Enzyme action

A dish is filled with agar jelly that contains starch. Four holes are cut into the jelly, and each hole is then filled as shown. After 30 minutes, which hole will be enclosed by the greatest starch-free area?

May/June 2015

A dish contains agar jelly mixed with starch. Four holes are made in the jelly, and each hole is filled as shown. After $30$ minutes, which hole will be surrounded by the largest area free of starch?

May/June 2015

X and Y are the reactants in a chemical reaction catalysed by the enzyme E. Z is the product. The first three steps of the reaction are shown. $X + E \rightarrow XE$ $Y + XE \rightarrow XYE$ $XYE \rightarrow ZE$ What is the fourth, final step in this reaction?

May/June 2016

Enzyme Q acts in the human alimentary canal. Fig. 6.1 illustrates how pH affects the rate of reaction of enzyme Q.

May/June 2016

What are the properties of enzymes?

May/June 2017

Which property of enzymes is accounted for by the lock and key hypothesis?

May/June 2017

During an enzyme reaction, where is the active site found, and where are the lock and key?

May/June 2018

During enzyme action, where is the active site located, and what is meant by the lock and key?

May/June 2018

Which statement concerning enzymes is incorrect?

May/June 2019

Food supplements are materials that are often added to a person's diet. They may come as tablets. The diagram shows the label on a food supplement. Use together with a balanced diet. Ingredients: • Amylase • Cellulase • Lipase • Protease This supplement could be suitable for a person whose pancreas is not making enough of some of the ingredients listed on the label.

May/June 2019

Six bean seeds were left to soak in cold water. Three of these were then boiled and allowed to cool. The boiled seeds and the unboiled seeds were cut into small pieces and placed on the top of agar jelly that contained starch. After two days, all the seeds were taken away and the jelly was tested using iodine solution. The diagram illustrates the outcome of the experiment. What is the explanation for the results with the non-boiled bean seeds?

May/June 2021

Which statement correctly describes enzymes?

May/June 2021

Six bean seeds were left to soak in cold water. Three of them were boiled and then allowed to cool. The boiled seeds and the unboiled seeds were cut into pieces and then put on the surface of agar jelly that contained starch. After two days, all the seeds were taken out and the jelly was tested with iodine solution. The diagram shows the outcome of the experiment. What is the explanation for the results with the non-boiled bean seeds?

May/June 2021

The human liver has a large amount of enzymes known as transaminases. These enzymes play a key role in amino acid metabolism. Amino acids are taken up from the alimentary canal and transported to the liver in a blood vessel.

May/June 2022

A student conducted two investigations on the action of yeast.

May/June 2022

The graph illustrates how substrate concentration affects the rate of an enzyme-controlled reaction. The results were obtained with a constant enzyme concentration at a temperature of 30^{\circ}C. Which statement explains the graph’s shape from X to Y?

May/June 2023

A dish contains agar jelly with starch. Four holes are made in the jelly, and each one is filled as shown in the diagram. After $30\,\text{minutes}$, which hole will be enclosed by the greatest starch-free area?

May/June 2024

A dish is filled with agar jelly that contains protein. Four holes are made in the jelly, and each hole is filled as shown in the diagram. After 30 minutes, which hole will have the greatest area around it with no protein?

May/June 2024

During an industrial process, milk is allowed to flow over jelly beads that contain the enzyme lactase. As the milk moves across the beads, it will make contact with lactase. By point X, all digestion of the milk has been completed. What is collected at X?

May/June 2024

What characteristics do enzymes have?

May/June 2025

The diagram illustrates an enzyme molecule. Which diagram depicts the substrate molecule for this enzyme?

May/June 2025

Give one example of a biological catalyst.

May/June 2025

What outcome would occur if an enzyme's active site were damaged?

May/June 2025

Catalase is an enzyme present in living cells. It speeds up the decomposition of hydrogen peroxide into oxygen and water. Some plant cells are a source of catalase. If plant material is crushed and mixed with water, a suspension containing the cell contents of the plant can be made. When hydrogen peroxide solution is added to this suspension, the oxygen released appears as gas bubbles. These bubbles gather to make a foam layer at the top of the suspension. The height of any foam formed can be measured. A greater height shows greater catalase activity. A student compared catalase activity in the cells of three plant species by measuring the foam height produced in each. Three cell suspensions, one each of celery, apple and potato, were supplied in separate beakers. The student used these steps: • stir the celery cell suspension in the beaker with a clean stirring rod • use a syringe to place $2\ \text{cm}^3$ of celery cell suspension into a clean test-tube • add $2\ \text{cm}^3$ of hydrogen peroxide solution to this test-tube using a clean syringe • begin timing at once • after $60$ seconds, measure the height of any foam formed and write down the result. Carry out the same steps with the apple cell suspension and then with the potato cell suspension. Fig. 1.1 shows the combined contents of each of the three test-tubes after $60$ seconds.

May/June 2025

The diagram shows an enzyme together with four molecules, A, B, C and D. Which of these molecules is the substrate for this enzyme?

Oct/Nov 2015

The diagram shows an enzyme molecule. Which substances could act as substrates for this enzyme?

Oct/Nov 2016

In the lock and key hypothesis, what acts as the lock and what acts as the key for the enzyme lipase?

Oct/Nov 2017

According to the lock and key hypothesis, which part acts as the lock and which part acts as the key for the enzyme lipase?

Oct/Nov 2017

Enzyme action may be described by the lock and key hypothesis. Where is the active site located, and does the substrate function as the lock or the key?

Oct/Nov 2018

Which of these statements about enzymes is correct?

Oct/Nov 2019

What occurs to an enzyme after it has catalysed a reaction?

Oct/Nov 2019

Which substrates and end products are linked to amylase and lipase?

Oct/Nov 2020

When an apple fruit is sliced open, the exposed surface of the apple tissue turns brown quickly and is less likely to be eaten. The diagram shows this colour change.

Oct/Nov 2020

The diagrams illustrate an enzyme molecule and several substrate molecules. Which diagram represents the substrate molecule for this enzyme?

Oct/Nov 2021

Which statement concerning enzymes is invariably correct?

Oct/Nov 2021

Explain the ‘lock and key’ hypothesis of enzyme action with a named example.

Oct/Nov 2021

Fats are split by the enzyme lipase to yield fatty acids and glycerol. In the ‘lock and key’ model of enzyme action, what represents the ‘lock’ and what represents the ‘key’ in this reaction?

Oct/Nov 2022

Amylases are enzymes produced by specific cells in animals and plants, and bacteria also make them. In humans, amylase is released into the alimentary canal in saliva and in pancreatic juice.

Oct/Nov 2022

Enzymes take part in many reactions inside living cells. Which statement explains the way enzymes act?

Oct/Nov 2023

Which statement gives a description of enzyme-catalysed reactions?

Oct/Nov 2023

A student is studying how an enzyme is used in fruit juice production. The student does the following: chops one apple into small pieces; places the same number of pieces into each of three beakers, A, B and C; adds $2\,\text{cm}^3$ of a dilute enzyme solution to the apple in beakers A and B; adds $2\,\text{cm}^3$ of distilled water to the apple in beaker C; keeps each beaker in a water-bath at a fixed temperature for 30 minutes; then filters the juice from each beaker into a separate measuring cylinder and notes the volume of juice gathered in each measuring cylinder.

Oct/Nov 2023

Hydrogen peroxide is a poisonous waste substance present in cells. The enzyme catalase, which is found in cells, decomposes hydrogen peroxide to form water and oxygen. hydrogen peroxide  catalase  water + oxygen If potato tissue is placed into a hydrogen peroxide solution in a test-tube, the catalase in the potato cells makes oxygen bubbles form. When detergent is added to the hydrogen peroxide solution, the oxygen bubbles become trapped and build up as a bubble layer that moves up the test-tube. The height of this layer shows how much catalase activity has taken place. A student used this method to investigate the activity of the catalase in potato tissue by following these instructions: • Label three large test-tubes A, B and C. • Add $5\text{ cm}^3$ of hydrogen peroxide solution to each test-tube. Hydrogen peroxide is an irritant that may damage eyes and skin. • Add $1\text{ cm}^3$ of detergent to the hydrogen peroxide solution in each test-tube. • Cut three pieces of potato measuring $10\text{ mm} \times 10\text{ mm} \times 10\text{ mm}$. • Put one of the pieces of potato into test-tube A. • Start the timer immediately and watch the potato piece. Oxygen bubbles will rise to the surface and make a layer at the top of the hydrogen peroxide solution. • Measure the height of this layer at 2, 4 and 6 minutes from the start and record these values. The height of the bubble layer should be measured from the top of the hydrogen peroxide solution to the top of the bubble layer, as shown in Fig. 1.1.

Oct/Nov 2023

Cubes of boiled egg white are put into test-tubes that contain $5\ \text{cm}^3$ of water. Boiled egg white has protein. As shown in the table, different additional substances are put into each test-tube. After the test-tubes have been left for eight hours, they are then checked for amino acids. Which test-tubes indicate that pepsin is an enzyme?

Oct/Nov 2024

Maltase is an enzyme located in the intestines of vertebrates, humans included.

Oct/Nov 2024

An experiment is carried out to determine how well different biological washing powders break down protein. Four cubes of cooked egg white (protein), each the same size, are prepared and their masses are recorded. The protein cubes are then placed in test-tubes containing $10\text{ cm}^3$ of solutions made from four different biological washing powders, all at the same concentration. The cubes are kept in the solutions at room temperature. After 24 hours, the protein cubes are taken out of the test-tubes and their masses are measured again. What is the percentage decrease in mass of the cube of protein in the most effective washing powder given to one decimal place?

Oct/Nov 2025

Which enzyme is added to fruit to help juice production?

Oct/Nov 2025

A large number of reactions in cells depend on enzyme activity. Which statement about enzymes is not correct?

Oct/Nov 2025

Four test-tubes are each filled with starch solution and amylase. As shown in the table, they are kept in water-baths at different temperatures and at different pHs. All the other conditions remain unchanged. After 30 minutes, iodine solution is added to every test-tube. The mixture in three of the test-tubes becomes blue-black. In which test-tube do the contents remain yellow-brown? A: temperature $35^\circ\text{C}$, pH $2.5$ B: temperature $35^\circ\text{C}$, pH $6.9$ C: temperature $75^\circ\text{C}$, pH $2.5$ D: temperature $75^\circ\text{C}$, pH $6.9$

Oct/Nov 2025

Apple juice is produced by chopping up apples and crushing them. If apple tissue is cut and crushed, its colour may deepen and it can turn brown. Some students studied how vitamin C affected colour change in apples after they were cut and crushed. The students carried out these steps: • Put a label on a large test-tube and pour in 5 cm3 of vitamin C solution. • Put a label on a second large test-tube and pour in 5 cm3 of distilled water. • Put a label on a third large test-tube and leave it without any liquid. • Prepare three apple cubes, each measuring 1 cm × 1 cm × 1 cm. Exclude all skin and core. • Slice each cube into many small pieces. Keep the pieces from each cube separate. • Place the pieces from one cube into the test-tube containing vitamin C solution. • Place the pieces from the second cube into the test-tube containing distilled water. • Place the pieces from the third cube into the test-tube with no liquid added. • With a glass rod, carefully crush the apple pieces at the bottom of each test-tube. • Wash the glass rod between uses in the different test-tubes. • Begin timing. At the start of timing, the students observed that the apple tissue in each test-tube was white. They checked the colour of the apple tissue in each test-tube after 5, 10 and 15 minutes and wrote down their observations. Fig. 1.1 shows part of one notebook: vitamin C: white → white → white distilled water: white → pale yellow → dark yellow no added liquid: yellow → dark yellow → brown

Oct/Nov 2025

Hydrogen peroxide is a toxic waste product found in living cells. Catalase is the enzyme that breaks hydrogen peroxide down into water and oxygen. Some students investigated catalase in tissues from different plants. They used small filter paper discs. These discs were placed on the cut surface of plant tissues so that they could soak up liquid from the cells. That cell liquid may have contained catalase. Fig. 1.1 shows how the students could determine whether catalase was present in tissues from different plants. Fig. 1.1 text: beaker containing hydrogen peroxide solution; filter paper disc soaked in liquid from plant cells; filter paper disc containing trapped bubbles of oxygen. A filter paper disc soaked in liquid from plant cells was dropped into the hydrogen peroxide solution and sank to the bottom. If catalase was present, bubbles of oxygen formed. The bubbles of oxygen were trapped in the filter paper disc making it float to the surface. The students were supplied with 2 cm \times 2 cm \times 2 cm cubes of tissue from three different plants labelled A, B and C, small filter paper discs and a beaker of hydrogen peroxide solution. The students carried out the following steps. • Cut the piece of plant tissue A in half. • Use forceps to put a filter paper disc onto a cut surface of plant tissue A, so that it could absorb liquid from the cells. • After 1 minute, use forceps to lift the filter paper disc off the cut surface of plant tissue A. • Drop the filter paper disc into the beaker of hydrogen peroxide solution and start timing at once. The filter paper disc will sink to the bottom of the beaker. • Watch the filter paper disc until it reaches the surface of the hydrogen peroxide solution, then stop timing. If a filter paper disc does not float within 4 minutes (240 seconds) stop timing and record the time taken for the filter paper disc to reach the surface as >240. • Record the time taken, to the nearest whole second, for the filter paper disc to reach the surface of the hydrogen peroxide solution. • Use forceps to take the filter paper disc out of the beaker of hydrogen peroxide solution and put it in the waste container provided. • Rinse and dry the forceps. • Repeat the procedure two more times with filter paper discs on the same cut surface of plant tissue A. • Carry out the whole procedure again for filter paper discs on plant tissue B and then once more for plant tissue C. Fig. 1.2 shows a student's notebook. The student has written their results to the nearest whole second. The result for the third filter paper disc on plant tissue A is missing from their notes. Fig. 1.2 text: repeat discs. plant A: 10, 10. plant B: 21, 16, 20. plant C: no disc floated at 4 minutes. Fig. 1.3 shows the time taken for the third filter paper disc on plant tissue A to reach the surface. Fig. 1.3 display: 9.31 SEC.

Oct/Nov 2025