Aqa Biol 5 Essay questions

So this is probably my weakest point in biology.
I'd consider myself to be quite good at biology, consistently getting A*-A's on past papers, however, there is something about the essay questions where I just really struggle on them.
Perhaps 14/25 if I'm lucky.
Thing is, I'd consider myself to be quite well versed in most aspects of biology, but I really struggle with getting relevant points down or writing down what they want.
For example, i've come across an essay question lipids in animals. If I came across that in my real exam i'd freeze, because all I can think of is plasma membrane and hormones. Of course there are lipids in As biology, so would it be recommended to ensure I know all of the AS specification aswell?
Tl;dr
Looking for advice on how to get better marks on the essay questions, wondering also if anyone finds them as tricky as I do, because I seem to be in a minority in my class when it comes to struggling with the essay writing.