What is the purpose of the pearl sac?

The pearl sac is a specialized tissue found within mollusks, particularly in the process of pearl formation. Its primary role is to enclose a bead nucleus, which is often introduced by human intervention, and to secrete nacre, the layer that eventually forms the pearl. This secretion process is essential as it allows the oyster or other mollusk to encase the irritant (such as a bead or a piece of organic material) with layers of nacre, leading to the creation of a lustrous pearl over time.

Understanding this function clarifies the significance of the pearl sac in the overall process of pearl cultivation and formation, contributing to the artistic and market value of cultured pearls. The other options, while related to the biology of mollusks, do not accurately reflect the specific purpose of the pearl sac in relation to pearl formation.