The process of natural selection has appeared quite often on the past papers that I've done as well as the actual exam I did last year. The carbon cycle is often on there-I resat B1 last June and there was a 6 mark question to do with the carbon cycle, and the carbon cycle was also in the January paper last year.
My main mistakes were always in the carbon cycle, it's pretty hard for me, so I'd suggest revising that more. There's always a bit on genes, I remember, as it's more a higher question.
There might be things to do with reading graphs and using data from graphs.