Which process is part of the science of chemistry?

The correct answer focuses on the alteration of the structure of molecules, which is a foundational aspect of chemistry. Chemistry is fundamentally concerned with the composition, structure, properties, and changes that matter undergoes during chemical reactions. When discussing molecules, the alteration implies chemical reactions that can result in the formation of new substances or changes in physical and chemical properties. This aligns perfectly with the study of chemistry, which includes understanding how atoms and molecules interact, bond, and undergo transformation.

The other choices relate to different scientific disciplines. The movement of objects pertains to physics, as it deals with the principles of force and motion. Examining living cells aligns with biological sciences, where the focus is on understanding life and biological processes. Understanding animal behavior is a topic within psychology and ethology, concentrating on the actions and interactions of animals, rather than chemical processes. Thus, the alteration of the structure of molecules distinctly represents a process central to the science of chemistry.