Five different modelled observed-frame galaxy spectra belonging to intrinsically the same galaxy at z = 0.04. The black line refers to the spectrum generated with the fiducial PROSPECTOR-β model parameters, while the red, green, magenta and blue curves show the spectra generated varying the IMF (‘Salpeter IMF’), the attenuation law (‘Calzetti k(λ)’), the AGN prescription (‘Temple+21 QSO’) and removing the gas component (‘No gas emission’), keeping the other model parameters fixed. The vertical bands mark the regions where some of the most prominent emission lines appear. The emission line names are reported in black. The spectra units are not arbitrarily rescaled to highlight the effect of varying the stellar population components at fixed physical properties of galaxies on the continuum flux.