1. We learned that cells have a cycle of growth and division Skin cells like this one grow divide and eventually die over a period of about two weeks. These are the cells replaced the most frequently in the human body Can you guess what cells are never replaced?

2. Neurons! Our brain cells

4. There are factors that control cell growth External Factors operate from outside the cell They can be physical or chemical. Some chemical factors are called growth factors External chemicals bind to the cell membrane This causes an internal cellular response Internal factors include enzymes and proteins that help a cell go through the cell cycle

5. Cells also die, this is called Apoptosis Cell Division Is Uncontrolled in Cancer

6. Cells differentiate to do different things

7. Cells working together make tissues

8. Tissues working together make organs

9. Organs working together make organ systems

10. Organ systems working together make organisms