Sperm make up just 10% of semen volume.
 

A. serves as a passageway for the primary oocyte: The primary oocyte completes its first meiotic division within the follicle and is released as a secondary oocyte during ovulation. The secondary oocyte then travels through the uterine tubes, not the vagina. The vagina is located distal to the site of fertilization and zygote development.

B. receives semen from the penis during sexual intercourse: The vaginal canal serves as the copulatory organ of the female reproductive system, designed to receive the male penis. Its distensible walls and mucosal lining facilitate the deposition of sperm near the external os of the cervix. This is a critical step for natural reproduction.

C. serves as a passageway for menstrual flow: The vagina provides the exit route for the functional layer of the endometrium and blood shed during the menses. This occurs when fertilization does not take place and progesterone levels decline. It connects the uterine cavity to the external environment for this physiological discharge.

D. serves as the birth canal: During parturition, the vagina expands significantly to allow the passage of the fetus from the uterus to the outside world. Its muscular layer and rugae provide the necessary elasticity for delivery. It represents the final portion of the passage during the second stage of labor.

B. false: Sexual reproduction entails the union of two gametes, specifically a haploid sperm and a haploid secondary oocyte, to form a diploid zygote. The gonads are the sites of gametogenesis but do not merge during fertilization. The fusion of genetic material occurs at the cellular level through a process called syngamy.