1. Chapter 5.3

3. Factors Cell division is controlled by external and internal factors. If cells weren’t controlled in some way, they would likely grow out of control.

4. External Factors This can consist of chemical and physical factors. An example of a physical external factor is cell-cell contact. This means when one cell touches another it will stop growing.

5. External Factors Chemical factors that are external are usually in the form of chemical signals. These travel from one cell to another. These are called growth factors. Different factors have different effects

6. Internal Factors These can happen after external factors attach themselves to other cells. Common ones are kinases and cyclins.

7. Apoptosis This is programmed cell death. Internal or external factors can activate self- destructive enzymes.

8. Cancer Uncontrolled cell growth is what cancer is. This means there is no regulation for the cell cycle, so it continues to grow. Cancers can be benign or malignant. Benign – cells stay together and are pretty harmless Malignant – cells break away and can metasize (spread through body)

9. Cancer Cancer cells won’t carry out normal cell functions This is why cancers are dangerous if they spread. They can cause entire tissues to shut down. Cancer is usually caused by damage or mutation that occur in the cell. Carcinogens are cells that can promote cancer.