1. Why do bone injuries generally heal, while injuries to the spinal cord and brain do not?
Bone tissues can regenerate fairly easy; in the area where the bone has been fractured, the bone will work to produce new cells and small blood vessels that will rebuild the bone. The new cells will cover the ends of each broken piece of bone until the gap between the bones has been closed and the bone has been repaired. However, like the brain, the spinal cord is part of the central nervous system. If the spinal cord is damaged in an accident, the sections below the injury will be cut off from the circuit of information to and from the brain. This means, all nerves - and all body parts - linked to these areas of the spinal cord will also be disconnected from the brain and will stop functioning. Unlike normal cells, nerve cells do not regenerate, so if the cells are damaged, they will not heal.
2. Why would it be useful to know why cancer cells can keep dividing when normal cells can only divide about 100 times?
Cancer is caused by abnormal behaviour in cells, so it's helpful to understand the difference between a healthy cell and a cancerous cell. Cancer cells are set apart by a few characteristics, including unchecked growth and reproduction. Healthy cells will stop reproducing when they receive signals from nearby cells to do so; cancer cells no longer respond to these signals. Most cells will also cease dividing and reproducing if there's an error in their DNA (known as a mutation). Cancerous cells, by contrast, reproduce despite the damaged DNA and take on powers of immortality instead of dying off. And, finally, while healthy cells will stay put, cancerous cells will move randomly around the body, spreading cancer and making it more difficult to treat. If the reason behind why cancer cells do this would be known, a cure for cancer could be made: the chemical that causes the cancer cells to react could be avoided, and therefore cancer would