Connect! • Where do embryos of the
pictured organisms develop?
Where Embryonic Development Occurs
• Embryonic development can occur externally
or internally.
A. EXTERNAL EMBRYONIC DEVELOPMENT:
• occurs outside the female’s body
• can occur in water or on land
1. In Water
• The eggs of many fish and amphibians are
fertilized externally and develop externally.
• The developing embryo’s source of food is the
yolk stored in the egg.
2. On Land
• The eggs of many birds and (and a few mammals)
develop externally on land after internal fertilization.
• Again, the developing embryo’s source of food is the
yolk.
• Adaptations of animals that develop on land are a shell
which provides protection and prevents water loss.
Chunk Questions
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What are the two types of development?
Define “external development”.
Where does it occur?
What type of fert and dev do amphibians and fish
use?
What is the function of the yolk?
What type of fert and dev do birds use?
What is an adaptation for land external
development?
What functions does it serve?
Why are duckbill platypuses and spiny anteaters
unusual mammals?
B. INTERNAL EMBRYONIC DEVELOPMENT
• involves the growth of the embryo inside the body of
the parent
• There are 2 types of internal development: placental &
marsupial
1. Placental Mammals
• These mammals have internal fertilization.
• The embryo develops internally within the uterus.
Pass folder with photo of cow uterus
around, for those interested in
looking…
Placental Mammals have placentas!
• The eggs of mammals have very little yolk and
therefore are very small.
human egg –
size of sharp pencil point
These eggs do not need a lot of yolk bc the
placenta exchanges nutrients, wastes, and
respiratory gases btwn the mother and the
embryo by active transport and diffusion.
• There is NO direct connection btwn
maternal and embryonic blood.
• An umbilical cord, containing blood
vessels, attaches the embryo to the
placenta.
placenta
Umbilical
cord
Notice that blood of embryo and mother do NOT mix!
So how does exchange of materials occur?
placenta
oviduct
umbilical
cord
ovary
embryo
uterus
amnion
cervix
vagina
Use this diagram to help label the diagram in your notes.
Chunk Questions
• If an organism has internal development, where does
fertilization occur?
The following questions refer to placental mammals…
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Where does the embryo develop?
Why are the eggs of placental mammals so tiny?
How does the embryo obtain needed nutrients and gases?
How does the embryo get rid of toxic wastes?
By what process do O2 and nutrients move into the embryo?
Explain the connection btwn mother and embryo in the
placenta.
• What does the umbilical cord do?
• So, what actually IS the placenta?
2. Marsupials
• These mammals also have internal fertilization with
internal embryonic development.
• Internal development occurs without direct
nourishment from the mother; instead, yolk is the
source of food.
There is NO placenta!
• The embryo is born prematurely compared to placental
mammals and completes its development externally in
a pouch. The source of food in this later stage is milk
from mammary glands located in the pouch.
Consider a newborn koala…
A newborn koala is approximately the size of a
gummi bear. It is born 35 days after conception
and immediately crawls into its mother's pouch,
where it stays for six to seven months, before
taking its first peek out.
Let’s look at the development of another
marsupial, the kangaroo…
Kangaroos have developed a
number of adaptations to a dry,
infertile continent and a highly
variable climate.
As with all marsupials, the young
are born at a very early stage of
development after a gestation of
31-36 days. At this stage, only
the forelimbs are somewhat
developed, to allow the newborn
to climb to the pouch and attach
to a teat.
In comparison, a human embryo
at a similar stage of development
would be about 7 weeks old, and
premature babies born at less
than 23 weeks are usually not
mature enough to survive.
• The joey will usually stay in the pouch for about 9 months
or (for the Western Grey) 180 to 320 days, before starting
to leave the pouch for small periods of time. It is usually fed
by its mother until the age of 18 months.
• Examples of marsupials include kangaroos and
opossums (only marsupial native to North
America)
Chunk Questions
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What type of fert and dev do marsupials have?
Do marsupials have a placenta?
How do the embryos get nourishment?
Describe marsupial embryos.
Name some marsupials.
What is the gestation period for kangaroos and koalas?
How is marsupial development different from placental?
How is marsupial development similar to placental?
Image Sources
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Bunny - oregonjon.wordpress.com/.../
Apple - organic-center.org/.../ripe-red-apple.jpg
Oppossum - 1.bp.blogspot.com/.../s400/oppossum.jpg
Trout - skywalker.cochise.edu/.../image022.jpg
Sea turtle - www.treehugger.com/2008/10/19-week/
Ostrich - photos.igougo.com/images/p303673-Oranjestad-O...
Kangaroo - www.royalpetclub.com/blog/wp-content/uploads/...
Stink bug eggs - www.edupic.net/.../hem_stink_bug_eggs01.JPG
Frog eggs - academic.emporia.edu/sievertg/tadpoles/devo.htm
Platypus photo and anteater - www.greenfieldpub.lib.in.us/.../platypus.jpg
Robin eggs www.wbu.com/chipperwoods/photos/robin.htm
Sea turtle eggs - naturescrusaders.files.wordpress.com/2009/06/...
Patchwork platypus - www.olliverlyle.com/.../images/platy5.gif
Duckbill cartoon - www.cartoonstock.com/lowres/shr0115l.jpg
Arthur and Baby Kate - http://pbskids.org/arthur/
Placenta diagram – E. Thomas
Embryo diagram and placenta sketch (modified by E. Thomas) - en.wikibooks.org/.../Reproductive_System
Slide 13 and 14– diagrams (modified by E. Thomas) - http://www.mikecurtis.org.uk/biol0image4_2.gif
Types of marsupials - visual.merriam-webster.com/images/animal-king.
Koala with baby - www.itee.uq.edu.au/~adc2010/koala.jpg
Newborn koala/gummi bear - www.koalajo.com/images/gummibear.jpg
Joey in pouch - en.wikivisual.com/images/4/4f/Joey_in_pouch.jp, blogs.courierpostonline.com/fishhead/files/20... ,
Kangaroo cartoon - www.cartoonstock.com/lowres/ato0120l.jpg
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