The effect of pH on enzymes (required practical): Organisation: Biology: GCSE (9:1)

• Enzyme

  Biological catalysts which speed up reactions without being used up

  
• Enzymes and temperature

  The enzyme rate increases as temperature increases up to an optimum, after which the enzyme becomes denatured

  
• Enzymes and pH

  The reaction rate decreases as the pH moves away from the enzyme's optimum pH

  
• Denature


  When the active site changes shape and can no longer bind to a substrate due to unsuitable temperature or pH

  
• Active site

  The part of an enzyme where the substrate binds

  
• Substrate

  Reactant of an enzyme catalysed reaction

  
• Product

  A substance produced in a chemical reaction

  
• Lock and key theory

  When a substrate fits into its enzyme just like a key fits a lock

  
• Optimum rate

  An ideal pH or temperature value that results in maximum enzyme activity

  
• Amylase


  A carbohydrase enzyme that breaks starch down into sugars

  
• Starch


  A large carbohydrate found in plants made up of many glucose molecules

  
• Iodine solution


  Turns from orange to blue-black in the presence of starch, will remain orange if starch has been broken down by amylase

  
• Buffer solution

  A solution that controls and keeps the pH of a solution to a specific range

  
• Water bath

  A container of water heated to a given temperature for control purposes

  
• Spotting tile

  Equipment used to observe the colour changes of small quantities of reacting mixtures

  
• Time taken for starch to break down

  The dependent variable or factor that is measured in this experiment to investigate pH and enzyme activity
• pH condition


  The independent variable or factor that is changed in this experiment to investigate pH and enzyme activity
• Temperature

  A variable that should be controlled in this experiment to ensure the results are valid
• End of reaction


  The reaction can be confirmed as complete when iodine on the spotting tile no longer changes colour from orange to blue-black

  
• Examples of other control variables

  To ensure the results are valid the volumes and concentrations of all solutions should be controlled
• Expected results

  Amylase will break down starch effectively at an optimum pH, this can be identified as the pH condition that causes iodine to remain orange the quickest