Sperm cells. Colored scanning electron micrograph (SEM) of human sperm cells or spermatozoa. These tiny male sex cells are produced in the testes, and are responsible for fertilization of the female egg (ovum). Each sperm has a rounded head which contains the male hereditary material (DNA) Some 300 million sperm are released by the male during ejaculation, while the female usually produces one large egg at a time. Only one sperm cell can fertilize the egg. Magnification: x2, 500 at 6x7cm size.