Question

(a) What are pearl oysters?
(b) Which other animals belong to the group'bivalvia'?
(C) Where does the pearl live?
(d) How does a natural pearl begin its life?
(e) When is nacre secreted?
(1) What is ‘Nacre' composed of ?
(g) How is the lustrous pearl formed ?
(h) Pick out from the passage a word that means, "Reflecting light evenly and efficiently
without glitter or sparkle.”​

Answer 1

• Pinctada is a genus of saltwater oysters, marine bivalve mollusks in the family Pteriidae, the pearl oysters. These oysters have a strong inner shell layer composed of nacre, also known as "mother of pearl".

• Bivalves: Phylum Mollusca, Class Bivalvia. Clams, mussels, oysters, and scallops are members to the class Bivalvia (or Pelecypodia). Bivalves have two shells, connected by a flexible ligament, which encase and shield the soft vulnerable parts of the creature.

• One family of nacreous pearl bivalves – the pearl oyster – lives in the sea, while the other – a very different group of bivalves – lives in freshwater; these are the river mussels such as the freshwater pearl mussel. Saltwater pearls can grow in several species of marine pearl oysters in the family Pteriidae.

• A natural pearl begins its life inside an oyster's shell when an intruder, such as a grain of sand or bit of floating food, slips in between one of the two shells of the oyster, a type of mollusk, and the protective layer that covers the mollusk's organs, called the mantle. ... Cultured pearls are made in the same way..

Answer 2

Notice :

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✎ These questions are from class 9th.

✎ English communicative paper SA-2.

✎ All the best :) ❤

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• (a) What are pearl oysters?

★ Pinctada is a genus of saltwater oysters, marine bivalve mollusks in the family Pteriidae, the pearl oysters. These oysters have a strong inner shell layer composed of nacre, also known as "mother of pearl".

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• (b) Which other animals belong to the group'bivalvia'?

★ Clams, mussels, oysters, and scallops are members to the class Bivalvia (or Pelecypodia). Bivalves have two shells, connected by a flexible ligament, which encase and shield the soft vulnerable parts of the creature.

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• (C) Where does the pearl live?

★ One family of nacreous pearl bivalves – the pearl oyster – lives in the sea, while the other – a very different group of bivalves – lives in freshwater; these are the river mussels such as the freshwater pearl mussel. Saltwater pearls can grow in several species of marine pearl oysters in the family Pteriidae.

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• (d) How does a natural pearl begin its life?

★ A natural pearl begins its life inside an oyster's shell when an intruder, such as a grain of sand or bit of floating food, slips in between one of the two shells of the oyster, a type of mollusk, and the protective layer that covers the mollusk's organs, called the mantle. Cultured pearls are made in the same way.

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• (e) When is nacre secreted?

★ Nacre is secreted by the epithelial cells of the mantle tissue of various molluscs. The nacre is continuously deposited onto the inner surface of the shell, the iridescent nacreous layer, commonly known as mother of pearl.

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• (f) What is ‘Nacre' composed of ?

★ Nacre (known as mother of pearl) is the iridescent inner shell layer of some mollusks. Nacre is composed of 95 wt% aragonite (a crystallographic form of CaCO3) and 5 wt% organic materials ( proteins and polysaccharides ).

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• (g) How is the lustrous pearl formed ?

★ A natural pearl (often called an Oriental pearl) forms when an irritant works its way into a particular species of oyster, mussel, or clam. As a defense mechanism, the mollusk secretes a fluid to coat the irritant. Layer upon layer of this coating is deposited on the irritant until a lustrous pearl is formed.

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• (h) Pick out from the passage a word that means, "Reflecting light evenly and efficiently without glitter or sparkle.”

★ A natural pearl begins its life as a foreign object, such as a parasite or piece of shell that accidentally lodges itself inside the mantle from where it Cannot be expelled. It causes some irritation to the oyster. To ease this irritant, the oyster's body begins to secrete a smooth, hard crystalline substance around the irritant. This substance is called 'nacre'. As long as the irritant remains within its body, the oyster will continue to secrete nacre around it, layer upon layer. Over time , the irritant will be completely encased by the silky crystalline coatings. And the result is a lustrous pearl. Nacre is composed of microscopic crystals of calcium carbonate aligned perfectly with one another, so that light passing along the axis of one crystal is reflected and refracted by another to produce a rainbow of light and colour.

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