May/June 2026 Paper 52

2026 · 2 questions · 14 parts · 30 marks

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

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

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Context for question 1

The avocado tree, Persea americana, is a cultivated food crop. The fruits of the tree are called avocados. Figure 1.1 shows a whole avocado and an avocado that has been cut to show the inside.

Figure 1.1, a whole avocado beside one cut in half, labelled whole avocado, exocarp (skin), mesocarp, seed and cut avocado

Avocados are removed from the tree (harvested) when they are mature (maximum size). Avocados ripen only after harvesting. As avocados ripen, the colour of the skin changes from bright green to dark purple and the mesocarp changes from hard to soft. Mesocarp cells in the avocado are a source of the enzyme catalase. The quantity of catalase in the mesocarp changes as the avocado ripens. Catalase catalyses the breakdown of hydrogen peroxide, as shown in Figure 1.2.

_{2}

_{2}

\to

_{2}

O + O

_{2}

1(a)Practical Techniques MeasurementEasy1 mark

A student decided to see the effect of catalase activity in avocados. The student removed the skin from an avocado and cut up some pieces of the mesocarp. The student placed some of the pieces of mesocarp into a beaker containing hydrogen peroxide solution. Tiny bubbles of oxygen were immediately released from the surface of the mesocarp, as shown in Figure 1.3.

Figure 1.3, a 250 cm3 beaker of hydrogen peroxide solution with three pieces of mesocarp resting on the bottom, each releasing bubbles of oxygen gas from its surface

Suggest one hazard of this method and the risk associated with the hazard and the precaution that should be taken.

Hazard, risk and precaution

0 words

1(b)(i)Experimental DesignEasy1 mark

The student planned to investigate the changes in catalase activity in avocados as they ripen. Identify the independent variable in the investigation.

1(b)(ii)Experimental DesignHard7 marks

Describe a method the student could use to measure changes in catalase activity in avocados as they ripen, using hydrogen peroxide solution. Do not include a risk assessment. 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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Context for 1(c)

After food crops such as avocados are harvested, they may be stored in cold conditions (cold storage) to delay ripening. Some scientists investigated the effect of cold storage for different lengths of time on catalase activity in avocados.

The scientists selected 100 avocado trees at random from the same field.
The scientists harvested one mature avocado from each tree.
Each of the 100 avocados had a mass of approximately 210 g.
The catalase activity in 10 of the avocados was measured immediately after harvest.
The remaining 90 avocados were divided into three groups and stored at $7^{\circ} C$ and 85% humidity for different lengths of time, as shown in Table 1.1.

Table 1.1

group	number of avocados	storage time / days
10d	30	10
20d	30	20
30d	30	30

1(c)(i)Experimental DesignEasy1 mark

Suggest a suitable method the scientists could use to select avocado trees at random.

Answer

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1(c)(ii)Plant Structure TransportEasy1 mark

Humidity is the concentration of water vapour in the air. The higher the humidity, the higher the concentration of water vapour in the air. Suggest a reason why the avocados were stored at 85% humidity.

Answer

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Context for 1(c)(iii)

After each storage time, 5 avocados from each group were tested for catalase activity. The remaining 25 avocados in each group were kept at

20^{\circ} C

and 80% relative humidity until they were ripe (soft enough to eat). When they were ripe, 5 avocados from each group were tested for catalase activity. The results are shown in Table 1.2.

1(c)(iii)Statistical Tests BiologyEasy1 mark

Complete Table 1.2 by calculating the 95% confidence intervals (95% CI) for groups 20dR and 30dR. Use the formula:

95% CI =

\overset{x}{ˉ} \pm (2 \times S E)

where

\overset{x}{ˉ}

= mean and

S E

= standard error.

group	when catalase activity was tested	mean catalase activity / arbitrary units	standard error (SE)	95% confidence interval (95% CI)
0d	immediately after harvesting	571	162	$571 \pm 324$
10d	after 10 days cold storage	615	169	$615 \pm 338$
20d	after 20 days cold storage	455	49	$455 \pm 98$
30d	after 30 days cold storage	550	112	$550 \pm 224$
10dR	after 10 days cold storage plus time to ripen	642	198	$642 \pm 396$
20dR	after 20 days cold storage plus time to ripen	822	206	Table answer r6_95% confidence interval (95% CI) 0 words
30dR	after 30 days cold storage plus time to ripen	736	179	Table answer r7_95% confidence interval (95% CI) 0 words

1(c)(iv)Tables GraphsEasy2 marks

On Figure 1.4, draw error bars showing the 95% CI for groups 20dR and 30dR that you calculated in 1(c)(iii).

Draw with the mouse or a finger.

1(c)(v)Interpreting Data Drawing ConclusionsHard4 marks

Outline the conclusions that can be made about the effect of cold storage on the mean catalase activity in avocados. State the evidence from Table 1.2 and Figure 1.4 that supports your conclusions.

Answer

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1(c)(vi)Statistical Tests BiologyMedium2 marks

The scientists decided that the t-test was not an appropriate choice of statistical test for this investigation. Suggest two reasons why the t-test is not an appropriate choice of statistical test for this investigation.

Answer

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