Enzymes Banker

1. (a) A student measured the rate of an enzyme reaction at different temperatures.A 20 °CB 30 °CC 40 °CD 50 °C [1]

1. (a) An enzyme from a human cell is tested at 10 °C, 25 °C and 37 °C. The rate increases as the temperature rises.Explain why the rate increases between 10 °C and 37 °C. [3]
2. (b) State the term used for the temperature at which an enzyme works fastest. [1]

Potato contains catalase, which breaks down hydrogen peroxide into water and oxygen. A student put 5.0 g of chopped potato into a flask with 10 cm³ of buffer solution and 10 cm³ of hydrogen peroxide. The oxygen was collected in an inverted measuring cylinder for 2 minutes. This was repeated with buffers of different pH.pH: 3, 5, 7, 9, 11volume of oxygen after 2 minutes / cm³: 4.5, 11.0, 18.5, 12.0, 3.0

1. (a) State the pH at which catalase in potato worked best in this investigation. [1]
2. (b) State the independent variable and the dependent variable. [2]
3. (c) State two variables that should be kept the same, and say how one of them could be controlled. [3]

1. (a) A student investigates the effect of pH on the activity of amylase. Which variable must be kept constant?A pH of the solutionB temperature of the mixtureC time taken for starch to be digestedD colour of the iodine solution [1]

1. (a) Complete the passage using suitable words.'Each enzyme works best at a particular pH, called its ____ pH. If the pH is too high or too low, the shape of the ____ ____ changes. The substrate no longer ____ into it, so fewer enzyme–substrate ____ are formed. The enzyme is said to be ____.' [5]

A student placed a tube of 5 cm³ starch solution and a tube of 1 cm³ amylase solution separately in a water-bath at 37 °C for 5 minutes, then mixed them and kept the mixture in the water-bath. Every 30 s, a drop of the mixture was added to a drop of iodine solution on a spotting tile.time / s: 0, 30, 60, 90, 120, 150, 180colour: blue-black, blue-black, blue-black, dark brown-black, brown-black, orange-brown, orange-brown

1. (a) State the time at which the starch had been fully digested. [1]
2. (b) Explain why the amylase and starch were placed in the water-bath separately for 5 minutes before they were mixed. [2]
3. (c) State the colour that iodine solution turns when starch is present. [1]
4. (d) Suggest one safety precaution needed in this experiment. [1]

1. (a) Why does the rate of an enzyme-controlled reaction fall when the temperature is raised well above the optimum?A The enzyme molecules are killed by the heat.B The substrate molecules move too fast to collide with the enzyme.C The shape of the active site changes, so the substrate no longer fits.D The enzyme is used up faster at high temperatures. [1]

Amylase was mixed with starch solution at five temperatures. A drop of the mixture was tested with iodine solution every 10 s until it no longer turned blue-black. The time taken was recorded.temperature / °C: 10, 20, 30, 40, 50, 60time for starch to disappear / s: 600, 300, 150, 90, 240, no end point after 900 s

1. (a) Calculate the rate of reaction at 40 °C and at 50 °C, using rate = 1000 ÷ time. Give each answer to 3 significant figures. [2]
2. (b) Describe the effect of temperature on the rate of reaction shown by the results. [3]
3. (c) Explain why the iodine never stopped turning blue-black at 60 °C. [2]

A student added 1 cm³ of liver extract (contains catalase) to 5 cm³ of hydrogen peroxide mixed with 2 cm³ of buffer in a narrow tube, and measured the maximum height of foam produced. Each pH was tested three times.pH 3: 4, 5, 4 mmpH 5: 12, 14, 13 mmpH 7: 30, 32, 31 mmpH 9: 18, 8, 20 mmpH 11: 6, 5, 7 mm

1. (a) Identify the anomalous result. [1]
2. (b) Calculate the mean height of foam at pH 3 (to 1 decimal place) and at pH 9 (leaving out the anomalous result). [2]
3. (c) Suggest one reason why the anomalous result may have occurred. [1]
4. (d) Write a conclusion for this investigation. [2]

Agar containing milk protein is cloudy. Paper discs were soaked in protease solution made up in buffers of different pH and placed on the milk agar. After 24 hours at 30 °C, the diameter of the clear zone around each disc was measured. Three discs were used for each pH.pH 4: 6, 7, 8 mmpH 6: 14, 15, 16 mmpH 8: 11, 12, 10 mmpH 10: 3, 4, 2 mm

1. (a) Calculate the mean diameter of the clear zone at each pH. [2]
2. (b) Calculate the percentage change in mean diameter between pH 6 and pH 8. Give your answer to 1 decimal place. [2]
3. (c) Explain why a clear zone forms around each disc. [2]
4. (d) Suggest one way to make the measurement of the clear zones more accurate. [1]

Biological washing powders contain enzymes, including proteases and lipases. The label on one powder says: 'Best results at 30–40 °C. Do not use above 60 °C.'

1. (a) Explain why the biological washing powder removes egg and blood stains well at 40 °C. [2]
2. (b) Explain why the powder works poorly if the clothes are washed at 90 °C. [2]
3. (c) Suggest why it can be cheaper for a family in Karachi to wash clothes with biological powder in cool tap water rather than with non-biological powder in hot water. [1]

Pectinase helps to release juice from fruit. A student mixed 20 g of crushed apple with 2 cm³ of pectinase at different temperatures, then filtered the mixture for 20 minutes.temperature / °C: 20, 30, 40, 50, 60volume of juice / cm³: 6.0, 9.5, 14.0, 11.0, 4.5A control with boiled pectinase at 40 °C gave 3.0 cm³ of juice.

1. (a) Calculate the percentage increase in juice volume from 20 °C to 40 °C. Give your answer to 2 significant figures. [2]
2. (b) Explain why some juice was produced in the control tube with boiled pectinase. [1]
3. (c) The student placed the beakers of apple pulp and pectinase in water-baths and mixed them straight away. Identify one source of error in this method and suggest an improvement. [2]
4. (d) State the temperature range in which the optimum temperature lies, and describe how the investigation could be extended to find it more precisely. [2]

1. (a) A patient with a fever has a body temperature of 40.5 °C. Suggest why a very high fever can be dangerous, in terms of enzymes. [2]
2. (b) Explain why it is an advantage for humans to keep their body temperature close to 37 °C. [2]

1. (a) Which statements about enzymes are correct?1 Extreme pH can change the shape of the active site.2 Enzymes are denatured at low temperatures such as 5 °C.3 Different enzymes can have different optimum pH values.A 1, 2 and 3B 1 and 2 onlyC 1 and 3 onlyD 2 and 3 only [1]

1. (a) Two protein-digesting enzymes, P and Q, were tested at different pH values. Enzyme P worked best at pH 2 and enzyme Q worked best at pH 8.Which row shows where each enzyme is most likely to act in the human alimentary canal?A P: mouth; Q: stomachB P: stomach; Q: small intestineC P: small intestine; Q: stomachD P: stomach; Q: mouth [1]

A student put a protease solution in two tubes.Tube A was kept at 2 °C for 30 minutes, then warmed to 37 °C and mixed with protein.Tube B was kept at 80 °C for 30 minutes, then cooled to 37 °C and mixed with protein.Tube A digested the protein normally. Tube B digested none of the protein.

1. (a) Explain the results for tube A and tube B. [4]
2. (b) Seeds kept dry in a freezer in a seed bank can still germinate many years later, but seeds that have been boiled never germinate. Use your knowledge of enzymes to suggest why. [2]

1. (a) Plan an investigation to find the effect of temperature on the activity of lipase.Lipase digests fat in milk into fatty acids and glycerol. Milk mixed with sodium carbonate solution and phenolphthalein indicator is pink; the pink colour disappears when enough fatty acids have been produced.In your plan, include the apparatus and the method, the variables you will control, and how you will make your results reliable. [6]

Some bacteria live in hot springs in northern Pakistan where the water is about 75 °C. An enzyme extracted from one of these bacteria has an optimum temperature of 75 °C.

1. (a) Suggest why the enzyme from the hot-spring bacterium is not denatured at 75 °C, but a human enzyme would be. [2]
2. (b) Explain why the bacterial enzyme works more slowly at 37 °C than at 75 °C. [2]
3. (c) Suggest one advantage of using an enzyme like this in an industrial process that runs at a high temperature. [1]

Yeast suspension (contains catalase) was added to hydrogen peroxide at five temperatures. The time taken to collect 10 cm³ of oxygen in a gas syringe was recorded.temperature / °C: 15, 25, 35, 45, 55time to collect 10 cm³ / s: 125, 64, 40, 52, 160

1. (a) Calculate the rate of oxygen production at 25 °C and at 45 °C in cm³ per second. Give your answers to 2 significant figures. [2]
2. (b) The student concluded that the optimum temperature is 35 °C. Explain why this conclusion may not be correct and suggest what further work would show the optimum more precisely. [3]
3. (c) Suggest why measuring the time to collect 10 cm³ of gas is better than collecting gas for a fixed long time, such as 10 minutes, at every temperature. [1]

Slices of mango were kept for 5 days at two temperatures. The mass lost because of decay was measured.kept at 4 °C (refrigerator): mass lost 3.2 gkept at 30 °C (kitchen in summer): mass lost 14.4 g

1. (a) Calculate how many times greater the mass loss was at 30 °C than at 4 °C. [1]
2. (b) Explain the difference in mass loss, in terms of the enzymes of decomposers on the mango. [3]
3. (c) Predict what would happen to the rate of decay if the mango slices kept at 4 °C were moved to 30 °C. Give a reason. [2]

1. (a) Which description of enzymes is correct?A carbohydrates that act as biological catalystsB proteins that act as biological catalystsC proteins that are used up in the reactions they controlD fats that speed up reactions in cells [1]

1. (a) State what is meant by a catalyst. [1]
2. (b) Name the product formed when amylase acts on starch. [1]
3. (c) Explain why amylase cannot digest protein. [2]

A student mixed starch solution with amylase and left it at 35 °C for 15 minutes. She then tested a sample of the mixture with Benedict's solution.

1. (a) Describe how the student should carry out the Benedict's test on the mixture. [2]
2. (b) The mixture turned brick red. Explain this result. [2]
3. (c) State the colour you would expect if Benedict's test was done on the starch solution before amylase was added. [1]

1. (a) An enzyme acts on only one substrate. Which feature explains this?A The substrate has a shape complementary to the active site of the enzyme.B The enzyme is denatured by all other substrates.C The enzyme has many active sites of different shapes.D The product has the same shape as the active site. [1]

1. (a) Describe how an enzyme molecule catalyses the breakdown of a substrate molecule. Use the terms active site and enzyme–substrate complex in your answer. [4]

Four tubes each contained 5 cm³ of starch solution at 35 °C:A: + 1 cm³ amylaseB: + 1 cm³ proteaseC: + 1 cm³ amylase that had been boiled and cooledD: + 1 cm³ waterAfter 15 minutes a drop from each tube was tested with iodine solution.

1. (a) State the result expected for each tube. [2]
2. (b) Explain what these results show about enzymes. [2]
3. (c) Explain why tube D is included. [1]

1. (a) Complete the table by naming the missing substances.Enzyme | substrate | product(s)amylase | starch | (i) ____protease | (ii) ____ | amino acidslipase | fats and oils | (iii) ____catalase | (iv) ____ | water and oxygen [4]

1. (a) Explain why enzymes are important to living organisms. [2]
2. (b) A liver cell contains hundreds of different enzymes. Suggest why so many different enzymes are needed. [2]

Some people cannot digest lactose, the sugar in milk. A dairy company in Lahore makes lactose-free milk by adding the enzyme lactase, which breaks lactose into glucose and galactose.

1. (a) Explain why lactase breaks down lactose but not sucrose, even though both are disaccharides. [2]
2. (b) The company adds a small amount of lactase to a large tank of milk. Explain why only a small amount of enzyme is needed. [2]
3. (c) A mutation in the gene for lactase changes one amino acid in the active site. Suggest how this could affect the enzyme. [2]

An enzyme was mixed with a fixed quantity of substrate at its optimum temperature. The mass of product was measured every minute.time / min: 0, 1, 2, 3, 4, 5, 6mass of product / mg: 0, 8, 16, 22, 26, 28, 28

1. (a) Calculate the initial rate of reaction over the first 2 minutes in mg per minute. [1]
2. (b) Explain why no more product forms after 5 minutes. [2]
3. (c) The experiment is repeated with twice the concentration of enzyme and the same amount of substrate. Predict the effect on the initial rate and on the final mass of product. Explain your answer. [3]