Basically the ISA' are as you say worth 25% of your final grade and don't aim for a C in your ISA it is very easy to get an A* in your ISA and will help you massively I got an A* in ISA and C,B,A in my exams and still got an A overall due to the ISA. If you got a C in the ISA and A*s in all 3 papers for each Unit you would probably get an A/A* overall. Make sure you get as near to 100% in those ISA' I can't stress that enough. You should do 3 attempts of your ISA for each Unit so that's 6 in total and the best one will be sent off hope this helps
Listen to any advice your teacher tells you, read around the subject you're doing ISA on (Paper 2 especially) , E.G if it's endothermic reactions, read online, in revision guide, textbook and you'll have a better chance in aceing paper 2!
If you're doing Paper 1, especially for Chemistry, but also other sciences, check out the nuffieldfoundation.org.uk for practical ideas, they are really helpful!
For sources on your data sheet, try and deliberately do 2 different ones, eg: one in a book with more info related to your practical and one website only with information on the topic. Then you can ace the 3 marker on sources with simple arguments.
Make sure you practice the 9 marker, if I were you, get this done first in the exam! Then worst is first and done!
Any further questions, just ask, I hope something helped!
Can anyone tell how they work, how many I do and if they are only 25% of the final grade will that dramatically affect my grade. I do Double Science by the way. And also if I get a C in my ISA but an A* in the exams what do you think I'll come out with overall?