Life cycles
Every living thing changes as it goes through its life from birth to death.
Some living things might not change very much; they may just become bigger versions of the baby animal.
In some animals, the adult will look completely different from the baby animal, which is known as metamorphosis.
The different changes that a living thing goes through from birth to its death is called a life cycle.
Watch: What are life cycles?
A life cycle is usually split into different stages and these stages are different depending on the species of animal.
Some animals will also have more stages in their life cycle that others, depending on how much more the animal changes between the start of its life and the end.
Learn about different life cycles.
NARRATOR: All animals are born… grow bigger… and older… and most go on have babies of their own.
This is what's called the life cycle.
All animals change during their life cycle…
But at different speeds.
Some of us don't change that much
We just get bigger and change our shape a bit
While some animals change completely as they grow up.
Compared to many animals the human life cycle is very slow.
We all grow old and die, but the life cycle never stops.
Fascinating facts
All animals and plants have a life cycle.
The echidna and platypus are the only mammals that give birth to eggs, not live young.
The Virginia opossum only carries its young for 12 days, the shortest gestation (birthing) period in mammals.
An African elephant's gestation period can last up to 22 months.
Ostriches lay the largest egg of any bird; it's the size of around 24 chicken eggs.
Baby fish are called a fry.
In an ant colony, the sole purpose of the queen is for reproduction; she is the only ant in the colony that lays eggs.
Stages in a life cycle
In some animals, each stage of a life cycle can be just a few days.
For some such as humans, each stage can take much, much longer.
No matter what type of animal it is, it will go through the same four events during its life cycle.
Birth
Animals grow and develop from an egg cell to an animal that is able to survive in the outside world.
In some creatures such as birds, amphibians and most reptiles, the parent lays an egg in which the baby grows and develops until it is ready to hatch. These are known as oviparous animals.
In other animals, called viviparous animals, the baby grows and develops inside the parent until the parent gives birth and the baby animal is born.
Growth
Between being born and becoming an adult the animal grows and changes.
The adult animal might become larger versions of the baby animal or they may change into an adult animal that looks completely different.
The time that it takes each species of animals to reach adulthood varies. Some animals like moths, butterflies and most type of fish leave their parents and need to look after themselves soon after birth.
Others such as humans need to stay with their parents for many years as they are unable to fend for themselves independently.
Reproduction
Once an animal has reached adulthood it is able to reproduce and make new offspring.
Death
When an adult animal nears the end of its life, parts of its body begin to weaken and it is also less able to fight off illnesses. This will lead to the animal dying, either because it is not able to avoid predators any more or because its body will stop working completely.
Slideshow: The life cycle of a butterfly
Image caption, Eggs
A European peacock butterfly's life cycle begins when an adult female butterfly lays eggs underneath a leaf.
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Did you know?
Mayflies are thought to have one of the shortest life cycles of an animal. They hatch from an egg into a nymph which may live underwater for up to two years.
Then, they come to the surface of the water, shed their skin to become a 'dun' before quickly shedding their skin again to be a 'spinner' - an adult mayfly.
The adult mayfly only lives for one or two days at the most during which time the females lay eggs to create the next generation of mayflies.
Life cycles of different animals
Mammals
Almost all mammals are viviparous which means that they give birth to live young (the only known mammals that lay eggs are the platypus and the echidna).
The babies grow and change into larger versions of the baby animal, and don’t undergo metamorphosis.
Amphibians
Most amphibians are oviparous which means that they lay eggs from which their babies hatch. Most amphibians, such as toads and frogs, undergo metamorphosis during their life cycle but there are some, like an axolotl, that don’t.
An amphibian often goes through large changes during its life cycle, and develops from a creature that lives in water to a creature that is able to survive on land.
Insects
Most insects undergo metamorphosis, but there are some that don’t. Most insect babies are called a larvae, which hatch out of an egg.
Larvae look very different to the adult that it will grow into (they sometimes look like little worm type creatures, like a caterpillar or a maggot) and these go through a pupal stage (a chrysalis for butterflies) where they become an adult.
In some insects, like crickets and cockroaches, the baby that hatches out of the egg is called a nymph, and looks much more like the adult, just smaller!
Birds
A bird life cycle always has an egg stage as birds are oviparous. They don’t go through metamorphosis; a baby bird looks just like a mini version of the adult bird, although sometimes they can have different colour feathers (or no feathers at all when they first hatch!).
Slideshow: The life cycle of a frog
Image caption, Frogspawn
Frogspawn are the eggs of a frog. They are the first stage of a frog's life cycle.
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Did you know?
In most animals it is the female parent that gives birth or lays the eggs that will hatch into their offspring.
The only known example of the male parent giving birth is in seahorses.
The male seahorse can give birth to up to 2000 baby seahorses at a time!
Watch: Different life cycles
Learn about different life cycles.
NARRATOR: Hey. You.
Excuse me. Could I…
Well, never mind, they're busy, they're all getting on with the business of life.
From starting off small, to growing up to producing the next generation all living things have a life cycle and each stage is as important as the last.
For these arctic fox cubs life is all play at the moment.
But there is a serious side to the fun and games, they are learning the skills they will need to survive as adults like hunting and chasing.
When the fox cub grows into an adult it will need to catch its own food and be able to survive the harsh conditions where it lives.
Only then will it have the chance to reproduce to make the next generation of arctic foxes.
To complete the arctic fox's life cycle.
Life cycles are as varied and diverse as life on Earth.
Whether it's a mammal, like the arctic fox or a bird, or a plant or an insect different groups of organisms all have different kinds of life cycles.
These are the seeds of the Alsomitra vine, a type of climbing plant.
The plants start life as these amazing gliding seeds.
Their incredible gliding shape helps distribute new plants all around the forest.
The seed germinates and a new vine begins to grow up towards the light.
When the vine's flower is pollinated by insects or other animals seeds will grow and the next generation is started.
The life cycle starts again.
One of the most amazing life cycles in nature can happen in your own back garden or local pond.
These are tadpoles. They've hatched from these small jelly covered eggs.
They don't look like much perhaps you might think they are small fish but they are about to go through an amazing transformation.
And turn into one of these.
Frogs and toads are amphibians and
they have an incredible life cycle.
Their remarkable transformation happens through a process we call metamorphosis.
The tadpole grows a spine, it grows legs, it loses its gills for breathing in water and grows lungs that can breathe air instead.
It even changes its digestive system to allow it to eat worms and insects.
The tadpole seems to change into a completely different creature.
But these adult frogs will start the next generation. The females will lay eggs and the hatching tadpoles will go through the same remarkable metamorphosis.
A transformation, that, if you're lucky you might be able to see happening in your own back garden or local park.
Amphibians are not the only animals that go through metamorphosis.
From the moment they emerge from their eggs caterpillars are eating machines.
They need to put on as much weight as possible, as quickly as possible. So they eat and eat and eat.
If this caterpillar was a human baby within a month it would be the size of a bus! Which is one big baby.
But all this eating is for a very good reason. Caterpillars need to store up a lot of energy as they will soon go through a remarkable transformation.
Like a tadpole, they will go through a metamorphosis and emerge as a completely different looking creature.
The adult butterfly will look for a mate the females will lay eggs and a new generation of hungry caterpillars will be born starting the life cycle all over again.
These eggs have been laid by the female osprey.
Ospreys are found all over the world but in the UK these osprey chicks, are very rare.
Like almost all birds, learning to fly is a big step in their life. Some get it quicker than others.
As adults, these magnificent birds of prey specialise in hunting fish.
They catch fish to survive, but when they reproduce and start the next generation they also need to catch fish to feed their young.
The growing they did as chicks and the skills they developed as young adults help them to survive and eventually produce the next generation of ospreys to start the life cycle again.
This mammal probably looks very familiar to you.
Like every other living thing in nature, we humans have a life cycle too.
We start out small, we grow and we learn new skills which we can use to look after ourselves as adults.
Just like other living creatures. And we reproduce the next generation. So the life cycle can start all over again.
So although it happens in an amazing amount of different ways from your back garden, to the local park to the farthest corners of the world we can see that all living things have a life cycle.
Life starts off small it grows into an adult and it produces the next generation so the whole process can start all over again.
I'm glad you agree.
Did you know?
There are over 390,000 different species of plants on our planet but that is only the ones which have been found and identified.
There could be many more that just haven't been discovered yet.
Important words
Birth – Birth is when a new baby or animal, enters the world. This can be from an egg, or by live birth.
Death – The end of an animal’s life.
Gestation – The time between the animal being reproduced and being born.
Growth – Animals might grow to become larger versions of the baby animal, or they may change into an adult animal that looks completely different.
Life cycle – The different changes that a living thing goes through from birth to its death.
Metamorphosis – A process which some animals, like butterflies, go through where the adult will look completely different from the baby animal.
Oviparous – Animals that lay eggs, in which their babies grow and develop until ready to hatch.
Reproduction – The process an animals uses to create its offspring.
Viviparous – Animals that have their young grow and develop inside the parent, until the parent gives birth and the baby animal is born.
Activities
Activity 1 – A frog's life cycle
Most amphibians go through metamorphosis during their lifetime. Here's an example of a frog's life cycle.
Activity 2 – Order the life cycle
Activity 3 – Quiz
Activity 4 – Fill in the blanks
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