def mod_ec_list(mod):
    """
    Returns a list of modifier elasticity coefficients of a model.

    Returns
    -------
    list of str
        The mod_ec_list is sorted alphabetically.

    See Also
    --------
    ec_list, cc_list, rc_list, prc_list

    """
    ecs = []
    modifiers = dict(mod.__modifiers__)
    for top_reaction in modifiers:
        for base_species in modifiers[top_reaction]:
            ec = 'ec%s_%s' % (top_reaction, base_species)
            ecs.append(str(ec))
    ecs.sort()
    return ecs