In chemistry I found drawing the bonding structures for complex compounds the most difficult, but I have heard it gets harder in year 13! But I have found all other topics in chemistry to be fine, although if you don't do maths you might struggle with the amount of substance calculations.
For biology, the most boring topic for me was microscopes and transpiration, but I did not find the topics very challenging but that's just me 🙂 I do maths a level alongside these, so you might need to brush up on your maths skills before September, as biology (and chemistry) has a lot of new maths in it like statistics!
Tips:
-In biology, make flashcards or notes on each topic after you cover it in the lesson as this really helps to consolidate your knowledge and make sure you understand the topics.
-In your revision for year 12 mocks, what really helped me get top grades throughout year 12 was to do past paper questions and recap on a couple of topics every week to make sure your knowledge is up to date and so you don't have to revise everything before a big exam.
-DO PAST PAPER QUESTIONS!!