Monai Elnaasani
Describe how enzymes concentrations can affect the rates of reactions and
how this can be investigated practically by measuring the initial rate
Past paper - June 2010, January 2015
1. Prepare five different concentrations of the enzyme protease, 0.5%-2.5%
2. Prepare 1% concentration of casein (main protein in milk) solution
3. Place 5cm3 of casein solution in five different test tubes
4. Keep the test tubes in a water bath at 40ºC for 10 minutes to equilibrate
5. Add protease solutions to each test tube and shake
6. Place them back in water bath
7. Note the time taken for the color of casein to disappear
8. Repeat for each concentration
9. Draw a graph, calculate the initial rate from the graph
Independent variable;
• Enzyme concentration
Dependent variable;
• Time taken to decolorize/ take enzymes to break down substrate
• Initial rate of reaction
• Activity of catalase
Control experiment;
• Repeat the experiment without the enzyme
Biological catalyst - enzymes produced by organisms to speed up rate of reaction
Activation energy - energy needed for a reaction to occur by causing bonds to break by
increasing the number of collisions
Initial rate;
• Y-axis divide X-axis = a.u./sec
• There should be enough substrate molecules to saturate the enzyme
• To ensure that substrate is not a limiting factor
• Fastest rate of reaction at initial rate the it decreases
• As reaction proceeds substrate concentration decreases
• As substrate gets used up by enzymes in reaction
• Substrate concentration should be constant in each test
Factors to keep constant;
• Substrate concentration
• pH by using a buffer
• Temperature using water bath not room temperature
• Time of reaction by a stopwatch
• Volume of enzyme by measuring cylinder or pipette
• Type of enzyme using same batch of enzyme
Pearson Edexcel Advanced Level Biology Unit 3 - notes for success
Describe how enzymes concentrations can affect the rates of reactions and
how this can be investigated practically by measuring the initial rate
Past paper - June 2010, January 2015
1. Prepare five different concentrations of the enzyme protease, 0.5%-2.5%
2. Prepare 1% concentration of casein (main protein in milk) solution
3. Place 5cm3 of casein solution in five different test tubes
4. Keep the test tubes in a water bath at 40ºC for 10 minutes to equilibrate
5. Add protease solutions to each test tube and shake
6. Place them back in water bath
7. Note the time taken for the color of casein to disappear
8. Repeat for each concentration
9. Draw a graph, calculate the initial rate from the graph
Independent variable;
• Enzyme concentration
Dependent variable;
• Time taken to decolorize/ take enzymes to break down substrate
• Initial rate of reaction
• Activity of catalase
Control experiment;
• Repeat the experiment without the enzyme
Biological catalyst - enzymes produced by organisms to speed up rate of reaction
Activation energy - energy needed for a reaction to occur by causing bonds to break by
increasing the number of collisions
Initial rate;
• Y-axis divide X-axis = a.u./sec
• There should be enough substrate molecules to saturate the enzyme
• To ensure that substrate is not a limiting factor
• Fastest rate of reaction at initial rate the it decreases
• As reaction proceeds substrate concentration decreases
• As substrate gets used up by enzymes in reaction
• Substrate concentration should be constant in each test
Factors to keep constant;
• Substrate concentration
• pH by using a buffer
• Temperature using water bath not room temperature
• Time of reaction by a stopwatch
• Volume of enzyme by measuring cylinder or pipette
• Type of enzyme using same batch of enzyme
Pearson Edexcel Advanced Level Biology Unit 3 - notes for success
