May/June 2026 Paper 53

2026 · 2 questions · 12 parts · 30 marks

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1(a)(i)1(a)(ii)1(a)(iii)1(b)(i)1(b)(ii)1(b)(iii)

–/19 mks

2(a)2(b)2(c)(i)2(c)(ii)2(c)(iii)2(d)

–/11 mks

Context for question 1

A student planned to investigate the rate of respiration in germinating seeds and then determine the respiratory quotient (RQ) of the germinating seeds. The student used the respirometer shown in Figure 1.1 for the investigation.

Figure 1.1, a respirometer: a boiling tube holding germinating seeds on gauze above sodium hydroxide solution, sealed with a bung carrying a 1 cm$^{3}$ syringe and tap, and connected by capillary tubing containing coloured liquid that runs down into a water bath fitted with a ruled scale

1(a)(i)Tables GraphsMedium3 marks

The student investigated the effect of temperature on the rate of respiration in the germinating seeds. The student planned to use a temperature range of

10

–

50^{\circ} C

in the investigation. The student read that in some species:

at lower temperatures, the rate of respiration approximately doubles for each $10^{\circ} C$ increase in temperature
the optimum temperature for respiration is approximately $40^{\circ} C$ .

Sketch a curve on Figure 1.2 to show the results that you predict the student will produce from this investigation. Include labelled axes. Do not include units or values on the axes.

Draw with the mouse or a finger.

1(a)(ii)Experimental DesignHard8 marks

The student was supplied with the respirometer in Figure 1.1, standard laboratory equipment and standard laboratory chemicals. Describe a method the student could use to take the measurements needed for calculating the rates of respiration at different temperatures. The description of your method should be set out in a logical way and be detailed enough for another person to follow.

Answer

0 words

1(a)(iii)Maths Skills BiologyMedium4 marks

The diameter of the capillary tubing shown in Figure 1.1 was

1 mm

. The student used this value and the measurements that were taken to calculate a rate of respiration at each temperature. Describe each step in the calculation that the student used to determine a rate of respiration.

Answer

0 words

Context for 1(b)

The student then decided to determine the RQ of germinating seeds from four different species of plant. The seeds of all the species are known to respire aerobically. For each species of plant, the student placed the germinating seeds in the respirometer and then measured the volume of oxygen used and the volume of carbon dioxide produced in one minute. The student decided to carry out all the measurements at

30^{\circ} C

. The results are shown in Table 1.1.

Table 1.1

species of plant	mean volume of oxygen used in one minute / mm $^{3}$	mean volume of carbon dioxide produced in one minute / mm $^{3}$
A	0.065	0.055
B	0.056	0.059
C	0.027	0.021
D	0.052	0.045

1(b)(i)Glycolysis Krebs Cycle Electron TransportEasy1 mark

Use Table 1.1 to calculate the RQ of species A.

1(b)(ii)Glycolysis Krebs Cycle Electron TransportMedium2 marks

The student suggested that the results for one of the species were not as expected and the procedure should be repeated for that species. With reference to Table 1.1, state the species, A, B, C or D, for which the procedure should be repeated. Give a reason for your choice.

Species

Reason

0 words

1(b)(iii)Evaluation UncertaintyMedium1 mark

Suggest an error in the procedure that could explain the results for the species you stated in 1(b)(ii).

Answer

0 words