20. How are natural and
artificial pearls created?

Gap-fill exercise

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Pearls are made small strange
particles deposit between the
and the mantle the oyster. These
trigger a defense by
the organism they are gradually
by calcium carbonate
secreted by the thus giving birth
pearls.

In the production of pearls
small fragment of covered with
mantle is inserted between
shell and the of an oyster a
pearl is around the graft.