Topics · Primary Science · Cycles: Life Cycles
Life cycles: the stages living things pass through
Every living thing goes through stages from birth to being able to reproduce. Which stages, and in what order, is what gets tested — and the biggest split is between animals that change completely and animals that do not.
- 311 exam papers analysed
- appears in 72% of P4 Science papers
- ~3 min read
01 Complete change: four stages
Butterflies, moths, beetles, flies, bees and mosquitoes go through four stages, and the young looks nothing like the adult.
The pupa stage is the giveaway. If a cycle has a pupa, it is complete change.
02 Incomplete change: three stages
Cockroaches, grasshoppers, crickets and dragonflies go through three stages. There is no pupa, and the young — the nymph — already looks like a small adult without wings.
It grows by shedding its skin several times until it is full size and winged.
03 Telling them apart in a question
Papers show an unnamed cycle and ask which kind it is, or which animal it could be. Two checks settle it.
| Animal | Stages | Pupa? | Young resembles adult? |
|---|---|---|---|
| Butterfly | 4 | ✓ | ✗ |
| Beetle | 4 | ✓ | ✗ |
| Cockroach | 3 | ✗ | ✓ |
| Grasshopper | 3 | ✗ | ✓ |
- Count the stages. Four means complete change; three means incomplete.
- Look for a pupa. Only complete change has one.
- Look at the young. In complete change it looks nothing like the adult; in incomplete change it looks like a small wingless version.
- Watch what the young eats. A caterpillar and a butterfly eat different things, so they do not compete — a common “why is this an advantage” question.
04 Other life cycles
Frogs go egg → tadpole → young frog → adult frog, changing from gills to lungs as they move from water to land.
Chickens and other birds go egg → chick → adult, with no dramatic change of form.
Humans and most mammals are born live rather than hatching, and grow through baby, child, adolescent and adult.
Plants run seed → seedling → young plant → adult plant that flowers and makes seeds, closing the cycle.
Whatever the organism, the cycle closes: the adult produces the stage it started from, which is why it is drawn as a ring rather than a line.
05 How to say them
These are words most children have never said out loud, and a word you cannot say is a word you avoid using. Capitals mark the syllable you lean on. Tap the speaker to hear it.
- life cyclemore than onelife cycles
The stages a living thing passes through from birth to being able to reproduce.
- larvasayLAR-vuhmore than onelarvae
The young stage in complete change, looking nothing like the adult. A caterpillar is a larva.
- pupasayPYOO-puhmore than onepupae
The resting stage in complete change, where the larva becomes an adult. Only complete change has one.
- nymphsaynimfmore than onenymphs
The young stage in incomplete change, resembling a small wingless adult.
- adultmore than oneadults
The fully grown stage, the one able to reproduce.
- reproducesayree-pruh-DYOOSS
To produce young, which closes the cycle.
06 What each level is tested on
The same topic, asked differently as it goes up. The percentage is the share of papers at that level in which it appears.
- P3
The stages of familiar life cycles, and the idea that the cycle repeats.
Practise P3 Cycles: Life Cycles — 9 questions →32% of P3 papers
- P4
Complete and incomplete change in insects, and the life cycles of frogs and chickens.
Practise P4 Cycles: Life Cycles — 10 questions →72% of P4 papers
- P5
Comparing cycles, and the advantages of each kind of change.
Practise P5 Cycles: Life Cycles — 9 questions →38% of P5 papers
- P6
Life cycles inside longer questions, and links to reproduction and the environment.
Practise P6 Cycles: Life Cycles — 8 questions →67% of P6 papers
07 Mistakes worth knowing about
Each of these is wrong. Decide why before you open it.
“All insects have four stages.”
Cockroaches, grasshoppers and dragonflies have three. The presence of a pupa is what separates the two groups.
“A nymph is the same as a larva.”
A nymph looks like a small adult and becomes one without a pupa. A larva looks completely different and must pupate first.
“A tadpole is a larva, so a frog has four stages.”
A frog's cycle is egg, tadpole, young frog, adult — and there is no pupa. Complete change is an insect term.
“The caterpillar and the butterfly compete for food.”
They eat different things, which is one of the advantages of complete change.
“The cycle ends at the adult.”
The adult reproduces, which returns it to the first stage. That is why it is a cycle.
Now try it
36 questions across 4 levels, marked as you go with the working shown.