The yolk contains large amounts of carbohydrates, fat, and protein. The yolk is also a reservoir of the vitamins and minerals that are essential for normal growth. These substances combine with the oxygen taken in through the pores of the shell and provide an abundant source of metabolic energy for the embryo. By-products of this process are carbon dioxide and water. The embryo to replace moisture lost through evaporation uses water.
Carbon dioxide is transpired through the pores of the shell.
Calcium absorbed from the yolk and shell are used by the embryo to make its bony structure, or skeleton.