Final answer:
The acrosomal reaction enables a sperm to release digestive enzymes necessary to penetrate the zona pellucida and fertilize the egg.
Step-by-step explanation:
When a sperm encounters an egg, it undergoes an acrosomal reaction. This reaction releases digestive enzymes from the acrosome of the sperm, which then digest a path through the granulosa cells and the zona pellucida. The acrosomal reaction is critical for the sperm to penetrate the protective layers surrounding the oocyte, which include the corona radiata and the zona pellucida, to achieve fertilization. The enzymes clear a path by degrading the glycoprotein matrix of the zona pellucida, eventually leading to the fusion of sperm and egg plasma membranes and the entry of the sperm nucleus into the oocyte.