Six processes that occur in living organisms distinguish them from nonliving things. All of these processes work together in a finely tuned balance; no system or part of the human body works in isolation. Disruption of these basic life processes can result in the destruction of cells and tissues, which may lead to illness or death.
Metabolism comprises all chemical reactions that occur in the human body. It includes catabolism, or the breakdown of chemical substances, and anabolism, or the buildup of chemical substances. Examples include respiration and digestion, both of which take in nutrients and convert them to useful energy. In the related process of excretion, the body rids itself of metabolic waste products, which would otherwise be lethal.
Responsiveness is the process of detecting and reacting to stimuli. A stimulus can be internal, such as a sudden pain or a change in body temperature; or external, such as a sight, sound or smell.
Many types of motion occur in the human body, ranging from the microscopic movements of the structures inside cells, to the full-body movements involved in running or jumping. Other examples of bodily motion include the movement of white blood cells toward foreign organisms, the circulation of blood and the contractions of muscle fibers that produce speech.
Growth occurs in the human body when cells increase in size or number. Anabolism must happen faster than catabolism in order for growth to take place.
Differentiation is a developmental process in which unspecialized cells change into specialized cells with distinct functional and structural characteristics. Through the process of differentiation, human cells are able to form tissues and organs.
The process of reproduction creates new cells or organisms. In asexual reproduction, cell division within the human body creates new cells for tissue repair or growth. In sexual reproduction, two human individuals produce a child who bears genetic material from both parents.