Final answer:
Semen consists predominantly of fluid from accessory glands such as the seminal vesicles, prostate gland, and bulbourethral gland, with only about 5 percent being sperm. The fluid is alkaline to ensure sperm motility, with seminal vesicles contributing about 60 percent of semen's bulk. The semen provides nutrients and an appropriate pH for the survival of sperm.
Step-by-step explanation:
The composition of semen includes sperm and fluids from various accessory glands. These glands contribute the majority of semen's volume, ensuring the viability and motility of sperm. Specifically, semen is composed of approximately 5 percent sperm and 95 percent seminal fluid. The accessory glands, including the seminal vesicles, prostate gland, and bulbourethral gland, secrete fluids that are integral to the composition of semen. The seminal vesicles produce a thick, alkaline solution, which is necessary for reversing the acidity of the vaginal environment. This solution contains mucus, fructose, which serves as a nutrient for the sperm's mitochondria, coagulating enzymes, ascorbic acid, and prostaglandins. These vesicles contribute to about 60 percent of semen's total volume. The prostate and bulbourethral glands also add their secretions, including substances that control pH and provide nutrients as well as compounds that assist in sperm delivery and motility. Moreover, the alkalinity in semen is crucial for sperm activation as sperm are only motile in an alkaline environment, which counteracts the acidity within the vagina. Ejaculates usually contain two to five milliliters of fluid with a sperm concentration of 50-120 million sperm per milliliter.