Name _______________________
Lakeland High School
Date ________________________
Biology/Mrs. Cropsey - Packet # 44
Internal vs. External Fertilization
 What is fertilization?
The union of sperm and egg cells to form a zygote
 How are sperm cells different from egg cells?
Sperm cells are smaller
Sperm cells can move – they swim with a flagellum
There are two types of fertilization – internal and external
Internal = inside the body
External = outside the body
Both types require a fluid environment-why?
So sperm can swim
External Fertilization
Definition:
Fertilization which occurs outside the body
 What types of organisms use external fertilization?
Water animals (such as fish)
 What are some disadvantages of external fertilization?
Eggs may wash away
Eggs can die / get eaten
Sperm may get lost
Sperm \ eggs may get swept away
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 What can these organisms do to make sure that at lease some eggs are fertilized?
Produce lots of eggs and lots of sperm, so at least some are fertilized.
Internal Fertilization
Definition:
Fertilization inside the body
 What types of organisms use internal fertilization?
Land animals – birds, reptiles, mammals
The fluid environment needed for the sperm to swim is
provided for by the female
 What is the advantage of this type of fertilization?
More protection
Note: There are fewer eggs produced by the female of a species that has internal
fertilization as compared to external fertilization, but both types require a large amount of
sperm to be produced by the male
 Why?
The eggs are protected so less chance of something happening to them,
but sperm can still get lost or die before they make their way to the egg.
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Development after fertilization
External Development
Definition: Development outside the body – usually in an egg
Examples: fish, birds, reptiles
 What problem does this create for the developing organism?
It is unprotected – open to effects of the weather, predators, etc.
Internal Development
The zygote remains in the female’s body and develops
(no shell is formed)
Examples: us, dogs, cats
Care of young
There are different degrees of parental care provided to the developing offspring
Examples:
Fish - no parental care
Birds- a little bit of parental care
Mammals-
a lot of parental care
 What do you think is the relationship between the amount of parental care
and the number of eggs produced?
The more care provided, the less eggs produced
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Summary Questions
1. Why do organisms in which external fertilization and external development
occurs produce large numbers of eggs?
2. Why wouldn’t external fertilization work on land?
3. In organisms that use internal fertilization, what are the 2 ways in which the
zygote can develop?
4. Describe the relationship between the amount of parental care and the survival of
the organism?
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