1. Testosterone is an endocrine secretion (a hormone) insofar as it is secreted into the bloodstream and affects organs throughout the body. It is a paracrine secretion insofar as it diffuses from the interstitial cells to the nearby seminiferous tubules and stimulates spermatogenesis.

2. The answer to this question is a matter of opinion that hinges on your view of biological versus psychological sexual identity. You could argue that, once discovered, the error of sexual identification should be corrected and the person should assume the role of his "genetic sex." On the other hand, you could argue that since the child has been raised as a girl and is known to everyone as a girl, she/he should continue to be treated as female in spite of a "chromosomal error."

3. Hemoglobin unloads less oxygen at lower temperatures than at higher ones. Thus, the sperm develop in a hypoxic environment.

4. Primary spermatocytes and all later stages are haploid. Thus, unlike spermatogonia, they are genetically different from the other cells of the body and would be subject to immune attack if antibodies or T cells could get to them.

5. Erection is brought about by high blood pressure in the erectile tissues of the penis. Drugs that lower the blood pressure can interfere with engorgement of the erectile tissues.

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