Required practical 5: effect of pH on amylase

• Iodine solution

  A chemical that turns dark blue-black in the presence of starch, allowing detection of whether amylase has broken down starch
• Using iodine solution to determine rate of reaction for amylase

  1. Add iodine solution to sample

  2. Observe color change

  3. No color change = starch digested

  4. Blue-black color = starch present
• Setting up the amylase required practical

  1. Prepare tubes with starch solution and pH buffer

  2. Place tubes in water bath at 37°C

  3. Add amylase, start timer

  4. Remove samples every 30 seconds, add to iodine solution

  5. Record time for all starch to be digested
• Independent variable


  The pH, which is changed between trials
• Dependent variable

  The rate of reaction of the amylase enzyme
• Control variables

  Concentration and volume of starch and amylase solutions, temperature maintained using water bath
• Amylase is an enzyme that breaks down starch into sugars
• Enzymes are biological catalysts made of protein that speed up chemical reactions without being consumed
• Enzymes have specific active sites that interact with their substrates
• Enzymes can be denatured by extreme temperature or pH, changing their active site shape
• Low pH (e.g. pH 2)

  Likely to denature amylase and slow down its activity
• pH closer to optimum (e.g. pH 7)

  Allows amylase to work faster and digest starch more quickly
• To improve the investigation, test more pH values near the optimum (e.g. pH 5-9) to identify the precise optimum pH for the amylase