Final answer:
When the first sperm binds to the oocyte, it triggers the acrosomal reaction, which enables the sperm to penetrate the zona pellucida and fuse with the oocyte's membrane, leading to fertilization.
Step-by-step explanation:
The events that take place when the first sperm binds to the oocyte can best be described as: the acrosome reaction takes place, leading to penetration of the zona pellucida, followed by fusion of the sperm and oocyte membranes.
The events unfold sequentially: as the sperm reaches the oocyte, it first must penetrate the surrounding corona radiata and then make contact with the zona pellucida. Binding to receptors on this glycoprotein membrane triggers the acrosomal reaction, releasing enzymes from the sperm's acrosome that clear a path through the zona pellucida. Ultimately, one sperm fuses with the oocyte's plasma membrane, allowing the sperm nucleus to enter the oocyte and marking the completion of fertilization.