Science
What is a life cycle?
Quick answer
A life cycle is the series of changes a living thing goes through from the start of its life to becoming an adult that can produce young, so the cycle begins again.
In one sentence
A life cycle is all the stages a living thing passes through as it is born, grows up and makes young of its own, so that the pattern starts again.
Explained
Every living thing grows and changes. When it becomes an adult it can reproduce, and its young go through the same stages. Because the end leads back to the beginning, scientists draw it as a circle.
Different living things have very different life cycles:
Mammals such as humans, dogs and elephants usually give birth to live young that look like small versions of their parents. The babies drink milk, grow, and eventually become adults.
Birds lay eggs with hard shells. The chick grows inside, hatches, and is cared for until it can fly and find food.
Amphibians such as frogs have a dramatic change called metamorphosis. They start as eggs (frogspawn) in water, hatch as tadpoles with tails and gills, grow back legs and then front legs, lose their tails and become froglets, and finally adult frogs that can live on land.
Many insects, including butterflies, change completely too: egg → caterpillar (larva) → chrysalis (pupa) → adult butterfly. Inside the chrysalis, the caterpillar's body is broken down and rebuilt, a bit like taking apart a toy-brick car and building an aeroplane from the same bricks.
Flowering plants go from seed to seedling to adult plant. The flowers are pollinated, make new seeds, and the seeds are spread by wind, water or animals.
Examples
| Living thing | Stages |
|---|---|
| Human | baby → child → teenager → adult |
| Chicken | egg → chick → adult hen or rooster |
| Frog | frogspawn → tadpole → froglet → frog |
| Butterfly | egg → caterpillar → chrysalis → butterfly |
| Sunflower | seed → seedling → flowering plant → seeds |
egg
hen
frog
butterfly
Common mistakes
- "A caterpillar grows wings inside its cocoon." Butterflies form a chrysalis; cocoons are silk cases made by moths. And the body is rebuilt, not just given wings.
- "All mammals give birth to live babies." The platypus and echidnas lay eggs.
- "Tadpoles are baby fish." They are young frogs or toads, which are amphibians.
Quick quiz
Life cycles
Check what you know with 4 quick questions.
Question 1 of 4
What is the correct order of a butterfly's life cycle?
Practise it
Try it
Draw a life-cycle wheel for an animal of your choice, then see how flowering plants make seeds in parts of a plant.
Print science activities for kids
For grown-ups
Related topics
Living things
Living things are organisms that grow, feed, get rid of waste, sense the world and reproduce. Plants, animals, fungi and bacteria are all alive.
Parts of a plant
The main parts of a flowering plant are the roots, stem, leaves and flowers. Each part has a job, from soaking up water to making food and producing seeds.
Evolution
Evolution is the way living things change over many generations. Individuals with features that help them survive tend to have more young, so those features become more common over time.
Habitats
A habitat is the natural home of a living thing, where it finds the food, water, shelter and space it needs to survive.
Electric circuits
An electric circuit is a complete loop that electricity flows around. A simple circuit has a battery, wires and a component like a bulb. If the loop is broken, the electricity stops.
Digestive system
The digestive system is the long tube and organs that break food down into tiny pieces your body can absorb for energy and growth, then get rid of what is left as waste.