Think of a puppy, a kitten and a baby. When they are small and when they are grown up, they almost look the same. Their bodies just went through different stages and they got bigger.
The same with a plant - it started of as a small plant and then grows into an adult plant but still almost looks the same as what is did when it was small.
All living things (plants and animals) grow and go through different stages in their lives. This is called a life cycle, but not all animal look the same from when they were born to when they become adults.
Some animals like insects and frogs looks totally different from when they were born and some just undergo a few changes. These changes that take place from one stage to another (and make them look different) is called metamorphosis.
If you look at the life cycle of a frog it all start with a female frog lying eggs. From the egg a tadpole hatches that almost looks like a little fish (it looks nothing like an adult frog). Changes will start taking place and the tadpole will first start growing hind legs and then front legs and lungs will also develop.
Eventually the tadpole will turn into a frog which then will grow to become an adult frog and if it is a female, it will lie eggs and the whole process or life cycle will start again.
There is a huge difference between the tadpole and the frog and this is called complete metamorphosis (the baby and the adult looks different from one another and the life cycle consist of 4 stages - the egg, tadpole, small frog/froglet and adult frog.)
For more information on the life cycle of a frog you can read here.
Another animal that goes through complete metamorphosis is a butterfly or a moth. There are also 4 stages and it is called the egg, the larva, the pupa and the adult.
The butterfly or moth does not hatch from the egg but it is a larva coming out of the egg - this looks like a worm. This larva will eat and grow.
Insects have an exoskeleton which means it has a hard covering on the outside of the body which cannot stretch, so the larva will have to shed its skin. We say it molts.
If the larva has eaten and grown enough it will enter the next stage where it will rest and become a pupa. Inside of the pupa the butterfly or moth is forming with wings and antennae and after a certain time the adult butterfly or moth will emerge.
Have a look at the video on the life cycle of a butterfly.
Some insects looks almost the same as the adults when they hatch but will only undergo a small change. An example of this is the locust. The baby looks like the adult with one small difference - it does not have wings.
As the baby grows it will molt a few times and start growing wings until it is an adult. The stages in between each time it molts is called an instar.
This is called imcomplete metamorphosis and has 3 stages - the egg, the baby (which is called a nymph) and the adult.
Watch the video on the differences of a complete and incomplete metamorphosis.
For more information on metamorphosis you can read here.
Can you explain the following words in your own words (if you are not sure, read the piece again and find the meaning)
- life cycle
- complete metamorphosis
- incomplete metamorhosis
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