Note: I have not answered Part B - the essay.
A. 1. Both the cancer incidence and mortality proportionally increases with age for persons over 40 years old with an approximate doubling in persons over 65 years.
2. With age, the general capacity and vitality of the body decreases. This includes the immune system. Thus, its capacity to detect and destroy anomalous cells that can cause cancer decreases as well which will lead to cancer.
B. 3. The American diet contains a larger amount of saturated fats compared with the largely soy-based Japanese diet. Furthermore, more alcohol is consumed by women in US. This together with the facts that in Japan women are more active, walk more and have children later in life may explain this trend.
C. 4. Smoking is an activity that is known to cause cancer due to specific nitrosamines (TSNAs), some of which are very potent carcinogens. Maintaining a low-fat, high fiber diet together with avoidance of alcohol overuse or exposure to toxic chemicals or excess sunlight are other activities that can prevent cancer.
5. Cancer develops when growth-promoting genes are permanently turned on. Cancer cells are able to divide many more times than the 40-60 times specific for normal cells. As they reproduce, cells loose parts of the enzyme called telomerase that protects the chromosome against damage. However, unlike normal cells, cancer cells can produce this enzyme. This leads to uncontrolled mitosis in these mutated cells, that ignore the usual density-dependent inhibition of growth.
D. 6. The self repair ability of the body extends at a cellular level where abnormal cells are destroyed or the damaged DNA is repaired. However, this is determined genetically as well, which leads to variation. Thus, the two workers will not have the same DNA repair ability. The worker that has a lower capacity will get cancer because his/her body is not able to repair the damage caused by the styrene. The second worker, who’s DNA repair capacity is better, will not get sick because the cells are able to repair the caused damage. The second worker may also get cancer if the exposure period or intensity increases. Then, the damage may exceed even this ”better” repair ability.
E. 7. A healthy immune system is capable of producing high amounts of immune system’s cells. Due to the high density of these ”defenders” the body is able to detect cancerous cells before they can increase in numbers and turn into tumors. Furthermore, an effective immune system may even have the capacity to destroy incipient or small tumors on its own. These cells are destroyed through several different mechanisms, specific to each ”defender” cell type.
8. The Acquired Immunodeficiency Syndrome (AIDS) is caused by HIV, which in fact are two species of Lentivirus. The HIV virus reproduces by using cells belonging to the body's immune system such as helper T cells (specifically CD4+ T cells), macrophages, and dendritic cells. By destroying these cells, the infection gradually destroys the body's immune system. Thus, the body will have no means to detect or effectively destroy cancer cells, due to decreased numbers of the immune system’s cells.
F. 9. The message in the cartoon alludes to the last research in cancer. The main purpose is to create some sort of vaccine that will teach the immune system to recognize and fight off cancerous cells. Instead of using dangerous medicine or chemotherapy that have many side effects and affect negatively the whole body, “teaching” the immune system to recognize cancer would be the best type of treatment.
G. 10. With age, the body constantly deteriorates and its functions worsen. This is thought to be caused by the finite number of times a cell can divide. The integrity of the genetic material is protected mainly by the enzyme telomerase. This prevents damage to the chromosomes. However, with each cell division, the amount of telomerase decreases and thus chromosomes slowly start to deteriorate. Normal cells can divide only 40-60 times.
Thus, with age the immune system becomes less and less effective and produces less ”defensive” cells. These cells are responsible for the recognition and destruction of mutated cells that give rise to cancer. With less of these cells, the body is not able to detect these cells in time. The immune system also is less effective in destroying or fight them over longer periods of time. Thus, age has a similar effect as HIV, but spread over longer periods of time.
