  Several galaxies, such as dwarfs and Irregulars as well as outer galactic
clouds have low metallicity. At low metallicities a reduction in the amount of
dust and heavy elements plays a significant role on the chemistry as well as
the heating and cooling of the gas in the molecular regions, called as Photon
Dominated Regions (PDRs). We present here the effects of reduced metallicity in
PDRs and study the important PDR cooling lines ([CII], [CI] and CO). Moreover
many observational evidences suggest that molecular clouds are clumpy. We model
the molecular emission from galaxies incorporating a mass spectrum of clumps.
We also compare our results with the semi-analytical results obtained by
Bolatto et al. (1999).
