Sperm cells. Coloured electron micrograph (SEM) of a human sperm cells, or spermatozoa. These are the male sex cells, they are produced in the testes and are responsible for fertilisation of the female ovum (egg). A sperm cell consists of a round head that contains the genetic material, and a tail that beats to propel the sperm. When a man ejaculates he releases millions of sperm cells, which travel along the female reproductive tract, through the cervix to the uterus (womb) and fallopian tubes, where one may fertilise an ovum. The tip of the head, the acrosome, contains enzymes that are released to help the sperm penetrate the egg. Magnification: x4000 when printed 10 centimetres wide.