A student investigates the rate of an enzyme-catalyzed reaction. The student proposed the … — ACT

A student investigates the rate of an enzyme-catalyzed reaction. The student proposed the following hypothesis:

*Hypothesis*: The rate of the reaction is directly proportional to the enzyme concentration at all temperatures, meaning that doubling the enzyme concentration will double the reaction rate regardless of the temperature.

To test this hypothesis, the student measured the reaction rate (in $\mu\text{mol/min}$ ) at enzyme concentrations of $1.0\text{ g/L}$ and $2.0\text{ g/L}$ across four different temperatures. The results are shown in the table below:

Temperature ( $^\circ\text{C}$ )	Reaction rate at $1.0\text{ g/L}$ enzyme ( $\mu\text{mol/min}$ )	Reaction rate at $2.0\text{ g/L}$ enzyme ( $\mu\text{mol/min}$ )
$15$	$12.4$	$24.8$
$25$	$22.1$	$44.2$
$35$	$31.5$	$63.0$
$45$	$10.2$	$12.1$

Which of the following statements best explains whether the data support the student's hypothesis, and how the hypothesis should be modified?

The data do not support the hypothesis, because doubling the enzyme concentration did not double the reaction rate at $45^\circ\text{C}$ ; the hypothesis should be modified to state that the direct proportion only holds below the temperature at which the enzyme denatures.Answer
B
The data support the hypothesis, because the reaction rate increased when the enzyme concentration was increased from $1.0\text{ g/L}$ to $2.0\text{ g/L}$ at all four tested temperatures.
C
The data do not support the hypothesis, because the reaction rates at $15^\circ\text{C}$ , $25^\circ\text{C}$ , and $35^\circ\text{C}$ show that the reaction rate is inversely proportional to the enzyme concentration.
D
The data support the hypothesis, because doubling the enzyme concentration resulted in an approximate doubling of the reaction rate when averaged across all four temperatures.

Answer

The data do not support the hypothesis, because doubling the enzyme concentration did not double the reaction rate at

45^\circ\text{C}

; the hypothesis should be modified to state that the direct proportion only holds below the temperature at which the enzyme denatures.

The correct answer is that the data do not support the hypothesis because doubling the enzyme concentration did not double the reaction rate at

45^\circ\text{C}

. The hypothesis must be modified to state that the direct proportion only holds below the temperature at which the enzyme denatures. This is supported by the data: at

15^\circ\text{C}

25^\circ\text{C}

, and

35^\circ\text{C}

, the rate doubled exactly, but at

45^\circ\text{C}

, the rate only increased slightly (from

10.2

12.1

). This deviation indicates the hypothesis is incorrect as written and requires a temperature limit.

Step-by-Step Solution

Identify the core prediction made by the student's hypothesis.

The hypothesis predicts that doubling the enzyme concentration will double the reaction rate at all temperatures.

This establishes the mathematical relationship that must be tested against the experimental data.

Analyze the experimental data for each temperature to determine if the rate doubles when enzyme concentration increases from

1.0\text{ g/L}

2.0\text{ g/L}

15^\circ\text{C}

12.4 \times 2 = 24.8

(doubled). At

25^\circ\text{C}

22.1 \times 2 = 44.2

(doubled). At

35^\circ\text{C}

31.5 \times 2 = 63.0

(doubled). At

45^\circ\text{C}

10.2 \times 2 = 20.4

, but the actual rate at

2.0\text{ g/L}

is only

12.1

(not doubled).

Checking each individual temperature test condition determines if the hypothesis holds under all circumstances.

Determine if the hypothesis is supported and how it should be modified.

Since the rate did not double at

45^\circ\text{C}

, the hypothesis is not supported. It must be modified to include a temperature limitation, recognizing that the direct proportion fails at higher temperatures (such as

45^\circ\text{C}

) where enzymes typically undergo thermal denaturation.

A scientific hypothesis must be revised or restricted when experimental evidence contradicts its predictions.

Key Concept

Evaluating and modifying a scientific hypothesis based on experimental results that contradict the initial prediction.

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