Final answer:
Sperm can live inside a woman's reproductive tract for 3 to 5 days, with the best chance of fertilization occurring if intercourse happens a few days before ovulation. The oocyte is viable for only about 24 hours after ovulation.
Step-by-step explanation:
During ejaculation, hundreds of millions of sperm are introduced into the vagina, where they embark on a challenging journey toward an oocyte (egg) for potential fertilization. Overcoming the acidic environment of the vagina and navigating past various barriers, such as thick cervical mucus and phagocytic leukocytes in the uterus, only a reduced number of sperm make it into the uterine tubes. After surviving these hurdles, the sperm can continue to live for 3 to 5 days within the most typical site for an oocyte encounter, increasing the chances of fertilization if intercourse occurs a few days prior to ovulation.
However, it's notable that an oocyte's viability span is much shorter, lasting only around 24 hours post-ovulation. Therefore, the timing of intercourse in relation to this period is crucial for successful fertilization. Once this window has passed, the likelihood of sperm meeting the oocyte diminishes substantially.