Characteristics of living organisms
The seven life processes shared by every living thing.
Learning objectives
What you need to be able to do
Teacher-mapped phrasing — check against the official Cambridge syllabus for exact wording.
- 1.1.1List and describe the characteristics of living organisms.
4 minute read
Characteristics of living organisms
Biology begins with a deceptively hard question: what counts as alive? A crystal grows. A river moves. A flame consumes fuel and produces waste. None of them are alive, because being alive means doing all seven of the following, not just one.
The seven characteristics
- Movement — an action causing a change of position or place.
- Respiration — chemical reactions that break down nutrient molecules in living cells to release energy.
- Sensitivity — detecting stimuli and responding to them.
- Growth — a permanent increase in size and dry mass.
- Reproduction — making more of the same kind of organism.
- Excretion — removal of the toxic waste products of metabolism and substances in excess.
- Nutrition — taking in materials for energy, growth and development.
The usual mnemonic is MRS GREN, taking the first letter of each.
Why "all seven" matters
A flame moves, releases energy, and produces waste, but it does not respond to stimuli in a controlled way, does not reproduce itself, and has no nutrition in the biological sense. A car uses fuel and moves but grows not at all. The set is what defines life, not any single member of it.
Think of it like this
MRS GREN is a checklist, not a menu. A restaurant that only serves one dish off a seven-item set menu has not served the set menu — and a thing doing only some of these is not alive.
Worked examples
Method, step by step
A student claims a candle flame is alive because it moves, uses fuel, gives out energy and produces waste gases. Give two characteristics of living organisms the flame does not show.
- 1Check each characteristic in turn against the flame.
- 2A flame does not reproduce to make more flames of its own kind as an organism does.
- 3A flame does not show sensitivity — it cannot detect and respond to stimuli in a controlled way. It also does not grow by permanent increase in dry mass.
Any two of: reproduction, sensitivity, growth (permanent increase in dry mass), or nutrition in the biological sense.
Common misconceptions
- Thinking movement means an animal walking — plants move too, growing towards light, just far more slowly than we notice.
- Confusing respiration with breathing. Breathing is the physical movement of air; respiration is the chemical release of energy inside cells, and happens in plants as well as animals.
- Assuming excretion and egestion are the same. Excretion removes waste made *by* the body's reactions; egestion passes out undigested food that never entered the cells.
In the exam
- If asked to define respiration, the mark is for "chemical reactions in cells that break down nutrient molecules to release energy" — never write "breathing".
- Growth must be described as a permanent increase in size **and dry mass** — a plant swelling with water has not grown.