Im in year 12 now and I disagree with the person above however I was always sitting the higher paper so my circumstances are a bit different. Over the summer just go over things but for science its all about recall at GSCE. I can say that as I take sciences at A level and its totally different. For my GSCE's I crammed a powerpoint to learn for each subject. If you aim to learn all of this from the spec over the summer (with what you have done so far) when it comes to your GSCE's you won't have to cram. Just start looking at stuff every day reading your textbook or CGP guide.
I like to read it out loud over and over then cover it and try and remember what it said without looking. If you do this and keep coming back to it you'll eventually remember the content. Simple maths skills too like percentage change/ increase etc will get you some extra marks on science papers. Also with graphs, dont only describe them as positive correlation or negative correlation etc, say they are increasing at an increasing rate or increasing at a decreasing rate for example. This is more specific and shows the examiner you are more confident in your maths skills for science.