PAG 4: Enzyme Reactions Flashcards
What is the independent variable in the investigation of the effect of temperature on catalase activity? (1)
Temperature
What is the dependent variable in the investigation of the effect of temperature on catalase activity? (1)
The rate of reaction
Describe the method for investigating the effect of temperature on catalase activity. (12)
- Use knowledge of enzyme activity to suggest a hypothesis
- Set up water baths at 40°C, 60°C, 80°C, and an ice bath. Use a thermometer to check temperatures
- Prepare 4 boiling tubes with the same volume and concentration of hydrogen peroxide
- Add equal volumes of a buffer solution to each boiling tube to maintain pH
- Set up the apparatus with a bung and an upside-down measuring cylinder in a water trough connected by a delivery tube
- Place each boiling tube in its respective water bath and allow to equilibrate for 5 minutes
- Use a 5 cm³ syringe to add the same volume and concentration of catalase to each tube
- Quickly seal the tube with a bung and start the timer
- Measure the amount of oxygen produced every 30 seconds for 3 minutes and record in a results table
- Repeat the experiment at each temperature at least twice and calculate the mean
- Calculate the rate of gas production in cm³ min⁻¹ for each temperature
- Draw a graph of rate of reaction against temperature
What is the independent and dependent variable when investigating the effect of enzyme (amylase) concentration on the rate of reaction? (2)
Independent variable: Concentration of amylase
Dependent variable: Rate of reaction
Describe the method for investigating the effect of enzyme (amylase) concentration on the rate of reaction. (10)
- Place iodine in potassium iodide solution onto a spotting tile and label wells
- Prepare boiling tubes with different amylase concentrations using serial dilutions
- Add the same volume and concentration of starch to the first boiling tube and start the timer
- At regular intervals, use a pipette to place a drop of the reaction mixture into the iodine wells
- Observe the colour change: dark blue-black if starch is present, orange-brown if no starch
- Time how long it takes for the colour to no longer turn blue-black
- Repeat the experiment at least twice and calculate the mean time
- Repeat for each amylase concentration
- Calculate the rate of reaction in mol dm⁻³ s⁻¹
- Plot a graph of rate of reaction against amylase concentration
What is the independent and dependent variable when investigating the effect of substrate concentration on an enzyme-controlled reaction? (2)
Independent variable: Concentration of hydrogen peroxide
Dependent variable: Rate of reaction
Describe the method for investigating the effect of substrate concentration on an enzyme-controlled reaction. (9)
- Set up 5 beakers with different hydrogen peroxide concentrations using serial dilutions
- Transfer each solution to a conical flask
- Set up the apparatus with an upside-down measuring cylinder in a water trough connected via a delivery tube
- Use a syringe to add the same volume and concentration of catalase to each conical flask
- Quickly put the bung on and start the timer
- Measure the volume of oxygen produced every 30 seconds for 3 minutes
- Repeat steps 2-5 for each substrate concentration
- Repeat at least twice and calculate the mean and standard deviation
- Plot a graph of rate of reaction against substrate concentration
Describe the method for performing serial dilutions with a dilution factor of 2. (4)
- Set up 5 boiling tubes
- Start with a 2.00% catalase solution and add 4 cm³ to the first boiling tube
- Using a syringe, transfer 2 cm³ from the first tube into the second tube. Add 2 cm³ of distilled water to make a 1.00% catalase solution
- Repeat this process to make 0.50%, 0.25%, and 0.13% solutions, ensuring each successive solution is half the concentration of the previous one
What is the initial rate of reaction? (1)
The rate of reaction at the start of the reaction
Explain why the initial rate of reaction is measured. (3)
At the start of the reaction, there is a known concentration of substrate
The substrate concentration decreases quickly as the reaction proceeds due to enzyme activity
Comparisons can only be made at the start when substrate concentration is the same for all levels of the independent variable
Describe how to use the results of your investigation to calculate the initial rate of reaction. (3)
Plot a graph of rate of reaction (y-axis) against time (x-axis)
Draw a tangent at time = 0
Calculate the gradient of the tangent to find the initial rate of reaction
If the student calculated the rate of reaction over the first 30 seconds, how would this calculated value differ from the true initial rate of reaction? (2)
The true initial rate of reaction would be greater as substrate concentration is highest at the start
More enzyme-substrate complexes would form initially, increasing the rate
Describe how to calculate the rate of reaction from time. (1)
Rate of reaction = 1/time
Suggest a safety risk and explain how to reduce this risk when handling enzymes. (2)
Handling enzymes may cause allergic reactions
Reduce risk by avoiding skin contact, wearing gloves, and using eye protection
Explain the effect of temperature on an enzyme-controlled reaction. (6)
As temperature increases, kinetic energy of molecules increases
More enzyme-substrate complexes form
The rate of reaction increases up until the optimum temperature
Above the optimum temperature, enzymes denature
Hydrogen bonds break, changing the shape of the active site
The substrate is no longer complementary to the active site, so no enzyme-substrate complexes form
Suggest an advantage of using a pH meter rather than a pH indicator. (2)
A pH meter gives numerical readings, so it is not subjective
It provides greater accuracy
Suggest a suitable control for an experiment investigating an enzyme-controlled reaction. (2)
Add boiled enzyme (or water)
Ensures any changes are due to the enzyme
Suggest why the tubes containing enzyme and substrate were left in the water bath for 5 minutes before mixing. (1)
To allow solutions to reach the temperature of the water bath and equilibrate
Explain how you could ensure that 5 minutes was long enough before mixing. (1)
Use a thermometer to measure the temperature of the solutions
Describe how the temperature could be controlled. (2)
Use a water bath and a thermometer
Take regular readings with the thermometer throughout the experiment
Describe how the pH could be controlled. (1)
Add a buffer
