Stellar population properties of bulges and discs and their corresponding distributions. Upper panel: Comparison of mean mass-weighted stellar metallicities of the bulges and the discs (with their uncertainties), colour-coded by disc stellar masses. The distributions in bulge (disc) metallicities are shown in the right (upper) joint histograms. Each bin in the metallicity histogram of the bulges is colour-coded by the mean disc mass in that bin. Lower panel: Similar to the upper panel but for stellar ages. The black diagonal line marks the 1:1 correlation.