Don't worry about the entrance exams you 'll pass them. They are not that hard. I really don't remember many of the questions bit in biology there are multiple questions and they are very easy as long as you study a bit.
I truly recommend you to study though, even if the exams are too easy because if you don't then it will be really hard to follow the course when you get in...
Start studying about oxidation numbers, acids and bases, ph, buffers, w/w and w/v, atomic orbitals and some basic knowledge from organic chemistry. Probably although i am not so sure there is going to be a question for cis-trans.
You have plenty of time to study and there is no reason to feel anxious about them.
I truly recommend you to buy AS/A calculation Chemistry book by Jim Clark which it is going to be really useful for the course. It is one of the best books i have ever read for chemistry and it is very understandable.
Two other books that they are really useful for the entrance exams and for the first semester as well are advanced biology and advanced chemistry.
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