The No Child Left Behind law requires that all teachers in the United States be highly qualified. To be highly qualified, you must have a bachelor's degree, have a teaching certificate and show satisfactory competence in each subject you teach. To show competence, you must either have a degree in the core subject you plan to teach, which in this case would be science, or pass a state exam in the subject you plan to teach.
To teach biology and chemistry, you should complete a major consisting of at least 32 credit-hours in biology and/or chemistry as part of a teacher education program. If you want a major in both areas, complete a double major. If you decide to just complete a major in one area, you should plan to take the Illinois teacher exam in the other area after you receive your initial teaching license, thereby adding the other area as an additional endorsement onto your teaching certificate.
If you complete a degree in biology or chemistry without completing a teacher education program, you can complete an alternate route program to obtain a teaching certificate. Alternate route programs consist of teacher preparation coursework and an internship.
Teachers in Illinois must pass state tests. To teach biology, you should take the Science: Biology Test 105. To teach chemistry, you should take Science: Chemistry Test 106. The tests are offered six times each year at various testing sites across the state of Illinois.