A group of students investigated the catalytic decomposition of hydrogen peroxide (H_2O_2)… — ACT

A group of students investigated the catalytic decomposition of hydrogen peroxide ( $H_2O_2$ ) into water and oxygen gas using yeast as a source of the enzyme catalase:

2H_2O_2(aq) \xrightarrow{\text{catalase}} 2H_2O(l) + O_2(g)

In Study 1, they mixed $10\text{ mL}$ of $3\%\ H_2O_2$ with $2\text{ mL}$ of a $5\%$ yeast suspension in a sealed flask at $20^\circ\text{C}$ and recorded the volume of $O_2$ gas collected in a gas syringe over 5 minutes. They repeated this procedure using $10\%$ , $15\%$ , and $20\%$ yeast suspensions.

In Study 2, they used a $10\%$ yeast suspension and repeated the procedure at temperatures of $10^\circ\text{C}$ , $30^\circ\text{C}$ , $40^\circ\text{C}$ , and $50^\circ\text{C}$ . The volume of $O_2$ collected at 5 minutes increased with temperature up to $40^\circ\text{C}$ but was extremely low at $50^\circ\text{C}$ .

The students want to perform a follow-up experiment to determine if the low $O_2$ production at $50^\circ\text{C}$ is due to the permanent thermal denaturation of catalase, or if the enzyme is simply temporarily less active at $50^\circ\text{C}$ but remains functional when returned to a lower temperature. Which of the following procedures would best allow the students to test this hypothesis?

A
Preheat a sample of the $3\%\ H_2O_2$ solution to $50^\circ\text{C}$ for 10 minutes, cool the sample back to $20^\circ\text{C}$ , and then mix it with the $10\%$ yeast suspension at $20^\circ\text{C}$ to measure the volume of $O_2$ produced over 5 minutes.
B
Mix the $10\%$ yeast suspension with $3\%\ H_2O_2$ at $50^\circ\text{C}$ , allow the reaction to proceed for 5 minutes, and then cool the entire mixture to $20^\circ\text{C}$ to measure the volume of $O_2$ produced over the subsequent 5 minutes.
Preheat a sample of the $10\%$ yeast suspension to $50^\circ\text{C}$ for 10 minutes, cool the sample back to $20^\circ\text{C}$ , and then mix it with $3\%\ H_2O_2$ at $20^\circ\text{C}$ to measure the volume of $O_2$ produced over 5 minutes.Answer
D
Mix the $10\%$ yeast suspension with $3\%\ H_2O_2$ at $45^\circ\text{C}$ and measure the $O_2$ produced, then immediately transfer the reaction flask to a $55^\circ\text{C}$ water bath and measure the volume of $O_2$ produced.

Answer

Preheat a sample of the

10\%

yeast suspension to

50^\circ\text{C}

for 10 minutes, cool the sample back to

20^\circ\text{C}

, and then mix it with

3\%\ H_2O_2

20^\circ\text{C}

to measure the volume of

O_2

produced over 5 minutes.

The correct procedure targets the yeast suspension containing the catalase enzyme, subjects it to the high temperature of

50^\circ\text{C}

, and cools it back down to the baseline temperature of

20^\circ\text{C}

before mixing it with fresh

H_2O_2

substrate. If the enzyme is permanently denatured, it will remain inactive at

20^\circ\text{C}

and produce little to no

O_2

. If the inactivation is temporary, the rate will recover to normal levels. By keeping the reactants separate during heating, this method avoids the confounding effect of reactant depletion.

Step-by-Step Solution

Identify the source of the enzyme (catalase) within the experimental setup.

The catalase enzyme is in the yeast suspension, not in the hydrogen peroxide substrate.

To test the thermal denaturation of catalase, the heat treatment must target the yeast suspension.

Formulate a method to test the reversibility of the high-temperature inactivation.

The yeast suspension must be heated to the target high temperature (

50^\circ\text{C}

) and then returned to a lower baseline temperature (

20^\circ\text{C}

) where it normally functions well.

If the inactivation is temporary, activity will recover at

20^\circ\text{C}

; if it is permanent (denaturation), activity will not recover.

Isolate the heat treatment phase from the reaction phase to control for confounding variables.

Keep the yeast suspension separate from the hydrogen peroxide while heating and cooling, and only mix them once the temperature is back to

20^\circ\text{C}

Mixing them during the heating phase would consume the substrate, introducing reactant depletion as a confounding variable that could explain the lack of subsequent gas production.

Key Concept

Isolating variables and controlling for reactant depletion when designing follow-up experiments to test the reversibility of temperature-induced enzyme inactivation.

Estimated Time:3m 0s

Question

Answer

Step-by-Step Solution

Key Concept

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