Different living things have different life cycles. Some are short (a fruit fly lives about 30 days) and some are long (a tortoise can live over 100 years). Some involve metamorphosis and some do not. Some animals lay eggs and some give birth to live young. But all life cycles share the same basic stages: begin, grow, reproduce, and begin again.
Create life cycle diagrams for a butterfly, a chicken, a dog, a frog, and a sunflower. Line them up and discuss: What is the same? What is different? How long does each one take? Does the baby look like the adult?
Now that you know what life cycles are, let's compare some to see how different living things do things differently — and what they all have in common.
Speed varies enormously. A fruit fly goes from egg to adult in just about two weeks, and lives only about a month. A chicken hatches from an egg in 21 days and starts laying eggs of its own within 5-6 months. A dog is born live, grows up over about 1-2 years, and might live 10-15 years. A human takes about 18 years to grow up and can live 80 years or more. A giant tortoise can live over 150 years! The basic stages are the same, but the speed is completely different.
How life begins is another big difference. Some animals hatch from eggs — birds, reptiles, fish, amphibians, and insects all start as eggs. Others are born live from their mother — most mammals, including humans, dogs, and whales. Plants begin as seeds. Each method works for the organism that uses it.
Body changes during growth also vary. Some animals look like miniature adults when they are born — a puppy looks like a small dog, a baby horse looks like a little horse. Others go through metamorphosis and look completely different at each stage — a caterpillar looks nothing like the butterfly it will become, and a tadpole looks nothing like a frog.
Number of offspring is another striking difference. A mother elephant has one baby at a time and spends years raising it. A mother sea turtle lays about 100 eggs at once and leaves them to survive on their own. A cod fish can release millions of eggs. Generally, the more care a parent gives, the fewer offspring it has; the less care it gives, the more offspring it needs to make sure some survive. Despite all these differences, every life cycle follows the same circle: begin, grow, reproduce, begin again.