The AP Biology course requires the completion of 12 major laboratories, commonly referred to as "The Dirty Dozen." These labs are chosen from important areas of modern biology and designed to challenge students to design and implement fair and controlled scientific investigations, formulate hypotheses, collect, analyze and communicate data, critically evaluate results and draw logical conclusions. Typically some multiple choice questions and/or one of the four essay questions has featured principles from one of the 12 recommended laboratories. However, the labs featured in the AP College Board manual are not a strictly mandated prescription for teachers. Alternative laboratory techniques, methods, or equipment may be used to address each set of objectives outlined in the manual.