The diffusion constant for the amino acid glycine in water has a value of 1.06 × 10-9 m2/s. In a 2.0-cm-long tube with a cross-sectional area of 1.5 × 10-4 m2, the mass rate of diffusion is m/t = 4.2 × 10-14 kg/s, because the glycine concentration is maintained at a value of 8.3 × 10-3 kg/m3 at one end of the tube and at a lower value at the other end. What is the lower concentration?