Name: PAST PAPERS PRACTICE PACKS - EXPERT … · €€€€€€€€€ The body uses enzymes...

PAST PAPERS PRACTICE PACKSENZYMES

Name:

Class:

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Comments:

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(a) Enzymes are used in body cells.

(i) What is an enzyme?

Draw a ring around the correct answer.

an antibody a catalyst a hormone

(1)

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(ii) All enzymes are made of the same type of substance.

What is this substance?


carbohydrate fat protein

(1)

(iii) Where is the enzyme amylase produced in the human body?


liver salivary glands stomach

(1)

(b) Enzymes are sometimes used in industry.

Draw one line from each enzyme to the correct industrial use of that enzyme.

Enzyme Industrial use

Changes starch into sugars

Carbohydrase

Removes grease stains from

clothes

Isomerase

Pre-digests proteins in some

baby foods

Protease

Changes glucose syrup into

fructose syrup

(3)(Total 6 marks)

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Diagrams A, B and C show cells from different parts of the human body, all drawn to the samescale.

A B C

(a) Which cell, A, B or C, appears to be best adapted to increase diffusion into or

out of the cell?

Give one reason for your choice.

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(b) (i) Cell C is found in the salivary glands.

Name the enzyme produced by the salivary glands.

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(ii) Use information from the diagram to explain how cell C is adapted for producing thisenzyme.

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(Total 4 marks)

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(a) The diagrams show the structures of a yeast cell and a bacterial cell.

(i) Both the yeast cell and the bacterial cell have structures A and B.

Name structures A and B.

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B .......................................................(2)

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(ii) The yeast cell and the bacterial cell have different shapes and sizes.

Give one other way in which the structure of the bacterial cell is different from thestructure of the yeast cell.

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(b) Sourdough bread is light in texture and tastes slightly sour. The bread is made usingtwo types of microorganism, a yeast and a bacterium. The bacterium can make acidssuch as lactic acid. The acid makes the bread taste sour.

The graph shows how the growth rates of the yeast and the bacteria change withtemperature.

Temperature in °C

(i) Sourdough bread rises fastest at 27°C.Use information from the graph to explain why.

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(ii) The bread tastes most sour if it rises at 32°C.Use information from the graph to explain why.

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(Total 7 marks)

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The body uses enzymes to digest (break down) large food molecules into smaller molecules.

(a) (i) Draw one line from each large food molecule to the enzyme that acts on it.

Large foodmolecule

Enzyme

amylase

starch

protease

fat

lipase

protein

isomerase

(3)

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(ii) Draw a ring around the correct answer to complete each sentence.

amino acids.

Starch is broken down into fatty acids and glycerol.

sugars.

amino acids.

Fat is broken downinto

fatty acids and glycerol.

fructose.

amino acids.

Protein is broken down into fructose.

sugars.

(3)

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(b) Bile helps digestion.

Where is bile produced?

Draw a ring around one answer.

liver mouth stomach

(1)(Total 7 marks)

The diagram below shows the human digestive system.5

(a) (i) What is Organ A?


gall bladder liver stomach(1)

(ii) What is Organ B?


large intestine pancreas small intestine(1)

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(b) Digestive enzymes are made by different organs in the digestive system.

Complete the table below putting a tick (✓) or cross (✕) in the boxes.

The first row has been done for you.

Organ producing enzyme

salivary

glandsstomach pancreas

smallintestine

Enzyme

amylase ✓ ✕ ✓ ✓

lipase

protease

(2)

(c) The stomach also makes hydrochloric acid.

How does the acid help digestion?

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(d) Draw one line from each digestive enzyme to the correct breakdown product.

Digestive enzyme Breakdown products

amino acids.

Amylase breaks downstarch into……

bases.

Lipase breaks downfats into…

fatty acids and

glycerol.

Protease breaks downproteins into…

sugars.

(3)(Total 8 marks)

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The diagram shows part of the human digestive system.6

(a) Name the parts of the digestive system labelled A, B, C and D.

A ................................................................................

B ................................................................................

C ................................................................................

D ................................................................................(4)

(b) A student has eaten a steak for dinner. The steak contains protein and fat.

(i) Describe how the protein is digested.

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(ii) Explain two ways in which bile helps the body to digest fat.

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(c) A group of students investigated the action of salivary amylase.The students:

• collected a sample of salivary amylase

• put a different pH solution and 5 cm 3 of a food substance in each of 6 test tubes

• added 1 cm 3 of salivary amylase to each of the 6 test tubes

• recorded the amylase activity after 10 minutes.

The results are shown in the table.

pH 7 6 5 4 3 2

Amylase activity inarbitrary units

12 10 3 0 0 0

(i) Name the food substance that amylase breaks down.

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(ii) Suggest what happens to the breakdown of this substance when food reaches thestomach.

Use information from the table to help you to answer this question.

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(Total 15 marks)

The diagram shows the human digestive system.

(a) Heartburn is a burning feeling caused when acid enters the oesophagus. The acid comesfrom the stomach.

(i) Which letter on the diagram shows the stomach?

(1)

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(ii) Name the acid the stomach produces.

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(iii) Medicines taken to treat heartburn contain chemicals that neutralise excess stomachacid.

What type of chemical will neutralise stomach acid?

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(b) Use words from the box and your own knowledge to describe how carbohydrates aredigested.

amylase starch sugars

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(c) Where in the body are the products of digestion absorbed?

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(Total 9 marks)

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A manufacturer of slimming foods is investigating the effectiveness of carbohydrases fromdifferent microorganisms.

Iodine solution is a pale golden brown, transparent solution. Starch reacts with iodine to form adark blue mixture.

Known concentrations of starch are added to iodine solution. The mixture is placed in acolorimeter which measures the percentage of light passing through the mixture.

Graph 1 shows the results.

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(a) Explain why less light passes through the mixture when the starch is more concentrated.

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(b) The manufacturer adds carbohydrase from each of three different microorganisms, A, Band C, to starch in flasks at 40 °C.

Every minute a sample of the mixture is added to iodine solution and placed in thecolorimeter.

Graph 2 shows these results.

(i) When the concentration of starch reaches 2 %, digestion is considered to besufficient for the next stage in the manufacture of the slimming food.

How long does this take for the most effective carbohydrase?

Show clearly how you work out your answer.

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(ii) Explain why the manufacturer carried out the investigation at 40 °C.

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(c) Carbohydrases convert starch into glucose. To complete the manufacture of the slimmingfood the glucose should be converted into fructose.

(i) Name the enzyme which would be used to convert glucose into fructose.

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(ii) Explain why fructose, rather than glucose, is used in slimming foods.

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(Total 8 marks)

(a) The graph shows the effect of pH on the activities of three enzymes, X, Y and Z.These enzymes help to digest food in the human digestive system.Each enzyme is produced by a different part of the digestive system.

pH

(i) What is the optimum (best) pH for the action of enzyme Z?

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(ii) The stomach makes a substance that gives the correct pH for enzyme action in thehuman stomach.

Name this substance. ..................................................................................................(1)

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(iii) Which enzyme, X, Y or Z, will work best in the human stomach?

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(b) In this question you will be assessed on using good English, organising information clearlyand using specialist terms where appropriate.

Different parts of the human digestive system help to break down molecules of fat so thatthey can be absorbed into the body.

Describe how.

To gain full marks you should refer to:

• the enzyme and where the enzyme is produced

• the products of digestion

• any other chemicals involved.

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(Total 9 marks)

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Enzymes are used in many industrial processes.

(a) Draw a ring around the correct answer to complete each sentence.

(i) An enzyme is

an antibody.

a catalyst.

a mineral.

(1)

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(ii) In industry, enzymes are used so that reactions work well at

all pH values.

higher pressures.

lowertemperatures.

(1)

(iii) In industry, the enzyme carbohydrase is used to change starch into

aminoacids.

fattyacids.

sugar.

(1)

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(b) The enzyme isomerase changes glucose into fructose. In industry, the enzyme isomeraseis attached to beads of gel in a glass tube, as shown below.

Give two advantages of using an enzyme attached to beads of gel.

Tick ( ) two boxes.

The enzyme would be denatured.

The enzyme can easily be used again.

The fructose does not have any enzyme in it.

The enzyme can also be used to pre-digest baby foods.

(2)(Total 5 marks)

Starch is broken down into sugar by amylase. Amylase is produced in the salivary glands.

(a) Name two other organs in the digestive system which produce amylase.

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(b) A colorimeter measures colour intensity by measuring the percentage of light that passesthrough a solution.Graph 1 shows the percentage of light passing through sugar solutions of differentconcentrations to which a test reagent has been added.

Students used a colorimeter to compare the starch-digesting ability of amylase enzymesobtained from two organs, P and Q.

• The students collected 5 cm 3 samples of amylase from P and Q and placed them intoa water-bath at 40 °C.

• Two test tubes containing 10 cm 3 samples of starch solution were also placed into thewater-bath.

• All the tubes were left in the water-bath for 10 minutes.

• Each amylase sample was added to one of the tubes containing the starch solution.

• The test tubes were placed back into the water-bath.

• Every minute, a few drops were taken from each tube, the test reagent was addedand the percentage of light passing through this solution was measured in thecolorimeter.

The tubes containing amylase samples and starch solution were left in the water-bath forten minutes before the amylase was added to the starch.

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Explain why.

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(c) Graph 2 shows how the readings from the colorimeter changed over the next 20 minutes.

(i) Use Graph 1 and Graph 2 to determine the concentration of sugar in the mixturefrom organ Q after 20 minutes.

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Answer ..........................mol per dm3

(1)

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(ii) Use your answer to (c)(i) to calculate the rate at which sugar was produced in themixture containing amylase from organ Q.

Show clearly how you work out your answer.

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Answer ...............................................mol per dm3 per minute(2)

(iii) Suggest why the amount of light passing through the mixture from organ P did notchange after 16 minutes.

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(iv) One of the students suggested that they could have completed their experiment morequickly if the temperature of the water-bath had been set at 80 °C.

This would not have been the case.

Explain why.

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(Total 10 marks)

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Fresh milk is a mixture of compounds including lipid, protein and about 5% lactose sugar.

Lactose must be digested by the enzyme lactase, before the products can be absorbed.

Lactase can be added to fresh milk to pre-digest the lactose. This makes ‘lactose-free’ milk,which is suitable for people who do not produce enough lactase of their own.

A student investigated the effect of changing pH and temperature on the digestion of lactose inmilk.

The results are shown in Tables 1 and 2.

Table 1

Effect of pH

Table 2Effect of temperature

pHTime taken to

digest lactose inminutes

Temperature

in °C

Time taken todigest lactose in

minutes

4.0 20 25 20

5.0 18 30 14

6.0 13 35 11

7.0 7 40 6

8.0 5 45 29

9.0 6 50 No digestion

(a) The label on a carton of lactose-free milk states:

‘Lactase is normally produced in the stomach of mammals.’

The results in Table 1 suggest that this statement is not true.

Explain how.

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(b) Explain, as fully as you can, the results shown in Table 2 .

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(c) Bile is produced in the liver and is released into the small intestine.

Bile helps the digestion of lipid in the milk.

Describe how.

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(Total 7 marks)

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A patient has a disease. The disease damages his pancreas.

A doctor prescribes a course of treatment for the patient:‘Take one capsule with each meal.’

Each capsule contains hundreds of small, dry beads.

The beads are made of enzymes. The pancreas normally produces these enzymes.

The outer coating of the capsule is made of lipid.

(a) One enzyme in the beads is lipase.

In a healthy person, lipase is made in the pancreas.

Name two other enzymes made in the pancreas of a healthy person.

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2 .....................................................................................................................(2)

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(b) The lipid coating on the capsule makes sure that the enzymes are not released until thecapsule reaches the small intestine.

Explain how.

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(c) The lipase in the beads does not digest the lipid coating around the capsule.

Suggest why.

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(Total 5 marks)

Some students investigated the effect of pH on the digestion of boiled egg white by an enzymecalled pepsin. Egg white contains protein.

The students:

• put a glass tube containing boiled egg white into a test tube

• added a solution containing pepsin at pH 7

• set up six more tubes with solutions of pepsin at different pH values

• left the test tubes for 24 hours at room temperature.

The image below shows one of the test tubes, at the start and at the end of the 24 hours.

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At start 24 hours later

(a) (i) Name the product of protein digestion.

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(ii) What type of enzyme digests protein?

Tick ( ) one box.

amylase

lipase

protease

(1)

(b) The egg white in each tube was 50 mm long at the start of the investigation.The table below shows the students’ results.

pHLength in mm of boiledegg white after 24 hours

1 38

2 20

3 34

4 45

5 50

6 50

7 50

(i) At which pH did the pepsin work best?

pH ..................................(1)

(ii) The answer you gave in part (b)(i) may not be the exact pH at which pepsin worksbest.

What could the students do to find a more accurate value for this pH?

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(iii) There was no change in the length of the egg white from pH 5 to pH 7.

Explain why.

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(c) Pepsin is made by the stomach.

Name the acid made by the stomach which allows pepsin to work well.

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(Total 8 marks)

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Trypsin is a protease enzyme. Trypsin will digest a protein called gelatine which covers thesurface of photographic film.

Some students investigated the time taken to digest the gelatine with trypsin.The students used five different concentrations of trypsin.

The rate of reaction was calculated from the time taken for the gelatine to be digested.

The graph shows the students’ results.

Percentage concentration of trypsin

(a) (i) Describe the relationship between the concentration of trypsin and the rate ofreaction.

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(ii) Use the graph to predict the rate of reaction with 6% trypsin.

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(b) In industry, trypsin is used to pre-treat some baby foods.In their experiment, the students used 1–5% trypsin at 20°C.The baby food manufacturers make most profit if they use 0.5% trypsin at 35°C.

Suggest why the manufacturers make most profit with these conditions.

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(c) (i) Describe the effect trypsin would have on the baby food.

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(ii) Apart from protease enzymes, give one other use of a named enzyme in industry.

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(Total 11 marks)

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A group of pupils investigated the digestion of fat by the enzyme lipase.

(a) What two substances are produced when fats are digested?

Tick ( ) two box.

Glucose

Fatty acids

Glycerol

Amino acids

(2)

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In the investigation:

• the pupils set up five test tubes

• each tube contained 1 cm 3 of fat and 10 cm3 of lipase solution

• each tube was kept at a different temperature for 24 hours.

(b) (i) Give one control variable in this investigation.

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(ii) What was the independent variable being investigated?

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(c) The pH of the solution in each tube was tested at the beginning of the investigation andafter 24 hours.

The results of the pupils’ investigation are shown in the table.

Tube Temperaturein °C

pH at thebeginning

pH after 24hours

1 0 Neutral Neutral

2 20 Neutral ‘Weak’ acid

3 40 Neutral ‘Strong’ acid

4 60 Neutral ‘Weak’ acid

5 80 Neutral Neutral

One pupil said, “We might not have found the best temperature for the lipase to work”.

What more could they do to find the best temperature?

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(d) The pupils then placed Tube 1 into a water-bath kept at 40 °C.The tube was left in the water-bath for 24 hours.

(i) What pH would you expect the contents of the tube to be after the extra 24 hours?

Tick ( ) one box.

Neutral

‘Strong’ acid

‘Weak’ acid

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(ii) Give the reason for your answer.

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(Total 8 marks)

A manufacturer is trying to improve the quality of the biological detergent he produces.

Scientists at his company carried out the following experiments on enzymes:

• Samples of lipase were collected from five different types of bacterium, A, B, C, D and E.• The samples were diluted to give the same concentration of lipase.• Agar jelly containing a lipid was prepared in a dish. This forms a cloudy mixture which

becomes clear when the lipid is digested.• Five small holes were cut into the agar.• Two drops of lipase solution from bacterium A was added to hole A.• This process was repeated for each sample of lipase.

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Diagram 1 shows the appearance of the dish.

Diagram 1

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Diagram 2 shows the appearance of the dish 24 hours later.

Diagram 2

(a) (i) Which type of bacterium, A, B, C, D or E, produced the most effective lipase in thisinvestigation?

Write your answer, A, B, C, D or E, in the box. (1)

(ii) Explain your answer.

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(b) The manufacturer plans to add the most effective lipase to the washing powders heproduces.

Suggest two other factors he should investigate before deciding which lipase is the mosteffective.

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(c) Many biological detergents cannot be used at high temperatures.

Explain why.

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(Total 5 marks)

The diagram shows the apparatus used to investigate the digestion of milk fat by an enzyme. Thereaction mixture contained milk and the enzyme.

In Experiment 1, bile was also added.

In Experiment 2, an equal volume of water replaced the bile.

In each experiment, the pH was recorded at 2 minute intervals.

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The results of the two experiments are given in the table.

Time in minutes

pH

Experiment 1: with bile Experiment 2: without bile

0 9.0 9.0

2 8.8 9.0

4 8.7 9.0

6 8.1 8.8

8 7.7 8.6

10 7.6 8.2

(a) Milk fat is a type of lipid.

Explain why the pH changed in experiment 2.

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(b) (i) For Experiment 1, calculate the average rate of fall in pH per minute, between 4minutes and 8 minutes.

Show clearly how you work out your final answer.

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................................. pH units per minute(2)

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(ii) The average rate of fall in pH per minute for Experiment 2 was 0.1 units of pH perminute.

Explain the difference in the rate of fall in pH when bile is present.

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(Total 5 marks)

A group of students investigated the effect of temperature on the action of the enzyme lipase.

The students:

• put 1 cm 3 of lipase solution into a test tube

• put 5 cm 3 of lipid into a different test tube

• put both tubes in a water bath at 5 °C for 3 minutes

• mixed the lipid with the lipase solution.

Every five minutes the students tested a sample of the mixture for lipid, until no lipid remained.The students repeated the experiment at different temperatures.

(a) To make their investigation fair the students needed to control some variables.

Give one variable the students controlled in their investigation.

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(b) The tubes of lipase solution and lipid were kept separately in the water bath for 3 minutesbefore mixing. Why?

Tick ( ) one box.

So that the lipase broke down the lipid quickly

So that the lipase and the lipid reached the right temperature

To give enough time for the lipase to break down the lipid

To give enough time for the water bath to heat up

(1)

The table shows the students’ results.

Temperaturein °C

Time taken until no lipid remainedin minutes

5 40

20 15

35 5

50 30

95 lipid still there after 120 minutes

(c) Describe the effect on the breakdown of the lipid of increasing the temperature from 5 °C to50 °C.

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(d) Suggest two ways in which the students could have improved their investigation.

Use information from the students’ method and the results table to help you.

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(e) (i) The lipase did not break down the lipid at 95 °C.

Why?

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(ii) At 35 °C the lipase broke down the lipid after 5 minutes.

What new substances will be in the tube?


amino acids fatty acids and glycerol sugars

(1)(Total 8 marks)

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Lipase is an enzyme that digests fat.

(a) (i) Complete the equation to show the digestion of fat.

Use the correct answer from the box.

glucose glycerol glycogen

fat fatty acids + ..................................(1)

(ii) Name one organ that makes lipase.

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(b) Some students investigated the effect of bile on the digestion of fat by lipase.

The students:1 mixed milk and bile in a beaker2 put the pH sensor of a pH meter into the beaker3 added lipase solution4 recorded the pH at 2-minute intervals5 repeated steps 1 to 4, but used water instead of bile.

Suggest two variables that the students should have controlled in this investigation.

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(c) The graph shows the students’ results.

(i) Why did the pH decrease in both investigations?

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(ii) Bile helps lipase to digest fat.

What evidence is there in the graph to support this conclusion?

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(iii) Suggest one reason why the contents of both beakers had the same pH at the end ofthe investigations.

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(Total 7 marks)

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Diagram 1 shows a cell from the pancreas.

Diagram 2 shows part of the cell seen under an electron microscope.

Part A is where most of the reactions of aerobic respiration happen.

(a) (i) Name part A.

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(ii) Complete the equation for aerobic respiration.

glucose + oxygen ......................... + ......................... (+ energy)(2)

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(iii) Part A uses oxygen.

Explain how oxygen passes from the blood to part A.

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(b) The pancreas cell makes enzymes.

Enzymes are proteins.

Describe how the ribosomes and part A help the cell to make enzymes.

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(Total 9 marks)

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

hydrogen peroxide water + oxygen

Figure 1 shows a 25-day-old broad bean seedling.

Some students investigated whether different parts of bean seedlings contained differentamounts of catalase.

The students:• put hydrogen peroxide into five test tubes

• added a different part of a bean seedling to each tube

• recorded the results after half a minute.

If there was catalase in part of the seedling, oxygen gas was given off.When oxygen gas is given off, foam is produced in the tubes.

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Figure 2 shows the results.

The students made the following conclusions:• most parts of a bean seedling contain catalase

• the seed contains a lot of catalase

• stems and roots have quite a lot of catalase

• the leaves have a little bit of catalase

• the seed coat has hardly any catalase.

The students’ teacher said that the students needed to improve their investigation in order tomake valid conclusions.

(a) In this question you will be assessed on using good English, organising informationclearly and using specialist terms where appropriate.

Describe how you would carry out an investigation to compare the amounts of catalase indifferent parts of bean seedlings.

You should include details of how you would make sure your results give a validcomparison of the amounts of catalase.

........................................................................................................................

........................................................................................................................

........................................................................................................................

........................................................................................................................

........................................................................................................................

........................................................................................................................

........................................................................................................................

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........................................................................................................................

........................................................................................................................

........................................................................................................................(6)

(b) Scientists investigated the effect of pH on the activity of the enzyme catalase in a fungus.

The table below shows the scientists’ results.

pH

Enzyme activity in arbitrary units

Test 1 Test 2 Test 3 Test 4 Test 5 Mean

3.0 0 0 0 0 0 0

4.0 6 5 8 4 7 6

5.0 38 65 41 42 39

5.5 80 86 82 84 88 84

6.0 100 99 96 103 102 100

6.5 94 92 90 93 91 92

7.0 61 63 61 62 63 62

8.0 22 22 21 24 21 22

(i) Calculate the mean enzyme activity at pH 5.0.

...............................................................................................................

...............................................................................................................

Mean = ......................... arbitrary units(2)

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(ii) On the graph paper in Figure 3, draw a graph to show the scientists’ results.

Remember to:• add a label to the vertical axis

• plot the mean values of enzyme activity

• draw a line of best fit.

Figure 3

(4)

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(iii) At what pH does the enzyme work best?

........................................(1)

(iv) Predict the activity of the enzyme at pH 9.0.

........................................ arbitrary units(1)

(v) Suggest why the enzyme’s activity at pH 3.0 is zero.

...............................................................................................................

...............................................................................................................(1)

(Total 15 marks)

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Fruit is crushed to release fruit juice.

More juice can be collected if the plant cell walls in the fruit are broken down.

Some students tested the effect on the volume of fruit juice that they could collect of:

• either boiling the fruit

• or adding the enzyme pectinase to the fruit

• or adding the enzyme amylase to the fruit.

In their first experiment the students:

• crushed 20 g of apple

• added 10 drops of water

• measured the volume of fruit juice that they collected.

Diagram 1 shows how they collected the fruit juice.

The students did three more experiments.

1 They added 10 drops of amylase solution to 20 g of crushed apple.

2 They added 10 drops of pectinase solution to 20 g of crushed apple.

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3 They added 10 drops of water to 20 g of boiled, crushed apple.

Diagram 2 shows these experiments.

(a) Give one control variable in this investigation.

........................................................................................................................(1)

(b) Using drops to measure the volume of water and enzyme added might lead to inaccurateresults.

Give one reason why.

........................................................................................................................(1)

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(c) The students’ results are shown in the table.

What was added to thecrushed apple

Was the appleboiled?

Volume of juicecollected

in cm3

10 drops of water No 1.2

10 drops of amylase solution No 1.2

10 drops of pectinase solution No 11.3

10 drops of water Yes 11.6

Explain as fully as you can the students’ results shown in the table.

Use all the information given to help you answer this question.

........................................................................................................................

........................................................................................................................

........................................................................................................................

........................................................................................................................

........................................................................................................................

........................................................................................................................(3)

(d) One student said:

‘If we add 10 drops of pectinase solution to crushed apple while it is boiling, we shouldcollect more juice than if we add 10 drops of water to boiled apple.’

This is not correct.

What volume of juice would you predict the students would collect if 10 drops of pectinasesolution were added to crushed apple while it was boiling?


1.2 cm3 11.3 cm3 11.6 cm3 22.9 cm3

(1)

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Explain your answer.

........................................................................................................................

........................................................................................................................

........................................................................................................................

........................................................................................................................(2)

(Total 8 marks)

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Denim jeans can be coloured with blue dye. The dye joins on to the fibres of the material. Somepeople like their denim jeans to look faded. This is called ‘stonewashed’. There are two differentways to make denim material look faded.

Traditional stone washing

• Denim material is put in a slowly spinning container with large stones.

• Very hot water is added.

• Washing takes up to five hours.

• Washing breaks some of the denim fibres and lets the dye come out from the fibres.

• Washing will work with any dye.

Bio-stonewashing

• Denim material is washed with enzymes in warm water.

• Washing takes half an hour.

• The enzymes let the dye come out from the fibres.

• Different enzymes are needed for different dyes.

• The enzymes are expensive.

• After the treatment the enzymes have to be removed from the denim.

(a) Use only the information above to answer this question.

(i) Suggest two advantages of using the bio-stonewashing method instead of thetraditional stonewashing method.

1 ............................................................................................................

...............................................................................................................

2 ............................................................................................................

...............................................................................................................(2)

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(ii) Suggest two disadvantages of using the bio-stonewashing method instead of thetraditional stonewashing method.

1 ............................................................................................................

...............................................................................................................

2 ............................................................................................................

...............................................................................................................(2)

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(b) Some blue dyes are made of protein.

What type of enzyme would be used to remove these blue dyes from denim?


carbohydrase lipase protease

(1)(Total 5 marks)

The table shows the mass of carbon dioxide passed into the atmosphere in one year.

Mass of carbon dioxidepassed into the atmospherein billions of tonnes per year

Animals 45

Plants 15

Microorganisms 60

Human activity 9

(a) (i) Calculate the total mass of carbon dioxide passed into the atmosphere in one year.

...............................................................................................................

...............................................................................................................

Answer = .................................................. billion tonnes(1)

25

(ii) Plants take 120 billion tonnes of carbon dioxide out of the atmosphere per year.

Use your answer to part (a)(i) to calculate the change in the mass of carbon dioxidein the atmosphere in one year.

...............................................................................................................

...............................................................................................................

Answer = .................................................. billion tonnes(1)

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(b) The drawing shows part of a campaign to encourage householders to reduce thetemperature of the water used to wash clothes.

Give two advantages to the environment of reducing the temperature of the water used towash clothes.

1 .....................................................................................................................

........................................................................................................................

2 .....................................................................................................................

........................................................................................................................(2)

(c) A householder reduces the temperature of the water he uses to wash clothes.He finds that some stains are not removed at the new temperature.He decides to use a biological washing powder.Biological washing powders contain enzymes.

(i) Draw a line from each enzyme in List 1 to the type of stain the enzyme will remove, inList 2.

List 1Enzyme

List 2Type of Stain

Starch

Protease

Fat

Lipase

Protein

(2)

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(ii) The biological washing powder would not have removed the stains from clothes if thewater had been at 65 °C.

Use one word from the box to complete the sentence.

killed denatured diffused

At 65 °C the enzymes would be ..............................................................................(1)

(Total 7 marks)

There are enzymes in biological washing powders. Biological washing powder has to be used attemperatures below 45 °C.

(a) The enzymes in biological washing powders do not work on the stains on clothes attemperatures above 45 °C.

Explain why.

........................................................................................................................

........................................................................................................................

........................................................................................................................

........................................................................................................................(2)

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(b) Some bacteria, called thermophilic bacteria live in hot springs at temperatures of 80 °C.

Scientists have extracted enzymes from these thermophilic bacteria. These enzymes arebeing trialled in industrial laundries.The laundries expect to increase the amount of clothes they can clean by using enzymesfrom thermophilic bacteria instead of using the biological washing powders the laundriesuse now.

(i) The laundries expect to be able to increase the amount of clothes that they can cleaneach day.

Suggest why.

...............................................................................................................

...............................................................................................................

...............................................................................................................

...............................................................................................................

...............................................................................................................(2)

(ii) Using washing powders with enzymes from thermophilic bacteria may be moreharmful to the environment than using the biological washing powders that laundriesuse now.

Suggest why.

...............................................................................................................

...............................................................................................................

...............................................................................................................

...............................................................................................................

...............................................................................................................(2)

(Total 6 marks)

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Biological detergents contain protease enzymes.

(a) The drawings show some apparatus and materials.

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In this question you will be assessed on using good English, organising information clearlyand using specialist terms where appropriate.

Describe how you would use the apparatus and materials shown in the drawings to find thebest temperature for removing stains from clothing.

You should include how you would make the investigation a fair test.

........................................................................................................................

........................................................................................................................

........................................................................................................................

........................................................................................................................

........................................................................................................................

........................................................................................................................

........................................................................................................................

........................................................................................................................

........................................................................................................................

........................................................................................................................

........................................................................................................................

........................................................................................................................

........................................................................................................................

........................................................................................................................

........................................................................................................................

........................................................................................................................(6)

(b) In a similar investigation a student investigated the effect of pH on the time taken to removea stain from pieces of cloth.

The table shows the student’s results.

pH of detergent solution

1 2 3 4 5 6 7 8 9

Time taken to removestain in minutes

20 19 17 14 10 4 8 12 16

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(i) On the graph paper below draw a graph to show the student’s results.

• Add a suitable scale and label to the y axis.

• Plot the student’s results.

• Draw a line of best fit.

pH of detergent solution(4)

(ii) Which is the best pH for using the detergent?

pH .................................................................(1)

(c) Scientists investigated the stability of a protease enzyme. The protease enzyme wasextracted from plants.

The scientists:

• pre-incubated samples of the enzyme at various temperatures for 30 minutes

• put each sample on ice for a further 10 minutes

• measured the percentage (%) remaining activity of the enzyme in each sample.This was done by incubating each sample with protein at 37 °C for 6 hours.

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The graph shows the scientists’ results.

Pre-incubation temperature in °C

The scientists recommended that the enzyme could be used in detergents at a temperatureof 60 °C.

Suggest why the scientists recommended a temperature of 60 °C.Use information from the graph and your own scientific knowledge in your answer.

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........................................................................................................................

........................................................................................................................

........................................................................................................................(3)

(Total 14 marks)

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The diagram shows an industrial process. Containers X and Y contain enzymes.

(a) Starch syrup slowly trickles into container X.The enzymes in container X convert the starch into glucose (sugar).The enzymes in container Y convert the glucose into fructose.

The equation shows what happens in containers X and Y.

Enzyme A Enzyme B

starch glucose fructose

Choose words from the box to name enzyme A and enzyme B.

carbohydrase isomerase lipase protease

Enzyme A ................................................

Enzyme B ................................................(2)

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(b) Fructose syrup is much sweeter than glucose syrup.

Why do manufacturers of slimming foods use fructose syrup rather than glucose syrup?

.....................................................................................................................................

.....................................................................................................................................(1)

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(c) Here are some of the properties of enzymes:

• they all work at atmospheric pressures

• they are easily broken down by high temperature or the wrong pH

• they are soluble in water, so it may be difficult to separate them from products

• they are expensive to buy

• they work well at 25 – 45 °C.

Use only the information above to answer these questions.

(i) Give two advantages of using enzymes in industry.

1 .......................................................................................................................

2 .......................................................................................................................(2)

(ii) Give two disadvantages of using enzymes in industry.

1 .......................................................................................................................

2 .......................................................................................................................(2)

(Total 7 marks)

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Isomerase is an enzyme which can change glucose into fructose.Fructose is often used instead of glucose in products like slimming foods.

In industry, isomerase is often ‘immobilised’ within beads of gel.The beads are placed in a glass column.The isomerase stays attached to the beads and a solution of glucose is allowed to flow betweenthe beads in the column.

The diagram shows how immobilised isomerase is used.

(a) An alternative method of changing glucose into fructose would be to mix a solution of theisomerase with the glucose solution in a large container.Suggest two advantages of using isomerase immobilised in a column of beads.

1......................................................................................................................

........................................................................................................................

2......................................................................................................................

........................................................................................................................(2)

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(b) A manufacturer investigated the effect of using different flow rates of glucose solution onthe rate of fructose production.

The table shows the results.

Flow rate in

dm3 per minute

Rate of fructoseproduction inmg per minute

1 150

2 325

3 480

4 608

5 650

6 650

7 650

The manufacturer decides to use a flow rate of 5 dm3 per minute.

Suggest why the manufacturer chose this flow rate.

........................................................................................................................

........................................................................................................................

........................................................................................................................

........................................................................................................................(2)

(c) Fructose is a much sweeter sugar than glucose.

Explain why manufacturers of slimming foods may wish to use fructose as a sweetenerinstead of glucose.

........................................................................................................................

........................................................................................................................

........................................................................................................................

........................................................................................................................(2)

(Total 6 marks)

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A manufacturer of slimming foods is investigating the effectiveness of carbohydrases fromdifferent microorganisms.

Iodine solution is a pale golden brown, transparent solution. Starch reacts with iodine to form adark blue mixture.

Known concentrations of starch are added to iodine solution. The mixture is placed in acolorimeter, which measures the percentage of light passing through the mixture.

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Graph 1 shows the results.

(a) (i) Explain why less light passes through the mixture when the starch is moreconcentrated.

...............................................................................................................

...............................................................................................................(1)

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(ii) The manufacturer could have used a white spotting tile, as shown below, instead of acolorimeter. Suggest two advantages of using a colorimeter in this investigationrather than a spotting tile.

1 ............................................................................................................

...............................................................................................................

2 ............................................................................................................

...............................................................................................................(2)

(b) The manufacturer adds carbohydrase from each of three different microorganisms, A, Band C, to starch in flasks at 40 °C. Every minute a sample of the mixture is added to iodinesolution and placed in the colorimeter.Graph 2 shows these results.

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(i) When the concentration of starch reaches 2%, digestion is considered to be sufficientfor the next stage in the manufacture of the slimming food.

Use information from graphs 1 and 2 to find how long this takes for the most effectivecarbohydrase.

...............................................................................................................

....................................................... minutes(2)

(ii) Suggest why the amount of light passing through the mixture containingcarbohydrase A did not change after 20 minutes.

...............................................................................................................

...............................................................................................................(1)

(c) Explain why the manufacturer carried out the investigation at 40 °C.

........................................................................................................................

........................................................................................................................

........................................................................................................................

........................................................................................................................(2)

(d) Carbohydrases convert starch into glucose. To complete the manufacture of the slimmingfood the glucose should be converted into fructose.

Explain why fructose, rather than glucose, is used in slimming foods.

........................................................................................................................

........................................................................................................................

........................................................................................................................

........................................................................................................................(2)

(Total 10 marks)

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Enzymes have many uses in the home and in industry.

(a) Which type of organism is used to produce these enzymes?

Tick ( ) one box.

Mammals

Microorganisms

Plants

(1)

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(b) Babies may have difficulty digesting proteins in their food. Baby food manufacturers useenzymes to ‘pre-digest’ the protein in baby food to overcome this difficulty.

Use words from the box to complete the sentences.

amino acids amylases proteases sugars

(i) Proteins are ‘pre-digested’ using enzymes called ................................................... .(1)

(ii) This pre-digestion produces .................................................................................... .(1)

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(c) A baby food manufacturer uses enzyme V to pre-digest protein.

He tries four new enzymes, W, X, Y and Z, to see if he can reduce the time taken topre-digest the protein.

The graph shows the time taken for the enzymes to completely pre-digest the protein.

The manufacturer uses the same concentration of enzyme and the same mass of proteinin each experiment.

(i) How long did it take enzyme V to pre-digest the protein? minutes(1)

(ii) Which enzyme would you advise the baby food manufacturer to use?

Draw a ring around your answer.

enzyme V enzyme W enzyme X enzyme Y enzyme Z

Give a reason for your answer.

...........................................................................................................................

...........................................................................................................................(2)

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(iii) Give two factors which should be controlled in the baby food manufacturer’sinvestigations.

Tick ( ) two boxes.

Oxygen concentration

Temperature

Light intensity

pH

(2)(Total 8 marks)

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Denim jeans can be coloured with blue dye. The dye joins onto the fibres of the material.Some people like their denim jeans to look faded. The faded look is called ‘stonewashed’.There are two different ways to make denim material look faded.

Traditional stonewashing

• Denim material is put in a slowly spinning container with large stones.

• Very hot water is added.

• Washing takes up to five hours.

• Washing breaks some of the fibres and lets the dye come out from the fibres.

• Washing will work with any dye.

Bio-stonewashing

• Denim material is washed with enzymes in warm water.

• Washing takes half an hour.

• The enzymes let the dye come out from the fibres.

• Different enzymes are needed for different dyes.

• The enzymes are expensive.

• After treatment the enzymes have to be removed from the denim.

(a) Use only the information above to answer these questions.

(i) Suggest two advantages of using the bio-stonewashing method instead of thetraditional stonewashing method.

1......................................................................................................................

........................................................................................................................

2......................................................................................................................

........................................................................................................................(2)

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(ii) Suggest two disadvantages of using the bio-stonewashing method instead of thetraditional stonewashing method.

1......................................................................................................................

........................................................................................................................

2......................................................................................................................

........................................................................................................................(2)

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(b) Some blue dyes are made of protein.

What type of enzyme would be used to remove these blue dyes from denim?


carbohydrase lipase protease

(1)(Total 5 marks)

We use enzymes in industry. These are some of the properties of enzymes:

• they work at low temperatures and this can save energy

• they work at atmospheric pressures and therefore use less expensive equipment


• they are soluble in water, so it is difficult to separate them from water-soluble products

• they are very expensive to buy.

33

(a) Use the information above to answer this question.

(i) Give two advantages of using enzymes in industry.

1 ..................................................................................................................................

.....................................................................................................................................

2 ..................................................................................................................................

.....................................................................................................................................

(ii) Give two disadvantages of using enzymes in industry.

1 ..................................................................................................................................

.....................................................................................................................................

2 ..................................................................................................................................

.....................................................................................................................................(4)

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(b) Different enzymes have different jobs:

• protease enzymes break down proteins so that they are easier to digest

• lipase enzymes break down fats

• carbohydrase enzymes break down starch into sugar for energy drinks

• isomerase enzymes break down glucose into fructose which is much sweeter.

Which enzyme is used:

(i) to help to get greasy stains out of clothes? ................................................................

(ii) in making slimming foods? ........................................................................................

(iii) in making baby foods? ...............................................................................................(3)

(Total 7 marks)

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Mark schemes

(a) (i) a catalyst1

(ii) protein1

(iii) salivary glands1

1

(b)

extra lines from any enzyme cancels that mark3

[6]

(a) B

no mark for “B” alone, the mark is for B and the explanation.

large(r) surface / area or large(r) membrane

accept reference to microvilli

ignore villi / hairs / cilia

accept reasonable descriptions of the surface eg folded membrane/ surface

do not accept wall / cell wall1

2

(b) (i) any one from:

• (salivary) amylase

• carbohydrase1

(ii) many ribosomes

do not mix routes. If both routes given award marks for the greater.1

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ribosomes produce protein

accept amylase / enzyme / carbohydrase is made of protein

or

(allow)

many mitochondria (1)

mitochondria provide energy to build / make protein (1)

accept ATP instead of energy1

[4]

(a) (i) A = (cell) wall

ignore cellulose1

3

B = cytoplasm1

(ii) any one from:

accept has DNA instead of a nucleus, but not just has DNA

• bacterial cell / it has no nucleus

allow no mitochondria

• DNA free in cytoplasm

ignore size

• has no vacuole / no vesicles

ignore strands of DNA1

(b) (i) yeast grows best / better / well or optimum temperature for yeast / more yeastpresent

allow yeast works best / better / well1

(yeast) makes CO2 or respires / respiration

allow fermentation1

(ii) bacterium grows best / better / well / more bacteria present or optimumtemperature for bacterium

ignore microorganisms / microbes

allow works / respires best / better / well1

(bacterium) makes (lactic) acid

do not allow wrong acid1

[7]

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(a) (i)

all three correct = 3 marks

two correct = 2 marks

one correct = 1 mark

extra line from a large food molecule cancels the mark3

4

(ii) sugars1

fatty acids and glycerol1

amino acids

must be in this order1

(b) liver1

[7]

(a) (i) stomach15

(ii) small intestine1

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(b)

salivaryglands

stomach pancreassmall

intestine

amylase ✓ ✕ ✓ ✓

lipase ✕ ✕ ✓ ✓

protease ✕ ✓ ✓ ✓

1 mark per correct row

or

if no correct row max 1 mark for any one correct column2

(c) enzyme / protease / pepsin most effective in acid conditions / low pH

accept optimum / correct pH

do not accept ref to incorrectly named enzymes

ignore killing bacteria

ignore acid breaks down food1

(d) Enzyme Breakdown products

3[8]

(a) A − saliva(ry) gland1

B − liver1

C − duodenumignore small intestine

1

D − pancreasaccept phonetic spellings

1

6

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(b) (i) any three from:• chewing / muscle contraction / mechanical digestion

allow churning• protease enzymes

allow pepsin / trypsin• in stomach / small intestine / duodenum / from pancreas• (break down protein) into amino acids

allow (poly)peptides3

(ii) neutralises acid pH / makes conditions alkaline1

so lipase can work1

emulsifies fat1

to give large(r) surface area for lipase / enzyme action1

(c) (i) starch

ignore carbohydrate1

(ii) breakdown stops

allow slows down1

because stomach produces / contains acid / has low pH1

and amylase cannot work in acid / low pH

accept amylase is denatured / changes shape1

[15]

(a) (i) A17

(ii) hydrochloric (acid) / HCl1

(iii) alkali / suitable named example

accept sodium hydrogen

carbonate / sodium bicarbonate / milk of magnesia /other brand namesallow bile (salts)ignore antacid

1

(b) • amylase breaks down starch1

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• (broken down) into sugars / glucose1

• digestion of starch in the mouth1

• (also) starch broken down in small intestine1

• amylase produced in salivary glands / small intestine / pancreas1

(c) small intestine

allow ileum / duodenum

do not accept large intestine1

[9]

(a) opaque / less transparent / blue

allow mixture becomes dark / black

ignore thicker1

8

(b) (i) 7 (minutes) or in range 6.7 to 7

award 2 marks for correct answer

if answer is incorrect evidence of selection of40(% light intensity) either in working or in graph2 for 1 mark

2

(ii) any two from:

• slower / takes longer at lower temperatures

• (40 oC is) optimum / best temperature

allow near to 37oC / body

temperature where enzymes work best

• enzyme denatured / destroyed / damaged at higher temperatures

allow description of denaturation2

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(c) (i) isomerase

allow phonetic spelling1

(ii) fructose is sweeter than glucoseneeded in smallerquantities or less is needed

2[8]

(a) (i) 8.6

accept value in range 8.5 to 8.71

9

(ii) hydrochloric acid / HCl

accept HCL

accept hydrogen chloride

ignore hcl / etc.1

(iii) X1

(b) Marks awarded for this answer will be determined by the Quality of WrittenCommunication (QWC) as well as the standard of the scientific response. Examinersshould also refer to the information in the Marking guidance.

0 marksNo relevant content.

Level 1 (1-2 marks)There is a simple description of part of a process or a reference to at least one of:mechanical digestion, lipase, product of enzyme action, bile, site of production or siteof digestion

Level 2 (3-4 marks)There is a description of at least one process linking ideas

Level 3 (5-6 marks)There is a clear description of the process including reference to the majority of:mechanical digestion, lipase, bile, where they are produced, products, function of bileand site of digestion / absorption

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Examples of biological points made in the response:

• mechanical breakdown in mouth / stomach

• fats →fatty acids and / or glycerol

• by lipase

• (produced by) pancreas

• and small intestine

• fat digestion occurs in small intestine

• bile

• produced by liver

• neutralises acid from stomach

• produces alkaline conditions in intestine

• refs. to increased surface area related to emulsification or chewing

• products are small molecules / water-soluble

• products absorbed by small intestine6

[9]

(a) (i) a catalyst110

(ii) lower temperatures1

(iii) sugar1

(b) The enzyme can easily be used again1

The fructose does not have any enzyme in it1

[5]

(a) pancreas

either order1

11

small intestine1

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(b) any two from:

• to give them time to come to temperature of the water-bath

accept so (they / both) are at the same temperature

• at / near body temperature / best / optimum temperature

• otherwise reaction would take place at a series of different temperaturesor sensible statement about control / fair test

2

(c) (i) 0.42

allow in range 0.42 to 0.4251

(ii) 0.021

correct answer with or without working

allow ecf from (c)(i) ie (c)(i) ÷ 20 correctly calculated for 2 marks

if answer incorrect 0.42 ÷ 20 or (c)(i) ÷ 20 gains 1 mark2

(iii) (all) starch digested / gone / used up / turned to sugar

allow the amount of sugar stays the same / maximum1

(iv) any two from

allow reference to active site once only as alternative to first orsecond bullet point

• enzyme destroyed / denatured / damaged / shape changed

do not accept killed

• unable to fit (starch molecule)

• starch can’t be digested

enzymes don’t work is insufficient2

[10]

(a) stomach is acidic / has low pH

allow any pH below 7

ignore stomach is not alkaline1

12

lactase works best / well in alkali / high pH / neutral / non-acidic conditions

allow any pH of 7 and above

accept works slowly in acid conditions

allow figures from table with a comparison

ignore reference to temperature1

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(b) any three from:

• (below 40(°C)) increase in temperature increases rate / speed of reaction

• reference to molecules moving faster / colliding faster / harder / more collisions

• enzyme optimum / works best at 40°C

allow value(s) in range 36 – 44

ignore body temperature unless qualified

• high temperatures (above 40°C) / 45°C / 50°C enzyme denatured

allow synonyms for denaturation, but do not allow ‘killed’

denaturation at high and low temperature does not gain this mark

ignore references to time / pH3

(c) any two from:

• acid neutralised or conditions made neutral / alkali

accept bile is alkaline

• (allow) emulsification / greater surface area (of lipid / fat)

allow description of emulsification eg fat broken down / broken upinto droplets

do not accept idea of chemical breakdown

• lipase / enzymes (in small intestine) work more effectively / better

allow better for enzymes

ignore reference to other named enzymes2

[7]

(a) protease

allow trypsin / peptidase

do not allow pepsin1

13

carbohydrase / amylase

do not allow sucrase / maltase / lactase1

(b) no lipase produced / found1

in stomach / mouth / before small intestineORaccept lipase only produced / found (1)in small intestine / pancreas (1)

if no other mark is awarded lipid is not broken down in the stomachor lipid is digested in small intestine gains 1 mark

1

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(c) enzymes only work in solution / when dissolvedorbecause enzyme / lipase / it is dry

allow enzymes only work in presence of water or enzymes do notwork when dry

ignore other physical conditions1

[5]

(a) (i) amino acid(s)

accept peptide(s)

do not allow polypeptide(s)1

14

(ii) protease1

(b) (i) 21

(ii) repeat

do not allow other enzyme / substrate1

using smaller pH intervals between pH1 and pH3

allow smaller intervals on both sides of / around pH2

allow smaller intervals on both sides of / around answer to (b)(i)1

(iii) enzyme / pepsin denatured / shape changed

do not allow enzyme killed

allow enzyme ‘destroyed’1

enzyme / pepsin no longer fits (substrate)

allow enzyme / pepsin does not work1

(c) hydrochloric (acid)

allow phonetic spelling

accept HCl

allow HCL

ignore hcl

do not allow incorrect formula –e.g. H2Cl / HCl21

[8]

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(a) (i) directly proportional

gains full marks

or0.1 rise in rate for 1% rise in concentration

accept increased concentration: increased rate or positivecorrelation or proportional for 1 mark

2

15

(ii) 0.6

allow ± 0.011

(b) (0.5% trypsin) cheaper

ignore more profit1

(35°C) faster reaction

allow (35°C) optimum / best temperature1

so takes less time to make product1

extra heating cost outweighed by savings on enzyme cost1

(c) (i) any two from:

• breaks down / digests food

allow pre-digests protein / foodallow easier for baby to digest

• from protein into amino acids / peptides

• makes soft(er) / runni(er)

allow description of texture changeallow make (more) soluble

2

(ii) correct named enzyme1

correct function

to gain 2 marks function must relate to correctly named enzyme

Eg

carbohydrase

accept amylase / maltase / lactase1

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starch → sugar or lactose → glucose or making sugar syrup

or

isomerase

glucose → fructose or making slimming foods

or

lipase

fats / oils → fatty acids or removal of grease stains

accept other correct example[11]

(a) fatty acids116

glycerol1

(b) (i) any one from:

• (same) amount / 1cm 3 fat

• (same) amount / 10cm 3 lipase / enzyme

• (kept for) 24 hours or (same length of) time1

(ii) temperature

allow heat / warmth1

(c) (carry out experiments) using more temperatures / smaller intervals

ignore repeat unqualified

do not accept longer time1

between 20 and 60 °C / around 40 °C

accept extra single temperature in range 20 °C – 60 °C but cannotbe 20 °C, 40 °C or 60 °C

1

(d) (i) ‘strong’ acid1

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(ii) enzyme works / not destroyed / not denatured / not damaged

do not accept enzyme not killed

accept any indication that the fat is digested

accept same as tube 3 / tube at 40 °C

accept optimum temperature / at or near body temperature1

[8]

(a) (i) B1

(ii) any one from:

• largest area of / most digestion (of lipid)

allow agar / jelly / mixture broken down / digested

do not allow digestion of bacteria / lipase

ignore digestion by bacteria

• largest clear area1

17

(b) any two from:

• effect of pH / pH described

• effect of temperature

• effect on different types of lipid / fat

• cost or allergic reactions or effect on skin / fabrics / orenvironment or interaction with other chemicals inpowder or shelf life

2

(c) enzymes / named enzyme denatured / destroyed

allow active site(of enzyme) altered1

[5]

(a) the enzyme must be lipase1

since fatty acid produced, which lowered the pH1

18

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correct answer with / without working

2

(b) (i) 0.25 or

if answer incorrect / missing, then evidence of gains 1 mark

(ii) bile provides optimum / suitable / best pH for enzyme actiontherefore the rate of the reaction increased

1[5]

(a) any one from:

ignore reference to recording results every 5 minutes orconcentrations of lipid / lipase

• (same) volume / amount / 1 cm 3 lipase

allow amount of solution

• (same) volume / amount / 5 cm 3 lipid

allow keep same volumes in the test tubes

• mixed after 3 minutes / same time before mixing

do not accept temperature1

19

(b) so that the lipase and the lipid reached the right temperature1

(c) any two from

ignore explanations

• decrease in time or faster (breakdown)

• then increase in time or then slower (breakdown)

• fastest / least time / optimum at 35°C2

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(d) any two from:

ignore ‘test at more temperatures’ unqualified

• test more regularly eg test every minute

any interval < 5min

• test at smaller temperature intervals

any value <15°C

allow test more temperatures in the range

• test between 50 (°C) and 95 (°C)

any value in range, eg test at 70

• repeat at same temperaturesor repeat the investigationor compare results with others

allow do it again2

(e) (i) (lipase / it) denatured / destroyed / changed shape

allow damaged / deformed

do not accept killed

ignore broken (down)1

(ii) fatty acids and glycerol1

[8]

(a) (i) glycerol1

(ii) pancreas / small intestine

accept duodenum / ileum

ignore intestine unqualified1

20

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(b) any two from:• type of milk• volume / amount of milk• vol. bile equals vol. water• volume of lipase• concentration of lipase• temperature

ignore time interval

ignore solution unqualified

do not allow pH

ignore starting pH

ignore volume / amount of bile / water

ignore concentration of bile

accept amount of lipase if neither volume nor concentration given2

(c) (i) fatty acid (production)1

(ii) faster reaction / digestion (with bile)orpH decreases faster (with bile)ortakes less time (with bile)orsteeper fall / line (with bile)

allow use of data

ignore easier1

(iii) all fat / milk digestedorsame amount of fatty acids presentor(lower pH) denatures the enzyme / lipase

allow all reactants used up

ignore reference to neutralisation

allow enzyme won’t work at low pH

do not allow enzyme killed1

[7]

(a) (i) mitochondrion / mitochondria

must be phonetically correct1

21

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(ii) carbon dioxide / CO2

1

water / H2O1

in either order

accept CO2 but not CO2

accept H2O or HOH but not H2O

(iii) diffusion1

high to low concentration

allow down a concentration gradient1

through (cell) membrane or through cytoplasm

do not accept cell wall1

(b) ribosomes make proteins / enzymes1

using amino acids1

part A / mitochondria provide the energy for the process

allow ATP

do not accept produce or make energy1

[9]

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(a) Marks awarded for this answer will be determined by the Quality of Communication (QC)as well as the standard of the scientific response. Examiners should also refer to theinformation in the Marking guidance and apply a ‘best-fit’ approach to the marking.


Level 1 (1−2 marks)The method described is weak and could not be used to collect valid results, howeverdoes show some understanding of the sequence of an investigation.

Level 2 (3−4 marks)The method described could be followed and would enable some valid results to becollected, but lacks detail.

Level 3 (5−6 marks)The method described could be easily followed and would enable valid results to becollected.

Examples of the points made in the response:• bean seedlings of same age• cut material from same part of each organ (for repeats) e.g. top 1 cm of stem / a

whole cotyledon / seed• equal mass of each organ

accept weight for mass• grind / homogenise• in equal amounts of water / buffer• equal volumes of hydrogen peroxide solution• equal concentrations of hydrogen peroxide solution• same temperature• temperature maintained in water bath• quantitative measure of gas production eg height of foam in mm / collect gas in

graduated syringe in cm3

• for same time period• repetitions (3+ times)• calculate mean for each.

6

22

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(b) (i) correct answer: 40

1 mark for 45 as the anomalous result has been included in thecalculation

or

1 mark for

or 2

(ii) vertical axis correctly labelled:‘Enzyme activity in arbitrary units’

allow ecf from (b)(i)1

points plotted correctly ±1 mm

deduct 1 mark for each incorrect plot2

suitable line of best fit

not feathery, not point to point1

(iii) 6.0 / 6

allow ± 0.1

if 6.0 not given, allow correct for candidate’s graph ± 0.11

(iv) in range 0 to 14 units

allow correct for candidate’s graph1

(v) enzyme denatured / enzyme (active site) shape changed

allow substrate no longer fits (active site)

ignore reference to temperature

do not allow enzyme dies1

[15]

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(a) any one from:

ignore control variables that are not given in the method, such as‘equally crushed’ or same time

do not accept volume of apple juice

• 20 g (of apple) or (same) mass / amount / weight of apple

ignore volume / size

• crushed (apple)

• 10 drops (of solution) or (same) number / amount / volume of drops

do not accept 10 drops of amylase alone

• apple or type of fruit

ignore type of apple1

23

(b) (may) have different volume / amount / sizes

ignore reference to human error

ignore don’t know / can’t measure size of drop1

(c) amylase has no / little effect on cell / walls / apple

accept ideas that refer to shape of enzyme being ‘incorrect’

or amylase does not breakdown / digest cell / walls / apple

accept amylase only breaks down / digests starch1

pectinase breaks down cell / walls / apple

allow digest for breakdown

allow shape of pectinase fits cell / walls / apple1

boiling breaks down cell / walls / apple1

(d) 11.61

enzyme / pectinase destroyed / denatured / damaged / broken down

do not allow kill1

only effect of boiling (relevant)1

[8]

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(a) (i) any two from:

• fibres not damaged

• machines last longer / machines not damaged by stones

• short er time or quicker

• low er temperature

allow cheaper / uses less energy as an alternative to shorter time /lower temperature, if these not given

2

24

(ii) any two from:

• different enzymes (for different dyes)

• enzymes expensive

no mark for expensive alone

• enzymes have to be removed (from denim material) (after washing / treatment)2

(b) protease1

[5]

(a) (i) 129125

(ii) 9

accept calculated difference between answer to (a)(i) and 1201

(b) less energy / power used

allow less fuel / named fuel used

ignore cost1

less pollution / carbon dioxideor less hot water / less heat released

allow less global warming / carbon emissions or reduced carbonfootprints

do not accept secondary effects alone, eg less melting of ice caps1

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(c) (i)

1 mark for each correct line

do not accept two lines from an enzyme2

(ii) denatured

if no answer on the line accept a clear indication of correct answerin the box

1[7]

(a) shape changed / destroyed (above 45 °C)

accept denatured

accept active site changed

do not accept enzyme killed1

26

(shape) doesn’t fit (other molecules / stain)1

(b) (i) any two from:

• can wash the clothes at higher temperature

• so wash / enzyme action will be quicker

do not accept idea of bacteria working faster

• enzyme not destroyed at high temperature / 80 °C

accept denaturation or description2

(ii) high(er) temperature / 80 °C uses more energy / fuel1

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more pollution / named (eg carbon dioxide / global warming) (from electricityproduction)

or

increased release of hot water (into the environment)1

[6]

(a) Marks awarded for this answer will be determined by the Quality of Communication (QC)as well as the standard of the scientific response. Examiners should also refer to theinformation on page 5, and apply a ‘best − fit’ approach to the marking.


Level 1 (1 − 2 marks)The method described is weak and could not be used to collect valid results howeverdoes show some understanding of the sequence of an investigation.

Level 2 (3 − 4 marks)The method described could be followed and would enable some results to becollected but lacks detail.

Level 3 (5 − 6 marks)The method described could be easily followed and would enable valid results to becollected.

examples of biology points made in the response:

• (use of measuring cylinder to) measure equal volumes of detergent solution• (use of dropping bottle to) apply same number of drops / amount of stain to each

piece of cloth• include stainless cloth as control• use of forceps to transfer cloths• use of test tubes as containers for detergent solution + stained cloth• use water bath to provide a range of temperatures• cloths left in detergent solution at each temperature• for same length of time or measure time taken to remove stain• repetition• assessing the stain removal

6

27

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(b) (i) y axis: labelled ‘Time (taken to remove stain in) minutes’ plus suitable scale

data spread greater than half of grid1

points or bars plotted correctly to within ± 1 mm

deduct 1 mark for each incorrect plot up to a maximum of 22

one suitable line of best fit drawn on graph

not feathery

not extrapolated to (0,0)

not point to point as on this occasion it is inappropriate1

(ii) 6 ± 0.1

accept ecf from student graph1

(c) activity of enzyme still very high / 84% / over 80%oronly lost 15% / 16% activity

allow above 60 °C marked decrease in activityallow 85%

1

any two from:

• rate of reaction high at 60 °C / higher than at lower temperatures

allow in terms of reaction kinetics / collisions• higher temperatures would increase (energy) costs

ormight damage cloth

ignore enzyme denaturation• higher temperatures / 60 °C is better (than lower temperatures) to remove other

stains / named stains

orbetter for killing bacteria / infection control

eg grease2

[14]

(a) A carbohydrase1

B isomerase1

(b) less needed (to get same effect)1

28

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(c) (i) they all work at atmospheric pressures1

they work well at 25 – 45 °C

accept any clear indication of correct statement(s) identified1

(ii) any two from:


• they are soluble in water, so it may be difficult to separate them from products

• they are expensive to buy

accept any clear indication of correct statement(s) identified

accept for 2 marks if written as two separate disadvantages2

[7]

(a) any two from:

• product not contaminated with enzyme or is pure

• enzyme can be reused

allow enzyme not wasted / less

enzyme is needed

• continuous flow process possible

• enzyme more stable / can be used at higher temperature

allow enzyme lasts longer

ignore refs. to cost / cheaper2

29

(b) maximum fructose production / maximum enzyme activity

accept optimum / best

or

increase in flow rate does not increase production1

higher rate leaves some glucose unchanged

allow glucose not wasted / extra glucose wastes money1

(c) less (fructose) needed (for same sweetness)

ignore fructose is sweeter unqualified1

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(less fructose ) → less fattening / fewer ‘calories’ignore refs. to cost / cheaper

1[6]

(a) (i) the darker blue colour produced absorbs more light130

(ii) colorimeter will have better resolution than eye1

less chance of human error1

(b) (i) 6.7 – 7 (minutes)

correct answer with or without working gains 2 marks

if final answer incorrect award 1 mark for evidence of selection of40(% light intensity) either in working or in graph 2

2

(ii) all starch broken down1

(c) because 40 °C is the optimum temperature for the enzyme’s action1

and the enzyme is denatured / destroyed / damaged at higher temperatures1

(d) fructose is sweeter than glucose1

therefore needed in smaller quantitiesorso fewer calories in the slimming food

1[10]

(a) microorganisms131

(b) (i) proteases clear indications of correct answer1

(ii) amino acids (both words) clear indications of correct answer1

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(c) (i) 141

(ii) mark independently

enzyme Z

clear indication of correct answer1

takes least time (to pre-digest protein) / works fastest

allow only 7 minutes / less time / faster

do not allow works best1

(iii) temperature1

pH1

[8]

(a) (i) any two from:

• fibres not damaged

• machines last longer / machines not damaged by stones

• short er time or quicker

• low er temperature

uses less energy or cheaper for energy as an alternative to shortertime / lower temperature, if neither of these given

no mark for cheaper unqualified2

32

(ii) any two from:

• different enzymes (for different dyes)

• enzymes expensive

no mark for expensive alone

• enzymes have to be removed (from denim material) (after washing /treatment)

2

(b) protease

apply list principle1

[5]

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(a) (i) work at low temperatures / save energy1

work at low or atmospheric pressures / need less expensive equipment1

(ii) any two from:

• easily broken down by high temperature / low pH

• difficult to separate from water-soluble products

• very expensive to buy2

33

(b) (i) lipase1

(ii) isomerase1

(iii) protease1

[7]

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Examiner reports

This question was about enzymes and their industrial uses. It was well answered by the majorityof students.

(a) (i) The vast majority correctly selected the term catalyst as a description of an enzyme,‘an antibody’ being the most common error.

(ii) Around three quarters of the students knew that an enzyme was made of protein(rather than carbohydrate or fat), although ‘carbohydrate’ distracted most of theothers.

(iii) Almost two-thirds of students knew that the enzyme amylase was made in thesalivary glands, with ‘stomach’ being selected by most of the remainder.

(b) In this question, students were required to link each of three enzymes, carbohydrase,isomerase and protease, to their correct industrial uses. Just under half got all three right.Most students knew that isomerase would change glucose into fructose, but the removal ofgrease stains from clothes proved to be a powerful distracter for the possible use of each ofthe other two enzymes.

1

(a) Only a little under half of students identified ‘B’ and gave an acceptable reason for theirchoice. Some decided that ‘C’ would be adapted for diffusion, due to the ‘larger numbers ofmitochondria / ribosomes’, presumably unaware that neither of these organelles is directlyinvolved in diffusion. Other difficulties arose in finding appropriate words to describe theincreased surface area of cell B, ‘villi’, ‘hairs’ and ‘cilia’ being common descriptions whichwere ignored by examiners.

2

(b) (i) A variety of enzymes and a number of other suggestions, some not even substances,were suggested. A common insufficient answer was ‘saliva’ as this is the digestivejuice which contains the amylase. A surprisingly large proportion of students couldoffer no suggestions and left the space blank.

(ii) The increased numbers of ribosomes was identified by many students who then wenton to describe the synthesis of protein by these organelles. Those students who tookthe alternative route, referring to ‘many mitochondria’ had more difficulty explaininghow these were involved in the production of the enzyme. Once again, the‘production’ or ‘use’ of energy by mitochondria or by respiration was a commonbiological misunderstanding.

This was the second of the two common questions.

(a) Just over half of the students were able to name both of structures A and B (cell wall andcytoplasm, respectively) on the diagrams of the yeast and bacterial cells. Some studentsoffered an amalgamation of the words ‘cytoplasm’ and ‘chloroplast’ for structure B. Whilealmost four fifths of students were able to describe one way in which the bacterial celldiffered from the yeast cell (e.g. lack of a nucleus or vacuole), some stated erroneously thatthe difference was that the bacterium had DNA, not understanding that the nucleus of theyeast cell also contained this substance.

3

(b) Very few students scored both marks in each of sections (i) and (ii). This resulted from aninability to apply what they should have known about yeast and carbon dioxide production,and the information given to them in the question about the bacteria and lactic acidproduction.

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(i) Students should have been able to tell from the graph that the given temperature of27°C was the optimum temperature for the growth of the yeast and hence for carbondioxide production and the associated rising of the bread.

(ii) Here 32°C was the optimum temperature for the growth of the bacteria and thus forlactic acid production: thus the bread would taste most sour if it rose at thistemperature.

(a) (i) Over sixty percent of candidates correctly linked all three substrates with the correctenzymes.

Those who made errors were much more likely to get two wrong, rather than just one,perhaps showing an element of guesswork, rather than logic. Perhaps the prefixes ofprotein and protease helped some candidates as, when candidates made errors, thiswas the pair most commonly correctly linked, with the enzymes responsible for thedigestion of starch and fat being less commonly matched.

The examiners were pleased to note that relatively few candidates lost marks bydrawing more than three lines, although some left a certain degree of speculation inexaminers’ minds by leaving their lines considerably short of the boxes.

(ii) It was surprising how many candidates missed the clues in the words for thebreakdown products of fats, often choosing the much less likely fructose.

Disappointingly less than half of candidates scored for all three answers here, therebeing an apparently high degree of guesswork, with some selecting amino acids forall three, perhaps in the hope that at least one would be correct.

(b) The stomach proved to be almost as popular as the liver as the source of bile.

4

(a) (i) Selecting the correct digestive organs posed no problem for the vast majority ofstudents.

(ii) Selecting the correct digestive organs posed no problem for the vast majority ofstudents.

(b) A surprisingly high number of students did not accurately recall the enzymes produced bydifferent digestive organs. Most students were only awarded the fall back mark of onecomplete column which was usually the salivary gland or small intestine.

(c) Just over half of the students provided a creditworthy response referring to enzymeeffectiveness in acidic conditions or reference to optimum / correct pH. Credit was notgiven for answers relating to the breakdown of food or killing bacteria without any links to acorrectly named enzyme / low pH.

(d) Matching the enzyme to the right breakdown product was straightforward and answeredcorrectly by almost all students.

5

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(a) Only about one quarter of students scored full marks on this question identifying parts of thedigestive system. Many students did not know the duodenum specifically and instead wrotesmall intestine which was ignored. Furthermore, many students could not identify thepancreas.

(b) (i) This question on protein digestion was answered well by the majority of studentsalthough examiners remarked that many students often wrote far too much withdescriptions of digestion of other substances eg fats. Absorption and deaminationwere also described in some responses.

(ii) This question on fat digestion saw a large spread in the quality of responses. Correctanswers needed a reference to pH neutralisation or alkaline conditions needed sothat lipase can work. Secondly, bile works to emulsify fats and thus give a largersurface area for enzyme action. Many students only gave answers that said what biledid, but did not explain how bile helps fat digestion. A few students (incorrectly)thought that bile contained enzymes.

6

(c) (i) A surprisingly large number of students did not correctly identify starch as thesubstance broken down by amylase. Carbohydrate was insufficient to gain the mark.

(ii) Almost half the students scored full marks. However, many explanations wereconfused in this question, with incorrect interpretations of the data and a failure toapply knowledge. Students should have identified from the data that break down ofthe substance stops or slows down in acidic conditions. Consequently, because thestomach is acidic, the amylase cannot work or is denatured.

(a) The vast majority were able to identify structure A on the diagram as the stomach.

(ii) Less than one-fifth knew that the acid produced by the stomach was hydrochloricacid.

(iii) More students knew that some sort of alkali would need to be present in a medicinethat would neutralise excess stomach acid.

(b) Most answers to this question were very poor, with half of the students scoring no marks atall for their accounts of carbohydrate digestion, despite being given the words amylase,starch and sugars for guidance. Many did not seem to know that starch was acarbohydrate or that starch was made of sugar molecules joined together. The site ofamylase production and the site of its action were not always distinguished – digestion ofstarch does not occur in the pancreas or in the salivary glands as some students inferred. Some also wasted time by writing about topics irrelevant to the question, such asabsorption and defaecation.

(c) Just over one-quarter of students knew that the site of absorption of the products ofdigestion was the small intestine.

7

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Given the information provided, it was noticeable that a significant minority of candidates chosenot to use it, in part (a). The suggestion that the more concentrated starch would be thicker wasnot considered to be worthy of the mark.

Part (b)(i) was not answered well. Once again, the instruction to show clearly how you workedout your answer was ignored by many candidates who might otherwise have been credited withone mark for getting part way; responses such as 5.4 were not uncommon. In this case, itappeared that candidates may have read off the value on graph 2 at 40% light but hadmisinterpreted the time scale. Unfortunately with no evidence for this, either on graph 2 or in thespace for working, no mark could be awarded. Many candidates seemed unaware that theyneeded to use both graphs to arrive at their answer and merely read off from 2% on graph 2,getting an answer of around three quarters of a minute.

8

In part (b)(ii) the significance of 40oC, being at or near the optimum was identified by mostcandidates, however it was less common for candidates to go on to explain why othertemperatures were less or not appropriate. Some candidates misinterpreted the information andbelieved that the carbohydrase would be working in the body, so it would be important to test it attemperatures close to body temperature, whilst others thought that it is microorganisms, ratherthan carbohydrase which were being tested. There remains the Additional Science /misconception that enzymes are denatured at temperatures below, as well as above, theiroptimum. It was pleasing to note that very few candidates referred to enzymes as being killed.

Isomerase was not a well known term, in part (c)(i). It was clear that the majority of candidateshad not considered this important in their revision, amylase and protease were both frequentincorrect responses, as were fructase and glucase, although these latter at least suggested thatcandidates were trying to use some logical thought.

Again in part (c)(ii), some candidates had clearly omitted this area of the specification from theirrevision. Those who had learned it often scored both marks, some giving more detail about therelative calorific content of glucose and fructose than was required, but showed a goodunderstanding of the topic. Weaker candidates often suggested that fructose contains less sugar,is less fattening or contains less energy.

This was the third of the three common questions.

(a) A little over half of students were able to read enzyme Z’s optimum pH from the graph as8.6. However, only a fifth of the students knew that hydrochloric acid was the substancethat generated the correct pH for enzyme action in the human stomach, with a little underone-third identifying enzyme X (showing an optimum pH of 1.9 in the graph) as the one thatwould work best in the stomach.

9

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(b) In this question, students were required to describe how the human digestive system wasable to break down molecules of fat so that they could be absorbed by the body. Thequality of written communication was also taken into account in the awarding of marks.Many students found this question very difficult with only a minority displaying a goodknowledge of fat digestion. Many knew that lipase was involved, although the term wasoften confused with ‘lipid’, and that fat was converted into fatty acids. Relatively few knewthat the lipase was produced in the pancreas and / or the small intestine (the mouth andstomach were common errors). A fair proportion knew that bile was involved but there wasmuch confusion about where it was made, its storage in the gall bladder being betterknown. Only a few were able to explain that the bile was alkaline and hence helped toneutralise the acid coming into the small intestine from the stomach (a common error wasto suggest that bile entered the stomach to neutralise the acidity); and few knew that thebile emulsified the fat, or were able to describe this process as the production of tinydroplets of fat (the breakdown of fat molecules was a common error here). Some studentsalso explained how initially the food could be broken down mechanically by the teeth andhow eventually the products of digestion could be absorbed by the small intestine. Manystudents were confused about which processes occurred where, about the name of theenzyme (‘amylase’ was a common error) and about the products of digestion (e.g. ‘aminoacids’ were sometimes suggested). One major mistake, made by a large proportion ofstudents, was to misinterpret the question and not limit themselves to the remit of fatdigestion. Consequently, these students wasted a great deal of time giving details ofcarbohydrate and protein digestion which were not required and for which no marks wereavailable. The only penalty incurred was that of wasting valuable time which could havebeen better devoted to gaining marks elsewhere.

(a) The catalytic properties of enzymes were well known but only around a half of studentswere able to answer part (ii) and (iii) correctly.

(b) Here students were presented with a diagram of a vertical column containing beads of gelwith the enzyme isomerase attached and had to select two advantages, from a list of foursuggestions, of using the enzyme attached to the beads of gel. This was perhaps a novelsituation to which students had to apply their understanding of the use of enzymes. Moreable students were able to work out that the enzyme could easily be used again and thatthe product would not be contaminated with enzyme. Only around a quarter of studentswere able to select both of these answers, with some students ticking only one box.

10

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(a) Most candidates gained at least one mark with examiners being willing to accept a widevariety of spellings of pancreas. Some hedged their bets as far as intestine was concernedand gave unqualified answers or used terms such as upper intestine; none of theseresponses being credited. Common incorrect answers included liver, stomach,and otherssuch as kidneys and lungs which are not part of the digestive system. Once morecandidates are encouraged to read the entire question carefully, as there was a significantminority of answers such as mouth and salivary glands.

(b) Those candidates who gained a mark most commonly referred to the significance of 40°C,being at or close to body temperature or the temperature at which enzymes work best.Relatively few recognised the importance of both enzyme and substrate being at the sametemperature to begin with, although the examiners suspected that some of these gainedthe mark fortuitously with loose use of language such as they are at the same temperature,possibly referring to all the tubes throughout the investigation.

Some students were, unfortunately, very confused and gave totally incorrect answers suchas time for the amylase and starch to diffuse through the water, the starch would becomesoft and easier to breakdown, so that light could pass through, to ensure they were sterileor to get rid of any glucose in the enzyme. Some misinterpreted the time reference asbeing time after mixing and responded by saying that the enzyme would (therefore) haveenough time to digest the starch. Others focused on either the starch or amylase alone.

Clearly incorrect references to the starch working best at this temperature gained no credit.Neither did answers that incorporated ideas of the amylase being activated or starting towork before mixing had taken place. Vague responses such as so the enzymes got to theright temperature for working or to make sure they got used to the temperature of the waterbath also gained no marks. Candidates should always be encouraged to give answerswhich are as precise as possible, particularly in the Higher Tier paper, to ensure that pointsmade are clearly creditworthy.

(c) (i) Many candidates managed to gain the mark. Incorrect responses usually involvedincorrect appreciation of the graphs. Some students simply read the value 32 fromgraph 2 and, despite the emboldened references in the question to use both graphs,failed to refer to graph 1 at all. Others took the y-axis in graph 1 as giving time and

read from the 20 value here to give an answer of 0.5 mol per dm3

(ii) Many candidates left the question unattempted. The most common error was to takethe answer from part (c)(i) and multiply, rather than divide, by 20 but other,often verycomplicated, attempts at calculations were seen. Candidates were notpenalised twicein this question so that an incorrect answer in part (c)(i) that was subsequently usedcorrectly in part (c)(ii) gained both marks. The value of showing working out inquestions such as this should always be emphasised. A mark was often given for acorrect method even though the final calculated answer was wrong.

(iii) Most able candidates gained the mark; many, however, appeared to be confused.The word light, in the question, opened the door for comments on photosynthesisparticularly as it was associated with a plateau on graph 2. Answers referred tooptimal light intensity, light no longer being a limiting factor and other factors such asCO2 concentration or temperature becoming limiting (for photosynthesis). Otherresponses described enzymes using up all of the light. Some answers, for example,the reaction was complete and amylase could not digest any more, were consideredtoo vague to gain credit whilst others showed misconceptions that the enzyme hadbeen used up or all the sugar had been broken down.

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(iv) Most candidates were able to gain at least one mark, invariably for having stated ordescribed that the amylase would have been denatured. Very occasionally studentsdisqualified their answer by going on to explain this in terms of the enzyme beingkilled. More often, however, answers were well developed and displayed excellentunderstanding of the active site and of substrate fit.

Candidates, however, sometimes failed to appreciate the need to make two clearpoints in order to gain the maximum marks. Answers that referred to denaturationand then simply added that the experiment would therefore not work lacked thenecessary detail for the second mark. Similarly, vague responses such as enzymeswork best at 40°C, the amylase would not work properly or temperatures above thatof the body are too hot were not credited as they do not refer specifically to events at80°C.

(a) Many students were able to explain that the contents of the stomach are acidic and that theevidence in Table 1 showed lactase was more active in alkaline conditions. Others only gothalfway to this, giving either one side or the other of this explanation. However aconsiderable number of students appeared to have little understanding of the pH scale,suggesting that ‘high pH means acid conditions’. These students then struggled to gain anymarks here.

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(b) Students often failed to refer to the rate of enzyme activity; choosing to describe the resultsin Table 2, rather than to ‘explain’ them as demanded by the question. This usually leftthem with no marks, despite having filled the available space. Those students who didattempt explanations often omitted to refer to temperatures below the optimum, thuslimiting their maximum mark to two. ‘Denaturation’ was a commonly known term, althoughsome believed that this happens at both high and low temperatures. There were very fewreferences to enzymes being ‘killed’. ‘Optimum’, along with an appropriate temperature wasalso commonly accepted.

(c) Only the neutralising effect of bile is described in the specification. Examiners alsoaccepted ‘emulsification’ or a description of this process. The advantage of both theseprocesses is the same, intestinal enzymes ‘work better / faster’. Students were sometimesconfused as to where bile was added to food, often describing neutralisation as being ‘inthe stomach’, rather than occurring after the food had left the stomach. References to‘helping lactase work faster’ may be true, but were not accepted as the question askedabout the digestion of lipid. The knowledge of bile, its composition and effects wassurprisingly sparse. Many believed that it ‘contains enzymes’ or ‘is an acid’ or that it simply‘breaks down fats’ and as a result marks for this final part were below what the examinershad hoped.

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(a) The majority of students were able to identify the two ‘other’ enzymes produced by thepancreas. Most common errors included naming both ‘amylase’ and ‘carbohydrase’ orincluding ‘lipase’ as one of their suggestions, although this had been clearly eliminatedfrom the possible responses by the information in the stem of the question. An example ofpoor examination technique; where students had not taken in all the information supplied inthe question. Further errors included the naming of ‘pepsin’, produced in the stomach,although some correctly named ‘trypsin’ as an example of a protease.

(b) Students often lost focus on what was going on in the intestine and the capsule, suggestingthat the lipase within the capsule would not break down the lipid coating until the correct pHand temperature were provided in the small intestine. There was a surprising number ofstudents who suggested that ‘lipase does not break down lipids, only fats’, which inevitablyscored no marks. Good students realised that the lipase is not released in the body untilfood reaches the small intestine, although it was accepted that this could be producedeither in the intestine itself or from the pancreas, as the pancreas was only ‘damaged’, notdestroyed.

(c) A wide variety of speculative suggestions were given in this part. These included, again,references to incorrect temperature and pH, although a good proportion of studentsrealised that, being dry, the enzymes would be inactive. A few good students extendedtheir explanations into the need for enzymes to be in solution to allow reaction with thesubstrate and formation of an enzyme-substrate complex or referred to the active site ofthe lipase.

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(a) (i) Less than one-third of students knew that amino acids (or, alternatively, peptides)were the product of protein digestion.

(ii) There was much more success in selecting protease as the name of the protein-digesting enzyme.

(b) (i) Almost two-thirds of students were able to select pH 2 from the table of data as thepH at which the enzyme worked best, although a significant minority chose a valuebetween 5 and 7 (the table showed that no reaction had taken place at these values,whereas pH 2 had the greatest decrease in length of the egg white).

(ii) Most students appreciated that the experiment would need to be repeated; however,this would not have improved the accuracy, as demanded by the question. Very fewstudents were able to qualify their answer with a suitable pH range around theiranswer for (i), and at smaller intervals of pH.

(iii) While a few students knew that denaturation of the enzyme would be the likely reasonfor it not working at pH 5 to 7, many thought that digestion of the protein was broughtabout by ’acid’ and argued that, since the solution was less acidic, digestion wouldcease. The most common mark awarded was for the idea that the enzyme did notwork at these pHs.

(c) Just over one-third of students knew that hydrochloric acid was responsible for the low pHin the stomach. Incorrect answers included ‘bile’ and ‘amino acid’.

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This was the second of the two common questions.

(a) (i) Over three quarters of the students were able to score at least one mark for theirdescription of the relationship shown in the graph between the concentration of aprotease enzyme (trypsin) and its rate of reaction, by stating that as one increased sodid the other. Both marks were available to those who were more precise and eitherstated that the rate was directly proportional to the enzyme concentration or usednumbers from the graph to indicate this, e.g. stating that a 1 unit increase inconcentration always caused a 0.1 unit increase in rate. Students who failed to scoreoften confused rate with ‘time’ and thus described the opposite of the actualrelationship.

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(ii) Given that the graph was a straight line, almost all students were able to predict thecorrect rate of reaction at 6 units of enzyme concentration by extrapolating beyondthe plotted data.

(b) Students were required to suggest why manufacturers of baby food would make more profitif they used a higher temperature than in the students’ investigation given in part (a) – 35°Crather than 20°C – and a much lower concentration of the enzyme. Most scored 1 mark forstating either that the rate of reaction would be faster at the higher temperature or that itwould be cheaper to use less enzyme. Very few went on to point out that the extra cost ofheating to a higher temperature might be balanced by the saving on enzyme cost or thatthe higher temperature would need to be maintained only for a short time due to theincreased rate of product formation. Some common misconceptions were that a lowerenzyme concentration increased the rate and that bacteria would be killed at 35°C thusextending the shelf life of the product.

(c) (i) Just over half of students knew that the trypsin would digest the baby food or wouldmake its texture softer. Very few knew that amino acids would be the product ofdigestion.

(ii) Although many knew the name of a non-protease enzyme used in industry(carbohydrase / amylase , isomerase and lipase being the most common answers),or they knew a use of an unnamed enzyme (e.g. making sugar syrup / slimmingfoods or removing grease stains from clothing), only around one tenth could give boththe name of the enzyme and its correct function. Where a second mark was gained, itusually relied on knowledge of human digestion, rather than industrial application(e.g. amylase turning starch into sugar). The nature of the stains removed bybiological washing powders was seldom specified.

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(a) More candidates selected either the two incorrect responses or ticked only one of theboxes, than identified both correct answers. Once again, failure to read the instruction totick two boxes was missed by far too many candidates. Not unexpectedly, fatty acid wasthe most commonly correct answer; after that the other three responses were chosen inalmost equal proportion.

(b) A significant number of candidates drew arrows to swap their answers to the two sectionsaround. Whilst this is an acceptable way of changing an answer, it would be more helpful toexaminers if an answer a candidate feels is incorrect was crossed out and replaced by analternative. It would appear that many candidates, having selected a response for part(b)(i), then arrived at part (b)(ii) and changed their minds, hence the need to swap answersaround. Interestingly, many of these swapped what would have been correct answers,around and thus gained neither mark.

(i) Answers such as fat or lipase were considered to be insufficient, as they do notindicate the factor that is being controlled.

(ii) Candidates were clearly confused about the variables, particularly the independentvariable, with time and amount of fat or lipase frequently seen amongst the incorrectanswers.

(c) Careful thinking was required, and many candidates only got part way through the process,recognising, for one mark, that carrying out the investigation at more temperatures wouldhelp to identify the best temperature. The second mark was much less often scored, ascandidates then had to go on to explain which additional temperatures it would be better touse. Those who used the results in the table to recognise that the lipase was most effectivebetween 20 and 60°C and either quoted this range or any value within it were rewarded fortheir efforts.

Unfortunately, having established that experimenting at more temperatures would behelpful, many candidates then went on to disqualify this mark by including all sorts ofadditional improvements. Thus further suggestions such as leave the tubes forlonger,change the pH and add more lipase all cost candidates the mark, although testing atshorter time intervals was ignored, as this would probably be required in an investigationinvolving smaller temperature intervals. Other candidates simply repeated some or all ofthe experimental details they had already been given.

(d) (i) Most candidates chose strong acid, and many went on to give a correct reason byrelating it to the table in part (d)(ii).

(ii) Common errors were thinking that the water would neutralise it or that the water bathwould get cold. Some candidates thought that the low temperature would havealready destroyed the enzyme.

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(a) This question exemplified the need for candidates to read question details very carefullybefore embarking on their answers. Some of the mistakes made arose from amisunderstanding of the context. As a result, the experiments were often seen as beingcarried out on detergents, bacteria, antibiotics or disinfectants rather than on enzymes. Thepoint about samples having been diluted to give the same concentration of lipase was oftenoverlooked. The outcome of a clear mixture following digestion of the lipid was sometimesread cursorily as being a cloudy one.

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(i) The vast majority of candidates correctly identified B as the most effective lipase.Those few who did not, most commonly suggested C and explained in part (a)(ii) thatthis was because none of the lipid had been digested.

(ii) In their answers to this part, the majority of candidates referred to the largest cleararea around B and gained the mark. Some, however, did not use comparative wordswhen they were needed. In this instance, candidates were asked to explain theirchoice of the most effective lipase and answers such as it changed from cloudy toclear failed to distinguish B from A, D or E and were, therefore, insufficient. Incorrectanswers referred to the area around B being the clearest or the only one not to gocloudy. Some candidates thought that the results implied more bacteria had beenkilled and even that B might have eaten the most bacteria. Others believed that Bhad a higher concentration of lipase or that B digested most lipase.

(b) Here the most common correct responses were temperature, cost and possible allergicreactions. pH as a factor was seen less frequently. Temperature was, on occasions,mistakenly given for both factors, firstly in relation to the optimum for the enzyme andsecondly in relation to denaturation. Other answers such as how effective they are atdigestion, the optimum conditions for the enzyme, if they are harmful to people and howfast they work were often too unspecific to be given credit. Some candidates referred toideas that underpin science investigations in general but which were inappropriate here,such as repeat to increase reliability, check to see if there are any errors or ensure it’s a fairtest. The question context of lipase was sometimes overlooked when candidatessuggested that other enzymes such as proteases should be tested.

(c) Some excellent answers were seen in this part. Candidates often understood denaturationperfectly and gave clear explanations relating to changes in the shape of the active site dueto the unravelling of amino acid chains which was detail far beyond the requirements of thequestion or the specification. Some failed to gain the mark because they made no mentionof enzymes, usually referring to they, which implied the detergent as a whole. Candidateswho gave unspecific responses, such as too hot for enzymes or enzymes become lesseffective also failed to pick up the mark. It was pleasing to note that relatively fewreferences were made to enzymes being killed. Other incorrect answers included ones thatsuggested the detergent would burn or that bacteria would die.

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It was disappointing that candidates did not do better on this question, as a whole. Candidatesmust spend considerable amounts of class time carrying out practical work and will also havedone coursework tasks. However the use of common terms such as ‘range’ and ‘interval’ alongwith ideas about experimental design were surprisingly weak.

(a) Many candidates appear confused between control variables that must be maintained forall experimental trials and the independent variable that only has to be maintained for eachseparate trial. As such, a considerable proportion of candidates made inappropriatesuggestions such as ‘temperature’, the independent variable, and ‘time’ which is unclear asit may refer to the dependent variable or the time spent in the water bath before mixing theenzyme and substrate. Other candidates, considered that the ‘amount of water in the waterbath’ was an important control variable. Candidates’ use of the term ‘amount’ (of lipid orlipase) was acceptable, in this case, although they should be encouraged to use moreprecise terms, such as ‘volume’.

(b) Answers to this were better, with three quarters of candidates realising that the time in thewater bath was to allow the lipid and lipase to reach the right temperature.

(c) Overall candidates who wrote less and stuck to a description of the effect got the bestmarks, in part (c). Many candidates tried to explain the effect as well as describe it. Anexplanation was not required and tended to result in candidates getting muddled and losingmarks. Many candidates who did this tended to say that ‘the increase in temperaturecaused the degrees (instead of time) to fall’. Misreading the question, thinking it referred tothe whole temperature range in the table, from 5 °C to 95 °C, also created problems andmany candidates answered with respect to events above 50 °C and missed the secondmarking point. Although not asked for, a common misconception seen was that the lipid, inthe mixture, was the one to get denatured. Another misconception was answering withrespect to lipid breakdown instead of time so the increase in temperature was linked to thedecrease in lipid, when in fact; the extent of lipid breakdown is the same at each of thetemperatures in the question. Descriptions that involved both time and rate of breakdownwere accepted by the examiners and it was common for answers that began with ratedescriptions, ‘it got faster’, ended with time descriptions, ‘then it took longer’.

(d) Reference to ‘repeat’ was a common acceptable answer; however other terminology thatcandidates ought to be familiar with was much less secure. Candidates frequently gavesuggestions such as ‘increasing the interval’ or ‘increasing the range’, however if they thenwent on to give examples, such as ‘test every 5 °C’, the examiners overlooked the error.The language of some candidates became so entangled that it was difficult to interpretexactly what they meant, answers such as ‘make the time 10 °C’ were not consideredadequate. Further candidates believed that ‘measuring in seconds, instead of minutes’would improve the investigation, when this would only make the numbers bigger.

(e) (i) The idea of denaturation of the lipase / enzyme was not as common as might havebeen expected, with many candidates only suggesting that 95 °C is ‘too hot forlipase’. Examiners were pleased to report that the number of candidates who referredto the enzyme being ‘killed’ was not as high as in recent examinations.

(ii) Although half the candidates correctly selected ‘fatty acids and glycerol’, almost asmany believed that lipids would break down into ‘amino acids’.

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This was the first of three standard-demand questions common to both the Foundation andHigher Tier papers. This question was about the digestion of fat.

(a) (i) Less than half of Foundation Tier students were able to select the answer glycerol asa product of fat digestion; ‘glucose’ being a common error.

(ii) About the same proportion knew that lipase was made in either the pancreas or thesmall intestine, the most prevalent errors being the ‘liver’ and the ‘stomach’, andsome answers lacked specificity − for example, the ‘intestines’.

(b) Approximately two-thirds of students were able to give at least one variable that shouldhave been controlled in the investigation of the effect of bile on the digestion of fat. Far toomany considered ‘time’ to be significant, although the 2-minute interval for taking pHmeasurements was entirely arbitrary. Another common, incorrect answer was ‘pH’, thisactually being the dependent variable. Where substances in the reaction mixture werementioned, it was often the ‘amount’ that was stated rather than the volume or theconcentration. Some students correctly identified temperature as a control variable.

(c) (i) Despite an equation having been given in part (a)(i) which showed that fatty acidswere produced when fat was digested, hardly any Foundation Tier students wereable to relate the fall in pH shown in the graph to fatty acid production. Many strangeideas were suggested about the nature of bile and water and their supposed effectson pH, although some students at least realised that an acid was produced in thereaction. Many students clearly did not understand the pH scale and stated that a fallin pH represented a decrease in the amount of acid present.

(ii) It was evident to almost half the students that the faster fall in pH in the presence ofbile provided evidence that bile helped lipase to digest the fat.

(iii) Only one-tenth of students could offer a suitable explanation for the levelling off ofthe pH towards the end of the investigation − such as the fat having been completelydigested or the pH now being so low that the enzyme was denatured.

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(a) (i) Given the diagram and the fact that part A of the cell was the site of aerobicrespiration, nearly 90% of students were able to identify it as a mitochondrion(generally stated as the plural ‘mitochondria’).

(ii) A similar proportion were able to complete the equation for aerobic respiration byinserting the terms carbon dioxide and water in the two blank spaces and, althoughstudents were at liberty to use chemical symbols if they wished, the latter were only

rewarded if they were correct (e.g. ‘CO 2’ and ‘H 2O’ were disallowed).

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(iii) This differentiated well amongst students of differing abilities and thoroughness. Mostknew that oxygen would enter the cell by diffusion; some went on to explain that thiswas because there was a higher concentration of oxygen in the blood than in the cell;and a smaller proportion described the route taken by the oxygen – e.g. via the cellmembrane or through the cytoplasm. A not uncommon irrelevance was expressed interms of oxygen diffusing from the alveoli of the lungs into the blood: this was beyondthe remit of the actual question.

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(b) This question differentiated well across the ability range. Students were reminded thatenzymes are proteins and then instructed to describe how ribosomes and part A (themitochondrion) helped the cell to make enzymes. Nearly three quarters of students wereable to make some headway with this question, generally for stating that protein synthesisoccurred on the ribosomes. Better students realised that energy, released in respiration inthe mitochondria, would be needed in the process; but only about one tenth were able toexplain that amino acids were joined together to make a protein molecule. Reference to the‘production’ or ‘making’ of energy by the mitochondrion was not rewarded by examiners.

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(a) In this section, students were provided with a description of a less-than-perfect method forassessing the relative amounts of catalase in the leaf, stem, root, seed and seed coat of abean seedling, as supposedly performed by a group of students. They then had to suggesthow the investigation could be improved in order to give a valid comparison of the amountsof catalase in the different parts of the seedling.

In this question, students were tested on their ability to use good English, organiseinformation clearly and use specialist terms where appropriate.

The question discriminated well across the entire ability range, with a little over half of thestudents scoring 3 or 4 marks and less than one-tenth scoring either 1 or 6 marks out of the6 available. Students gave varying amounts of detail in their accounts, the most basicpoints being the need for equal volumes of hydrogen peroxide and equal masses of thedifferent parts of the bean seedling. Further appropriate details included some numericalmeans of determining the amount of oxygen released (e.g. measuring the height of thefoam produced with a ruler or collecting the oxygen in a gas syringe or upturned measuringcylinder) over a set time period, controlling other variables, such as the temperature,repeating the procedure several times and calculating the mean amount of oxygenproduced by each part of the seedling. It was surprising how many students forgot toinclude a description of how they would measure the volume of oxygen released (‘find theresults’ being a totally inadequate phrase), or forgot to mention repetitions.

(b) This section involved data handling from a set of results obtained in an investigation of theeffect of pH on the activity of catalase.

In part (i), students had to calculate the mean enzyme activity from the five measurementsgiven for one of the pH values. It should have struck students that one of the results wasanomalous (it was approximately 50% greater than each of the other four values) and sothis value should not have been included in the calculation of the mean, giving an answerof 40 arbitrary units; just under half of the students calculated this value. However, just overhalf the students included the anomaly and thus calculated a mean value of 45.

In part (ii), students were required to plot a graph of the results. Any error occurring in part(i) was allowed for in this section. Nearly two-thirds of students scored full marks for theirgraph plotting. Occasionally there was a plotting error (as would be anticipated with onesmall square on the graph paper representing 2 units), or the student forgot to label they-axis, or joined point-to-point with straight lines instead of drawing a line of best fit asinstructed. The most remarkable error, however, was to rule a single straight line of positivegradient somewhere through the points instead of constructing a bell-shaped curve.

In part (iii), nearly all students correctly selected the optimum pH value as pH6, althoughallowance was made for a slightly different value if the student’s graph warranted this (e.g.6.1 or 6.2).

In part (iv), again nearly all students were successful in predicting the activity of theenzyme at pH9.0. Since this involved extrapolation beyond the data, a wide range of whatseemed to be sensible values was allowed by examiners, between 0 and 14 arbitrary units.

In part (v), only half the students realised that the enzyme had zero activity at pH3.0because it had been denatured.

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(a) The correct control variables that were most frequently seen were the ‘amount of apple’and ‘10 drops’. Some students did not gain the mark as they referred to 10 drops ‘of water’or ‘of amylase’, which are values of the independent variable. Reference to all of water,amylase and pectinase or to 10 drops of solution was required, if 10 drops was qualified. Anumber of students scored no mark for the amount of juice collected, the dependentvariable.

(b) References to human errors such as ‘incorrect counting’ or ‘losing count’ were ignored, aswas being ‘unable to measure the size of a drop’. The idea that the drops might be ofdifferent sizes was required for the mark. Ideas about possible variations in the density ofenzymes were sometimes given but were not mark-worthy. Students should be reminded topay careful attention to the command words.

(c) The question required an explanation and not a description. However a large proportion ofstudents spent considerable time filling the space and more beyond with often quitedetailed descriptions, all to no avail. Students usually noticed the differences between thedifferent treatments, but appeared loathe to suggest why these differences might havehappened. Here students might have pointed out that ‘pectinase breaks down apple’, thusallowing the collection of a considerable amount of juice. Conversely ‘amylase does notbreak down apple’ would have gained a further mark. The added observation that ‘boilingbreaks down apple’ would have gained a third mark. Students could have gained all threemarks in three succinct sentences, but rarely did. Those students who did refer to breakdown of the apple often stopped after describing only one or two of the treatments, thuslimiting their potential mark.

(d) All the different volumes of juice were chosen by students, but 11.6cm3 was the required

answer. Students who choose 22.9cm3 never went on to score any marks for anexplanation, simply suggesting that the two parts of the treatment, boiling and pectinase

would have an additive effect . Those who chose 1.2cm3 or 11.3cm3 sometimes did stillgain a mark for the idea that the enzyme would be ‘denatured’. It was extremely rare for a

candidate to point out that the result of 11.6cm3 was the effect of the boiling only. Almosttwo thirds of the students scored no marks here, surprisingly forgetting that hightemperatures denature enzymes, with some students even suggesting that the enzymewould ‘work faster at higher temperatures such as boiling’.

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(a) The evaluation part of this question, was not set in the same way as previous evaluationquestions. This appeared to confuse many candidates

(i) Here in most cases, a distinct comparison of the two methods was required. Thosecandidates who only chose the bullet points were unable to gain the marks. The factthat, in the bio-stonewashing method, for example, ‘washing takes half an hour’ isnot, in itself, an advantage; the advantage is that this is a shorter time than would betaken in the traditional stonewashing method. There were relatively few answersabout damage to fibres and only rare suggestions regarding potential damage to themachines caused by the stones.

(ii) Candidates were far more successful in this part, selection from the bulleted pointswas sufficient to gain the marks. Although in most cases examiners are willing toaccept a clear indication of the selected point, without it needing to be written out infull, loose answers referring to economics, ‘it is expensive’, were not credited as the‘it’ was not considered to be sufficiently clear, considering the stem of the question. Inthis example reference also needed to be made to ‘the enzyme(s)’, as it is likely,given the information, that both methods have their own, different, expenses.

(b) Most candidates correctly selected ‘protease’, with ‘lipase’ being the most commonincorrect suggestion.

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(a) (i) Even those students who had forgotten to bring a calculator with them were able tocalculate the total mass of carbon dioxide as almost all students gave the correctanswer ‘129’.

(ii) Proved to be a little more demanding, some students choosing to add the 120 to theiranswer in (a)(i), while others having showed the necessary calculation, ‘129 – 120’,failed to get it right. Unfortunately the calculation was considered to be sostraightforward that no marks were available for this. Those students who had arrivedat the wrong answer in (a)(i) were not disadvantaged as examiners credited thecorrect answer to the relevant deduction.

(b) Students were asked for environmental advantages. Those who chose to go down differentroutes were not credited. Thus those who discussed ‘cost’, the ‘use of less water’ or the‘re-using of water from the machine’, along with ideas that the ‘cooler temperature wouldnot destroy enzymes’, were not rewarded. Good answers focused on the ‘reduced demandfor energy’, which could be expressed in a number of ways, and the consequent ‘reductionin pollution’. Examiners accepted examples of suitable pollutants such as carbon dioxideand greenhouse gases and their immediate effect of global warming, however secondaryconsequences, such as the ‘melting of ice-caps’ were considered to be too far removedfrom the focus of the question and were not credited.

(c) (i) A good proportion of students gained both marks, with relatively few gaining nomarks.

(ii) Three-quarters selected the correct term, the most common incorrect answer was‘killed’.

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Candidates appeared to have coped quite well with the novel situation presented in part (b) ofthis question.

(a) Part (a), though, required clear knowledge of the details regarding enzyme action providedin the specification. The great majority of candidates described enzyme destruction, withmost of these quoting ‘denaturation’, although this term is not a specification requirement.Relatively few, though explained that this would result in enzyme and (chemicals within the)stain being unable to ‘fit’ together. Over the past few examination sessions examiners havebeen pleased to report a decline in the use of the term ‘killed’ or ‘died’ in reference toenzymes; however an appreciable number of examiners reported an increase in the use ofsuch terms this session.

(b) (i) Candidates were able to apply their understanding effectively and frequently arrivedat two or all three of the marking points. Occasionally poor explanations made theexaminers unsure whether the enzymes were in the washing powder or still in thebacteria; those conveying the latter idea were not awarded at least one of the marks.

(ii) The majority of candidates made the expected connection between the use of ahigher temperature and the potential need to use additional energy with itsconsequent effect on suitably qualified emissions from power stations. Weakercandidates, though, often misunderstood vital components of the information,suggesting possible ‘damage to the hot springs’ caused by ‘removing bacteria fromthem’ or the polluting effects of transport as a result of ‘carrying bacteria a long way’.

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(a) In this question, students were tested on their ability to use good English, organiseinformation clearly and use specialist terms where appropriate.

The essence of the question was to examine whether students could give a sufficientlydetailed account of an investigation of the effect of temperature on protein stain removalfrom cloth by a biological detergent. There were some very good accounts, with almost halfthe students gaining full marks. The essential details were the use of standardised amountsof both stain and detergent, a range of suitable temperatures maintained by a water bath,some suitable criterion for producing quantitative results (eg the time taken to remove thestain at each temperature), repetitions and the calculation of mean values for eachtemperature. Many students omitted some of these details, especially the criterion fordetermining the results, and a few described an inappropriate investigation with varyingamounts of the detergent.

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(b) The graph was usually plotted well, with about half of the students scoring full marks. Thescale chosen for the vertical axis was generally sufficiently large and usually correctlylabelled, including units. Points were generally plotted accurately. However, the line of ‘bestfit’ caused problems for many who did not appreciate that such a line could changedirection once an optimum value was passed. In part (ii), nearly all students were able togive pH6 as the optimum value, irrespective of the pattern of the line they had drawn.

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(c) Many students found this question difficult, although the vast majority were able to make atleast one valid point in their answer, usually that the graph showed the activity of theenzyme was still very high (84%) at the recommended temperature of 60°C. Only a fewbetter students could explain that the relatively high temperature of 60°C would give ahigher rate of reaction than at lower temperatures, or point out that temperatures higherthan this would be more expensive to maintain and might possibly damage the cloth thatwas being washed.

In part (a) it was clear that many candidates were unfamiliar with the names of the enzymes, asa considerable proportion of candidates failed to achieve both marks.

Given that fructose is sweeter than glucose, many candidates only got as far as repeating thisinformation in part (b). Alternatively they picked up the reference to ‘slimming foods’ andsuggested that ‘fructose contains less fat’ or ‘fructose has less sugar’, rather than the need forless of it in food to produce the same degree of sweetness.

Part (c) was regularly well done and many candidates achieved full marks. In some cases, thosethat did not gain all four marks chose to ignore the instruction to use only the informationprovided and so amended the enzyme properties given to such an extent that they were notrecognisable or wrote comments about industrial uses of enzymes. A few candidates addedexplanations to their answers, some believing that the high cost of enzymes was an advantageas it meant higher prices could be charged for products. A common error was including ‘easilybroken down’ as an advantage.

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(a) Sufficient information was provided in the stem of this question, and in the diagram, toenable students to deduce that the immobilised enzyme remained attached to the beads inthe glass column and thus would not contaminate the product and would still be availablefor re-use. Many students pointed out that it was a continuous flow process for fructoseproduction, rather than a stop-start batch process. However, fewer than half of the studentswere able to suggest even one advantage of using the immobilised enzyme.

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(b) Nearly all students scored 1 mark in this section for deducing from the table that there was

no improvement in fructose production at flow rates in excess of 5 dm3 per minute. Lessthan one-eighth could amplify upon this by pointing out that higher flow rates would haveleft unchanged glucose contaminating the fructose in the product, or would simply wastethe extra glucose. Many thought a higher flow rate would be a waste of ‘energy’, despitethe diagram showing that flow was by a gravity feed, hence requiring no energy input.

(c) Having been told that fructose was much sweeter than glucose, just over two-thirds ofstudents were able to state that less fructose would be required for the same effect ontaste. However, further amplification on the merits of fructose was generally financial ratherthan biological, with only about one-fifth of students pointing out that a lower sugar contentin the slimming food would make it less fattening / lower in calories.

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In part (a), most candidates correctly identified microorganisms, however mammals was also apopular, incorrect, choice. Once again, it is vital that candidates are encouraged to read all theinformation, rather than simply answering what they believe the question to be, as mammalscertainly produce enzymes, but not those used in the home and in industry.

Correct answers to part (b)(i) were more often given than to part (b)(ii) and it might seemreasonable that thoughtful candidates, who happened not to have revised this part of their work,were able to work out the response to part (b)(i), from the prefixes, more easily than they mightarrive at the answer to part (b)(ii).

A large majority of candidates were able to correctly read the scale in part (c)(i), although 13minutes was a common wrong answer.

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In part (c)(ii) many candidates correctly identified Z as the enzyme and explained their reasoningin terms of it taking the shortest time or working the fastest, the examiners were willing to acceptthe slightly ambiguous faster acting or shorter time. Some candidates selected W, which wasincorrect, but went on to provide a correct reason and gained one mark. Other candidates madeit difficult for examiners to be quite sure what they were describing by referring to time goingquicker, although again examiners were generous with this sort of phrase.

Once more, in part (c)(iii) the need to read, and follow, instructions was highlighted with anumber of candidates ticking only one box, when the need to tick two boxes was emboldenedtwice in the question and furthermore, the mark allocation implied that more than one answerwas required. As a result only around half the candidates ticked two correct boxes.

(a) (i) Many students failed to gain the marks by not giving comparative answers whenreferring to time or temperature. Thus ‘takes half an hour’ was insufficient as this didnot explain why bio-stonewashing is better than the traditional method. What wasrequired here was some reference to the time taken by the traditional method. Asimple addition such as ‘only’ to that response would have been sufficient, oralternatively, that bio-stonewashing ‘takes less time’, but not ‘takes a short time’.

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(ii) Without this issue, students did much better, over three quarters gaining both marks.A few students managed to mix up the two methods and gave reverse answers.Some of these recognised their error and added double-ended arrows, which is anacceptable way of showing that answers should be reversed.

(b) The link between protein and ‘protease’ was more straightforward, with the majority ofstudents selecting the correct response.

(a) Most candidates were able to extract the correct advantages and disadvantages from theinformation.

(b) Most candidates were able to correctly ascribe protease, fewer ascribed lipase; and veryfew ascribed invertase.

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