(a) : The process of fusion of a sperm with anovum is called fertilization. During fertilization, asperm comes in contact with the zona pellucida layerof the ovum and induces changes in the membranethat block the entry of additional sperms. Thus, itensures that only one sperm can fertilize an ovum.The secretions of the acrosome help the sperm enterinto the cytoplasm of the ovum through the zonapellucida and the plasma membrane. In contact withthe surface of egg covering, the acrosome releases itscontained hydrolytic enzymes, also called spermlysins. It is known as acrosomal reaction. Acrosomereaction results in dissolving of corona cells anddegeneration of zona pellucida which helps in spermpenetration.