A gastight (non-ventilated) cuvette system has been developed, allowing optimized, well-documented, and identical plant cultivation at 0 and 1 g. It is equipped for control of CO2 & O2 and for compensational gas exchange measurement. The cuvette houses the arrangement for dew-point air conditioning and the water cycle is closed by means of capillary conductors. The growth medium provides uniform water distribution and stores great amounts of nutrient solution. All four gas flows for compensating photosynthesis and respiration are measured by a computerized method (“automatic pulse expansion dosimetry”) which generates gas pulses of known mass at modulated frequency. The existing lab version is designed for easy translation into flight hardware. Problems with ethylene accumulation prevented definite experimental runs.