Struggling with biology

I'm not doing poorly with the other sciences, or any of my other subjects, but I constantly get poor marks in bio. I revise for bio just as much as I do for my other subjects, and do as many past paper questions as I can, but I can never seem to achieve as well as I feel like I could do. Any tips?

My advice would be to focus less on practice questions and more on learning the large amount of content to begin with. It's best to get the marks you can on the knowledge questions so you don't have to score as highly on the more difficult data evaluation questions.
Once you are confident with the course content, you can look at question structures and mark schemes on the big questions (6 marks ish) because they usually follow a similar structure/point system.

I also wouldn't so strict with how much time you revise each subject for because you may find yourself revising biology more for some topics and e.g chemistry less for particular topics. It's good to be flexible and give as much as is needed.

I hope this helps.