Effects of Temperature & pH (Cambridge O Level Biology)

Exam Questions

2 hours18 questions
1a
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3 marks

The digestive systems of young mammals are not fully developed.

Enzymes such as amylase, maltase and protease are often added to baby food to aid chemical digestion.

(i)
Suggest why the temperature of baby food must be controlled when the enzymes are added.
[2]
(ii)
State one other condition that must also be controlled to optimise enzyme activity.
[1]
1b
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2 marks

The optimum temperature for the enzymes in the baby food to work was found to be 37°C. 

Fig. 1 below shows a graph of the activity of an enzyme as temperature increases. enzyme-activity

Fig. 1

Add the following labels to the graph:

  • Optimum temperature
  • Denatured enzyme 
1c
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2 marks

The label on the jar of baby food states that food must be thrown away if heated above 37°C. 

Explain the need for this label. 

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2a
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4 marks

A student investigated the effect of pH on the activity amylase on starch solution. The student used iodine solution as an indicator to see when the amylase was active. 

Their results are shown in the table below. 

pH of solution time for iodine test to stop turning blue-black
/ seconds
2 196
4 187
6 42
8 54

(i)

Describe why the student used iodine solution. 

[2]

(ii)

Calculate the range of results for the time in seconds

[2]

2b
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2 marks
 
(i)

State which of the pH values tested is the optimum for amylase.

[1]

(ii)

Explain your answer to part (i)

[1]

2c
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3 marks

Another student concluded that the optimum pH was not shown in the results in Table 1. 

Explain why the student concluded this. 

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1a
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2 marks

The effect of temperature on enzyme activity was investigated. The results are shown in Fig. 1.cie-igcse-2023-specimen-q6a

Fig. 1

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

[1]

(ii)

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

[1]

1b1 mark

State one factor other than temperature that affects enzyme activity.

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

Table 1

insoluble molecule enzyme soluble molecules

starch

amylase

reducing sugars

fat

lipase  
 

protease

 

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

The first row has been done for you.

1d
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1 mark

List the chemical elements present in fats.

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2a
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2 marks

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

The effect of temperature on catalase activity was investigated. 

The results are shown in Fig. 1

2018-nov-s1-061031-q8a

Fig. 1

(i)

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

[1]

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

[1]

2b
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1 mark

State one factor other than temperature that affects enzyme activity.

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3a
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2 marks

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

Fig. 1

Describe what has happened to the enzyme. 

3b
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1 mark

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

3c
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2 marks

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

Fig. 2 shows the results. range-of-ph

Fig. 2

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

3d
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2 marks

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

Explain why this farmer's suggestion may be incorrect. 

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4a
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1 mark

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

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

solution-of-

Fig. 1

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

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



4b
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7 marks
The student’s results are shown in 

 

Table 1

                                                Table 1 

temperature (°C) volume of carbon dioxide gas released in 15 minutes
/ cm3
repeat 1 repeat 2 repeat 3
25 25 22 24
30 33 26 35


(i)
Calculate the mean rate of gas produced at 25°C in cm3/minute.

Give your answer to 1 decimal place.

 [3]

(ii)
The rate of gas produced at 30°C is greater than at 25°C.

Use your knowledge of enzymes to explain why.

[3]

(iii)
The teacher tells the student to repeat the results for 30°C. 

Explain why the teacher advised this. 

[1]

4c
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2 marks

Enzymes can be inhibited by chemicals called phenols during fermentation.

Phenols bind to amino acids on enzyme molecules.

Suggest how phenols inhibit enzymes.

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5a
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3 marks

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

Carbohydrate digestion, by amylase, begins in the mouth.

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

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

Table 1 - Effect of pH

pH time taken to digest starch / minutes
3.0 38
4.0 26
5.0 17
6.0 13
7.0 7
8.0 8

   

Table 2 - Effect of temperature

temperature / •C time taken to digest starch / minutes
10 20
20 14
30 11
40 6
50 12
60 23

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

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

Use the results in Table 1 to explain why.

5b3 marks

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

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1a
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2 marks

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

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

Explain why. 

1b
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2 marks

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

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

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

Suggest why.

1c
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4 marks

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

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

Fig. 1

Compare the results of the two washing powders.

1d
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3 marks

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

Evaluate this claim.

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2a
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2 marks

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

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Fig. 1

From these reactions, determine what conclusion can be drawn about the function of enzymes.
[2]
2b
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3 marks

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

Fig. 2

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

Table 1 shows the scientist's results. 

Table 1

pH catalase activity / arbitrary units
Trial 1 Trial 2 Trial 3 Trial 4 Trial 5 Mean
2.0 0 0 0 0 0 0
2.5 2 3 3 2 4 3
3.0 12 12 9 8 10 10
3.5 15 26 16 14 17  
4.0 25 23 29 24 22 25
4.5 32 30 35 36 35 34
5.0 46 44 42 45 42 44
5.5 54 52 55 52 51 53
6.0 58 59 58 60 62 60
6.5 42 40 45 43 42 42

Calculate a mean result for pH 3.5

2c
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4 marks

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

graph-paper

Fig. 3

2d
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5 marks

Use Table 1 and the graph to answer the following:

(i)

Describe the results shown in the graph.

[3]

(ii)

Predict the catalase activity at pH 7.

[1]

(iii)

Explain why the catalase activity is zero at pH 2.

[1]

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3a
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2 marks
A group of students carried out the following practical to establish the effect of temperature on protein breakdown:
    1. Place a drop of biuret solution into every well in a spotting tile.
    2. Put 4 cm3 of 1 % protein solution into a boiling tube.
    3. Put 4 cm3 of pepsin solution into a second boiling tube.
    4. Put both boiling tubes into a water bath at 20 °C.
    5. After 4 minutes add the pepsin solution to the protein solution together in one boiling tube, mixing together with a stirring rod.
    6. After 20 seconds add a drop of the protein/pepsin mixture to a drop of biuret solution in one well of the spotting tile.
    7. Repeat step 6 until the biuret solution no longer changes colour.
    8. Repeat steps 1–7 at 10 °C (using an ice water bath), 30 °C, 40 °C and 50 °C.

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

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

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

3b
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1 mark

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

protein-digestion-graph

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

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

3c
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2 marks

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

3d
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2 marks

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

The absorbance was measured at approximately 1.14 arbitrary units.

Suggest a reason for this result.

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