Control Variables

• Stopwatch
  • Ensure the time is the same for all tests
  • As we are measuring how fast the reactants turn into products
• Temperature
  • Ensure the temperature is the same when doing substrate concentration tests
  • By using a controlled temperature water bath
• pH level
  • Ensure the pH level is the same when doing the experiment
  • By adding a pH buffer
  • If not done, the lipid will release fatty acids when broken down, causing a decreased level of pH, causing the enzymes to denature and change their active site which changes the reaction speed

Factors

• 4 Factors are being investigated in this experiment
  • Temperature
  • pH
  • Enzyme
  • Substrate concentration
• Milk is used as it contains a protein called casein, that gets digested by enzymes
• Milk is white and opaque, and as this protein is digested the solution gets more and more translucent
• This allows light to pass through more easily
• A calorimeter is used to see how much light has passed through the solution, so that we can measure
• Lipid Breakdown Experiment - Why was a buffer used?
  • when a lipid is broken down, it releases fatty acids, these fatty acids would reduce the pH
  • this would denature the enzymes, changing the shape of their active site
  • this effecting the charges of the R groups of the amino acids at the active site
  • all this would cause a change in the rate of the reaction

Determining Initial rates of reaction

1. Draw a tangent starting from the start of the reaction of the graph
2. Select two random points of the tangent
3. Find the gradient of the tangent using y2-y1/x2-x1 or rise/run

• Why is it important to measure the initial rate of the reaction rather than an average rate over a longer period of time? (mark scheme)
  • the initial rate is not affected by a change in the substrate concentration
  • reactants are lost over time, reducing the rate of the reaction

Effect of Substrate Concentration

• As the substrate concentration increases, the rate of the reaction increase (positive correlation)
• This is because there are more substrate molecules to collide with the active site of the enzymes
• The rate of the reaction starts to level off, as the substrates increase, because there are no more enzymes/active sites available - enzyme concentration becomes a limiting factor