Embryo - Life Sciences 4 All

• Result of fertilisation is a diploid zygote (called egg)
• Three different reproductive strategies in vertebrates
which are based on the relationships between
zygote and parents / female (protection, nutrition
and development of embryo) are called ovipary,
ovovivipary and vivipary.
OVIPARY: The fertilised eggs develop and hatch
outside the mother's body.
• The female releases her fertilised eggs into the
environment (outside the body of female).
• The fertilised egg / zygote is enclosed by a protective shell.
• Egg yolk provides nutrition for the embryo.
• Fertilisation can be internal or external
OVIPARY in aquatic conditions
• Most fish, amphibians and lower aquatic
• Needs large numbers of eggs.
• Larval stage self-sufficient; don’t compete
with parents – use different food sources.
• External fertilisation.
• Fertilised eggs and larvae easily dispersed by
sea currents.
OVIPARY in terrestrial (land) environments –
maximising reproduction
• Protective shell (leathery shell in case of reptiles)
prevents embryo from drying out. Shell of embryo of
birds is hard and brittle (breaks easily).
• Fewer eggs in e.g. birds and reptiles – energy can be
used for more food in large egg (yolk and albumin),
hatching and protection, parental care.
• Female reptile makes a hole in soil to lay her eggs in it.
The sun incubates them. Birds: Parent(s) sit on the eggs
to keep them warm. Birds feed young one’s.
• Young reptiles are very vulnerable to predators.
• Development of amnion important factor in success.
See the amniotic egg.
Hard shell good protection for developing embryo;
prevents embryo from drying out.
OVOVIVIPARY refers to the development of a fertilised egg
enclosed with a soft shell that is retained (kept) in the
mother's body. The young hatch within the mother's body
and are then born.
• The developing young obtain nutrients from the yolk of the
egg. Parents take no part in feeding the embryo.
• Ovovivipary occurs in some insects, some fish and some
reptiles. Specific examples puff adder, Cape chameleon.
• Internal fertilisation, egg shell is soft, eggs hatch inside body,
appears to be born alive, egg yolk nutrition, mother for
(ovo+vivi+parity (a noun), egg-live-birthing)
OVOVIVIPARY – how is reproduction
1. Fewer eggs needed – higher survival rate of
2. Developing embryo much less vulnerable to
3. Developing embryo not subject to
environmental changes e.g. temperature.
4. Young born fully developed, can feed and
escape predators more easily.
5. Occurs in some fish and reptiles.
Young puff adder being “born alive”
after hatching inside mother; note position of cloaca.
Lorraine Kuun, July 2011
Vivipary refers to the development of the embryo
in the female’s body uses nutrients from her body.
• Internal fertilisation, no egg shell, covered by
• Nutrition via placenta from the mother to
the embryo. Waste is also passing through
the placenta from the embryo to the mother.
• Young one’s have parental care. Study the detail
during human reproduction.
maximising reproduction
• Occurs in placental mammals, some sharks and
• Fertilisation internal, no shell
• Placenta responsible for nutrition – young born
• fewer eggs necessary
• energy available for nourishment and protection
of embryo, as well as parental care
Elephant and Bamboo shark
Some differences
Internal and external
Internal fertilisation
Internal fertilisation
Fertilised eggs laid
Fertilised eggs kept
outside the body some inside the body
examples enclosed by a enclosed by a soft shell
leathery or calcareous
Zygote, embryo and
foetus develop in the
uterus -protected by
Embryo gets it’s food
from the yolk
Embryo gets it’s food
from the yolk
Gets it’s food from
mother via the umbilical
Egg hatches outside of
the body
Egg hatches inside the
body just before birth
Live young born
With or without
parental care
With or without
parental care
Parental care