ANNA WRIGHT / SCIENCE PHOTO LIBRARY ANNA WRIGHT / SCIENCE PHOTO LIBRARY
Fertilization. Artwork of a sperm cell (black) penetrating a human egg cell (round). Once this happens, rapid chemical changes make the outer layer (zona pellucida, pink) of the egg thicken, preventing any of the other sperm entering the egg. The head of the successful sperm releases the genetic material that it contains, and this mixes with the genetic material carried by the egg. The resulting zygote then has the full set of genes required to develop into a new human. The sperm cell (spermatazoon, male) and the egg cell (ovum, female) are the gametes (reproductive cells). Some 300 million sperm are released in ejaculation, but only 1 ovum every menstrual cycle (about 1 month).
Model release not required. Property release not required.