Name _______________________
Lakeland High School
Date ________________________
Biology/Ms. Tsai
Internal vs. External Fertilization
Review
 What is fertilization?
The union of sperm and egg to form a zygote.
 How are sperm cells different from egg cells?
Sperm is smaller
Sperm can move
There are two types of fertilization – internal and external


inside
outside
 What do both types require? (Hint: think of how fertilization occurs?)
Both need a fluid environment
External Fertilization
Definition:
Fertilization outside the body
 What types of organisms use external fertilization?
Frogs and fish
--Happen in water
 What are some disadvantages of external fertilization?
 the eggs could get eaten
 the current could wash the eggs away
 the sperm might get lost
 What can these organisms do to make sure that at lease some eggs are fertilized?
Lay lots of eggs and have lots of sperm
External Development
Definition:
Development of the embryonic organism outside the body
 What problem does this create for the new organism?
Unprotected -- so can get eaten
open to weather conditions
Internal Fertilization
Definition:
Fertilization inside the body
 What types of organisms use internal fertilization?
Land animals
--humans, birds, bees, reptiles
 What are some of the advantages of this type of fertilization?
Protected
 How do you think the number of eggs produced in organisms that use internal
fertilization compare with the number of eggs produced in organisms that use
external fertilization?
Less eggs in internal
 Why?
Less chance of them being destroyed
Development after fertilization
After fertilization, either
1. The zygote is enclosed in a protective shell and released by the female
Example:
Birds
Snakes
OR
2. The zygote remains in the female’s body and develops (no shell is formed)
Example:
Mammals -- like us
Care of young
There are different degrees of parental care provided to the developing offspring
Examples:
Fish
-- no parental care
Bird
-- some parental care
Mammals
-- highest level parental care
 What do you think is the relationship between the amount of parental care
and the number of eggs produced?
* low parental care

large amount of eggs produced
* high parental care

low amount of eggs produced
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. What is the relationship between the amount of parental care and the survival of the
organism?