Pg.+137

Pg. 137 (absent)
1. An allergy is when the immune system overreacts to antigens that are not dangerous to the body, while autoimmune disease is a disease in which the immune system attacks the body's own cells.

2. It is important for immune-system cells to recognize all of the body's own cells because if it doesn't, the body would begin to attack other parts of the body.

3. A cell dividing at an uncontrolled rate is what characterizes a cancerous cell.