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We study star formation processes in the disc of the weakly barred granddesign spiral galaxy M100 (NGC 4321) from a variety of images tracing recentmassive star formation, old and young stars, dust, and neutral hydrogen.Differences between arm and interarm regions are specifically studied bydecomposing the images into arm and non-arm zones. We find from a comparison ofthe morphology in H$\alpha$, HI and dust that while the first two arecoincident over most of the disc, they are offset from the dust lanesespecially along the inner parts of the spiral arms: a picture which isindicative of a density wave shock moving through the arms. HI is formed nearthe young massive stars as a result of photo-dissociation. From radial profileswe find that in the region of the star-forming spiral arms the exponentialscale lengths for H$\alpha$, blue and near-infrared light, and 21 cm radiocontinuum are equal within the fitting errors. The scale lengths for theinterarm region are also equal for all these tracers, but the arm scale lengthsare significantly longer. This points to a common origin of the profiles instar formation, with little or no influence from radial population gradients ordust in the disc of this galaxy. The longer arm scale lengths are equivalent toan outwardly increasing arm-interarm contrast. We argue that the radialprofiles of radio continuum and HI, as well as CO, are also directly regulatedby star formation, and discuss the possible implications of this result for theinterpretation of observed CO intensities in and outside spiral arms. Wediscuss the radial atomic hydrogen profile in some detail. Its almost perfectlyflat shape in the region of the star-forming spiral arms may be explained byphotodissociation and recombination processes in the presence of a limitedComment: 14 pages, latex, includes 6 ps figures. Uses mn.sty . Two additional  figures available at ftp://star.herts.ac.uk/pub/Knapen/mn/ , files  haonbi.pps.gz and hionbi.pps.gz . MNRAS, accepte

Global morphology and physical relations between the stars, gas and dust in the disc and arms of M100