The mark scheme is arguably more important than the question paper. often include mark schemes that show you exactly where marks are awarded. For example:
45 minutes, 50 marks. Includes short-answer and multiple-choice questions. 0893 Science Past Papers
(Mark scheme gives credit for "temperature", "volume/conc. of acid", and "time to see effervescence stop / collect gas volume per minute".) The mark scheme is arguably more important than