Answer to Question 1
Vaccines consist of killed or weakened versions of pathogens or an antigen that is similar to but less dangerous than the disease antigen. Vaccination causes the body's immune system to produce antibodies against the pathogen without actually causing the disease. If the actual pathogen should invade the body at a later time, immune memory cells will recognize the pathogen and produce antibodies specific to it. These will quickly quell the infection.
Answer to Question 2
1. Disorders of sexual desire relate to a lack of sexual appetite or fear of sex. Lack of desire may be caused by stress or boredom whereas phobic responses may be related to more serious issues such as abuse.
2. Disorders of sexual arousal are generally related to dysfunction (the most common being erectile dysfunction).
3. Disorders of orgasm include premature or delayed ejaculation in men and difficulty or delay in reaching orgasm in women.
4. Pain disorders involve pain during intercourse and include dyspareunia, pain experienced by women during intercourse, and vaginismus, a forceful contraction of the vaginal muscles that prevents penetration.
True-color view of Mars seen through NASA's Hubble Space Telescope in 1999
Color-enhanced scanning electron micrograph of HIV virus (red) infecting T-helper cells (green).
An example of a cover letter sent in response to a classified ad.
How to solve word problems with two unknowns (Question 3)
Linear dose-response curve
economic question