Many bacteria have acquired the ability to produce an enzyme called penicillinase, which destroys penicillin. All enzymes are proteins. The ability to produce the new protein penicillinase came from a change in the bacterial DNA * genetic mutation. probability photosynthesis

In an experiment examining the effects tai chi on arthritis pain, callahan (2010) selected a large sample of individuals with doctor-diagnosed arthritis. half of the participants immediately began a tai chi course and the other half (the control group) waited 8 weeks before beginning. at the end of 8 weeks, the individuals who had experienced tai chi had less arthritis pain that those who had not participated in the course.