You can elect to take Biology E or Biology M on a specific test day, but not both. They are both offered six times a year: October, November, December, May and June. The Biology E and M tests are both 60-minute, 80-question exams, scored on a 200 to 800 scale. On a specific test day, Biology E and Biology M test-takers will take 60 identical questions, while the other 20 questions will be E- or M-specific. Taking Biology E on one test date does not preclude you from taking Biology M on another test date.
The E in Biology E refers to Ecology, and 20-question section specific to Biology E will center on ecology topics, including populations and ecosystem behaviors. An analysis by The Princeton Review laid out seven areas of ecology most tested on the Biology E. Those focus areas include biomes, nutrient cycles, ecosystems, succession, food and energy pyramids, population growth, and community interactions.
The M in Biology M corresponds to Molecular, and the 20-question specific section will be based around the molecular build-ups, including cell structure, human anatomy and compounds; both organic and inorganic. The Princeton Review did an extensive review of past Biology M tests, and the extra 20 questions came from seven areas: enzymes, mitosis, cellular respiration, DNA, RNA, biochemistry, and cells.
Be sure to note that no matter if you elect E or M, 12 percent of the shared part of the questions will be made up of whichever subject you do not choose. So you will have 37 percent of the questions on the E or M you choose, 12 percent on the other, and the other 51 percent come from three areas: Classical Genetics, Evolution and Diversity, and the biology of organs.