Final answer:
Semen is composed of sperm produced by the testes and seminal fluid produced by the seminal vesicles, prostate gland, and bulbourethral glands. These various components contribute to semen's volume, nutritional content, and optimal environment for sperm survival and transport.
Step-by-step explanation:
The composition of semen includes sperm and seminal fluid, with the latter comprising a vast majority of the volume. Semen is formed by contributions from various structures within the male reproductive system. Specifically, the sperm, which make up about 5 percent of the semen's volume, are produced by the testes and stored in the epididymis. The seminal fluid, which provides nutrients, electrolytes, pH buffering, and other important compounds for the sperm, is produced by several accessory glands. These glands include the seminal vesicles, which contribute a fructose-rich fluid to nourish the sperm; the prostate gland, which adds additional fluid containing enzymes, prostate-specific antigen, and other substances; and the bulbourethral glands, which secrete a mucus-like fluid that lubricates and neutralizes acidity in the urethra during ejaculation. Collectively, these components facilitate the transport and survival of spermatozoa.