Final answer:
The secondary oocyte is protected from immune attacks by the corona radiata and the zona pellucida, which serve as barriers during fertilization.
Step-by-step explanation:
The secondary oocyte is shielded from immune attack by several protective layers. Upon ovulation, the secondary oocyte is covered by the corona radiata, an outer layer of follicular cells, and beneath that, the zona pellucida, a thick glycoprotein membrane just outside the oocyte's plasma membrane. Both layers serve as crucial barriers during the process of fertilization, with the zona pellucida playing a key role in the binding of sperm to the oocyte and preventing polyspermy after a sperm has penetrated.