(Image Source: Public Domain)
We acknowledge that a person's sex and gender are two different things, as discussed here. Sex is defined as, "either of the two major forms of individuals that occur in many species and that are distinguished respectively as female or male, especially on the basis of their reproductive organs and structures."
In this article, we will be referring to "male" and "female" in reference to the scientific classification of a reproductive system and not a person's gender identity.
In order to initiate fertilization, a sperm must first fuse with the plasma membrane of the female egg cell (known as the zona pellucida) and then penetrate through the membrane to fertilize it. Generally speaking, many sperm fuse to an egg cell, making it the “easy” part. Actually getting sperm to penetrate through the egg's external shell can, and often is, the more difficult activity. In order to accomplish this, sperm cells go through a process known as the acrosome reaction, which occurs in the sperm as it approaches the egg.