Maintenance of an organism is the collection of processes to stay alive, excluding production processes. The Dynamic Energy Budget theory delineates two classes

• Somatic maintenance. This comprises mainly the turnover of structural mass (mainly proteins) and the maintenance of concentration gradients of metabolites across membranes (e.g., counteracting leakage). This is related to maintenance respiration.
• Maturity maintenance. This comprises the maintenance of defence systems (such as the immune system), the preparation of the body for reproduction.