AIM: How Is Internal Fertilization and
Development Different from External
Fertilization and Development
Sexual Reproduction:
23
Sperm
+
23
Egg
Fertilization
46
Zygote
A fertilized egg cell is called a Zygote
Characteristics of Sexual Reproduction:
1) Is the creation of a new individual from 2
parents
2) Offspring are not genetically identical
to the parents
INTERNAL FERTILIZATION
• Eggs and sperm meet inside the female’s
body
• Occurs in most land vertebrates
• Ex. Reptiles, birds, mammals
EXTERNAL FERTILIZATION
• Eggs fertilized
outside
female’s body
• Occurs mostly in
aquatic
environments
–Ex. Fish,
amphibians
• HAZARDOUS –
many eggs and
sperm are
produced so some
survive
• Eggs and sperm
may not meet,
they may be eaten
or environmental
conditions may
change
Embryonic Development
An embryo is a developing offspring.
Development can be either
INTERNAL or EXTERNAL,
depending on the organism.
What is the difference between
internal and external
development?
What is the difference between
internal and external
fertilization?
INTERNAL DEVELOPMENT
• Embryo develops inside the female,
placenta provides nourishment
Human Fertilization
• Internal fertilization – male
penis is used to introduce
sperm into female’s vagina.
Where does fertilization
usually occur?
• Fertilization occurs
in the fallopian
tubes (oviduct)
How many eggs are released a month
by a female?
Normally one
egg is released
per month,
however,
sometimes
TWO can be
released at the
same time.
Ovulation
What happens after fertilization?
The embryo travels to the
uterus and implants itself in
the uterus lining