  We study influence by models of inter-stellar medium (ISM) on properties of
galaxies in cosmological simulations. We examine three models widely used in
previous studies. The ISM models impose different equations of state on dense
gas. Using zoom-in simulations, we demonstrate that switching the ISM models
can control formation of giant clumps in massive discs at redshifts
$z\sim1$--$2$ while their initial conditions and the other settings such as
stellar feedback are unchanged. Thus, not only feedback but ISM models can also
be responsible for clumpy morphologies of simulated galaxies. We find, however,
that changing the ISM models hardly affects global properties of galaxies, such
as the total stellar and gas masses, star formation rate, metallicity and
stellar angular momentum, irrespective of the significant difference of
clumpiness; namely the ISM models only change clumpiness of discs. In addition,
our approach provides a test to investigate impact by clump formation on the
evolution of disc galaxies using the same initial conditions and feedback. We
find that clump formation does not significantly alter the properties of
galaxies and therefore could not be the causes of starburst or quenching.
