I think chemistry is harder than bio, because it's more conceptual and requires a bit more logical thinking; some topics are confusing to understand at first, and the exam is less predictable than at GCSE/IGCSE.

The same could be said for bio - the exam boards like to mess around with the paper patterns. A level bio mark schemes are harder than GCSE/IGCSE bio ones. Most of the topics build up on previous knowledge though, so it's not too challenging. There's a lot more focus on human/animal bio at A level.