Human and animal babies growing inside the mother’s womb can draw oxygen and nourishment from the mother via the umbilical cord. However, for the animals that hatch from the eggs, like chickens and the other birds, the breathing process cannot be as simple as that because the egg shell is devoid of any holes.
Now, How is Oxygen supplied to the little Chick nestled Inside an Egg?
Carbon dioxide is one of the byproducts of the process of energy production. Even if oxygen is used to produce energy, the carbon dioxide produced thereof can be fatal in a confined space like an egg. So how would that carbon dioxide be removed in the absence of any holes in the eggshell?
‘Air Sac’ and the Diffusion of gases
An egg has been shaped by the Nature such that it not only protects the chick but also ensures that all its biological needs are met until it is ready to hatch.
There are two membranes beneath the egg shell. When a chicken lays an egg, it is warmer than the air around it. Gradually, the egg begins to cool off and thus, the material lining the shell shrinks slightly and pulls away from the inside walls.
This shrinking creates a separation between the two membranes that were previously stuck together and a small ‘air sac’ containing oxygen is formed. So now that the air sac is formed, we need to figure out how oxygen is taken in, and carbon dioxide is exhaled out from the egg.
The basic process of diffusion is at play here. The egg shells are porous, and an egg weighing 60 grams has more than 10,000 pores in its shell to facilitate the diffusion process. So, the fresh oxygen enters the air sac inside the egg through the porous shell while the carbon dioxide is removed in a similar manner. The pores in the egg shell also expedite the exchange of nutrients like water.
It is also important to note that, the color of the egg is indicative of the diet of the bird. The more the yellow or orange pigment containing plants are included in the diet of the hen, more yellow would the egg be.