An enzyme is a complex _________ that catalyzes chemical reactions into other substances.

An enzyme is a complex protein that plays a crucial role in catalyzing chemical reactions in living organisms. Proteins are large, complex molecules made up of chains of amino acids and have diverse functions, including acting as enzymes. Enzymes accelerate chemical reactions by lowering the activation energy required for reactions to occur, thereby facilitating processes like metabolism and digestion.

Considering the other options, an atom is the smallest unit of matter and cannot perform the functions of an enzyme by itself. Lipids are a group of organic compounds, including fats and oils, which primarily serve as energy storage or structural components in cells, but do not function as catalysts in chemical reactions. Minerals are inorganic substances essential for various bodily functions, but they do not have the molecular structure or properties necessary to catalyze reactions like enzymes do. Therefore, identifying enzymes as complex proteins highlights their essential role in biochemical processes.