2. 6. Development of the Embryo
What is an embryo???
Embryo – Early stages of development immediately following implantation of the zygote; body parts are forming
Zygote
Egg Sperm

4. How does a Zygote develop into a fully developed multi-celled organisms?
Cleavage: Series of rapid mitotic cell divisions that increases # of cells (not size)

5. EARLY STAGES OF DEVELOPMENT
Zygote
2 Cell Stage
8, 16, 32 Cell Stage
4 Cell Stage
Blastula – hollow ball of cells
Gastrula
Morula – solid ball of cells

6. A = zygote
B= 2 cell stage
C= 4 cell stage
D,E = 8-16 cell stage
F= Blastula ( ball of cells w/hollow center)
Note: Up until this point, all the cells are identical to one another!

8. Differentiation – To become different body parts; specialized
Gastrulation - formation of gastrula; cell begins to indent; differentiation occurs
Differentiation – To become different body parts; specialized
Ectoderm (outer)
Mesoderm - Middle
Endoderm - Inner

9. The organ systems of a human develop from the following germ or embryonic layers:
Ectoderm Mesoderm Endoderm
Skin Circulatory Respiratory
Hair Muscles Digestive
Nails Bones
Nervous Sys. Excretory
Reproductive

10. Stem Cells
Undifferentiated cells that have the ability to become ANY specialized cell when given the proper signal.
Stem cells can be retrieved from cells of:
1. The embryo (highly controversial)
2. From “deprogrammed” adult cells
(no embryo involved = no controversy)

12. Development
For an embryo to develop, the following conditions are needed:
a. Food
b. Warmth
c. Protection
d. Oxygen
e. Waste Removal

13. Two Types of Development
External Development – development of the young occur OUTSIDE the mother’s body
1. In Water (External Fertilization)
ex: fish, frog
- Food – in yolk of egg
- Oxygen + wastes – diffuse from water

15. (Internal Fertilization)
A featherless Chicken!!!
On land
(Internal Fertilization)
Ex: Birds, Reptiles
a. Shell – Protection
b. Amnion – fluid filled sac around embryo (or fetus). Fluid is for protection, cushioning, and shock absorber
c. Yolk Sac – sac filled with food
d. Allantois – sac to store solid wastes and acts as a respiratory membrane
e. Chorion – outer most membrane

17. B. Internal Development (Internal Fertilization)
Placental Mammals:
Embryo develops in the uterus
Nutrients are obtained from the placenta (temporary organ) by the process of DIFFUSION
Umbilical cord contains blood vessels that carry nutrients, water and oxygen TO the fetus and wastes away from the fetus
Amnion provides protection
Fewer offspring and a lot Parental Care

18. Ways a mother can have a healthy pregnancy
Avoid drugs and alcohol
Eat healthy
Prenatal vitamins
exercise

22. Non-placental mammals
Marsupials: Kangeroo, Koala Bear
Embryo is born undeveloped
Development is completed inside a pouch which has mammary glands