Growing up: life cycles
Biology · Key Stage 1 · The School
How humans grow
Humans start as a baby. Then they become a toddler. Then a child. Then a teenager. Then an adult. Later, an older adult. Each stage looks a little different. This is called a life cycle. Growing up takes many years to finish.
A chicken's life cycle
A chicken starts as an egg. Inside, a chick grows. The chick hatches out. It grows into a young chicken. Then it becomes an adult hen or rooster. Egg, chick, adult — three main stages. Chickens take a few weeks to hatch.
A frog changes shape completely
A frog starts as an egg in water. It hatches into a tadpole. The tadpole has a tail and no legs. Slowly, legs grow. The tail shrinks away. It becomes a frog. This big change is called metamorphosis.
Same idea, different journeys
Humans grow bigger but keep the same basic shape. Frogs change shape completely on the way. Chickens hatch from an egg, like frogs, but keep a similar shape while growing. Every life cycle has stages. The stages are not always the same.
Let us follow one case. Suppose a farm gets eggs that can hatch. The farmer wants chicks on a Friday. A chicken egg takes about 21 days to hatch. So when must the farmer start? Count back 7 days. That is a Friday. Count back 7 more days. That is a Friday again. Count back 7 more days. That is a Friday once more. 7 and 7 and 7 make 21. So 21 days is 3 weeks. The farmer puts the eggs in an incubator on that Friday, 3 weeks before. An incubator is a warm box that keeps eggs warm. The eggs stay in it for 21 days. Then the chicks hatch, close to the Friday the farmer wanted. The life cycle has moved from egg to chick.