Final answer:
Snails growing shells represent a chemical change because they form new substances, mainly calcium carbonate, through a biochemical process.
Step-by-step explanation:
Snails growing their shells can be considered a chemical change because new substances are formed during the process. A snail's shell is primarily composed of calcium carbonate, which is secreted by the mantle tissue of the snail. As the snail grows, its shell grows with it, continually adding new layers of calcium carbonate in a pattern dictated by the animal's genetics and environmental conditions. This transformation where the soft organic tissue generates the hard shell material is a biochemical process that involves chemical changes at the molecular level. Furthermore, snails and other mollusks can be adversely affected by changes in their environment, such as ocean acidification, which can cause their shells to dissolve while they are still alive, underscoring the chemical nature of their shells.