An egg yolk's the part of an egg which serves as the food source for the developing embryo inside. Prior to fertilization the yolk together with the germinal disc's a single cell. It's one of the few single-cells that can be seen by the naked eye. The egg yolk's suspended in the egg white (known more formally as albumen or ovalbumin) by one or two spiral bands of tissue called the chalazae. As a food, yolks are a major source of vitamins and minerals. They contain all of the egg's fat and chol… (More on Yolk)