Biology 9700/31 May/June 2021: question paper and mark scheme
Cambridge AS & A Level Biology (9700), Paper 3 (Advanced Practical Skills 1), May/June 2021. Read both free below, or download them. Done the paper? Get it marked by AI against this mark scheme.
Plant cells contain the enzyme catalase which catalyses the breakdown of hydrogen peroxide, releasing oxygen.
When hydrogen peroxide solution and a sample of potato tissue are put into a syringe, some of the solution comes out of the syringe nozzle as the oxygen is released.
You are going to investigate the effect of surface area of potato tissue on the activity of catalase.
You are provided with the materials shown in Table 1.1 and Table 1.2.
Table 1.1
labelled contents hazard volume / cm3
H hydrogen peroxide solution irritant 40
Table 1.2
labelled material details quantity
P potato cylinders same diameter 4
If any of H comes into contact with your skin, wash off immediately with cold water.
It is recommended that you wear suitable eye protection.
Wear gloves to protect your hands when using H.
1. Cut the potato cylinders in the beaker labelled P to a length of 20 mm. Put the 20 mm cylinders back into the beaker labelled P.
To investigate the effect of surface area, you will cut the cylinders into a different number of pieces as shown in Table 1.3.
Table 1.3
length (h) length of original cylinder number (n) of each small piece
/ mm of pieces to put into the syringe
/ mm
1
20 20
2
20 10
4
20 5
10
20 2
You now need to calculate the total surface area of the potato tissue that will be put into the syringe. An example of how to do this is shown in Fig. 1.1 on page 4.
EXAMPLE:
One cylinder has length of 20 mm
length, h = 20
diameter = 4 mm radius, r = 2 mm
surface area of one cylinder = 2 π r 2 + 2 πr h
= (2 × 3.14 × 22) + (2 × 3.14 × 2 × 20)
= 276.32 mm2 where: π = 3.14 r = radius of cylinder h = height or length of cylinder
Fig. 1.1
The total surface area depends on the number of pieces, n.
Total surface area = surface area of one cylinder × number of pieces
= (2 πr 2 + 2 π r h)n
(a) (i) Measure the diameter of one of the cylinders and calculate the radius, r.
r = …… [1]
(ii) All of the cylinders have the same diameter (standardised).
State one other variable that should be standardised in this investigation.
…… [1]
(iii) Complete Table 1.4 to calculate the total surface area of potato tissue to put in the syringe.
Show your working in the space provided in Table 1.4.
Table 1.4
surface area total surface show your working in this n h / mm r / mm of one piece area column
/ mm2 / mm2
1 20
Mark scheme
Examiners should consider the context and scientific use of any keywords when awarding marks. Although keywords may be present, marks
should not be awarded if the keywords are used incorrectly.
The examiner should not choose between contradictory statements given in the same question part, and credit should not be awarded for any
correct statement that is contradicted within the same question part. Wrong science that is irrelevant to the question should be ignored.
terms with which they may be confused (e.g. ethane / ethene, glucagon / glycogen, refraction / reflection).
5
10 2
[2]
Carry out step 2 to step 22.
2. Remove the plunger from a 10 cm3 syringe.
3. Put one 20 mm potato cylinder into the barrel of the syringe.
4. Put the plunger back into the syringe and push it to the 4 cm3 mark, as shown in Fig. 1.2.
plunger
10 barrel
4 potato cylinder
nozzle
Fig. 1.2
5. Put the nozzle of the syringe into the beaker containing H.
6. Pull the plunger out to the 10 cm3 mark so that H enters the syringe, as shown in Fig. 1.3.
air
bubbles
10
5 hydrogen peroxide
4 solution, H
Fig. 1.3
7. Hold the syringe above the beaker labelled For waste. Push the plunger so that the level of H is at the 5 cm3 mark, as shown in Fig. 1.4.
10
5 level of H at 5 cm3
4
beaker labelled
For waste
Fig. 1.4
8. Wipe the nozzle with a paper towel to remove excess H.
9. Hold the syringe above the beaker labelled For waste. Start timing.
Count the number of drops released in 1 minute. Record the results in (a)(iv).
10. Put the syringe into the beaker labelled B.
11. Cut a cylinder from step 1 into two pieces. Each piece should be 10 mm in length, as shown in Table 1.3 and Table 1.4.
12. Remove the plunger from an empty 10 cm3 syringe.
13. Put the two 10 mm pieces from step 11 into the barrel of the syringe.
14. Repeat step 4 to step 10.
15. Cut a cylinder from step 1 into four pieces. Each piece should be 5 mm in length, as shown in
Table 1.3 and Table 1.4.
16. Remove the plunger from an empty 10 cm3 syringe.
17. Put the four 5 mm pieces from step 15 into the barrel of the syringe.
18. Repeat step 4 to step 10.
19. Cut a cylinder from step 1 into 10 pieces. Each piece should be 2 mm in length, as shown in
Table 1.3 and Table 1.4.
20. Remove the plunger from an empty 10 cm3 syringe.
21. Put the ten 2 mm pieces from step 19 into the barrel of the syringe.
22. Repeat step 4 to step 10.
(iv) Record your results in an appropriate table.
[5]
(v) State the independent variable.
…… [1]
(vi) Suggest an appropriate control for this investigation.
…… [1]
(vii) Identify two sources of error in step 3 to step 22. For each source of error suggest an improvement to the method which will reduce the effect of the error.
error 1 ……
improvement 1 ……
error 2 ……
improvement 2 ……
[4]
(viii) The procedure described by step 1 to step 22 investigated the effect of surface area on catalase activity, by measuring the number of drops released in 1 minute.
Describe how you would modify the procedure to investigate the effect of changing temperature on the activity of catalase in the potato tissue.
…… [1]
(b) A student investigated the effect of hydrogen peroxide concentration on the activity of catalase. The student measured the distance the solution moved along a clear plastic tube attached to a syringe, as shown in Fig. 1.5.
10 20 30 40 50 60 70 80 90 100
potato plunger pieces clear ruler hydrogen nozzle plastic peroxide tubing
Fig. 1.5
The results are shown in Table 1.5.
Table 1.5
percentage concentration of distance moved in 1 minute hydrogen peroxide / mm
0.2 11
0.4 18
0.8 50
1.5 69
3.0 73
6.0 73
(i) Plot a graph of the data in Table 1.5 on the grid in Fig. 1.6.
Use a sharp pencil for drawing graphs.
Fig. 1.6
[4]
(ii) Suggest an explanation for the results between 0.2% and 6.0% hydrogen peroxide.
…… [2]
[Total: 22]
2 J1 is a slide of a stained transverse section through a plant leaf.
(a) Set up the microscope so that you can observe the section on J1.
Use a sharp pencil for drawing.
(i) Draw a large plan diagram of the whole section of the leaf on J1. Your drawing should show the correct shapes and proportions of different tissues.
Use one ruled label line and label to identify the epidermis.
[5]
(ii) Observe the ring of cells surrounding the vascular tissue in the centre of the section on J1.
Select a line of four adjacent cells that make up this tissue.
Each cell that you draw must touch at least one of the other cells.
• Make a large drawing of this line of four cells.
• Use one ruled label line and label to identify the cell wall of one cell.
[5]
(b) Fig. 2.1 is a photomicrograph of a stained transverse section through a leaf of a different type of plant.
Fig. 2.1
(i) Identify the observable differences between the section on J1 and the section in Fig. 2.1.
Record the observable differences in Table 2.1.
Table 2.1
feature J1 Fig. 2.1
[3]
(ii) The presence of a thick waxy cuticle in the leaf section in Fig. 2.1 supports the conclusion that the plant is adapted to live in a dry environment.
Observe the leaf section in Fig. 2.1.
Suggest one other observable feature in the section in Fig. 2.1 which supports this conclusion.
Explain how this feature would prevent water loss.
…… [1]
(c) Fig. 2.2 is a photomicrograph of the same leaf section that is in Fig. 2.1.
Fig. 2.2
You will need to use the grid to find the area of the palisade layer and the total area of the leaf section in Fig. 2.2.
Each square of the grid is 1 cm2.
In some squares the palisade layer or the leaf section does not fill the whole square.
(i) Describe the method you will use to decide which of these squares to include.
…… [1]
(ii) State the area of the palisade layer and the total area of the leaf section in Fig. 2.2.
area of palisade layer = …… cm2
total area of the leaf section = …… cm2
[2]
(iii) Calculate the area of the palisade layer as a percentage of the total area of the leaf section.
Show your working.
[1]
[Total: 18]
Mark scheme
The error carried forward (ecf) principle should be applied, where appropriate. If an incorrect answer is subsequently used in a scientifically
necessary and any exceptions to this general principle will be noted.
‘List rule’ guidance
For questions that require n responses (e.g. State two reasons …):
• The response should be read as continuous prose, even when numbered answer spaces are provided.
• Incorrect responses should not be awarded credit but will still count towards n.
• Read the entire response to check for any responses that contradict those that would otherwise be credited. Credit should not be
awarded for any responses that are contradicted within the rest of the response. Where two responses contradict one another, this should
be treated as a single incorrect response.
• Non-contradictory responses after the first n responses may be ignored even if they include incorrect science.
PUBLISHED
Calculation specific guidance
Correct answers to calculations should be given full credit even if there is no working or incorrect working, unless the question states ‘show
your working’.
For questions in which the number of significant figures required is not stated, credit should be awarded for correct answers when rounded by
For answers given in standard form (e.g. a × 10n) in which the convention of restricting the value of the coefficient (a) to a value between 1
Unless a separate mark is given for a unit, a missing or incorrect unit will normally mean that the final calculation mark is not awarded.
Guidance for chemical equations
; separates marking points
/ alternative answers for the same marking point
R reject
A accept
I ignore
AVP any valid point
AW alternative wording (where responses vary more than usual)
ecf error carried forward
underline actual word underlined must be used by candidate (grammatical variants accepted)
max indicates the maximum number of marks that can be given
ora or reverse argument
mp marking point
PUBLISHED
Question Answer Marks
1(a)(i) correct radius and mm ; 1
1(a)(ii) any one of: 1
1 volume of hydrogen peroxide ;
2 concentration of hydrogen peroxide ;
3 temperature ;
4 same type / age / species of potato ;
1(a)(iii) shows the surface area of one cylinder multiplied by the number of pieces ; 2
correct total surface area ;
1(a)(iv) 1 heading for independent variable: 5
number of pieces / surface area, and mm2 / total surface area and mm2, and before heading for dependent variable and
no units in body of table ;
2 heading for dependent variable:
number of drops ;
3 results for all samples ;
4 number of drops for the smallest surface area less than for the largest surface area ;
5 total surface area recorded for the independent variable ;
1(a)(v) total surface area ; 1
1(a)(vi) any one of: 1
1 boiled potato ;
2 use distilled water instead of hydrogen peroxide ;
1(a)(vii) 1 identifies one error and gives reason e.g. drop size varies ; 4
2 describes measuring the total volume dropped as an improvement to the procedure ;
3 identifies one error and gives reason e.g. hard to cut potato pieces to equal sizes ;
4 describes the use of a more precise tool e.g. vernier caliper gauge, as an improvement to the procedure ;
1(a)(viii) same surface area and uses 5 different temperatures ; 1
PUBLISHED
Question Answer Marks
1(b)(i) 1 x-axis: percentage concentration of hydrogen peroxide 4
and
y-axis: distance moved in 1 minute / mm ;
2 scale on x-axis: 1% to 2 cm, labelled at least every 2 cm
and
scale on y-axis: 20 mm to 2 cm, labelled at least every 2 cm ;
3 correct plotting of all six points using small crosses or dots in circles ;
4 six plots joined with thin line passing through all points ;
1(b)(ii) more successful collisions or more enzyme substrate complexes formed ; 2
all active sites are saturated ;
Question Answer Marks
2(a)(i) 1 uses most of the available space and no shading ; 5
2 no cells drawn ;
3 correct proportions of vascular bundle ;
4 draws sunken stomata in the epidermis ;
5 label line and label to epidermis ;
2(a)(ii) 1 uses most of the available space and all lines sharp and continuous ; 5
2 draws only four whole cells and each cell touches at least one other cell ;
3 two lines around each cell and three lines where cells touch ;
4 draws correct shape of cells ;
5 label line and label to one cell wall ;
PUBLISHED
Question Answer Marks
2(b)(i) records correct differences: 3
any three of, e.g.:
feature J1 Fig. 2.2
number of vascular bundles many fewer ;
ring of cells around vascular bundle present absent
shape of stem diamond curved ;
trichomes absent present ;
2(b)(ii) trichomes / rolled leaf, and traps a layer of water vapour and reduces the water potential gradient ; 1
2(c)(i) count squares that are half full and more than half full and full as 1 ; 1
2(c)(ii) counts and records the area of the palisade layer ; 2
counts and records the total area of the leaf ;
2(c)(iii) shows area of palisade layer divided by area of leaf multiplied by 100 ; 1
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On this page, free: the mark scheme for AS & A Level Biology 9700/31, May/June 2021 (9700_s21_ms_31), and the question paper (9700_s21_qp_31), to read or download, with each question's marking points written out underneath.
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Biology 9700/31 for May/June 2021 is out of 40 marks, with 2 hours to answer it, across 2 questions.
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