Despite many studies about the star formation in spiral galaxies, a complete and coherent understanding of the physical processes that regulate the birth of stars has not yet been achieved. Furthermore, many attempts have been done to understand how environmental processes affect the star formation in galaxies which inhabit rich clusters. In our work, we focus on some of the main open questions about star formation in galaxies: in particular we study the relationship between gas and star formation rate (SFR) and we investigate how galaxies that inhabit rich clusters have their star formation activity shaped by the local enhancement in the galaxy density. Our analysis shows that the bulk of the SFR correlates with the molecular gas, but the atomic gas can be important or even essential in supporting the star formation activity, especially at the edge of the disks. Moreover, we show that cluster member galaxies which suffer from moderate HI removal have their molecular component and their SFR quenched, while highly perturbed galaxies show also evidences of truncation in the star forming disks.