1. Unit 3 Lesson 4 How Do Animals Reproduce?
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2. Unit 3 Lesson 4 How Do Animals Reproduce?
Life in Full Circle
Like plants, animals have life cycles. Most animals reproduce sexually.
During sexual reproduction, sperm from a male joins an egg from a female.
The fertilized egg can then develop into a new animal.
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3. Unit 3 Lesson 4 How Do Animals Reproduce?
Life in Full Circle
In some animals, such as many kinds of fish, eggs are fertilized outside the female’s body.
In other animals, such as birds, eggs are fertilized inside the female’s body.
After the eggs are fertilized, birds lay the eggs.
Bird parents protect the eggs until they have hatched.
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4. Life in Full Circle After the young are born, they grow and change.
Unit 3 Lesson 4 How Do Animals Reproduce?
Life in Full Circle
After the young are born, they grow and change.
Over time, newborns develop into youths. Youths continue to develop until they grow into adults.
Adult animals made with one another to produce offspring.
An animal’s life cycle ends when the animal dies.
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5. Unit 3 Lesson 4 How Do Animals Reproduce?
Bringing Up Baby
Some animals, such as turtles, are on their own as soon as they hatch from their eggs.
Other animals, such as penguins, give their young a great deal of care.
Penguins keep their young warm and fed until they are strong enough to take care of themselves.
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6. Unit 3 Lesson 4 How Do Animals Reproduce?
Bringing Up Baby
Animals such as deer, bears, rabbits, cats, and kangaroos take care of their young by feeding them milk.
These animals care for their young for months or years until the young can live on their own.
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7. Unit 3 Lesson 4 How Do Animals Reproduce?
Growing Up
Just like other animals, humans go through stages of development. It takes many years for a human baby to grow into an adult.
After a human egg is fertilized, it grows inside the mother. After nine months, the baby is born.
When babies are born, they have no teeth. They are not able to walk on their own.
Babies grow into toddlers. Toddlers learn how to walk and how to speak.
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8. Unit 3 Lesson 4 How Do Animals Reproduce?
Growing Up
As a child grows, they develop many physical and mental skills.
During the teenage years, boys and girls start looking more like adults.
During adulthood, people reach maturity.
As an adult ages, they lose some of their physical abilities.
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9. Unit 3 Lesson 4 How Do Animals Reproduce?
My, How You’ve Changed!
In complete metamorphosis, an animal goes through four different stages in its life cycle.
An egg hatches into a larva.
A larva develops into a pupa.
A pupa develops into an adult.
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10. Unit 3 Lesson 4 How Do Animals Reproduce?
My, How You’ve Changed!
A butterfly goes through complete metamorphosis.
The larva of a butterlfy is called a caterpillar.
The caterpillar grows into a pupa.
Inside a chrysalis, the pupa becomes an adult butterfly.
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11. Unit 3 Lesson 4 How Do Animals Reproduce?
My, How You’ve Changed!
What are the stages in a butterfly’s life cycle?
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12. Unit 3 Lesson 4 How Do Animals Reproduce?
My, How You’ve Changed!
Some insects, such as dragonfiles and termites, go through a different series of changes.
In incomplete metamorphosis, an animal goes through three different stages in its life cycle.
First, the animal hatches from an egg as a nymph.
Nymphs look like tiny adults without wings.
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13. My, How You’ve Changed! As the nymph grows larger, it molts.
Unit 3 Lesson 4 How Do Animals Reproduce?
My, How You’ve Changed!
As the nymph grows larger, it molts.
Molting happens when an insect sheds its hard outer skeleton.
After several moltings, the insect, which now has wings, reaches its adult stage.
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14. Unit 3 Lesson 4 How Do Animals Reproduce?
My, How You’ve Changed!
What are the stages in the life cycle of a grasshopper?
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15. Unit 3 Lesson 4 How Do Animals Reproduce?
Saving the Sea Turtles
Some kinds of animals, such as sea turtles, are endangered. There are not many of them left.
Scientists study the life cycles of these endangered animals to try to save them and help them increase their numbers.
To rear sea turtles, scientists collect the eggs.
When the eggs hatch, the young turtles are cared for until they can be released into the wild.
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