3. Zygote: fertilized cell created by the union of the egg and sperm >200 types of human cells Embryonic stem cells –Created during earliest divisions –Potential to become any type of cell

4. Determination –Stem cells commit to a specific type –Few weeks into development –Irreversible

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

7. Programmed cell death (apoptosis) between the fingers

8. Cell: Basic unit Tissue: Group of cells –4 types Organ: Groups of tissue –Ex: lung contains each tissue Organ System: Group of organs working together –Digestive System Organism: all organ systems working together

9. Click on picture to play video clip

10. Muscle: contracting cells –Skeletal, cardiac cells

11. Connective Tissue: Support the body –Bone, fat, tendons

12. Epithelial: protection sheet of cells –skin, stomach lining

13. Nerve Tissue: Transmit electric signals –Brain & Spinal Cord

14. Homeostasis Reactions & enzymes work best in specific conditions Control systems adjust to internal/external changes –pH, temp, fluids Constant internal environment maintained

15. Control Systems Sensors (aka: receptors) –Gather information about the body and environment –Ex: skin senses cold temps Control Center –Receives information from the sensors –Ex: Brain registers the cold Communication Center –Messages sent throughout the body to respond –Ex: Message from brain  nervous system  target Targets –Body part that changes its activity –Ex: Muscles start to shiver

16. Negative Feedback Loops Regulates most of the body Counters changes in the body that move conditions away from a set point –Reverses the change Keeps internal environment stable

20. Positive Feedback Loop Increases the changes away from set points Important when rapid changes needed Ex: Skin Cut –C–Clotting proteins increased to seal the wound