Number density of young (top row) and old (middle row) galaxies in the mass-metallicity plane, obtained using both the volume and completeness statistical corrections. Following the same colour-code of Fig. 3, we show the distributions obtained without the use of the aperture corrections (left panels) and the distributions obtained implementing aperture corrections (right panels). The contours identify the levels containing 16%, 50%, 84%, and 97.5% of the complete galaxy sample. The bottom panels display the median relations (solid lines) and the respective 16^th and 84^th percentiles (shaded area) as a function of mass, for old (magenta) and young (blue) galaxies. The solid and dot-dashed black lines identify the median MZRs obtained with the passive and star-forming sample, respectively. The dotted horizontal lines in the mass-metallicity planes indicate the solar metallicity of Z_⊙ ≡ 0.02.