Question

A pearl oyster secretes pearls to______.
A. Regenerate injured part
B. Protect itself against invading parasites.
C. Harden its mantle cavity
D. Isolate damaged tissue of the body

Answer 1

Hint:-A pearl may be a hard, glistening object produced within the soft tissue (specifically the mantle) of a living shelled mollusk or another animal, like fossil conulariids. a bit like the shell of a mollusk, a pearl consists of carbonate (mainly aragonite or a mix of aragonite and calcite) in minute crystalline form, which has deposited in concentric layers.

Complete step-by-step solution:-
The principal causative thing about pearl formation during a Pinctada margaritifera is the presence of a nucleus. It is often of organic or inorganic origin, like parasites, adults or larvae, molluscan eggs, decaying parts of plants, sand grains, epithelium or blood cells of an equivalent animal, etc. These tiny particles or organisms enter the oyster when the shell valves are open for feeding and respiration. These foreign bodies may become embedded between the shell and mantle. In response to the present stimulus, the foreign body is invigorated by the outer epithelium of the mantle and a pearl-sac is made around it. Pearls aren't produced without the formation of the pearl-sac. The pearl-sac springs from the interior or external layer of the epithelium of the mantle or of the gill plates. The epithelial cells of the pearl-sac secrets the nacre which becomes deposited over the foreign body, forming a pearl in due course of your time . These pearls are produced either within the mantle, in other soft tissues of the oyster, or between the mantle, and therefore the interior surface of the shell.
So, the correct answer is option B

Note:-
Such pearl production is accidental and occurs very rarely. they're generally small and irregular. Large and spherical pearls are still rarer to seek out . When the extraneous matter becomes fixed to the shell, only the exposed portion becomes covered by the pearl-sac leading to a blister pearl.