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 $zsim1$--$2$ 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.
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