Development of the Zygote

BC Science Probe 9Section 3.4Pages 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 Australiaor 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