The enzyme peroxidase is found in many organisms. It catalyzes the breakdown of hydrogen peroxide into water and oxygen gas. The rate of peroxidase activity at different pH values was assessed by students in the lab. The students’ results are shown in graph 1.

Graph 1. Effect of pH on peroxidase activity

The figure presents a bar graph with 4 bars. The horizontal axis is labeled p H, and the four bars are labeled 3, 5, 7, and 9. The vertical axis is labeled Relative Peroxidase Activity, and no numbers are indicated along it, but an arrowhead is present at the top of the axis. The relative heights of each bar, with respect to the vertical axis, are approximately as follows. The bar for p H 3 reaches a height equivalent to one third of the vertical axis. The bar for p H 5 reaches the top of the vertical axis. The bar for p H 7 reaches a height equivalent to two thirds of the vertical axis. The bar for p H 9 reaches a height equivalent to one quarter of the vertical axis.

If the experiment is repeated at pH 11, the observed activity level of the enzyme will most likely be

Question

The enzyme peroxidase is found in many organisms. It catalyzes the breakdown of hydrogen peroxide into water and oxygen gas. The rate of peroxidase activity at different pH values was assessed by students in the lab. The students’ results are shown in graph 1.

Graph 1. Effect of pH on peroxidase activity

The figure presents a bar graph with 4 bars. The horizontal axis is labeled p H, and the four bars are labeled 3, 5, 7, and 9. The vertical axis is labeled Relative Peroxidase Activity, and no numbers are indicated along it, but an arrowhead is present at the top of the axis. The relative heights of each bar, with respect to the vertical axis, are approximately as follows. The bar for p H 3 reaches a height equivalent to one third of the vertical axis. The bar for p H 5 reaches the top of the vertical axis. The bar for p H 7 reaches a height equivalent to two thirds of the vertical axis. The bar for p H 9 reaches a height equivalent to one quarter of the vertical axis.

If the experiment is repeated at pH 11, the observed activity level of the enzyme will most likely be

BlackTom AI · Accepted Answer

Enzyme activity depends on pH: each enzyme has an optimal pH at which activity is maximal, and activity decreases as conditions deviate from that optimum due to changes in enzyme charge, substrate binding, and possible denaturation.

1) Relevant knowledge points and concepts
- Enzymes have an optimal pH; peroxidase in this dataset shows a clear optimum near pH 5.
- Deviations from optimal pH (especially toward extremes) generally reduce catalytic activity because ionizable side chains change charge and tertiary structure can be disrupted.

2) Step-by-step reasoning
- Read the bar heights: pH 5 is highest (set as 100% relative activity), pH 7 is lower, pH 3 is low, and pH 9 is very low.
- The pattern shows activity rising from pH 3 to a peak at pH 5, then declining at pH 7 and dropping further at pH 9.
- Extending that trend to more alkaline pH (pH 11) predicts further reduction in activity because the environment moves even farther from the enzyme’s optimum.

3) Calculations / intermediate steps (relative values)
- Assign relative values from the graph: pH 5 = 100%; pH 7 ≈ 67%; pH 3 ≈ 33%; pH 9 ≈ 25%.
- Moving from pH 9 to pH 11 is an additional shift away from optimum; activity is expected to fall below ~25% (pH 9 level).

4) Why the correct answer is correct
- Because the enzyme’s activity already shows a decreasing trend in the alkaline range (pH 7 → pH 9), further alkalinization to pH 11 will most likely reduce activity further due to altered ionization of residues and partial denaturation, so activity at pH 11 will be lower than at pH 9.

5) Why the other options are incorrect
- "the same as pH 7": pH 7 has substantially higher activity (~67%); the trend is decreasing toward higher pH, so equality is unlikely.
- "greater than pH 9": contradicts the observed declining trend in alkaline conditions.
- "between pH 5 and pH 7": that would imply much higher activity (between 67–100%), which conflicts with the pattern of decreasing activity beyond pH 5.

6) Conclusion
- Therefore the most likely observation at pH 11 is lower than the level at pH 9, which matches the provided correct answer.

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