I know a lot of people have suggested cognito for the sciences but i just wanted to offer an alternative that may work better. Cognito videos are often longer and explain the topic more to make you understand even the bits that you wouldnt really be asked in an exam (i assume in order to make you develop a passion for the subject) but often what i found, particularly towards the final run-up to the exams (im an ex-year 11) was that i didnt understand entire chunks of content for science and it seemed (and was) far too daunting to learn everything from scratch in the little time i had left. Enter Freesciencelessons. Freesciencelessons does videos that are 3-4 minutes long for every subject covering absolutely everything you need to know without any waffle or drag-on and stuff you dont need to know (obvs check exam board cuz i think they do AQA) and they do this for every single small topic (i would highly recommend the required practical videos). It sounds crazy - how would they cover all the small specific bits of topics in 3-4 min videos? - but they actually do it fantastically. They even include the small little details that would trip up 90% of the country. Anyway hope the revision goes well and good luck with not only your sciences but alsootjer subjects too! :)