Qu'est-ce qui permet aux oiseaux de pondre des œufs à coquille dure ?

Pour comprendre la réponse

Calcium is the key mineral that hardens bird eggshells. In the shell gland of the oviduct, birds deposit calcium carbonate (CaCO3) as calcite crystals, creating a tough, protective shell that’s still porous enough for gas exchange. Without enough calcium, birds lay thin or soft-shelled eggs.

Context check: keratin builds feathers and beaks, not shells; phosphorus mainly pairs with calcium in bones; magnesium is only a trace component in shells. Memory tip: eggshells, seashells, chalk, and limestone are all mostly calcium carbonate—think “calcium creates the casing.”