Closed ecological life support systems incorporating plants represent the only potential for achieving self-sufficiency in an extraterrestrial biosphere. A model of input/output metabolic mass flow rates for a plant module in an Engineered Closed/Controlled EcoSystem is presented. Wheat crop was chosen as a case study for modeling metabolic mass flow rates. Coefficients for the mass flow rates, for each metabolic element, are determined per unit area of wheat production. The coefficients are utilized to compute the area of edible biomass production necessary to accommodate human food requirements. This model for computing metabolic mass flow rates can be applied for any crop under specified growing conditions.