Diapositiva 1

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UNIT4
The reproduction function
EMBRYONIC DEVELOPMENT
Natural Science 2. Secondary Education
2
UNIT4
Embryonic development
EMBRYONICDEVELOPMENT
OVOVIVIPAROUS
OVIPAROUS
VIVIPAROUS
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Natural Science 2. Secondary Education
3
UNIT4
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
4
UNIT4
Embryonic development
The structure of the egg
Amnion this forms the amniotic sac, which holds
the amniotic fluid where the embryo floats.
Vitelline membrane this encloses the yolk, which
the embryo feeds on.
Embryo
Shell keeps the embryo from drying out but
allows O2 and CO2 to pass through.
Membranes they serve as the eggs excretory
system, collecting waste, and the respiratory
system, letting CO2 out and O2 in.
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Natural Science 2. Secondary Education
5
UNIT4
Embryonic development
Viviparous animals

• The embryos of these animals develop inside the
  mothers 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 mothers 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
6
UNIT4
Embryonic development
The embryo in viviparous animals
Amnion forms the amniotic sac, which holds the
amniotic fluid where the embryo floats.
Embryo
Umbilical cord connects the embryo to the
placenta.
Placenta extracts nutrients and oxygen for the
embryo from the mothers blood.
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Natural Science 2. Secondary Education
7
UNIT4
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.
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Natural Science 2. Secondary Education