During ejaculation, millions of sperm are deposited into the female's vagina. Despite the extraordinary number of cells transferred from male to female, the chances of fertilization are very low. Explain why
What will be an ideal response?
Once sperm enter the female's reproductive tract, there are many physiological and anatomical obstacles that separate sperm from eggs. Among them, the acidic secretions of the vagina kill most sperm. As well, sperm cells swim randomly, so it is mostly by chance that any of the cells enter the vagina through the cervix, travel in the correct direction once in the vagina, and move into an oviduct that contains an egg at a time following ovulation. The journey is long, so sperm may deplete their energy reserves before reaching the egg, and even if they make it to the egg, the zona pellucida must be penetrated by enzymes in the acrosome. The life of a sperm cell is finite, and in most cases it does not survive long enough to achieve all of the tasks necessary to fertilize an egg.
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