Calcium Carbonate in Oyster Shells
Oyster shells are primarily composed of calcium carbonate, making them the correct answer to the question. Let's explore why oyster shells contain this compound in detail.

Composition of Oyster Shells
- Oyster shells are made up of calcium carbonate in the form of calcite crystals. This compound gives the shells their characteristic hard and durable structure.
- Calcium carbonate is a common mineral found in the shells of various marine organisms, including oysters, clams, and corals.

Function of Calcium Carbonate
- Calcium carbonate provides structural support and protection to the soft tissues of the oyster. It forms a hard shell that shields the animal from predators and environmental factors.
- The presence of calcium carbonate also helps regulate the internal pH levels of the oyster, maintaining homeostasis within the organism.

Formation of Oyster Shells
- Oyster shells are formed through a process called biomineralization, where calcium carbonate is deposited in layers by the oyster's mantle tissue.
- The mantle secretes a protein matrix that serves as a scaffold for the crystallization of calcium carbonate, leading to the growth of the shell over time.

Uses of Calcium Carbonate
- Calcium carbonate is not only essential for the structure of oyster shells but also has various industrial applications. It is used in the production of cement, paper, plastics, and dietary supplements.
- In agriculture, calcium carbonate is added to soil to improve pH levels and provide essential nutrients to plants.
In conclusion, oyster shells are primarily composed of calcium carbonate, which plays a crucial role in the formation and function of these marine organisms' protective coverings.