All animals pass through different stages of life
as they grow into fully developed adults. The first
stage is the start of a new life, and for most animals
the final phase is when they breed to start the
cycle over again. For some animals, such as most
mammals, these stages are very similar. For others,
such as many insects, every stage is quite different,
and involves a complete transformation, or
metamorphosis, from the previous stage.Life cycles
3 Wriggling out of the
jelly into the water, the
tadpole uses a sticky fluid
to cling to an aquatic plant.(^2) An embryo develops
inside the egg and
starts to move, using
energy supplied by the
yolk of the egg.
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DOG ▶
A dog’s life cycle is typical of
many mammals, because it starts life as
a smaller version of its parents. As it
grows bigger, its internal organs
develop so it can eat an adult diet, and
eventually produce its own young.
(^4)
solid food provided by its The older puppy can eat
mother, and begins to learn
vital skills through play.
◀ FROG
Most amphibians, such as frogs, have
complex life cycles. A typical frog lays
eggs in water, and these hatch out as
fish-like tadpoles. The tadpoles develop
lungs and legs, and hop out of the
water as tiny froglets, eventually
becoming fully grown adult frogs.
(^5) Lungs develop, the
tail shrinks, and the new
froglet hops out of the
water to live on land, where
it hunts small animals.
(^4)
it develops back legs, then front As the tadpole grows older,
legs, and its body starts to look
like that of a frog.
(^1)
containing hundreds of eggs An adult frog lays frogspawn
protected by jelly, which swells
up in the water.
6 The fully grown dog now
looks to find a mate to produce
puppies of its own.
(^2) For the first two
weeks, the puppy
cannot see the
world around it.
(^1)
puppy cannot eat solid food, so it Blind and helpless, a newborn
lives on its mother’s milk.
3 After about two weeks,
the puppy can see, but its
digestive system can still
only cope with milk.
(^5) Though
not able to
breed just yet,
this young
dog can find
its own food.
Tail shrinks to a
stump as the froglet
learns to use its legs
to swim and hop
Young tadpole has
three pairs of feathery
gills, which absorb vital
oxygen from the water
6 Living mainly on land, the
adult frog will return to the
water in spring to find a mate
and either lay or fertilize eggs.
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