This image shows sperm and an egg (or ovum) at the moment of conception by in vitro fertilisation (IVF). The egg is surrounded by protective cumulus cells around the outside surface, coloured yellow. The sperm need to penetrate the membrane surrounding the egg, called the zona pellucida, if successful fertilisation is to occur. Light micrograph. Wellcome Image Awards 2009 | Winners' gallery | Scientific and medical images - Arunn