  We present an extensive exploration of the impact of 29 physical parameters
in the oxygen abundance for a sample of 299 star-forming galaxies extracted
from the extended CALIFA sample. We corroborate that the stellar mass is the
physical parameter that better traces the observed oxygen abundance (i.e., the
mass-metallicity relation, MZR), while other physical parameters could play a
potential role in shaping this abundance, but with a lower significant impact.
We find that the functional form that best describes the MZR is a third-order
polynomial function. From the residuals between this best functional form and
the MZR, we find that once considered the impact of the mass in the oxygen
abundance, the other physical parameters do not play a significant secondary
role in shaping the oxygen abundance in these galaxies (including the gas
fraction or the star formation rate). Our analysis suggests that the origin of
the MZR is related to the chemical enrichment evolution of the interstellar
medium due, most likely, to the build-up of stellar mass in these star-forming
galaxies.
