Passage: Despite its dangers, radioactivity has several uses. For example, it can be used to determine the ages of ancient rocks and fossils. It can also be used as a source of power to generate electricity. Radioactivity can even be used to diagnose and treat diseases, including cancer. Cancer cells grow rapidly and take up a lot of glucose for energy. Glucose containing radioactive elements can be given to patients. Cancer cells take up more of the glucose than normal cells do and give off radiation. The radiation can be detected with special machines like the one in the Figure below . The radiation may also kill cancer cells. You can learn more about medical uses of radiation at this URL: http://www. youtube. com/watch?v=v_8xM-mLxJ8. Answer: energy
Cancer cells take up glucose for what reason?