1.3 The Cell Cycle in YOUR Body Some common chromosome counts: Dogs 78 Tomatoes 24 Humans 46 Black Molly (fish) 46 Cell need to divide for the following reasons: 1. Normal Cell Replacement a) Cells die of old age and need to be replaced. See pg 25 for cell life spans. About 3 billion cells die in your body every minute. a) Cells die due to damage or when they don’t get enough food or oxygen. b) Regeneration - Healing of damaged tissue or the replacement of body parts is called regeneration. (NOTE: see note under Figure 1.17 – pg 26) Growth As organisms grow larger, their cells stay the same size. They just get more of them. Aging Aging is connected to the slowing of the cell cycle. The cells do not divide as often or as quickly. Cancer Caused when the DNA of a cell becomes damaged by: Tobacco Asbestos Certain chemicals some viruses Radioactivity UV radiation The damage injures but does not kill the cell. The cell no longer functions properly and the DNA no longer has correct information about when and how quickly to divide. The result: Useless cells divide often and quickly forming a lump. If the cancer cells can easily be transported the cancer can spread all over. The lump crowds out good cells and use up a lot of food and oxygen. 1. Explain a process in the human body in which there is evidence of the cell cycle at work. A process in the human body in which there is evidence of the cell cycle at work would be growth and development. 2. Give two reasons why cells die. Reasons why cells die include: Damaged Programmed to live a certain amount of time – no longer needed Lack of food or oxygen Failed mitosis 3. How do scientists currently explain the aging process? Scientists currently explain the aging process as the cell cycle is slowing down. 4. Describe what happens when cells divide uncontrollably. Cancer is what happens when cells divide uncontrollably. These cells are like weeds in a garden, choking out the healthy plants/cells. 5. Using your knowledge about cancer and cell division, explain how you think sunscreen can help reduce the risk of skin cancer. I think sunscreen can help reduce the risk of skin cancer because it blocks the UV rays and prevents them from damaging the genetic material. 6. Some cells live for years, while others live for only a few days. Why do you think some cells might be replaced faster than others? I think some cells might be replaced faster than others because some cells are damaged more quickly by their environments (stomach acid). 7. The muscle cells of the heart were once thought to stop dividing when a person reached the age of nine. Thus, heart attacks, which kill heart cells, were believed to cause permanent damage to the heart muscle. New research has discovered that mitosis does occur in the heart later in life. What do you think this new discovery means for people who have heart attacks? (2) This new discovery means your body is capable of regenerating heart cells. This gives heart attack survivors hope for recovery.