(i) Plasma Membrane: Its function is associated with sperm capacitation, acrosome reaction and sperm-egg fusion. (ii) Acrosome: Acrosome contains hydrolytic enzymes (called sperm lysins) which are capable of dissolving the membranes covering the ovum. (iii) Middle piece: They have spirally arranged mitochondria around the axial filament which produces energy that helps the sperm to swim.