Life cycles — Biology, 7–10 years
Living things change in stages, from beginning to adult and sometimes back to a new beginning.
A life cycle has stages
A life cycle shows the usual stages a living thing passes through, such as birth, growing, becoming an adult and producing young. The stages can look very different: a butterfly begins as an egg, then becomes a caterpillar, pupa and adult.
Why notice the cycle?
People needed to know when animals would hatch, grow or reproduce, so they could care for them and understand changes in nature. Careful observations of eggs, young animals and adults revealed repeating patterns; the idea came from comparing these stages over time.
A frog’s cycle
Follow one frog: 1) an egg hatches into a tadpole; 2) the tadpole grows hind legs, then front legs; 3) its tail shrinks and lungs develop; 4) the young frog leaves the water. An adult frog can later lay eggs, beginning the cycle again.
Not every young animal looks small
It is reasonable to think that a baby animal is just a smaller version of its parent, because puppies and kittens look that way. But many young animals change form: a caterpillar does not look like a butterfly, and a tadpole does not look like a frog. Both still belong to the same life cycle.
Cycles around us
Gardeners use life cycles to know when to sow seeds and when insects may appear. Animal carers use them to provide the right food and space for eggs, young animals and adults. Watching a frog pond through spring can show several stages without disturbing the animals.
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