The enzyme-filled cap covering most of the sperm head, important for penetrating the oocyte, is called the:

1. The sperm has three regions: head, mid-piece, and tail. 2. The head carries a compact haploid nucleus and a specialized enzyme-filled cap structure. 3. This cap is called the acrosome, filled with lysosomal enzymes needed for fertilization. 4. The flagellum and axial filament are tail structures for movement, not the enzyme cap, so they are ruled out. _Source: OpenStax Anatomy and Physiology (CC BY 4.0), Ch 27 "The Reproductive System", p.1284-1285 §Structure of Formed Sperm_