When Joan Carlson started teaching high school biology more than 30 years ago, the Advanced Placement textbook was daunting enough, at 36 chapters and 870 pages. But as an explosion of research into cells and genes reshapes our sense of how life evolves, the flood of new material has been staggering. Carlson’s AP class in Worcester, Mass., now confronts a book with 56 chapters and 1,400 pages, along with a profusion of animated videos and Web-based aids that supplement the text.

And what fuels the panic is that nearly every tongue-twisting term and microscopic fact is fair game for the year-end test that decides who will receive college credit for the course.

“Some of the students look at the book and say, ‘My gosh, it’s just like an encyclopedia,’ ” Carlson says. And when new AP teachers encounter it, “they almost want to start sobbing.”

As AP has proliferated, spreading to more than 30 subjects with 1.8 million students taking 3.2 million tests, the program has won praise for giving students an early chance at more challenging work. But many of the courses have been criticized for overwhelming students with facts to memorize and then rushing through important topics. Students and educators alike say biology, with 172,000 test-takers this year, is one of the worst offenders.

AP teachers have long complained that lingering for an extra 10 or 15 minutes on a topic can be a zero-sum game, squeezing out something else that needs to be covered for the exam. PowerPoint lectures are the rule. The homework wears down many students. And studies show that most schools do the same canned laboratory exercises, providing little sense of the thrill of scientific discovery.

All that, says the College Board, is about to change.

Next month, the board, the nonprofit organization that owns the AP exams as well as the SAT, will release a wholesale revamping of AP biology as well as U.S. history — with 387,000 test-takers, the most popular AP subject. A preview of the changes shows that the board will slash the amount of material students need to know for the tests and provide, for the first time, a curriculum framework for what courses should look like. The goal is to clear students’ minds to focus on bigger concepts and stimulate more analytic thinking. In biology, a host of more creative, hands-on experiments is intended to help students think more like scientists.

The changes, which are to take effect in the 2012-13 school year, are part of a sweeping redesign of the entire AP program. Instead of just providing teachers with a list of points that need to be covered for the exams, the College Board will create these detailed standards for each subject and create new exams to match.