1. Development of the Zygote
BC Science Probe 9
Section 3.4
Pages 88-92

2. Development of the Zygote
As you know: sperm + egg = zygote
But what happens next?

3. 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

4. Seeds In plants, the ovary actually becomes the fruit!
Once the plant’s egg has been fertilized, it is called a seed.

5. 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.

6. Seeds

7. Seed Anatomy
There are 2 different types of seeds that get produced by flowering plants.
Seeds contain something called seed leaves or cotyledons.

8. Seed Anatomy
Bean plants are called dicotyledons because they produce seeds with 2 seed leaves.

9. Seed Anatomy
Corn plants are called monocotyledons because they only produce one seed leaf.

10. 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

11. Eggs Most animals lay eggs. Eggs have The zygote Some nutrients
Some kind of protection (shell, jelly, egg case)

12. Eggs
Some animals produce single egg cases with multiple (thousands) embryos in one.
tapeworm

13. Eggs
Others produce eggs that contain only a single embryo surrounded by a shell.
birds
reptiles
These are called amniotic eggs.

14. Eggs
Amniotic egg

15. 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

16. 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

17. 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.

18. Eggs
These mammals care for their eggs during incubation just like birds do.

19. Embryos Develop in the Mother
All other mammals have their embryos develop in the mother.

20. 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.

21. 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

22. Embryos Develop in the Mother

23. Embryos Develop in the Mother