The nutritional requirements of the crew will be influenced by such factors as activity, physical and psychological stress, individual size of the members, and individual metabolic rates. The food intake will have to be adjusted to meet these requirements. It is necessary to know the nutritional requirements of each astronaut and the way in which these are altered by the conditions of space flight in order to estimate needs on long missions. Without this information, the food supplies for the longer flights may be too much, too little, or improperly balanced. Where dependence would not be on stored food alone, but on food produced en route, more exact information on requirements is needed to determine the capacity of food production units. In the discussion of bioregenerative systems, it was suggested that food materials could be produced by photosynthetic organisms (e.g., algae, duckweed, and other higher plants) or by nonphotosynthetic organisms (e.g., _Hydrogenomonas_). In contrast to the use of living organisms, reprocessing waste materials by chemical treatment or the actual synthesis of high-energy compounds has been suggested. No chemical system has yet been demonstrated as workable for the economical production of food in space, and the systems considered produce materials which may be converted to food, but are not food as such. Algal cultures have had the most extensive investigation as food in space, but the technical problems of using this material as a food source have not yet been solved. It is apparent from the investigations to date that algae will require treatment before they can be used as food. In limited trials, difficulties have been experienced with amino acid deficiencies, digestibility, high residues, and gastric distress. Processing methods which would be applicable in space travel and the possibility of secondary conversion by other animals or plants should be systematically investigated. chapter 8 _Significance of the Achievements_ SIGNIFICANCE TO SCIENCE One of the most critical research areas of the space program is bioscience. Of both practical and philosophical significance in exploring the origins of life and the possibilities of life on other planets, bioscience also promises much in medical aspects. Space offers biologists completely new environmental factors, such as the effects of zero gravity and of removal from Earth’s rotation. These effects have been studied in attempts to advance understanding of basic mechanisms of physiology and biological rhythms. These studies can be of great value in dealing with problems of disease and metabolic disorders.