Final answer:
Hundreds of millions of sperm are deposited in the vagina during ejaculation, but most are immediately destroyed by vaginal acidity, blocked by cervical mucus, or destroyed by uterine leukocytes. Only a few hundred or thousand may reach the site of the oocyte. However, only one sperm is needed to fertilize an egg, and it must be capacitated to penetrate the oocyte.
Step-by-step explanation:
Fertilization and Sperm Survival in the Female Reproductive Tract
During ejaculation, hundreds of millions of sperm are released into the vagina. However, this environment is particularly harsh for the sperm due to its acidic nature, which immediately destroys millions of them. Additionally, the thick cervical mucus can block many from further passage, and phagocytic uterine leukocytes destroy thousands more. Consequently, only a few hundred or possibly a few thousand sperm actually make it to the site where they may encounter the oocyte. The process of capacitation then enhances the surviving sperm's motility and prepares them to penetrate the oocyte.
Although it may only take one sperm to fertilize an egg, the journey to the oocyte is perilous, and most sperm do not survive. Despite the initial large number of sperm deposited, environmental factors within the female reproductive tract greatly reduce their number. However, those that survive are well equipped for the task at hand, having undergone capacitation, which is vital for successful fertilization.