yes it is and it (apparently) builds on the topics learnt at AS but I'm not an A level student so I don't know how much harder A2 is. Some people may find it easier as what they learn at AS helps them breeze through A2..
A2 is harder but it will build on what you learnt in AS. I'm about to start A2 and i have already done an A2 module in maths (I know you asked for Bio and Chem) but i have seen the topics for Chem and they seem fairly straight forward. However, you will need a good foundation of AS to continue with ease.
This is for OCR A
I do OCR Biology and Chemistry at A2. Biology gets alot harder, with more complex idea's and models, whereas Chemistry doesn't get that much harder to be honest. But the last module of Chemistry for A2 is alot of maths, so if you struggle with maths then you may find it difficult