Anatomy and Physiology II Practice Test 2025 - Free Anatomy Practice Questions and Study Guide

The acrosome is a specialized structure that covers the nucleus of a sperm cell and is crucial for fertilization. It contains lytic enzymes known as hydrolytic enzymes, which are vital for penetrating the zona pellucida, the protective outer layer surrounding the ovum. When a sperm cell reaches the egg, the acrosome releases these enzymes to break down the barriers, allowing the sperm to access and fertilize the egg. This function is essential in the reproductive process, ensuring that the sperm can successfully reach and merge with the ovum to initiate fertilization.

In contrast, the cell membrane encloses the entire sperm cell but does not have the specific enzymatic functions attributed to the acrosome. The nucleosome is a structural unit of chromatin in the nucleus that packages DNA in eukaryotic cells, and the nucleolus is a region within the nucleus involved in ribosome synthesis, neither of which plays a role in sperm’s ability to penetrate the egg. Thus, the acrosome's unique function and structure distinctly identify it as the correct answer.