The charter shall provide for the appointment of a city clerk, a treasurer, one or more assessors, a fire chief, a police chief, a health officer, a city solicitor, a general assistance administrator, and such other officers as may be necessary to administer all departments which the elected body and the charter shall establish. Assessors shall, prior to appointment, have demonstrated knowledge of property appraisal or assessment and of the laws governing the assessment and collection of property taxes. The powers and duties of appointed officers and heads of departments shall be those prescribed by state law, by the charter or by ordinance. Unless otherwise provided in the charter or by law, the term of office of any appointed officer shall begin upon his or her appointment and qualification for office and shall end upon the appointment and qualification of his or her successor.