Enzymes are biological catalysts used within living organisms to speed up reactions. 

Describe the induced-fit model of enzyme action.

Inhibitors are molecules that can affect the rate of enzyme-catalysed reactions.

Describe how a non-competitive inhibitor can reduce the rate of an enzyme-controlled reaction.

A scientist investigated the effect of caffeine on the hydrolysis of proteins by the enzyme trypsin. Their results are shown below. 

Suggest two variables the scientist should have controlled in his investigation.

Use the diagram above to explain why caffeine is described as a non-competitive inhibitor.

A student investigated the hydrolysis of cellulose using the enzyme cellulase. The student prepared 10 cm³ of different concentrations (mg dm^-3) of cellulose solution.

He then added the same concentration of cellulase to each cellulose solution. He measured the time in seconds for cellulase to completely hydrolyse the cellulose. 

Write the column headings the student should use in their results table.

Predict the trend you would expect to see in the results.

Inhibitors can be added to enzyme-catalysed reactions to decrease the rate of reaction.

Explain how a competitive inhibitor works to reduce enzyme activity.

Describe and explain how the action of competitive inhibitors can be reduced in an enzyme-catalysed reaction.

A scientist investigated the effect of temperature on the hydrolysis of sucrose using the enzyme sucrase. The graph shows his results. 

Calculate the rate of reaction in the first 3 hours at 40°C.

Explain the difference between the initial rates of reaction at 40°C and 55°C.

Explain the difference in the rates of reaction at 40°C and 55°C between 4 and 7 hours.

When potatoes are peeled, the enzyme tyrosinase is released from the cells.

This enzyme converts colourless tyrosine into a brown pigment called melanin.

Ascorbic acid or a protease enzyme can be added to potato slices to prevent this browning.

Explain why the addition of ascorbic acid prevents potato slices from browning.

Explain how a protease enzyme can have the same effect as ascorbic acid.

A student investigated the activity of tyrosinase by measuring the amount of melanin formed. Her results are shown below. 

Explain the results shown in the graph.

The room temperature in which peeled potatoes are kept can affect how quickly they turn brown.

Plan an investigation into the effect of temperature on the enzyme tyrosinase.

Amylase is an enzyme responsible for hydrolysing starch into maltose. 

Describe a chemical test you could carry out to test for the presence of amylase in a sample.

Explain why the structure of amylase results in a positive test for the method you have described in the previous question.

Explain why amylase only catalyses the breakdown of starch into maltose.

A student conducted an investigation to explore how altering the pH level affects the rate of a reaction catalysed by the enzyme amylase.

Amylase is responsible for breaking down starch into maltose.

The steps of the investigation are shown below:

1. The student prepared agar plates containing starch and created four equally sized wells in the agar of each plate.
2. In four separate test tubes, the student placed amylase solution with different pH values.
3. Once the optimum temperature was reached, a drop of each amylase solution was added to one of the four wells.
4. The plates were then incubated for one hour at the optimum temperature.
5. After one hour, the student covered the agar with iodine solution.

The diagram shows his results.

Describe how the student could ensure each amylase solution was at a different pH before adding to the wells.

Explain the appearance of the plate surrounding the well at pH 6.

Explain how a pH of 9 affects the activity of amylase.

Suggest how the results may have been different if the student had left the plate at room temperature instead of incubating them at optimum temperature.

Pepsin is an enzyme found in the stomach of mammals where it is responsible for digesting protein. 

Scientists originally devised the lock and key model to explain how enzymes work.

Explain how this model works.

More recently, scientists use the induced-fit model to explain enzyme action.

Suggest why most scientists now accept the induced-fit model as being true.

A scientist investigated the effect of increasing substrate concentration on the activity of the enzyme pepsin.

The diagram below shows his results.

Explain the results shown in the graph.

On the graph, draw a curve you would expect to see if a competitive inhibitor was added to this reaction.

A technician investigated the effect of temperature on the rate of an enzyme-controlled reaction. The graph below shows his results.

Describe the results shown in the graph.

Explain the shape of the curve between 10°C and 30°C.

Explain the shape of the curve between 30°C and 50°C.