What makes something alive: MRS GREN
Biology · Key Stage 2 · The School
A test for being alive
How do you know if something is truly alive, and not just moving, like a toy car? Scientists use a simple test. Something is alive only if it does ALL seven life processes. A helpful way to remember them is the phrase MRS GREN. Each letter of that phrase stands for one process. Learning the phrase makes the seven processes far easier to recall later.
The first letters: M R S
M is for MOVEMENT — living things can move, at least some part of themselves. R is for RESPIRATION — releasing energy from food. S is for SENSITIVITY — reacting to things around them, like light or touch. Even a plant shows sensitivity, by slowly turning towards sunlight.
The rest: G R E N
G is for GROWTH — getting bigger over time. R is for REPRODUCTION — making more of their own kind. E is for EXCRETION — getting rid of waste. N is for NUTRITION — taking in food or making their own. Together, the seven letters cover everything a living thing must do. Miss even one, and something is not truly alive.
A toy car can move. That is one tick. But can it respire, releasing energy from food? No — it runs on a battery, not food. Can it sense its surroundings and react on its own? No. Can it grow, reproduce, excrete waste, or take in nutrition? No, to every single one. A toy car passes only one of the seven tests. That is nowhere near enough. A toy car is not alive, and MRS GREN shows exactly why, one letter at a time.