3. Zygote: fertilized cell created by the union of the egg and sperm Zygote divides into Embryonic stem cells –Potential to become any type of cell Average human: –100 trillion cells –Over 200 types of human cells 23 chromosomes Egg Cell 23 chromosomes zygote Stem cells

4. Determination –Few weeks into development –Genes program the stem cell to become a specific cell –Irreversible Stem cells

5. Differentiation –Cells acquire the structures & functions of a specialized cell –Specific genes activated

6. Quick Questions Do your muscle cells have the same DNA as your skin cells? Yes Do your skin cells have the same DNA as your brain cells? Yes Do your brain cells have the same DNA as your liver cells? Yes So if all your cells have the same DNA, how do they know to do different jobs? Stay tuned for the answer

7. Stem cell (soon to be muscle cell) Stem cell (soon to be nerve cell) If these cells have the same DNA, how will the top cell know to become a muscle cell? Gene AGene BGene CGene DGene EGene FGene G Gene AGene BGene CGene DGene EGene FGene G These light switches are symbolic of the genes inside each stem cell.

8. Stem cell (soon to be muscle cell) Stem cell (soon to be nerve cell) ON During “differentiation”, certain genes are activated in some cells, but deactivated in others. Gene AGene BGene CGene DGene EGene FGene G Gene AGene BGene CGene DGene EGene FGene G What do genes direct cells to create? The proteins created in the top cell will cause the stem cell to become a muscle cell…. The proteins created in the bottom cell will cause the stem cell to a nerve cell.

9. Differentiation –Cells acquire the structures & functions of a specialized cell –Specific genes activated Brain cells Muscle cells Skin cells Pancreas cells

11. Programmed cell death (apoptosis) between the fingers & toes

12. Incomplete Apoptosis (Webbed Toes)

13. Muscle Tissue Contracting cells Skeletal, cardiac cells Connective Tissue Support the body Bone, fat, tendons Epithelial Tissue protection sheet of cells skin, stomach lining Nerve Tissue Transmit electric signals Brain & Spinal Cord Cell: Basic unit Tissue: Group of cells –4 types Organ: Groups of tissue –Ex: Heart contains muscle & connectivetissue Organ System: Group of organs working together –Respiratory System Organism: all organ systems working together

14. YouTube Review: Levels of Organization

15. 1)What is a zygote? 2)What is the specific function of a stem cell? 3)How does “determination” differ from “differentiation”? 4)Cells are programmed to die during a process called ______. 5)From smallest to largest, name the 5 levels of organization. 6)Name the four types of tissues. 7)Which tissue is able to stretch and contract? 8)Which tissue transmits electric signals? 9)Which tissue covers and protects the body? 10)Which tissue connects the body?