Enzymes

Enzymes are large molecules and biological catalysts.

What type of molecule is an enzyme?

A catalyst changes the rate of a chemical reaction.

What happens to the mass of a catalyst during a chemical reaction?

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The mass of the catalyst decreases.

The mass of the catalyst stays the same.

The mass of the catalyst increases.

Figure 13 shows a model of enzyme action.

Name X and Y in Figure 13.

Name the model shown in Figure 13.

Amylase is an enzyme that breaks down starch.

A student investigated how changing the pH affected the activity of amylase.

This is the method used.

1. Heat a test tube containing 2 cm³ of amylase solution at pH 5.0 in a water bath at 35 °C.

2. H eat a test tube containing 2 cm³ of starch solution in the same water bath.

3. Transfer the amylase solution into the test tube of starch solution and mix.

4. After 30 seconds remove a drop of the amylase–starch mixture and test the drop for starch.

5. Repeat step 4 until no starch is detected.

6. Record the total time taken for no starch to be detected.

7. Repeat steps 1 to 6 using amylase solution at different pH values.

Explain why the solutions are all placed in the same water bath.

Describe the test for starch.

Give the result of the test if starch is present.

Table 4 shows the results.

Which range of pH values had the fastest rate of reaction?

Tick (✓) one box.

pH 5.0 to pH 5.5

pH 6.0 to pH 6.5

pH 7.0 to pH 7.5

pH 8.0 to pH 8.5

How could the method be improved to obtain a more accurate pH value for the fastest rate of reaction?

Enzymes are large molecules and biological catalysts.

What type of molecule is an enzyme?

A catalyst changes the rate of a chemical reaction.

What happens to the mass of a catalyst during a chemical reaction?

Tick (✓) one box.

The mass of the catalyst decreases.

The mass of the catalyst stays the same.

The mass of the catalyst increases.

Figure 1 shows a model of enzyme action.

Name X and Y in Figure 1.

Name the model shown in Figure 1.

Amylase is an enzyme that breaks down starch.

A student investigated how changing the pH affected the activity of amylase.

This is the method used.

1. Heat a test tube containing 2 cm³ of amylase solution at pH 5.0 in a water bath at 35 °C.

2. Heat a test tube containing 2 cm³ of starch solution in the same water bath.

3. Transfer the amylase solution into the test tube of starch solution and mix.

4. After 30 seconds remove a drop of the amylase–starch mixture and test the drop for starch.

5. Repeat step 4 until no starch is detected.

6. Record the total time taken for no starch to be detected.

7. Repeat steps 1 to 6 using amylase solution at different pH values.

Explain why the solutions are all placed in the same water bath.

Describe the test for starch.

Give the result of the test if starch is present.

Table 1 shows the results.

Which range of pH values had the fastest rate of reaction?

Tick (✓) one box.

pH 5.0 to pH 5.5

pH 6.0 to pH 6.5

pH 7.0 to pH 7.5

pH 8.0 to pH 8.5

How could the method be improved to obtain a more accurate pH value for the fastest rate of reaction?

A student investigated the effect of pH on the rate of starch digestion.

This is the method used.

1. Add 2 cm³ of amylase solution at pH 5.0 to a test tube.

2. Add 2 cm³ of starch solution to the same test tube.

3. Start the timer.

4. Remove one drop of the amylase-starch mixture after 30 seconds.

5. Test the drop for starch.

6. Remove a drop of the amylase-starch mixture every 30 seconds until no starch is detected.

7. Record the total time taken for no starch to be detected.

8. Repeat steps 1 to 7 using amylase solution at different pHs.

The student kept all the solutions in a water bath at 37 °C

What is the independent variable in the investigation?

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Describe the test for starch.

Give the result of the test if starch is present.

Table 3 shows the results.

What is the pH range the student used?

Use Table 3.

At the optimum pH the enzyme works fastest.

What is the optimum pH for amylase enzyme?

Use Table 3.

How could the investigation be improved to get a more accurate value for the optimum pH?

Tick (✓) one box.

What is the best way for the student to display the results?

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This question is about the enzyme amylase.

Amylase can only digest starch.

Explain why amylase cannot digest other substances.

Students investigated the effect of pH on the rate of starch digestion.

This is the method used.

1. Add 2 cm³ of amylase solution at pH 5.0 to a test tube in a water bath at 37 °C

2. Add 2 cm³ of starch suspension to the same test tube.

3. Start the timer.

4. Remove a drop of the amylase-starch mixture after 30 seconds.

5. Test the drop for starch.

6. Repeat steps 4 to 5 until no starch is detected.

7. Record the total time taken for no starch to be detected.

8. Repeat steps 1 to 7 using amylase solution at different pHs.

Which is the dependent variable in the investigation?

Tick (✓) one box.

Describe the test for starch.

Give the result of the test if starch is present.

The amylase solution and starch suspension were kept in the water bath at 37 °C for 10 minutes before being mixed.

Why were the amylase and starch kept at 37 °C for 10 minutes before being mixed?

Table 2 shows the results.

Student A concluded that:

‘The optimum pH for amylase is 7.5’.

Give one reason why this conclusion could be correct.

Use Table 2.

Student B concluded that:

‘The optimum pH is between 7.0 and 8.0 but may not be 7.5’.

How can student B determine a more accurate value for the optimum pH?

Use Table 2.

This question is about hydrogen peroxide.

The formula of hydrogen peroxide is H₂O₂

Name the elements in a molecule of hydrogen peroxide.

How many atoms are in a molecule of hydrogen peroxide?

Hydrogen peroxide decomposes to produce oxygen and water.

Write the word equation for the reaction.

A student investigated the decomposition of hydrogen peroxide.

The student used manganese dioxide as a catalyst.

The student measured the volume of oxygen produced.

The student collected the oxygen in a gas syringe.

Figure 7 shows a gas syringe.

What is the volume of oxygen in the syringe?

Figure 8 shows how the volume of oxygen collected varied with time.

Which point on Figure 8 shows when the reaction is fastest?

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Which point on Figure 8 shows when the reaction has stopped?

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The student repeated the investigation using raw potato instead of manganese dioxide.

An enzyme in the potato acts as the catalyst.

Draw one line from each catalyst to the type of substance the catalyst is.

The student repeated the investigation using boiled potato instead of raw potato.

The enzyme in the boiled potato did not catalyse the reaction.

How will the rate of decomposition of hydrogen peroxide using boiled potato compare with the rate using raw potato?

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Hydrogen peroxide (H₂O₂) decomposes to produce oxygen gas and water.

Balance the equation for the reaction.

Two catalysts that can be used in the reaction are raw potato and

manganese dioxide.

A student compared the rate of decomposition of hydrogen peroxide using:

• a cube of raw potato as the catalyst

• crushed raw potato as the catalyst.

The student kept all other variables constant.

The hydrogen peroxide decomposed at a different rate when using a cube of raw potato compared with using crushed raw potato.

Explain why.

The student repeated the investigation using boiled potato instead of raw potato.

When boiled potato is added to hydrogen peroxide no bubbles of oxygen are observed.

Explain why.

The student then investigated the rate of decomposition of hydrogen peroxide using manganese dioxide as the catalyst.

The student measured the volume of oxygen produced every 5 seconds for 50 seconds.

Figure 12 shows the results.

Determine the rate of reaction at 15 s

Catalase is an enzyme.

What type of molecule is an enzyme?

Hydrogen peroxide decomposes in the presence of catalase.

This is the equation for the reaction:

Describe how the student could test for the gas produced.

A student investigated the effect of pH on the activity of catalase.

Describe how the student could use an indicator to measure the pH of a solution.

Table 6 shows the results.

What is the optimum pH for catalase in this reaction?

Use Table 6.

How could the student find a more accurate value for the optimum pH?

Tick (✓) one box.

Explain the result for catalase at pH 3.0

Catalase is an enzyme.

What type of molecule is an enzyme?

Hydrogen peroxide decomposes in the presence of catalase.

This is the equation for the reaction:

Describe how the student could test for the gas produced.

A student investigated the effect of pH on the activity of catalase.

Describe how the student could use an indicator to measure the pH of a solution.

Table 1 shows the results.

What is the optimum pH for catalase in this reaction?

Use Table 1.

How could the student find a more accurate value for the optimum pH?

Tick (✓) one box.

Explain the result for catalase at pH 3.0