AQA A Level Biology Paper 1 June 2025 question paper 7402/1

The digestion and absorption of lipids involves:

• emulsification by bile salts

• micelles.

Explain each of the following.

The role of micelles in the absorption of lipids

Describe and explain the arrangement of phospholipid molecules in the cell-surface membrane.

Describe how mRNA is obtained from pre-mRNA.

Describe how RNA polymerase joins RNA nucleotides.

Figure 1 shows the energy contained in molecules during an enzyme-controlled reaction.

Which expression represents the activation energy (E_a) of this reaction?

Tick (✓) one box.

In 1914, a group of scientists investigated enzyme action.

After studying their results, the scientists reached the following conclusions:

Our current understanding of enzyme action is based on the induced-fit model.

Describe similarities and differences between the conclusions from 1914 and our current understanding of enzyme action.

Complete Table 1 by adding a tick (✓) if the feature is present in the biological molecules.

Lactase catalyses the hydrolysis of lactose.

A student investigated the effect of galactose on lactase activity.

The student used the following method.

1. Mix together (in tube X) solutions of lactose, galactose and lactase in a 15: 3: 1 volume ratio so that the total volume is 90 cm³

2. Leave the mixture at 30 °C for 10 minutes.

3. Measure the glucose concentration in the mixture.

4. Repeat steps 1 to 3 with two different mixtures.

Calculate the volume of galactose solution used in tube X.

Table 2 shows the student’s results.

Galactose is a competitive inhibitor of lactase.

Use this information and your knowledge of enzymes to explain the results obtained in Table 2.

Give:

• one change the student could make in tube X to confirm that galactose is a competitive inhibitor

• the result you would expect.

Name three structures that are found in some prokaryotic cells but are not found in all prokaryotic cells.

Table 3 shows the resolution of three types of microscope.

Table 4 shows information about yeast cells and mitochondria.

Identify the correct microscope to use in each of the following investigations.

Use your knowledge of microscopes and information in Table 3 and Table 4.

Give two reasons for each choice of microscope.

Investigation 1 – to study the living cells in a yeast culture that contains both living cells and dead cells. The living cells remain colourless and the dead cells are stained blue when a dye is added.

Type of microscope

Investigation 2 – to observe the three-dimensional structure of mitochondria.

Type of microscope

Pears are a type of fruit.

When pears ripen, the:

• fructose concentration increases in cell vacuoles

• volume of cell vacuoles increases.

Figure 2 shows information about a pear cell’s vacuole membrane.

• Carrier protein X is linked to an ATP hydrolase enzyme.

• Carrier protein Y co-transports H⁺ ions and fructose molecules in opposite directions.

Explain why the volume of the vacuoles in pear cells increases when pears ripen.

Your answer should refer to the role of:

• ATP hydrolase

• carrier protein X and carrier protein Y.

A respiratory inhibitor caused a change in pH of the solution within the vacuole.

Use information in Figure 2 to explain how.

Explain how a change in the expression of the genes coding for the carrier proteins can increase the rate of ripening of pears.

Crab blood contains the respiratory pigment haemocyanin.

Figure 3 shows the dissociation curve for oxyhaemocyanin in a species of crab at two temperatures.

Crabs use gills for gas exchange.

Use Figure 3 to explain how the increase in temperature affects the ability of haemocyanin to load or unload oxygen at the gills and in tissues.

Refer to high pO₂ and low pO₂ in your answer.

Figure 4 shows the colour of haemocyanin with increasing concentrations of oxygen.

A calibration curve can be used to determine the percentage oxygen saturation of haemocyanin in a sample of crab blood.

You are given samples of crab blood in which the percentage oxygen saturation of haemocyanin is known.

Use all the information provided to:

describe how you could produce a calibration curve for the percentage oxygen saturation of haemocyanin in crab blood

identify one control variable used in the procedure to obtain data for the calibration curve.

One control variable

Ghost crabs live on sandy beaches.

Ghost crabs can run for a long time before they get tired and have to stop.

A scientist calculated the mean time ghost crabs could run for at different speeds before they stopped.

Figure 5 summarises the scientist’s results.

A ghost crab running at 0.14 m s^–1 covered a distance of 504 m in 1 hour.

Use Figure 5 to calculate the extra distance this crab could cover if it continued running at 0.14 m s^–1 before it stopped running.

Show your working.

Figure 6 shows the data points from individual crabs that were used to plot the curve in Figure 5.

Figure 6

Figure 6 not reproduced here due to third-party copyright restrictions.

The figure is adapted from Figure 1 in https://journals.co.za/doi/pdf/10.10520/AJA00445096_586

The scientist selected the crabs at random from one sandy beach. Before the investigation, the crabs were equally rested and fed identical diets.

Use information in Figure 6 to suggest why the line of best fit in Figure 5 is not a good indicator of the time ghost crabs can run for.

Figure 7 shows how human sperm cells are produced in the testes from diploid A₁ epithelial cells.

Use Figure 7 to calculate the minimum number of A₁ cells needed to produce

Give your answer in standard form.

Show your working.

A₁ cells

A PS cell goes through interphase before a meiotic division.

A scientist determined that the mass of DNA in one PS cell at the start of interphase is 8 arbitrary units.

Draw a bar chart in Figure 8 showing the mass of DNA in one cell in each of these phases:

• at the start of interphase

• at the end of interphase

• at the end of the first meiotic division

• at the end of the second meiotic division.

A PS cell contains 46 chromosomes.

Figure 9 shows the appearance of six of those chromosomes just as a PS cell enters meiosis.

Using the information in Figure 9, draw chromosomes in Figure 10 as they would appear in one cell at the end of the first meiotic division.

A mutation can produce a gamete with one extra chromosome.

Name the type of mutation that produces a gamete with one extra chromosome.

Explain how meiosis can produce a gamete with one extra chromosome.

Strains of bacteria with antibiotic resistance are common in hospitals.

Use your knowledge of selection to explain why.

Antibiotic resistance alleles are located in plasmids.

There are 11 different types of plasmid inside cells of the bacterium Bacillus thuringiensis.

A scientist determined the:

• length of each type of plasmid in kilobase pairs (kbp)

• mean plasmid copy number (mean number of each type of plasmid per cell).

Table 5 shows the scientist’s results for 5 of these plasmids.

The Spearman rank correlation coefficient (r_s) between plasmid length and mean plasmid copy number is determined using this equation.

where Σd² = the sum of all d² figures n = 5 (the highest rank number)

Use information in Table 5 and the formula to calculate the r_s value for this set of data.

Show your working.

The scientist determined that the r_s value between plasmid length and mean plasmid copy number for all 11 types of plasmid is –0.94

What can you conclude from this r_s value?

The length of the single circular (non-plasmid) DNA molecule in a B. thuringiensis cell is 5400 kbp

The total length of all plasmid DNA molecules in a B. thuringiensis cell is 65% greater than the length of the single circular DNA molecule.

Calculate the total number of kbp in all the plasmid molecules in a B. thuringiensis cell .

Show your working.

A growing population of B. thuringiensis cells includes a:

• germination phase

• growth phase

• dormant phase.

A scientist incubated a culture of B. thuringiensis cells at 20 °C

At intervals, the scientist:

• measured the cloudiness of the culture

• determined the mean plasmid B copy number per cell.

Cloudiness is a measure of the number of cells in a culture.

Figure 11 shows the scientist’s results.

Using information in Figure 11, what can you conclude about binary fission and the

replication of plasmid B in the different phases of a growing population of B. thuringiensis ?

Scientists investigated chloroplasts taken from leaf cells of the species Nicotiana tabacum.

The scientists took chloroplasts from leaf cells of a healthy plant and from leaf cells of a mutant plant.

Chloroplasts are contained in several different types of specialised cells in N. tabacum leaves.

What terms are used to describe an organisation of specialised cells in an organism when:

• all the cells are of one type

• the cells are of more than one type?

Cells of more than one type

Figure 12 shows images of chloroplasts from N. tabacum cells observed with an electron microscope.

Identify the parts labelled Q and R.

Use the images in Figure 12 to predict how photosynthesis could be affected in the mutant plants.

Justify your answer.

Scientists investigated the rate of photosynthesis in healthy plants and in mutant plants.

Table 6 shows the scientists’ results.

Chlorophyll a and chlorophyll b are two types of chlorophyll molecules used in photosynthesis.

The scientists’ results did not support what they predicted from Figure 12 (on page 28) would be the effect of the mutation on photosynthesis.

Use information in Table 6 to describe and explain the effect of the mutation.

Describe the roles of ribosomes, tRNA and ATP in the process of translation.

Describe and explain the adaptations of leaves that maximise gas exchange.

Do not refer to organelles in your answer.

Describe the pathway taken by blood between a kidney and the coronary arteries.

Include names of the major blood vessels (arteries and veins) and heart valves involved.