sperm cells have three parts having different uses :-
  i . head - contains nucleus and hydrolytic enzymes 
  ii. neck - contains proximal  centriole which gives support to axial filament of sperm . 
  iii. middle - contains power house i.e. mitochondrial spiral . 
  iv . tail - by this part sperm is able to move or swim in fluid medium from testis to ovum .
when sperm reaches to ovum then its tail is left behind and his head get penetrated and forms zygote