How to deal with bad teachers?

I’ve got a horrible biology teacher. Can you believe that when we ask her questions, she says we’re asking stupid questions and refuses to explain? I have never yet met a teacher who has not been absolutely delighted to answer questions from a student. Most teachers tell us that when we’re asking questions, at least they know we’re listening, that we’re bothering to work at all. A friend introduced the idea of writing to the school, either to the HoD or principal, but some other clmates voiced concerns that doing so might be seen as undermining her authority. Another friend from a different school had a similar problem just last year, and they wrote the letter to the teacher herself asking her to change her teaching techniques. The result was that the teacher promised to try to change, but in the end, nothing much happened. Our test is in two weeks and she has not opened the textbook once on the chapters we're being tested on. Should I wait and see if our results are bad enough?