PAG 4: Rates of Enzyme Controlled Reactions

What specific reaction is used to investigate the effect of temperature on enzyme activity?

• The breakdown of hydrogen peroxide by the enzyme catalase.

What are the independent and dependent variables in the temperature investigation?

• Independent Variable: Temperature.

• Dependent Variable: Rate of reaction (measured by volume of oxygen produced).

How do you control pH during the enzyme-temperature investigation?

• By adding equal volumes of a suitable buffer solution to each boiling tube.

Why must the apparatus be allowed to equilibrate for 5 minutes before adding the enzyme?

• To ensure the hydrogen peroxide solution reaches the target temperature of the water bath/ice bath.

Describe the apparatus setup used to measure the rate of reaction for catalase.

• A conical flask/boiling tube containing the reaction mixture is connected via a delivery tube to an upside-down measuring cylinder in a water trough to collect and measure the gas (O₂) produced.

What reaction is used to investigate the effect of amylase concentration?

• The breakdown of starch by amylase.

How is the rate of reaction measured in the amylase investigation?

• By measuring the time taken for the starch to disappear (iodine test no longer turns blue-black).

What is the positive and negative result for the iodine test for starch?

• Positive (Starch present): Dark blue-black.

• Negative (Starch absent): Orange-brown.

How do you calculate the rate of reaction for the amylase experiment?

• Rate = Concentration of starch / Time taken.

What are the independent and dependent variables when investigating substrate concentration?

• Independent Variable: Concentration of hydrogen peroxide (substrate).

• Dependent Variable: Rate of reaction (volume of gas produced).

How is the data analysed for the substrate concentration experiment?

• Calculate the mean and standard deviation for each concentration¹⁴.

• Calculate rate of gas production (cm³ min^-1).

• Plot a graph of rate of reaction against substrate concentration.

Describe the process of making a serial dilution with a dilution factor of 2.

• Add a set volume (e.g., 2cm³) of distilled water to a series of tubes.

• Add a set volume (e.g., 2cm³) of the starting solution (e.g., 2.00%) to the first tube containing water.

• Mix, then take the same volume (2cm³) from this tube and add it to the next tube.

• Repeat the process. This halves the concentration at each step.

If you start with a 2.00% solution and perform a serial dilution with a dilution factor of 2, what are the concentrations of the next three tubes?

1.00%, 0.50%, and 0.25%.