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AP®BiologyCollege BoardExam QuestionsUnit 3: Cellular EnergeticsEnzymes

Enzymes (College Board AP® Biology): Exam Questions

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Enzymes

1
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Enzymes play a critical role in lowering the activation energy required for a chemical reaction to occur. In a metabolic pathway, enzymes bind to specific substrates to facilitate this process. Which of the following best explains how enzymes lower the activation energy of reactions?

  • By breaking down substrates into smaller molecules before reactions occur.

  • By providing heat to reactants, increasing their kinetic energy.

  • By destabilizing bonds within the substrate, making it more reactive.

  • By working together with another enzyme in the pathway to collectively lower the activation energy.

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2
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A researcher is studying the effect of cyanide, a non-reversible inhibitor, on mitochondrial enzymes during cellular respiration. When cyanide binds to cytochrome oxidase, it halts the production of ATP.

Which of the following best explains why cyanide is considered a poison?

  • It lowers the activation energy needed for mitochondrial reactions

  • It permanently blocks the active site, preventing the enzyme from catalyzing reactions

  • It increases the efficiency of cellular respiration

  • It causes an increase in substrate concentration, leading to faster reactions

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3
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Enzymes are biological catalysts that function optimally at certain temperatures. Researchers conducted an experiment to observe how temperature affects the activity of the enzyme amylase, which breaks down starch.

They measured the amount of starch remaining over time at three different temperatures: 25°C, 37°C, and 50°C. The results are shown in the table below.

Time (minutes)

Starch remaining at 25°C (%)

Starch remaining at 37°C (%)

Starch remaining at 50°C (%)

0

100

100

100

10

80

50

60

20

65

10

40

30

50

0

20

Which of the following conclusions is best supported by the data?

  • Amylase works most efficiently at 25°C

  • The rate of starch breakdown is highest at 37°C

  • Amylase denatures at 25°C, reducing its activity

  • 50°C is the optimal temperature for amylase activity

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4
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In a study, researchers examined how competitive and non-competitive inhibitors affect the enzyme maltase, which breaks down maltose into glucose. They measured the rate of glucose production in reactions with and without inhibitors.

Bar chart showing glucose production rates: 50 mg/min with no inhibitor, 45 mg/min with competitive inhibitor, and 20 mg/min with non-competitive inhibitor.

Which of the following claims is best supported by the experiment's data?

  • Competitive inhibitors reduce the total amount of product formed

  • Non-competitive inhibitors inhibit the enzyme faster than the competitive inhibitor

  • Increasing substrate concentration would not affect the outcome with a competitive inhibitor

  • Competitive inhibitors are more effective than non-competitive inhibitors

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5
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Lactase is an enzyme that breaks down lactose, the primary sugar in milk, into glucose and galactose. This enzyme is crucial for lactose digestion in mammals.

Researchers were investigating the effects of pH on lactase activity to understand why some individuals experience lactose intolerance. They conducted an experiment measuring lactase activity across a range of pH values, keeping all other factors constant. The results of their experiment are shown in the graph below.

Graph showing relative lactase activity percentage against pH. Activity peaks around pH 6.5, with lower activity at pH 5 and 8.

Activity is expressed relative to the optimum of the enzyme. Which of the following conclusions about lactase is best supported by the data?

  • Lactase functions optimally in highly acidic environments, such as the stomach

  • The enzyme has a broad pH tolerance, maintaining high activity across all pH levels

  • Lactase has an optimal pH range near neutral, consistent with its function in the small intestine

  • The enzyme's activity increases linearly with pH due to increased ionization of its active site

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