May/June 2026 Paper 51

2026 · 2 questions · 16 parts · 30 marks

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

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

–/13 mks

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

The common woodlouse, Oniscus asellus, is a small invertebrate animal that is found in many areas of western and northern Europe.

Figure 1.1 shows some O. asellus.

Figure 1.1, five common woodlice (Oniscus asellus), shown clustered together on a plain background, with a 10 mm scale bar beneath them

A student wanted to investigate the effect of temperature on the rate of respiration in O. asellus. The student set up a respirometer as shown in Figure 1.2. A stand and clamp were used to hold the respirometer in position.

Figure 1.2, a respirometer: a syringe and three-way tap sit above a bung fitted into a large test-tube; inside the test-tube, gauze separates O. asellus (above) from sodium hydroxide pellets (below); a glass tube runs from the bung to a horizontal ruler, where a drop of coloured liquid sits at the marked start point

To determine the rate of respiration in O. asellus, the student:

opened the three-way tap and used the syringe to move the drop of coloured liquid to the start point
closed the three-way tap
measured the distance moved by the drop of coloured liquid in a known time period.

Predict the direction of movement of the drop of coloured liquid during the investigation. Explain your answer.

Answer

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1(a)(ii)Experimental DesignEasy1 mark

Suggest a suitable control for this investigation.

Answer

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1(a)(iii)Experimental DesignHard6 marks

Describe a method, using the respirometer shown in Figure 1.2, that the student could use to investigate the effect of temperature on the rate of respiration in O. asellus. You should use temperatures from

5^{\circ} C

35^{\circ} C

, so that the O. asellus are not harmed in the investigation.

Your method should be set out in a logical order and be detailed enough to allow another person to follow it.

Answer

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1(a)(iv)Maths Skills BiologyEasy1 mark

The student used the data, collected in the investigation, to calculate the rate of respiration in O. asellus at each temperature as a volume per unit time (mm

^{3}

min

^{- 1}

Describe how the student calculated the rate of respiration in units of mm

^{3}

min

^{- 1}

Answer

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1(b)(i)Experimental DesignMedium1 mark

The student then investigated the effect of different respiratory substrates on the rate of fermentation in yeast cells. The solutions of respiratory substrates were boiled to remove oxygen. The solutions were then cooled before mixing with the suspension of yeast cells.

A small test-tube was filled with 3 cm

^{3}

of a yeast suspension and 2 cm

^{3}

of a 20% glucose solution. The small test-tube was placed inside a large test-tube, as shown in Figure 1.3.

Figure 1.3, a hand holding a pencil that is pushed through a small test-tube, positioning it upright inside a large test-tube; the small test-tube contains the mixture of yeast suspension and 20% glucose solution

The test-tube was turned through

18 0^{\circ}

and placed in a test-tube rack for 30 minutes. During this time, gas was produced and collected as shown in Figure 1.4.

Figure 1.4, the same large test-tube after being turned through 180 degrees, so the small test-tube (still holding the mixture of yeast suspension and 20% glucose solution) points downward, with the gas produced collecting in the space above it inside the large test-tube

The student determined the volume of gas collected in the small test-tube after 30 minutes. This was used as a measure of the rate of fermentation. The student repeated the experiment using a 20% maltose solution. The student obtained data from five replicates using a 20% glucose solution and from five replicates using a 20% maltose solution.

Identify the independent variable in this investigation.

1(b)(ii)Practical Techniques MeasurementEasy1 mark

The student was provided with a 50% stock solution of glucose.

Describe how the student could use the stock solution to make 10 cm

^{3}

of a 20% glucose solution.

Answer

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1(b)(iii)Experimental DesignEasy2 marks

The student standardised the volume of the yeast suspension and the volume of the respiratory substrate solutions.

State two other variables that should be standardised in this investigation.

Answer

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1(c)(i)Tables GraphsEasy1 mark

The results of the investigation are shown in Figure 1.5.

Figure 1.5, a bar chart of mean volume of gas collected after 30 minutes in cm3 against respiratory substrate, with a bar of about 1.9 for glucose and a shorter bar of about 1.45 for maltose

Identify the type of data shown by the respiratory substrate in Figure 1.5.

1(c)(ii)Interpreting Data Drawing ConclusionsMedium1 mark

State a conclusion for the investigation, using evidence from Figure 1.5 to support your conclusion.

Answer

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1(c)(iii)Glycolysis Krebs Cycle Electron TransportMedium2 marks

Suggest why the rate of fermentation in yeast cells is different with glucose as a respiratory substrate compared with maltose as a respiratory substrate.

Answer

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