IB DP Biology Topic 2: Molecular biology 2.5 Enzymes Question Bank HL Paper 1

IB Biology HL (HIGHER level)- 2024 – Practice Questions- All Topics

Topic 2.5 Enzymes

Topic 2 Weightage : 10% 

All Questions for Topic 2.5-Enzyme & Substrate, Enzyme Catalysis, Enzyme Specificity, Enzyme Activity, Enzyme Experiments, Enzymes in Industry, Models of Action, Types of Enzymes, Lactose Intolerance


The graph shows the activity of an enzyme at different temperatures.


What does the dashed line in the graph represent?

    1. Increasing temperature increases substrate concentration.

    2. Increasing temperature affects the active site.

    3. Increasing temperature increases the rate of reaction.

    4. Increasing temperature decreases the movement of particles.


Ans: B

Enzymes are proteins that catalyze chemical reactions in living organisms. They have a specific three-dimensional structure that allows them to interact with other molecules and speed up chemical reactions. When an enzyme denatures, its structure changes and it can no longer interact with other molecules in the same way. This can cause the rate of reactions to slow down or even stop.
On denaturation, the shape of the active sites by the enzymes gets deformed or altered due to which the substrate does not fit into the assigned enzymes anymore. This leads to slowing down of the rate of reactions or even stopping.
Factors such as high temperatures can cause an enzyme to lose its shape (denature) and stop working. Each enzyme has an optimum pH range. Extreme high temperatures can cause an enzyme to lose its shape (denature) and stop working.


The graph shows the progress of the same enzyme-controlled reaction at two different temperatures.


Which statement is clearly supported by the data?

    1. The amount of product produced initially occurs at a lower rate at 40 °C

    2. The optimum temperature for the reaction is 40 °C

    3. The lower the temperature, the slower the rate of the reaction

    4. The enzyme is denatured at 40 °C


Ans: C

Enzymes are proteins that act as biological catalysts, meaning they speed up reactions without being used up. As temperature increases to the optimum, the kinetic energy of the enzyme and substrate increases, causing more collisions between the enzyme and substrate. This causes the formation of more enzyme-substrate complexes, leading to an increase in enzyme activity. However, an increase in temperature beyond the optimum causes the enzyme’s active site to become denatured. In most enzyme-controlled reactions occur slowly at low temperatures, enzyme activity is low because the enzyme and substrate molecules have less kinetic energy so there are fewer collisions between them


The activity of amylase from two bacterial species and a fungus was measured at different pH levels and constant temperature. The results are shown in the graph.

Which statement about the effect of pH on amylase can be concluded?

A. A. oryzae amylase has the highest optimum pH.

B. A change in pH affects amylase most in B. licheniformis.

C. The optimum pH is 6 in B. subtilis.

D. Amylase activity at pH 8 is the lowest in B. licheniformis.



Amylase is an enzyme that breaks down starch into sugars. It is produced by many organisms, including bacteria such as Bacillus licheniformis. The activity of amylase depends on several factors, such as temperature, substrate concentration, and pH. The optimal pH for amylase activity varies depending on the source of the enzyme. For B. licheniformis, the optimal pH is around 6 to 6.5, and the enzyme becomes less active at higher or lower pH values. This may be due to changes in the electrostatic interactions or the conformation of the enzyme at different pH levels. Some mutations in the gene encoding amylase can also affect the pH profile of the enzyme.

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