ROGER HARRIS / SCIENCE PHOTO LIBRARY ROGER HARRIS / SCIENCE PHOTO LIBRARY
Fertilisation. Computer artwork of one of a group of human sperm (spermatozoa, orange) successfully penetrating an egg (ovum, lower left). The egg is the female reproductive cell and the sperm are the male reproductive cells. Only one sperm can penetrate the egg's thick outer layer (zona pellucida) and fertilise it. Fertilisation occurs when DNA (deoxyribonucleic acid) released by the sperm fuses with DNA contained in the egg. Women release a single egg at a time, whilst men release around 500 million sperm. The sperm use their tails to travel through the female reproductive tract. Only a few thousand sperm reach the egg, located in one of the Fallopian tubes.
Model release not required. Property release not required.