Final answer:
Commonly precipitated solids by water-dwelling organisms for shells and skeletons are calcium carbonate (CaCO3) and silica (SiO2), vital for the formation of protective structures in marine life.
Step-by-step explanation:
The solids most commonly precipitated by water-dwelling organisms to build their shells and skeletons are calcium carbonate (CaCO3) and silica (SiO2). These compounds are used by various marine organisms to construct their external protective structures. Calcium carbonate is a major constituent of the shells of mollusks and the exoskeletons of corals. Silica, on the other hand, is commonly used by organisms such as diatoms and radiolarians to form their intricate shells or tests.
Precipitation of these substances from aqueous solutions is often tied to biological activity, and the availability of calcium, carbonate, and silica ions in seawater is a key factor in shell and skeleton formation. The solubility of calcium carbonate is particularly interesting because it can vary with changes in pH and the presence of carbon dioxide, directly impacting the precipitation process that forms shells and other structures. Silica also has its solubility that influences how organisms can uptake it from the water to form their structural components.