unfamiliar object is alive. A flame can spread, use fuel and give off waste gases, yet that does not make it an organism. A better judgment uses several observations over time and asks whether they form a coordinated pattern of life. A dormant seed may show little visible activity while still carrying out very slow life processes and retaining the capacity to resume obvious growth.

Explanation

Movement can involve a whole organism or only one part

Movement is an action that changes the position of an organism or part of an organism. An animal walking from shade into sunlight changes place, but movement does not require travel. A leaf turning, a flower opening, a pupil narrowing and a hand withdrawing all involve parts changing position. Slow plant movements still count even when they are difficult to notice without repeated measurements or time-lapse observations.

Movement and sensitivity often appear together but answer different questions. Sensitivity is shown by detecting a change and responding to it; movement may be the visible action used in that response. If a shoot bends toward one-sided light, the bend is movement, while the directed response to the light provides evidence of sensitivity. Describing both processes avoids treating them as interchangeable.

Worked example

Applied scenario: a snail retracts its feelers

A snail is travelling across a surface. When a feeler lightly touches a leaf, the feeler retracts and the snail changes direction. The snail's travel and the change in position of the feeler are movement. The touch is a change in the external environment, and the directed retraction after contact is evidence that the snail detected the change, so sensitivity is also shown.

The same observation can therefore support more than one characteristic, but the reason must be stated for each. Calling the retraction only movement misses the stimulus-response relationship. Calling it only sensitivity misses the physical change in position. Nothing in this short observation directly demonstrates growth, reproduction, excretion or nutrition.

Explanation

Respiration releases energy inside living cells

Respiration is the collection of chemical reactions in cells that break down nutrient molecules and release energy that can be used in metabolism. The released energy supports activities such as muscle contraction, active growth, repair and maintaining internal conditions. Respiration occurs continuously in living cells, including plant cells, although its rate can vary greatly.

Breathing is the physical movement of air into and out of gas-exchange surfaces; it is not another name for respiration. Breathing and gas exchange help supply oxygen and remove carbon dioxide in many animals, but the energy-releasing reactions themselves occur in cells. A plant does not breathe with lungs, yet its living cells respire by day and by night.

Worked example

Applied scenario: germinating seeds warm an insulated flask

Two insulated flasks are kept under the same conditions. Flask A contains germinating seeds, while flask B contains an equal mass of boiled, cooled seeds. After several hours, A is warmer but B is unchanged. Because the main planned difference is whether the seeds are living, the temperature rise is evidence that reactions in the living seeds released energy during respiration.

The observation does not mean that heat is the useful purpose of respiration; some released energy becomes heat while cells use energy for other processes. The boiled seeds provide a comparison, helping to rule out warming caused simply by the flask or room. This scenario supports respiration but does not by itself demonstrate all seven characteristics.

Worked example

Common-error check: an athlete breathes faster

After a fast run, an athlete's breathing rate increases. The visible chest movements show ventilation, not the chemical process of respiration itself. However, the change is connected to increased respiration in active muscle cells because those reactions release energy for contraction and create a greater demand for exchange of gases.

A precise answer separates observation from inference: faster breathing is directly observed; increased cellular respiration is inferred from the muscles' increased energy demand. Saying 'breathing releases energy' is incorrect because air movement does not break down nutrient molecules. This distinction remains important even when breathing rate and respiration rate change together.

Explanation

Sensitivity links a detected change to a response

Sensitivity is the ability to detect a change in the internal or external environment and respond to it. The change is a stimulus, and the resulting action or adjustment is the response. External stimuli include light, sound, touch and temperature. Internal changes, such as falling water availability, can also lead to responses that help an organism manage its conditions.

A valid example identifies both parts of the relationship. 'The lamp became brighter' names only a stimulus. 'The pupil became narrower after the lamp brightened' identifies a change followed by a response. The response need not be conscious and need not involve the whole organism; plants and microorganisms can also respond to environmental changes.

Worked example

Applied scenario: testing a shoot with one-sided light

A young shoot is photographed at the same time each day while light reaches it from the left. Its tip changes from vertical to curved leftward. The sequence gives evidence of movement because the tip changes position. It also gives evidence of sensitivity because the direction of the response is associated with the direction of the external light stimulus.

A stronger investigation would compare this shoot with similar shoots receiving light evenly, while keeping water, temperature and time the same. That comparison is not needed to define sensitivity, but it makes the interpretation more convincing. The example remains about recognising movement and sensitivity, not explaining the detailed mechanism of the bending.

Explanation

Growth is a permanent increase in size and dry mass

Biological growth is a lasting increase in an organism's size and dry mass. Dry mass is the mass remaining after water has been removed, so it is useful for separating the production of new biological material from a temporary gain of water. Length, volume or fresh mass can support a growth claim, but each may be influenced by water or posture and should be interpreted carefully.

A dry seed that swells after soaking has increased in fresh mass and volume, but much of that change can be reversed if the water is lost. The swelling alone is not secure evidence of growth. By contrast, a seedling whose dry mass rises over time has added material that remains after water is removed, matching the idea of a permanent increase.

Worked example

Worked data: deciding whether seedlings grew

Two equal-sized groups of seedlings are grown under identical conditions. One group is sampled and dried to constant mass on day 4, giving an average dry mass of 2.4 g per seedling; the matched group is sampled and dried on day 10, giving 3.0 g per seedling. The difference is 3.0 - 2.4 = 0.6 g, and the increase relative to day 4 is (0.6 / 2.4) × 100 = 25%. The matched-group result supports average growth because drying removes water before mass is compared.

Different groups are needed because drying is destructive: a dried day-4 seedling cannot continue growing for measurement on day 10. Equal group size, identical growing conditions and average mass make the comparison fairer. The conclusion should remain limited to the sampled population and period: average dry mass was 0.6 g greater in the day-10 group. The data do not prove that every individual grew by exactly that amount.

Explanation

Reproduction makes new organisms of the same kind

Reproduction consists of processes that produce new organisms of the same kind as the parent organism or organisms. An individual can remain alive without reproducing, so reproduction is different from a process required continuously for that individual's immediate survival. Across generations, however, reproduction allows a species to continue.

Repair and growth do not automatically count as reproduction. A cut healing replaces damaged material within the same organism; it does not create another organism. By contrast, a plant runner that develops into a separate new plant is reproduction. The important question is whether a new organism is produced, not simply whether cells or body material increased.

Worked example

Applied scenario: runners, roots and a new strawberry plant

A strawberry plant sends a horizontal runner across the soil. At a node, roots and leaves develop. The connection later breaks, leaving a separate plant capable of continuing on its own. This is evidence of reproduction because a new organism of the same kind has been produced from the parent plant.

Several other characteristics occur during the sequence: the runner and leaves increase in dry mass, showing growth, and materials are obtained for nutrition. Even so, the feature that makes the event reproduction is the formation of a separate new plant. A longer root on the original plant would be growth but would not alone create a new organism.

Explanation

Excretion removes wastes made by metabolism and excess substances

Excretion is the removal from an organism of waste products made by metabolic reactions and of substances present beyond the organism's requirements. Carbon dioxide produced during respiration is a metabolic waste. Urea made from the breakdown of excess amino acids is another example, while excess water and mineral ions may also need to be removed.

Egestion is different: it is the removal of undigested food that was never absorbed into the body's cells. Faeces may contain excretory substances too, but undigested remains are egested rather than produced by metabolism. Secretion is also distinct because a useful substance is released for a function; the biological role of the material matters, not merely the fact that it leaves a cell or organism.

Worked example

Applied scenario: sorting materials that leave a mammal

Consider four materials leaving a mammal: carbon dioxide in exhaled air, urea in urine, excess water in urine and undigested plant fibre in faeces. Carbon dioxide and urea are metabolic wastes, while the water is beyond requirements, so their removal is excretion. The undigested fibre was not absorbed and was not produced by cells, so its removal is egestion.

The route out of the body does not define the process by itself. Exhalation removes carbon dioxide, urine carries several excretory substances, and faeces chiefly carries egested material. To classify an example, ask where the substance came from and whether it is a metabolic waste, an excess substance or unabsorbed food.

Explanation

Nutrition supplies materials for energy, growth and development

Nutrition is the taking in of materials needed for energy, growth and development. Animals obtain nutrient-containing food by feeding and then make useful materials available to their bodies. Green plants take in raw materials and use light energy to make nutrient molecules. These routes differ, but both supply or produce the materials on which the organism depends.

Nutrition and respiration are linked but are not the same. Nutrition provides nutrient molecules or the materials used to make them; respiration breaks down nutrient molecules in cells and releases energy. A meal does not release usable energy merely by entering the mouth, and a plant's production of food should not be confused with its continuous cellular respiration.

Worked example

Applied scenario: a seedling changes its source of materials

During early germination, a seedling uses stored nutrient material from the seed. After leaves expand in light, the plant takes in raw materials and makes nutrient molecules that can support further growth. Both stages concern nutrition because materials are being obtained or made available for energy, growth and development.

Respiration occurs alongside nutrition: cells break down nutrient molecules and release energy for processes such as growth. If the seedling's dry mass later increases, that is evidence of growth, while bending toward light can provide evidence of sensitivity and movement. Naming the evidence for each process prevents one observation from being used as a vague answer for several characteristics.

Worked example

Applied scenario: interpret a mystery organism over one week

An unfamiliar organism is observed for a week. It moves toward a shaded region after the temperature rises, takes in nutrient-rich liquid, releases carbon dioxide, increases in dry mass and later produces two smaller organisms like itself. The location change is movement; the directed change after warming supports sensitivity; taking in material is nutrition; carbon dioxide release is evidence consistent with respiration and excretion; added dry mass is growth; and producing new organisms is reproduction.

The interpretation uses a pattern rather than one isolated sign. Carbon dioxide alone would need care because non-living reactions can also release gases, but its presence alongside coordinated responses, nutrition, permanent growth and reproduction gives much stronger evidence. The observations identify characteristics without requiring the organism to be assigned to any taxonomic group.

Worked example

Applied scenario: why fire is not classified as an organism

A fire can become larger, spread across fuel, consume material and release carbon dioxide. Those surface similarities do not establish biological growth, movement, nutrition or excretion because they arise from combustion rather than coordinated processes of an organism. In particular, the fire's increase is not a permanent increase in biological dry mass produced by life processes.

This comparison shows why a mnemonic must not become a tick-box based only on everyday wording. Biologists interpret the nature and coordination of the processes and gather multiple lines of evidence. The seven characteristics describe living organisms; they are not a rule that every object showing loose analogies to several words must be alive.

Original practice, not an official examination paper. Readnary is not affiliated with the awarding body. Prepared with AI assistance.