Chicken eggs' porous shell allows gases to pass through, facilitating oxygen diffusion into the egg and carbon dioxide diffusion out.
The chick embryo obtains oxygen from the air cell, a small air pocket formed during egg cooling after being laid.
Chick embryo's chorioallantoic membrane (CAM) is a network of blood vessels near eggshell, where oxygen diffuses from air cells into the bloodstream.
Chick embryo's blood contains carbon dioxide, a waste product of metabolism, which diffuses into the air cell & out through eggshell pores as it grows
Before hatching, the chick pecks at the air cell, providing its first breath of fresh air a few days before hatching.
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