I did biology, chemistry and history A Levels and am now in my first year of university studying BA History. I picked two science A Levels because I was interested in science and wondered if I would do a biomedical science degree. I picked history A Levels because I loved it. I ended up picking a history degree because I realised I hate practicals.
So far, I haven’t had any issue with my modules. While I haven’t done a module specifically focused on political history yet, most of my Britain module this semester was and I haven’t found it difficult. Everyone has done different subjects at A Level, some may not have done history. There will also be international students who know very little about UK politics. While you may have to search up what a word or two means, that isn’t very much and you will also be doing modules where you have no/very little underlying knowledge for that week. On my modules this semester was on global history, where at least half of it was Islamic history and exploration in Africa and Asia. I knew nothing about that, but the readings and general research were very effective. No one has made fun of me for my subject choices. In fact, we barely talk about what someone studied at A Levels or what grades people got.
In terms of your concerns about Biology A Level generally, I did OCR A and got a grade A in the exam. I’ve found that lots of practice questions (In the two years, I did every AS paper probably more than once and did most of the A Level papers). Just a useful note, make sure you leave some papers you haven’t touched for just before the actual A Levels. Also, make sure you are very strict with the mark scheme, don’t think that I almost got and so I will give myself the mark as you won’t get it in the real thing. Also, your teachers should be there to help, if they are not, try asking someone else in the department.
Hope this helps
Feel free to ask me more questions