Give the function of Nebenkern and Zona pellucida.

Answer: Nebenkern supplies energy for sperm movement; zona pellucida protects the ovum and controls sperm entry.

• Nebenkern: the mitochondrial spiral coiled around the axial filament in the middle piece of the sperm. It produces ATP that provides energy for the beating of the tail, i.e. for the motility of the sperm.
• Zona pellucida: the thick, transparent, non-cellular glycoprotein layer around the secondary oocyte (ovum). It protects the ovum, has receptors that bind sperms of the same species and, after the entry of one sperm, hardens (zona reaction) to prevent polyspermy.