Animals are just one type of model that scientists use in biomedical research to simulate biological functions and organizations:
Molecular models simulate the interactions and functions of molecules and how these molecules form larger structures like proteins and DNA. For example, molecular models help scientists understand how protein structures inside heart cells cause the heart to contract and pump blood.
Cellular models simulate how structures interact inside a cell and how a cell functions. For example, cellular models help scientists understand how cells produce an electrical charge that causes the heart to beat.
Tissue models simulate how cells interact to form tissues and how the tissues function. For example, tissue models help scientists determine how the many electrical cells in the heart synchronize to produce electrical charges at the same time.
Organ models simulate how multiple tissues organize and function as organs. For example, organ models help scientists understand how the four different chambers of the heart work together to pump blood throughout the body.
System models simulate how multiple organs interact and form a system. For example, system models help scientists understand how the heart, arteries, veins, and capillaries (called the cardiovascular system) all work together to move blood from the heart to the body.
Organism models simulate how different systems work together to allow an animal to respond to its environment. For example, organism models help scientists understand how stress causes high blood pressure.
Many questions about molecular, cellular, tissue, and even organ functions can be investigated using test tube, cell culture, and tissue culture models. But some questions, such as how the digestive system interacts with the cardiovascular system or how the environment affects an organism, can only be answered using animal models.