Seven tests, and a living thing passes all of them.
Movement, respiration, sensitivity, growth, reproduction, excretion and nutrition. A car moves and a fire grows, but only a living organism truly shows all seven. Learn the exact definitions, because the examiners mark the wording.
Every living organism shows all seven characteristics of life, often remembered as MRS GREN: movement, respiration, sensitivity, growth, reproduction, excretion and nutrition. Each has a precise definition. Respiration happens in cells and releases energy; growth is a permanent increase in size and dry mass; excretion removes the waste products of metabolism. Non-living things may seem to show one or two, but never all seven, and never by the processes that happen in cells.
Fig. 1: the seven characteristics of living organisms (MRS GREN)
Section 01
Seven characteristics, every one of them.
Pick the dog in the simulator and test each characteristic in turn, then do the same for the plant. Read the explanation for each one: both organisms show all seven, even though the plant never walks anywhere.
Characteristic
Definition to learn
Example
Movement
an action by an organism or part of an organism causing a change of position or place
a dog running; a flower opening and closing
Respiration
the chemical reactions in cells that break down nutrient molecules and release energy for metabolism
every cell of the dog and the plant, day and night
Sensitivity
the ability to detect and respond to changes in the internal or external environment
a dog turning towards a sound; a shoot growing towards light
Growth
a permanent increase in size and dry mass
a puppy growing into an adult as its cells divide
Reproduction
the processes that make more of the same kind of organism
dogs having puppies; flowers making seeds
Excretion
the removal of the waste products of metabolism and substances in excess of requirements
carbon dioxide breathed out; urea in urine
Nutrition
the taking in of materials for energy, growth and development
a dog eating food; a plant absorbing carbon dioxide, water and mineral ions
Examiner trap
Respiration is not breathing. Breathing moves air in and out of the lungs; respiration is the chemical reactions in cells that release energy. A plant has no lungs, but every one of its living cells respires all the time.
Section 02
It looks alive, but it is not.
Now switch the simulator to the car, the fire and the salt crystal. Each seems to show some characteristics, but look at the reason the sim gives every time you test one.
Car: it moves and burns fuel with oxygen, but that is combustion in an engine, not chemical reactions inside cells. It takes in fuel only for energy, never for growth, and it never makes more cars.
Fire: it uses oxygen, gives out carbon dioxide and gets bigger, but it has no cells, cannot detect or respond to anything, and its smoke and ash are not products of metabolism.
Salt crystal: it can grow in a salty solution, but only by adding particles to its outside. That is not growth in the biological sense, because no new cells are made.
The rule: to be alive, an organism must show all seven characteristics, carried out by its own cells.
Examiner trap
Growth means a permanent increase in size and dry mass. A seed that swells by absorbing water gets bigger, but it has not grown, because water is not part of dry mass and can be lost again. Always write both parts of the definition.
Stage 1 · Learn
Check what the sim just showed you
Four quick checks. Each correct answer earns XP and records this skill on your profile.
Quick check+10 XP
Which is the correct definition of respiration?
Quick check+10 XP
In the simulator the car takes in fuel. Why does this not count as nutrition?
Quick check+10 XP
A salt crystal gets larger in a salty solution. Why is this not biological growth?
Quick check+10 XP
The simulator says a plant shows movement. Which observation shows this?
Section 03
Plants show all seven too.
Students often say plants do not move or excrete. The definitions show why they do.
Movement: the definition includes part of an organism changing position. Flowers open and close, and leaves turn to face the light.
Excretion: oxygen from photosynthesis and carbon dioxide from respiration are waste products of metabolism, and they leave through the leaves.
Nutrition: plants make their own food by photosynthesis, but they still take in materials: carbon dioxide, water and mineral ions from the soil.
Sensitivity: shoots grow towards light and roots grow downwards, so plants detect and respond to changes even though they have no nervous system.
Stage 2 · Exam
Exam-style questions
Unlocks once the four checks above are done. Worth more XP, written to IGCSE Paper 2 and Paper 4 standard.
Finish the four checks above to unlock the exam questions
Exam style+20 XP
Which definition of excretion is correct?
Exam style+20 XP
A student measures the growth of bean seedlings. Which measurement shows growth most reliably?
Exam style+20 XP
Which list contains only processes carried out by every living organism?
Exam style+20 XP
A flame uses oxygen, releases carbon dioxide and gets bigger. Which statement explains why it is not alive?
Skill unlocked
Characteristics of living organisms, mastered.
This skill is now recorded on your profile. Keep the chain going.