Controlled variables – pH, enzyme concentration, volume and type of enzyme close enzyme Proteins that act as biological catalysts, meaning they speed up reactions without being used up ...

Get ready for your exams with this BBC Bitesize GCSE Combined Science Energy changes (AQA) exam preparation ... if this is the control variable: Acid concentration: Volume of Acid: Temperature change: ...

The proportion of students receiving A*-C grades in their GCSE exams has risen for the first time in three years. Just over 68.8% of exam entries were in this bracket - an increase of 0.7 ...