Download Embryonic development

UNIT
4
The reproduction function
EMBRYONIC DEVELOPMENT
Natural Science 2. Secondary Education
UNIT
4
Embryonic development
EMBRYONIC
DEVELOPMENT
There are three types, depending on
where it takes place
OVIPAROUS
VIVIPAROUS
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Natural Science 2. Secondary Education
OVOVIVIPAROUS
UNIT
4
Embryonic development
Oviparous animals
• These animals hatch from an egg which the mother lays in the
environment.
• The embryo feeds on the nutritive stores contained in the yolk of the egg.
• Once it has developed, it hatches, which is when the new individual
breaks the shell and emerges from the egg.
•There are two types of eggs:
• Eggs without a shell: these are found in aquatic animals and must
be laid in a wet environment or they will dry up.
• Eggs with a shell: they are laid on land so they do not dry up.
Toads are oviparous: they lay
their eggs in the water, as
their eggs do not have shells
and would dry up on land.
Natural Science 2. Secondary Education
UNIT
4
Embryonic development
The structure of the egg
Amnion: this forms
the amniotic sac,
which holds the
amniotic fluid where
the embryo floats.
Yolk
Vitelline membrane:
this encloses the
yolk, which the
embryo feeds on.
Embryo
Membranes: they
serve as the egg’s
excretory system,
collecting waste, and
the respiratory system,
letting CO2 out and O2
in.
Natural Science 2. Secondary Education
Shell: keeps the
embryo from drying
out but allows O2 and
CO2 to pass through.
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UNIT
4
Embryonic development
Viviparous animals
• The embryos of these animals develop inside the mother’s uterus.
• The embryo feeds on nutrients that pass from the mother through
the placenta.
• When the new individual has developed, it comes out of the
mother’s body: this is called birth.
• All mammals, with the exception of monotremes (the platypus and
the echidna) and some sharks, are viviparous.
Boars are
viviparous
animals.
Natural Science 2. Secondary Education
UNIT
4
Embryonic development
The embryo in viviparous animals
Embryo
Umbilical cord:
connects the
embryo to the
placenta.
Natural Science 2. Secondary Education
Amnion: forms the
amniotic sac, which
holds the amniotic
fluid where the
embryo floats.
Placenta: extracts
nutrients and oxygen
for the embryo from
the mother’s blood.
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UNIT
4
Embryonic development
Ovoviviparous animals
• These animals develop inside an egg, but the mother keeps
the egg inside her body until it hatches.
• The embryo feeds on the food reserves contained in the egg.
When the embryos are fully developed, hatching takes place,
just as it does in oviparous animals.
• The young are alive when they come out of the mother.
• Certain sharks, vipers and some insects are ovoviviparous.
Many sharks are
ovoviviparous.
Natural Science 2. Secondary Education
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