A weak immune system leaves the body defenseless and an immunodeficiency can develop. In contact with a certain antigen, the immunodepressed person is unable to create antibodies since his cells are no longer functioning. A simple flu can end up developing into pneumonia and also lead to death. It is the case with HIV patients, that the virus destroys their immune system making them susceptible to these microorganisms. In this scenario, people with HIV are very susceptible to opportunistic diseases that take advantage of the individual's debilitating state to manifest themselves.
Two examples of opportunistic diseases that can harm a person with HIV are: pneumcyistis carinii and Kaposi's sarcoma.
Intrinsic Motivation is when you engage in an activity solely because you enjoy it and get personal satisfaction from it. Extrinsic is when you engage in the activity solely for a reward.