However, whereas walking is a low-impact activity because one foot is always in contact with the ground, in jogging and in running, impact is introduced. This is a high-impact exercise that places strain on the body, notably the joints of the knee.
Most background radiation comes from natural sources, while most artificial radiation comes from medical examinations, such as x-ray photographs. Radiation can damage cells and make them cancerous.
DNA and NUCLEAR DIVISION. Background. is an abbreviation for deoxyribonucleic acid, but it is usually known by its initials alone. DNA is found in practically all living organisms, and it is now known to carry information from one cell to the next, and from one generation to the next.