Development of the Zygote

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