Animal life cycles
Describe differences in the life cycles of mammals, amphibians, insects, and birds, comparing metamorphosis with direct development
What a learner can do afterwards
- Describe the life cycle of a mammal, amphibian, insect, and bird with key stages for each
- Compare metamorphosis, including complete and incomplete metamorphosis, with direct development using named animals
- Identify development patterns in named animals and explain why resemblance to an adult alone does not identify an animal's group
1 · Read
You have followed living things through life-cycle stages. Young animals grow into adults, and some adults reproduce. Not every individual has young. In direct development, the young already have the adult's basic body form. Their bodies still mature as they grow. Metamorphosis changes body form between young and adult stages. A puppy grows without metamorphosis, so growing bigger alone does not show metamorphosis.
A dog gives birth to puppies. A puppy already has a dog's basic body form and grows into an adult dog, which may later reproduce. A chicken develops inside an egg, hatches as a chick and grows into an adult chicken. Adult chickens may reproduce and produce more eggs. Dogs and chickens have direct development: their young have the adult's basic body form, though their bodies still mature. Neither has a caterpillar or pupa stage.
A butterfly has complete metamorphosis: egg, caterpillar, chrysalis, adult butterfly. The caterpillar is its larva. The chrysalis is its pupa stage. Development continues inside the pupa before the adult emerges. This is not a sleeping or dead animal. The adult butterfly may reproduce, starting another generation.
In this pond-frog example, eggs hatch into tadpoles with tails and gills. As the tadpoles develop, legs grow and tails shrink. A froglet still has some tail; an adult frog has none. These changes are metamorphosis. There is no chrysalis stage. The adult may later reproduce and produce another generation.
A grasshopper has incomplete metamorphosis: egg, nymph, adult. The nymph resembles a small adult and grows by shedding its outer covering, called moulting. It has no pupa stage. A butterfly has complete metamorphosis: egg, caterpillar, chrysalis, adult butterfly. Its chrysalis is a pupa. Both animals have metamorphosis, but their stages differ. A pupa is not required for every kind of metamorphosis.
Compare the named examples before making a rule. Dogs and chickens have direct development. Butterflies and the pond frogs described here have metamorphosis. Birds and mammals have direct development, but some amphibians also hatch looking like small adults. Grasshopper nymphs resemble adults too. Resemblance alone cannot identify an animal's group.
Compare each animal's stages. Dogs and chickens have direct development. Butterflies, grasshoppers and the pond frogs described here have different patterns of metamorphosis.
The animal life-cycle lesson, questions and flashcards were written for this dataset.
The two animal life-cycle readings were written for this dataset.
More to read
Follow the changes in a pond frog
A record of the pond-frog example begins with eggs, then tadpoles. The tadpoles swim with tails and breathe through gills. Later entries show growing legs and shrinking tails. A froglet still has some tail. The adult frog has none.
These changes are metamorphosis. The animal is developing a different body form, not just becoming larger. There is no chrysalis in this sequence. A tadpole is an active young animal, not a resting stage.
Amphibians have varied life cycles. Some hatch looking like small adults. When you compare animals, say which example you mean instead of treating one frog sequence as a rule for every amphibian.
An egg does not tell the whole life cycle
Chicks, butterfly caterpillars and grasshopper nymphs all hatch from eggs. That shared beginning does not mean they develop in the same way.
The chick grows into an adult chicken through direct development. Its basic body form is already present, though its body still needs to mature.
The caterpillar later becomes a chrysalis, then an adult butterfly. This is complete metamorphosis. The grasshopper nymph grows through moults and becomes an adult without a pupa. This is incomplete metamorphosis.
Compare the stages after hatching. A pupa distinguishes the two insect patterns here. Hatching from an egg alone does not distinguish them.
2 · Watch
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