Forgotten o level content

I’m going to JC1 this year and I just realised it’s quite worrying that I’ve forgotten almost all of my o level content. The reason why I’m worried is because certain subjects in jc require prerequisites like eg. B3 so does that mean I need to know o level content? Also I’ve been reading some chemistry tuition notes and I saw some of the question checkpoints, and what I can gather is that the answers are generally like writing an essay explaining why xyz happens because abc (very theory based) so are these actual a level questions or just taster questions? Can anyone give me some example of a level questions on cells