The major source of bicarbonate ions in our body is from carbon dioxide produced in cellular respiration.

B. true: Approximately 60 to 70 percent of semen volume is produced by the seminal vesicles, while 25 to 30 percent comes from the prostate gland. The sperm cells, along with a small amount of fluid from the epididymis, constitute only about 10 percent of the final ejaculate. This ensures the sperm are suspended in a protective, nutritive medium.

A. vagina: Although the vagina is often considered an internal structure, it is the only choice listed that belongs to the female reproductive system and is accessible from the exterior. In many introductory anatomical contexts, the vaginal orifice is grouped with the vulvar structures. It represents the interface between the internal organs and the external environment.

B. scrotum: The scrotum is a component of the male reproductive system that houses the testes outside the pelvic cavity. It has no anatomical presence in the female body. Its primary function is thermoregulation for spermatogenesis, which is an exclusively male physiological process.

C. seminal gland(s): These are male accessory glands that produce the majority of the fluid volume found in semen. They are located posterior to the urinary bladder in males. Females do not possess seminal vesicles or equivalent glands that produce seminal fluid components.

D. uterine tube: The uterine tubes, or fallopian tubes, are strictly internal reproductive organs located within the pelvic cavity. they connect the ovaries to the uterus and are the site of fertilization. They are not visible externally and are not classified as part of the vulva or external genitalia.