Final answer:
In human reproductive biology, only a few hundred sperm out of hundreds of millions that are deposited in the vagina during sexual intercourse actually reach the egg.
Step-by-step explanation:
In human reproductive biology, hundreds of millions of sperm are deposited in the vagina during sexual intercourse. However, only a few hundred sperm actually reach the egg. Many sperm are overcome by the acidity of the vagina, blocked by mucus in the cervix, or attacked by leukocytes in the uterus. Those few sperm that do survive undergo capacitation, which improves their motility and ability to penetrate the egg.