Biological and physical-chemical life support systems historically have been developed separately and counter-poised. To sustain long-term life support, the problem is to distribute optimally the functions between biological and physical-chemical processes in an integrated life support system (LSS) conforming to the terms and conditions of a particular mission.The basic constructive process in an integrated LSS is the synthesis of human food based on the photosynthesis of higher plants and further biochemical transformations of the primary biomass. In the foreseeable future this function can be efficiently performed by the biological component of the system only. The complementary side effects produced by photosynthesis are carbon dioxide absorption, emission of oxygen and purification of water and atmosphere. The functions of the physical-chemical processes in an integrated LSS are destructive - final oxidation of all organic products of human vital activity and biological components of the system, fine purification of atmosphere and water, transformation of the primary biomass for human food, and preparation of the nutrient media for plants. Long-term “Bios” LSS experiments demonstrate that combined action of the biological and physical-chemical component is beneficial for the efficiency and completeness of environment regeneration.To create a life support system based on biological and physical-chemical processes is the optimum solution providing full-valued conditions for existence and efficient work of people at a lunar base.