Question

Nacre is the mother layer of
(a) Ink secretion
(b) pearl secretion
(c) excretion
(d) None of the above

Answer 1

Hint: An inorganic or organic composite material that is present as a layer on mollusks particularly Bivalves i.e, oysters whose materials are used commercially for their beauty and sturdiness.

Complete answer:
Molluscus produce an inorganic or organic composite material caller nacre. It is also known as the mother of pearls. Mollusks produce nacre as an inner shell layer. It is also present on pearls. Nacre is resilient, strong, and has phenomena to change color when the illumination angle changes. Most of the ancient organisms of bivalves, gastropods, and cephalopods contain nacre. In pearl oyster and freshwater pearl mussel, the outer layer and inner layer are made up of nacre.

Additional Information: - In Molluscs shell, the inner layer is like ceramic material and is considered porcelaneous. It is not nacreous.
- Hexagonal platelets of aragonite which are arranged in a continuous hexagonal parallel lamina are present in a nacre.
- Tablets shaped depending on the type of species, rectangular tablets are seen in pinna.
- Because of the thickness of aragonite, nacre appears iridescent because its wavelength is closely related to visible light wavelength.
- Epithelial cells of mantle tissue in mollusks secrete nacre which helps to protect soft tissues from parasites and damaging debris.
- It is done either by forming successive layers of nacre or by attachment of blister pearl to the inner surface of the shell or free peart to mantle tissue. This process is called encystation. The encystation process continues as long as the Molluscs live.
So, the correct answer is 'pearl secretion'

Note: Nacre formation varies from group to group. The nacre layer is formed of single crystals in hexagonal close packing seen in bivalves, twinned crystals are seen in gastropods, and pseudohexagonal monocrystals are seen in cephalopods.