Antonyms for the term "chemical models" can include "natural materials," "organic compounds," "bio-based substances," or "physically formulated compounds." These alternative terms describe substances or materials that are derived from natural sources, such as plants or animals, or are formulated without the use of synthetic chemicals. Natural materials, for example, refer to raw materials that have not undergone any chemical manipulation or alteration, including wood, stone, and clay. Organic compounds are carbon-containing substances that are found in living organisms, such as DNA or proteins. Bio-based substances are derived from renewable sources, such as corn, sugarcane or soybeans. Physically formulated compounds are substances that are created by mixing or blending physical ingredients, rather than chemically synthesizing them.