Why do oysters make pearls? © Getty Images

Why do oysters make pearls?

Who’d have thought the immune response of a mollusk could result in something so pretty?

Asked by: Susan Bragg, Barnstaple

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It’s an immune response designed to protect the oyster from a parasite or an injury (not just a grain of sand as is commonly believed). Cells from the mantle of the oyster form a pearl sac around the irritation. The pearl sac then secretes calcium carbonate and conchiolin protein that builds up in layers to form an impermeable barrier.


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