Enzymes (Cambridge (CIE) IGCSE Biology)

The effect of temperature on enzyme activity was investigated. The results are shown in Fig. 1.

Fig. 1

(i)

State the optimum temperature for the enzyme in Fig. 6.1. Give your answer in °C.

[1]

(ii)

State why there is no enzyme activity at 60 °C.

[1]

State one factor other than temperature that affects enzyme activity.

Table 1 shows some large insoluble molecules, some digestive enzymes and some smaller soluble molecules that are produced during digestion.

Table 1

Complete Table 1 by writing the names of the missing enzyme and molecules.

The first row has been done for you.

List the chemical elements present in fats.

State where in the digestive system protease is secreted.

Catalase is an enzyme that catalyses the breakdown of hydrogen peroxide into water and oxygen. 

The effect of temperature on catalase activity was investigated. 

The results are shown in Fig. 1

Fig. 1

(i)

State the temperature at which catalase is most active in Fig. 1. Give your answer in °C.

[1]

(ii)

Explain why there is no enzyme activity at 60°C. 

[1]

State one factor other than temperature that affects enzyme activity.

Digestive enzymes are used in chemical digestion to break down large insoluble molecules to smaller soluble molecules.

The boxes show some large insoluble molecules, some digestive enzymes and some smaller soluble molecules that are produced during digestion.

Draw one straight line from each enzyme to the insoluble molecule it acts on. 

Draw another line from each enzyme to the smaller soluble molecule that is produced.

Draw a total of six lines.

[5]

Digestive enzymes are secreted in different parts of the body. 

Gastric proteases are found in the stomach. 

Suggest the optimum pH for gastric protease. 

Extended only

Fig. 1 shows an enzyme in its optimum pH and in a pH that is much lower.

Fig. 1

Describe what has happened to the enzyme. 

Extended only

Sketch an appropriate substrate for the enzyme shown in Fig. 1

Extended only

A farmer tested a range of pHs on the soil in a section of a field and recorded the percentage of germination of carrot seedlings at each pH. 

Fig. 2 shows the results. 

Fig. 2

Describe and explain which pH is the optimum pH for the carrot seedlings. 

Extended only

Another farmer suggested they plant radish seedlings at the carrot seedling's optimum pH shown in Fig. 2. 

Explain why this farmer's suggestion may be incorrect. 

During the fermentation of yeast, enzymes that break down sugar release carbon dioxide gas. The volume of carbon dioxide released can be used to measure how fast these enzymes are working.

A student investigates if fermentation works faster at two different temperatures: 25°C or 30°C. They measured the volume of carbon dioxide released in 15 minutes. Fig. 1 shows the apparatus she uses.

Fig. 1

The student used a gas syringe, as shown in Fig. 1 to collect and measure the volume of carbon dioxide released. They could have measured the volume of carbon dioxide by collecting the gas over water in a measuring cylinder.

Use the information provided in Fig. 1 to suggest why it is better to use a gas syringe.

The student’s results are shown in 

Table 1

(i)

Calculate the mean rate of gas produced at 25°C in cm³/minute. Give your answer to 1 decimal place.

 [3]

(ii)

The rate of gas produced at 30°C is greater than at 25°C. Use your knowledge of enzymes to explain why.

[3]

(iii)

The teacher tells the student to repeat the results for 30°C.  Explain why the teacher advised this. 

[1]

Extended

Enzymes can be inhibited by chemicals called phenols during fermentation.

Phenols bind to amino acids on enzyme molecules.

Suggest how phenols inhibit enzymes.

Extended only

Salivary amylase is an enzyme that is produced and secreted by salivary gland cells in the mouth.

Carbohydrate digestion, by amylase, begins in the mouth.

Starch, a polysaccharide, is hydrolysed into the disaccharide maltose by the enzyme salivary amylase.

The effect of changing pH and temperature on the digestion of starch was investigated by a group of students. The results are shown in Table 1 and Table 2 below.

Table 1 - Effect of pH

Table 2 - Effect of temperature

A student reads the following statement on the Internet: ‘The main site for carbohydrate digestion is the small intestine.’

One of the students states that salivary amylase must be responsible for digesting starch in the small intestine. The student is incorrect.

Use the results in Table 1 to explain why.

Using the results shown in Table 2, explain how temperature affects digestion.

Extended only

A second form of amylase, pancreatic amylase, is responsible for continued carbohydrate digestion in the small intestine.

Explain how the digestion of food by enzymes in the intestine is not inhibited by the acid produced in the stomach.

Extended only

The pancreas is an organ that produces enzymes used in digestion. 

Explain the importance of enzyme specificity in the digestion of food.

Extended only

Pancreatic cancer develops when a malignant tumour grows inside the pancreas.

One symptom of pancreatic cancer is weight loss.

With reference to enzymes, explain how pancreatic cancer may cause a person to lose weight.

Extended only

Certain types of antibodies, called monoclonal antibodies, have been used to treat pancreatic cancer. 

Compare the activity and nature of antibodies with those of enzymes.

Extended only

Biological washing powders contain enzymes and have to be used at temperatures below 45 °C.

Stains on clothes that are washed at temperatures above 45 °C are not always removed.

Explain why. 

Extended only

Thermophilic bacteria are a special type of bacteria that live in hot springs at temperatures of 80 °C.

Scientists have extracted enzymes from thermophilic bacteria. The scientists added these enzymes to biological washing powder in the lab and tested them on a range of lab produced stains on cotton cloth.

It is expected that by using the washing powder the user can increase the cleaning performance of their laundry cycle.

Suggest why.

Extended only

The scientists compared two different washing powders each containing a different enzyme from thermophilic bacteria.

They washed stained items of clothing for different periods of time and recorded the percentage of stain removal. Their results are shown in Fig.1 below. 

Fig. 1

Compare the results of the two washing powders.

Extended only

A scientist released a report with the claim, "A 30 minute wash can rid your clothes of 95% of stains with new thermophilic washing powder".

Evaluate this claim.

Enzymes are involved in controlling cell division. Fig. 1 shows how cell division can be accelerated by two enzymes, enzymes X and Y, in cancerous liver cells. Most cancer cells produce both enzymes X and Y.

Cancer cells are likely to develop into cancerous tumours inside the liver by uncontrolled cell division. 

Fig. 1

Some people carry a genetic mutation that inhibits enzyme X. A drug company has produced a medicine that inhibits enzyme Y. This medicine has been trialled in people who have the mutation and liver cancer.  The medicine has been found to be successful at treating liver cancer. 

Explain why. 

Explain why the medicine could not be used to treat liver cancer in a patient that does not have the genetic mutation.

Extended only

Glutaminase is another enzyme that has shown success in treating cancer. It is within a group of enzymes called amino acid deprivation enzymes which act on and destroy specific amino acids in cancerous cells. 

Explain the action of the glutaminase on amino acids in cancer cells.

Extended only

Fig. 1 illustrates the results of two enzyme-controlled reactions involving two different types of enzyme.

Fig. 1

From these reactions, determine what conclusion can be drawn about the function of enzymes.

Extended

Catalase is an enzyme found in many different tissues in plants and animals. It speeds up the rate of the following reaction.

Fig. 2

A scientist investigated the effect of pH on the activity of the enzyme catalase in a geranium plant.

Table 1 shows the scientist's results. 

Table 1

Calculate a mean result for pH 3.5

Extended

Use the grid below to draw a graph of the scientist's results. 

Fig. 3

Extended

Use Table 1 and the graph to answer the following:

(i)

Describe the results shown in the graph.

[3]

(ii)

Predict the catalase activity at pH 7.

[1]

(iii)

Explain why the catalase activity is zero at pH 2.

[1]

A group of students carried out the following practical to establish the effect of temperature on protein breakdown:

• Place a drop of biuret solution into every well in a spotting tile.

  • Put 4 cm³ of 1 % protein solution into a boiling tube.

  • Put 4 cm³ of pepsin solution into a second boiling tube.

  • Put both boiling tubes into a water bath at 20 °C.

  • After 4 minutes add the pepsin solution to the protein solution together in one boiling tube, mixing together with a stirring rod.

  • After 20 seconds add a drop of the protein/pepsin mixture to a drop of biuret solution in one well of the spotting tile.

  • Repeat step 6 until the biuret solution no longer changes colour.

  • Repeat steps 1–7 at 10 °C (using an ice water bath), 30 °C, 40 °C and 50 °C.

The concentration of protein present in the solution can also be measured using a colorimeter.

In a colorimeter, the amount of light that cannot pass through a solution is measured; giving the ‘absorbance’ of a solution. The darker the colour, the higher the absorbance.

Suggest advantages of using the colorimeter method rather than the method used by the students.

The graph below shows a calibration curve of concentration of protein versus absorbance.

An experiment was carried out to investigate the effect of a protease enzyme on a 1 % protein solution.

The absorbance at 30 °C was 0.8 arbitrary units after 20 seconds.Using the calibration curve, estimate the final concentration of protein in this solution after 20 seconds.

Explain why the concentration of protein in the solution at 10 °C after 1 minute is different from the concentration at 30 °C after 1 minute in the graph in part (b).

The student repeated the experiment but incubated the protease and 1% protein solution at 80 °C.

The absorbance was measured at approximately 1.14 arbitrary units.

Suggest a reason for this result.