BBC bitesize - Read all the pages and test yourself with the quiz at the end. There is also a video on translating source code into machine code.

Craig and Dave - Watch videos 85 through to 88 to cover entire 2.5 subtopic

101Computing - Full of nice tasks that help with revision

Exam question walkthrough - For the questions on 2.5, do questions 14 up to (and including) q18

End of topic test - A test that covers all of 2.5