Enzymes

A teacher investigates the effect of different enzymes on starch. They want to find out if the enzyme breaks down the starch into sugar.

This is the method they use:

• Add 1 cm³ of an enzyme to 5 cm³ of starch solution in a boiling tube.

• Leave the mixture for 5 minutes.

• Add Benedict’s solution to the mixture.

• Place the boiling tube in a hot water bath.

• Record the colour of the Benedict’s solution after heating.

Benedict’s solution is a blue solution that, when heated, forms a coloured precipitate if sugar is present.

Fig. 16.1 shows how the teacher tested for the presence of sugar in the mixture.

Fig. 16.1

The teacher repeats the method with different enzymes.

Identify the dependent variable in this investigation.

Suggest one hazard in this investigation and the precaution the teacher should take.

Complete the table.

The concentration of sugar in mixture C stated in the table is not an accurate value.

How can the student tell that it is not an accurate value?

The amount of light absorbed by different colours can be measured.

The graph compares absorbance with the percentage of sugar concentration.

The teacher investigates the light absorbed by the different coloured mixtures.

They record an absorbance of 0.2 for mixture C.

Use the graph to find the sugar concentration of mixture C.

The answer to (i) is outside the range stated in the results table.

Suggest how the student could improve their method to find out how precise their measurement is for mixture C.

A teacher investigates the effect of different enzymes on starch. They want to find out if the enzyme breaks down the starch into sugar.

This is the method they use:

• Add 1 cm³ of an enzyme to 5 cm³ of starch solution in a boiling tube.

• Leave the mixture for 5 minutes.

• Add Benedict’s solution to the mixture.

• Place the boiling tube in a hot water bath.

• Record the colour of the Benedict’s solution after heating.

Benedict’s solution is a blue solution that, when heated, forms a coloured precipitate if sugar is present.

Fig. 12.1 shows how the teacher tested for the presence of sugar in the mixture.

Fig. 12.1

The teacher repeats the method with different enzymes.

Identify the dependent variable in this investigation.

Suggest one hazard in this investigation and the precaution the teacher should take.

Complete the table.

The concentration of sugar in mixture C stated in the table is not an accurate value.

How can the student tell that it is not an accurate value?

The amount of light absorbed by different colours can be measured.

The graph compares absorbance with the percentage of sugar concentration.

The teacher investigates the light absorbed by the different coloured mixtures.

They record an absorbance of 0.2 for mixture C.

Use the graph to find the sugar concentration of mixture C.

The answer to (i) is outside the range stated in the results table.

Suggest how the student could improve their method to find out how precise their measurement is for mixture C.

The diagram shows the volume of gas collected during an enzyme reaction in an upside down measuring cylinder.

Bottom of

What is the volume of collected gas in the measuring cylinder?

6 cm³ A

8 cm³ B

12 cm³ C

14 cm³ D

A scientist investigates the effect of temperature on anaerobic respiration in yeast.

The diagram shows the apparatus they use.

This is the method they follow:

• Collect the gas produced by the yeast for five minutes.

• Increase the temperature of the water bath.

• Repeat the investigation with fresh sugar solution.

• Do each temperature three times.

Suggest why the scientist used fresh sugar solution each time.

Identify one variable the scientist should keep constant throughout the experiment.

Tick (✓) one box.

Which gas is collected by the scientist in the gas syringe?

When calculating the mean for 55 °C, they did not include Trial 1.

Give the reason why.

Plot the mean values from the table on the graph.

Draw a curve of best fit.

Anaerobic respiration is an enzyme-controlled reaction.

Explain the results between 15 °C and 35 °C. Include ideas about enzyme particles.

The scientist concludes that the best temperature for anaerobic respiration is approximately 40 °C.

How could they alter their investigation to identify a more accurate temperature?

*(i) Describe and explain the pattern in the results.

Use ideas about the lock and key hypothesis in your answer.

Describe how the student could improve their investigation to find a more accurate optimum pH for the enzyme.

Catalase is an enzyme found in potato. Catalase breaks down hydrogen peroxide to form water and oxygen.

A student investigates the activity of catalase.

This is the method they follow: – Cut equal sized pieces of potato. – Put one piece of potato into a conical flask. – Add 50 cm³ of dilute hydrogen peroxide. – Collect the oxygen produced in 15 minutes using a measuring cylinder full of water.

Fig. 15.1 shows the set-up of their investigation.

The student then repeats the investigation, increasing the number of potato pieces each time.

Each time the student repeats the investigation they use 50 cm³ of new dilute hydrogen (a) (i) peroxide.

Explain why they need to replace the dilute hydrogen peroxide.

Explain why the student does not need to replace the potato pieces already in the flask when repeating the investigation.

Plot a graph of the results and draw a line of best fit.

Use the graph to find the expected volume of oxygen produced when 4 pieces of potato are used.

Use the data in the table to calculate the rate of reaction when the student used 6 pieces of potato.

Give your answer to 2 significant figures.

Rate of reaction =........ cm³ / min

The reaction is exothermic.

Suggest how the student could improve their investigation to control the temperature.

Explain why the student leaves the test tubes in the water bath for 5 minutes before mixing them.

The table shows the student’s results.

Explain the result for 20 °C.

Explain why amylase works slowly at 50 °C but no longer works at 60 °C.

The student has investigated the effect of temperature on the activity of amylase.

Describe how they could develop their investigation to find the effect of pH on the activity of amylase.

Which gas makes the bubbles?

* The students think they could improve their method.

They will count the bubbles three times at each temperature. This would show up any anomalous results.

Describe other ways they could improve their method to obtain more precise and repeatable results.

For each improvement explain why it is needed.

The students count the bubbles three times at each temperature. They then calculate the mean number of bubbles at each temperature.

The table shows their results.

Plot the results on the grid.

Draw a line of best fit.

Respiration is an enzyme controlled reaction.

Use ideas about enzymes to explain the pattern in the results.

A student investigates an enzyme controlled reaction. She collects the gas produced during the reaction in a gas syringe.

The diagrams show the volume of gas in the gas syringe at the start and after five minutes.

What is the rate of the reaction?

A 0.625 cm³ / min

B 1.6 cm³ / min

C 3.6 cm³ / min

D 8 cm³ / min