The largest cell in the world is an ostrich’s egg. Sometimes weighing over 3 pounds, the ostrich’s egg is composed of a single cell, as all other animal eggs are.
Ostrich eggs must be large because they have to have sufficient room to accommodate the large chick that must develop inside. Ostriches are the largest living birds, and as they sometimes reach over 300 pounds in weight, the eggs must be able to withstand the mother’s weight while she performs her incubation duties. By comparison, a human ova is barely visible to the naked eye and has a diameter of about one-tenth of a millimeter.