AQA A Level Biology Paper 2 June 2025 question paper 7402/2

In the following passage, the numbered spaces can be filled with biological terms.

Write the correct biological term beside each number below that matches the space in the passage.

The equation for the aerobic respiration of glucose is:

Six carbon dioxide molecules are produced from each glucose molecule.

Use your knowledge of the link reaction and Krebs cycle to explain why.

An inhibitor of the electron transfer chain was added to aerobically respiring yeast cells.

As aerobic respiration was inhibited, the following changes occurred:

• oxygen uptake decreased

• ATP production decreased

• ethanol was produced.

Explain the changes in the yeast cells following the addition of the inhibitor.

Oxygen uptake decreased

ATP production decreased

Ethanol was produced

What term is used to describe the maintenance of a stable internal environment?

A high blood glucose concentration can cause dehydration of body cells.

Explain why.

Do not refer to ADH or the role of the kidneys in your answer.

The hormone glucagon is involved in maintaining a stable blood glucose concentration.

Which is not a result of the action of glucagon?

Tick (✓) one box.

Figure 1 shows one of the physiological systems involved in controlling blood pH.

Use the information in Figure 1 to outline the principles of negative feedback.

Vigorous exercise causes a change in blood pH and in the rate of ventilation.

Use Figure 1 to describe and explain these changes.

A student determined the dry mass of lettuce leaves. The equipment used was an oven and a weighing balance.

Describe how the student could use this equipment to determine the dry mass of lettuce leaves.

The student then used a calorimeter to determine the chemical energy stored in a sample of lettuce leaves with a dry mass of 1.50 g

The 1.50 g sample was fully combusted in a calorimeter.

The volume of water in the calorimeter was 150 cm³

The increase in temperature of the water was 18.2 °C

4.18 J of heat energy are required to increase the temperature of 1 cm³ of water by 1 °C

Use this information to calculate the heat energy released, in kJ g^–1, of dry mass of lettuce leaves.

Show your working.

Biomass can be measured as the dry mass of tissue per given area. Some crop plants are grown in large greenhouses (glasshouses) where optimum growing conditions can be maintained.

Growing crop plants at higher temperatures than their optimum temperature can decrease their biomass.

Use your knowledge of net primary production to explain why.

People with the inherited blood disorder haemophilia A (HA) have a reduced ability to clot blood. One variant of HA is due to an inversion mutation in the F8 gene. This mutation causes the production of a non-functional form of the protein, factor VIII. Factor VIII is not an enzyme.

Explain how an inversion mutation can cause the production of non-functional factor VIII.

Currently, the most effective treatment for HA is weekly or monthly injections of factor VIII. Scientists investigated the effectiveness of a gene therapy product, Roctavian, as a treatment for HA. Roctavian contains a viral vector that has the DNA coding for factor VIII.

The scientists:

• selected 112 male volunteers with severe HA, who were at least 18 years of age

• treated each volunteer with a single injection of Roctavian into their blood

• recorded the number of bleeding episodes (internal bleeding) in these volunteers over a two-year period (set A results)

• compared these data with the number of bleeding episodes per year in the volunteers before receiving Roctavian (set B results).

Table 1 shows the scientists’ results.

A value of ±2 × SD from the mean includes over 95% of the data.

Use all the information provided to evaluate the use of Roctavian as a treatment for HA.

Haemophilia C is an autosomal recessive condition.

Two parents are both heterozygous for the haemophilia C allele.

Calculate the probability of these parents producing a son who has haemophilia C.

Explain what is meant by the term phenotype.

In genetic crosses, the observed phenotypic ratios obtained in the offspring are often not the same as the expected ratios.

Suggest two reasons why.

Do not refer to sex-linkage or autosomal linkage in your answer.

In sweet pea plants, the F allele for purple flowers is dominant to the f allele for red flowers. The L allele for long pollen is dominant to the l allele for round pollen.

A scientist carried out a genetic cross between a plant with purple flowers and long pollen (heterozygous for both genes) and a plant with red flowers and round pollen.

Table 2 shows the results of this cross.

Use your knowledge of autosomal linkage to explain the results in Table 2.

Your answer should include:

• an explanation of what is meant by autosomal linkage

• a comment about the relative proportions of the different genotypes of gametes produced in this cross.

Figure 2 shows a drawing of a myelinated motor neurone.

Name the parts labelled A to D.

Osmotic demyelination syndrome (ODS) results in destruction of the myelin sheath of neurones in the brain.

ODS can increase reflex response times.

Explain why.

The parasympathetic nervous system (PNS) uses acetylcholine as its neurotransmitter. Atropine is an anticholinergic drug that attaches to postsynaptic receptors.

Atropine can be used to increase the heart rate in patients with bradycardia (a slower than normal heart rate).

Use the information provided to explain how atropine causes an increase in the heart rate.

One study has suggested that the atropine dosage for severely obese male patients should be 0.01 mg kg^–1 of lean body weight (LBW).

LBW is determined by using this equation.

where TBW = total body weight BMI = body mass index

Calculate the suggested dosage of atropine, in mg, for a severely obese male patient whose:

• TBW = 115.2 kg

• BMI = 41

Give your answer to 3 significant figures.

Show your working.

Figure 3 shows Gammarus pulex, commonly known as a freshwater shrimp.

A student used a choice chamber to investigate the effect of light intensity on the movement of G. pulex.

The student:

• collected 30 shrimps from a freshwater stream

• added freshwater and gravel substrate from the same stream to each segment

• used layers of black paper on the lid of the choice chamber to reduce the percentage light intensity in 3 segments of the choice chamber as shown in

Figure 4

• placed 30 shrimps at the centre of the choice chamber

• waited 10 minutes before counting the number of shrimps in each segment.

Figure 4

The student stated that ‘the procedure used in this investigation helps to ensure the validity of any conclusions made’.

Suggest and explain three features of this investigation that justify this statement.

Table 3 shows the student’s results.

The student observed directional movement by G. pulex.

Name the type of behaviour shown by G. pulex and suggest an advantage to G. pulex of this behaviour.

Use the information in Table 3 in your answer.

Type of behaviour

The student analysed the results in Table 3 using the chi-squared test (χ²) and

Table 4 shows the critical values of χ² at different probability (P) values for different degrees of freedom.

State a null hypothesis for this investigation and explain why the χ² test was the appropriate statistical test to use.

Explanation for using a χ₂ test

Using the calculated χ² value of 11.87 and the information in Table 4, what can you conclude from this investigation?

You should include the terms probability and chance in your answer.

A study of cells from a human embryo found that 2.66 × 10^–7 % of the genome of one cell had changed due to mutation.

You can assume that:

• the genome contains 3 × 10⁹ nucleotides

• the mean rate of mutation is 1.14 mutations per cell cycle

• the cell cycle lasts 24 hours.

Use this information to calculate the age of the embryo in days.

Show your working.

The genome of the bacterium Escherichia coli is approximately 4.6 million base pairs in length and contains around 4000 genes.

The analysis of the genome of E. coli allows the proteome to be determined more easily than that of eukaryotes.

Explain why.

Determining the proteomes of bacteria has helped provide protection for individuals and populations against some infectious diseases.

Explain how.

Scientists investigated the relationship between one type of variable number tandem repeat (VNTR) and the risk of breast cancer occurring in women.

The scientists determined the risk of breast cancer occurring in women:

• with 2, 3 or 4 repeats of the VNTR

• without the VNTR.

They calculated the odds ratio (OR) of breast cancer occurring with 2, 3 or 4 repeats of the VNTR.

An OR is a measure of how strongly an outcome is associated with a risk factor.

The OR formula is:

risk of breast cancer occurring with the VNTR: risk of breast cancer occurring without the VNTR

Table 5 shows the scientists’ results.

A student concluded that the number of repeats of the VNTR is associated with the risk of breast cancer occurring in women.

Evaluate the student’s conclusion.

Cystic fibrosis (CF) is a recessive inherited disorder caused by a defective CFTR gene.

Table 6 shows the number of people with CF and the estimated population of the UK in 2020 and 2022.

Calculate how many more people had CF than was expected in 2022.

You can assume the relative frequency of CF in a population remains constant.

Show your working.

Additional number of people

CF can be caused by a three-base deletion mutation in the CFTR gene. This deletion

creates a recessive allele called F508del.

DNA probes and gel electrophoresis were used to screen two parents and their two children for the F508del allele. One of the children was diagnosed with CF.

Figure 5 shows the results.

What is a DNA probe?

The identity of each family member can be determined from the relative position of the bands shown in Figure 5.

Use information in Figure 5 to:

• complete Table 7

• explain how you identified the child with CF.

You can use F to represent the dominant CFTR allele and f to represent the recessive F508del CFTR allele.

In tropical rainforests, there is a high biodiversity of animal species (lines 1–3).

Explain why.

Nutrient recycling occurs rapidly on the ground of tropical rainforests (lines 4–5).

Explain how two abiotic factors in these rainforests enable the rapid rate of recycling.

The recycling of nitrogen-containing compounds from dead organic matter sustains the growth of plants (lines 5–7).

Describe the roles of bacteria in this recycling.

Natural regeneration of rainforests occurs by secondary succession (lines 8–10).

Describe the process of secondary succession.

Farming practices have prevented the natural regeneration of rainforests by secondary succession (lines 12–14).

Suggest two farming practices that prevent the natural regeneration of rainforests by secondary succession.