Nucleus and acrosome. Structure of a sperm (spermatozoa) It consists of four parts $i.e.$, Head, Neck, Middle piece and tail, enveloped by a plasma membrane. Head It is the enlarged end of a sperm, containing the large haploid nucleus,$ i.e.$, condensed chromatin body and is capped by acrosome. The acrosome contains hydrolytic enzymes that help in dissolving membranes of the ovum for fertilization. Neck It contains proximal centriole which is necessary for the first cleavage division of zygote and the distal centriole that is connected to the tail filament. Middle piece It contains a number of mitochondria that provide energy for the movement of the tail that facilitate sperm motility essential or fertilization. Tail It consists of axial filaments surrounded by the plasma membrane. It helps the sperms to swim in a fluid medium