Final answer:
Semen consists of sperm made in the seminiferous tubules and secretions from the prostate gland, bulbourethral glands, and seminal vesicles, which provide necessary nutrients and create an environment conducive to sperm motility and viability.
Step-by-step explanation:
Semen is composed of spermatozoa, which are made in the seminiferous tubules, and secretions from the prostate gland, bulbourethral glands, and seminal vesicles. The spermatozoa make up about 5% of the total volume of semen, with the rest being contributed by these accessory glands. These glands produce fluids that are essential for the sperm's viability, motility, and ability to fertilize an egg.
For example, the seminal vesicles produce a thick, yellowish, and alkaline fluid that accounts for approximately 60-70% of the semen's volume. This includes nutrients like fructose, which provides energy to the sperm, and alkaline properties that counteract the acidic environment of the vagina, rendering it conducive to sperm survival and motility.