Cells and organisation · Classify
Life processes and what living things are made of
A candle flame moves, grows, feeds and makes waste. So what stops it being alive?
Start here
Watch a candle for a minute
It moves. Feed the wick and it grows. It takes in oxygen and gives out carbon dioxide, water and soot. Open a door and it leans away. Touch a second wick to it and there are two flames.
Is a candle flame alive?
It is not alive — and the reason is not on that list of behaviours. A flame does nearly all of them. What settles it is what a flame is made of.
Biologists describe living things by seven life processes. Their initials spell MRS GREN.
- Movement
- Respiration
- Sensitivity
- Growth
- Reproduction
- Excretion
- Nutrition
Your turn · test four things
Run the seven tests
Pick a specimen. Say what you think first. Then work through the seven tests and see how far they get you.
Candle flame
A wick, some wax and a supply of air.
Before you test it — alive, or not alive?
Tap each test to run it.
0 of 7 lit
Six of seven — and still not alive.
Only respiration fails, and even that one is a near miss: a flame really does take in oxygen and give out carbon dioxide. Counting behaviours cannot settle this.
Oak seed
An acorn in a drawer. It has been there four years.
Before you test it — alive, or not alive?
Tap each test to run it.
0 of 7 lit
Three of seven — and it is alive.
The seven are things an organism can do across its life, not a checklist for this second. A sleeping seed scores badly and is still alive.
Robot vacuum
Bumps around the kitchen, finds its charger, empties into a bin.
Before you test it — alive, or not alive?
Tap each test to run it.
0 of 7 lit
Two of seven — not alive.
It is better than a flame at looking alive and worse at scoring. Behaviour is a poor test in both directions.
Yeast in dough
A spoonful of dried yeast, warm water, flour and sugar.
Before you test it — alive, or not alive?
Tap each test to run it.
0 of 7 lit
Seven of seven — alive.
And every one of those jobs is done by a single cell. One cell is a whole organism here.
Key fact
The seven processes describe what living things do. They do not decide whether something is alive.
Think again
“If it moves and grows, it must be alive.”
The flame lit six lamps. The seed lit three. One of them is alive and it is not the one with the higher score.
6 of 7
Candle flame — not alive
Doing the behaviours is not the same as being alive.
3 of 7
Oak seed — alive
The seven are things it can do across its life, not a checklist for this second.
What settles it
Every living thing is made of cells.
A candle flame
Hot glowing gas. No cells, so not alive — whatever it does.
An acorn
Cells, packed with a food store and ticking over slowly.
You
Around thirty trillion cells, all working at once.
One cell is enough — yeast manages on one. You are somewhere near thirty trillion. A flame has none, so however it behaves, it never joins the club.
Your turn · sort all eight
Living, once living, never living
Three boxes, not two. Something can be made of cells that stopped working a long time ago.
- Moss on a wall
Living — Green, growing, made of cells that are working right now.
- Yeast in bread dough
Living — Single cells, feeding on sugar and budding into new ones.
- A woodlouse under a stone
Living — Moves, feeds, breeds — and it is built from cells.
- A wooden spoon
Once living — Wood is the leftover walls of tree cells. The cells themselves died when the tree was cut.
- A leather boot
Once living — Skin is a tissue. Tanning preserves it long after the animal has gone.
- A lump of coal
Once living — Squashed plants from around three hundred million years ago. No cells left, but it was part of living things.
- A granite pebble
Never living — Crystals that grew from cooling molten rock. No cells were ever involved.
- A candle flame
Never living — Hot glowing gas doing six of the seven processes and made of no cells at all.
Now the answers are showing — how many of your eight matched?
Nobody marks this but you. The ones that did not match are the ones worth reading again.
Mastery ladder
Not started yet.
Rungs 3 and 4 you mark yourself.
Rung 1 · Recall
Which one of these is true of every living thing, with no exceptions?
Rung 2 · The one that catches people
A robot vacuum crosses the floor on its own, senses the stairs and drives to its charger when the battery is low. Which statement is right?
Rung 3 · Explain
A candle flame moves, grows, gives out waste gases, and can start a second flame. Explain why a scientist still says it is not alive.
Rung 4 · Take it somewhere new
A probe on Mars finds orange crust that spreads across rock, takes in one gas and gives out another. Write the one test you would run to settle whether it is alive, and say what result would mean “alive”.
Key note
The seven life processes — MRS GREN — describe what living things do. Being made of one or more cells is what makes a thing living.
Going further
A virus is not made of cells, and on its own it does none of the seven — it cannot even copy itself without getting inside a cell. So most biologists do not count viruses as living. A few argue the line is in the wrong place, and that argument is still open.
Before this lesson
- Nothing — this is where the unit starts.
Connects to
At GCSE this becomes
- Cell theory, and the argument over where the line around “living” belongs.
Where to next
Stuck on why a flame isn’t alive?
Never light a candle to test this at home without an adult with you.
Lesson content © MrBadmusAI.