Download Development of the Zygote

Development of the Zygote
BC Science Probe 9
Section 3.4
Pages 88-92
Development of the Zygote
• As you know: sperm + egg = zygote
• But what happens next?
Development of the Zygote
• Once the zygote divides it becomes an
embryo.
• The embryo can be protected while it
develops in a few different ways:
– Seeds
– Eggs
– The mother
Seeds
• In plants, the ovary actually becomes the fruit!
• Once the plant’s egg has been fertilized, it is
called a seed.
Seeds
• The plant seed contains the embryo, as well as
stored food to help the plant until it can
produce its own (photosynthesis).
• The food in seeds is in the form of starch or
sugar.
Seeds
Seed Anatomy
• There are 2 different types of seeds that get
produced by flowering plants.
– Seeds contain something called seed leaves or
cotyledons.
Seed Anatomy
• Bean plants are called dicotyledons because
they produce seeds with 2 seed leaves.
Seed Anatomy
• Corn plants are called monocotyledons
because they only produce one seed leaf.
Seed Anatomy
• All seeds contain structures that will grow into
the main parts of the plant.
• To understand the diagrams better, take a
couple of minutes to look up the following
definitions:
– Germinate
– Radicle
– Hypocotyl
– Epicotyl
Eggs
• Most animals lay eggs.
• Eggs have
– The zygote
– Some nutrients
– Some kind of protection (shell, jelly, egg case)
Eggs
• Some animals produce single egg cases with
multiple (thousands) embryos in one.
– tapeworm
Eggs
• Others produce eggs that contain only a single
embryo surrounded by a shell.
– birds
– reptiles
• These are called amniotic eggs.
Eggs
• Amniotic egg
Eggs
• Amniotic egg
– The embryo is cushioned by the amnion (a fluid
filled sac)
– The yolk sac stores food for the embryo
– The allantois holds wastes produced by the
embryo
– The chorion controls movement of gases and also
wastes
– The albumen cushions and is additional food
Eggs
• Different animals care for their eggs in
different ways:
– Birds sit on them to keep them warm
– Sea turtles bury them in the sand and the babies
dig themselves out
– Tapeworms release their egg cases and the eggs
are released in the feces on the host animal
usually to be eaten by other animals that they can
use as a host
Eggs
• Mammals that lay eggs are called
monotremes.
– There are 3 kinds
• Duck-billed platypus
• 2 kinds of spiny anteater
• They all live in Australia
or New Guinea.
Eggs
• These mammals care for their eggs during
incubation just like birds do.
Embryos Develop in the Mother
• All other mammals have their embryos
develop in the mother.
Embryos Develop in the Mother
• Marsupials:
– Kangaroos, koalas, opossums…
– The embryos don’t develop for very long in the
uterus
– The young are born very tiny and immature so
they crawl from the birth canal to the pouch
where the can attach to a nipple on a mammary
gland.
– They can return to the pouch to feed once they
are mature enough to venture out.
Embryos Develop in the Mother
• Placental mammals
– Humans, etc.
– Embryos develop much longer in the mother.
– The word placental comes from placenta.
• Find the following definitions to better understand
placental mammals:
– Placenta
– Fetus
– Umbilical cord
Embryos Develop in the Mother
Embryos Develop in the Mother