IB Biology exam revision has historically been an issue around exam time due to the lack of legitimate resources–for instance, there are few decent textbooks for IB Biology specifically, and there is essentially only one notable study guide.
More or less, here are the current book resources available to IB resources: (course companion and study guide)
The study guide is pretty decent, though it is not the most concise for some items. I haven’t used the course companion, so check out the Amazon reviews for a more objective opinion.
The best Internet resource I have found so far for IB Biology would definitely be Click4Biology, which is a site created by an IB teacher, I believe, for students. It lists every major syllabus point for Biology, and has all the topics for Bio SL and HL. It even has options!
For most syllabus lines, there are images along with the text so it’s not just a huge wall of text. There are also summary items for complex body cycles so you don’t forget.
Click4Biology is available here.