Excellent textbooks recommended (the two first ones are required).
Biology IB Oxford University Press
IB Higher Level Biology Pearson Press
IB Biology Hodder Education
Biology for the IB Diploma Cambridge University Press
Campbell Biology (Pearson)
Textbooks have plenty of questions for you to practice. Try to answer and then check your answers with the answers provided. The answer to the IB Biology Oxford textbook can be found here and for the the IB Biology Pearson textbook here. The more you practice, the more prepared you will be.
These sites contain summarized information which is great to facilitate understanding but is not detailed enough for the IB Biology exams.