A galvanic cell is assembled with a zinc electrode in 1.0 M ZnSO₄ (colorless) and a copper electrode in 1.0 M CuSO₄ (blue). After the cell has been operating for some time, the blue color of the copper(II) solution becomes noticeably lighter, while the zinc electrode shows visible pitting. Determine the direction of electron flow through the external circuit: from the zinc electrode to the copper electrode, or from the copper electrode to the zinc electrode.