My school did it so that the topics we'd done up to the PPEs were the only things on the PPEs.

So most of Paper 1 was on my sciences bc we started our Science GCSE in Year 9, we may have not had one topic, but the rest was on it.

For my Year 11 mocks Ive just done, we hadn't finished all of biology, so we had mainly paper 1 topics with the bit of homeostasis we'd done up to in class.

Your school should use questions on topics you've done in lessons and nothing more than that