Monochromatic images of the AR NOAA 12356 observed by IRIS showing the intensity of different transition region spectral lines. From left to right: Si iv 1402.77 Å , O iv 1399.78 Å and 1401.16 Å and S iv 1406.93 Å. The units are phot s^-1 arcsec^-2 cm^-2. The yellow, light blue and red coloured boxes represent the regions where we acquired the plage, loop and bright point spectra respectively, which are shown in Fig. 5. The time halfway through the IRIS raster is indicated in each panel.