AQA A Level Biology Paper 1 June 2023 question paper 7402/1

Give the three structural features found in all virus particles and describe the function of one of these features.

Function of one named feature

Explain why viruses are described as acellular and non-living.

Give one reason why antibiotics are not effective against viruses.

Chitin is a polysaccharide. The chitin monomer is a β-glucose molecule with one OH group replaced by an NHCOCH₃ group. NHCOCH₃ can be represented by N(Ac).

Figure 1 shows the monomer that forms chitin and the chitin polymer.

Chitin has a similar structure to cellulose.

Use Figure 1 to describe three ways the structure of chitin is similar to the structure of cellulose.

Chitin keeps the tracheae open in the tracheal system of gas exchange in an insect. Gas exchange does not occur in the tracheae.

Explain the importance of one adaptation of the gas exchange surface in the tracheal system of an insect.

Lignin is a polymer found in the walls of xylem vessels in plants. Lignin keeps the xylem vessel open as a continuous tube.

Explain the importance of the xylem being kept open as a continuous tube.

The human disease, malaria, is caused by infection with a single-celled eukaryotic organism.

Figure 2 shows a diagram of Plasmodium vivax, one of the species that can cause malaria.

Other than the Golgi apparatus, name one structure in Figure 2 which shows that P. vivax is a eukaryote.

Describe two functions of the Golgi apparatus in a eukaryotic cell.

P. vivax evolved from a common ancestor in Africa. As humans migrated around the world, new strains of P. vivax evolved.

P. vivax is now extremely rare in Africa but there are several different strains of P. vivax in other parts of the world.

Figure 3 shows a phylogenetic diagram of the evolution of these different strains.

What does Figure 3 suggest is the order of human migration out of Africa?

Tick (✓) one box.

There are an estimated 229 million cases of human malaria worldwide per year. 94% of these cases are found in Africa, but are not caused by P. vivax. P. vivax does cause 61% of the cases of human malaria outside Africa.

Use this information to calculate the number of cases worldwide caused by P. vivax each year.

In Africa today, most of the human population are resistant to malaria caused by P. vivax.

Use your knowledge of natural selection to explain why this resistance is so common in Africa.

Some hospital patients suffer from diarrhoea caused by infection with the bacterium Clostridium difficile. The C. difficile bacteria release toxins. These toxins cause the diarrhoea.

The toxins damage the cells lining the ileum, causing them to lose their microvilli. The damage to the cells reduces the absorption of the products of digestion and reduces the absorption of water, resulting in diarrhoea.

Explain why the damage to the cells lining the ileum reduces absorption of the products of digestion and why this reduces absorption of water.

Not all patients in hospital with C. difficile develop diarrhoea.

Scientists measured the anti-toxin antibody concentration in hospital patients with and without C. difficile infection.

They measured the anti-toxin antibody concentration four times:

• on admission to hospital (day 0)

• on day 3

• on day 6

• on the day the patient left the hospital.

Figure 4 shows the scientists’ results.

The scientists suggest that the anti-toxin antibody could be given to some patients as a form of passive immunity.

Use Figure 4 to suggest how this passive immunity would work and which patients should be offered this anti-toxin antibody.

To be used as passive immunity treatment, the anti-toxin antibody would be injected. If it was given by mouth, it would be digested.

Describe how the anti-toxin antibody would be digested.

A student investigated the use of cinnamon oil as an antimicrobial substance. She investigated the effect of cinnamon oil on the growth of five different bacterial cultures grown on agar plates.

The student added 100 mm³ of each bacterial culture from its glass bottle onto a separate agar plate. She spread each bacterial culture evenly over the agar using a spreader.

Describe the aseptic techniques she should use.

On each agar plate, the student cut a well (a hole) in the agar.

The well had a diameter of 6 mm. The student added 50 mm³ of cinnamon oil into the well.

Calculate the minimum depth of the well to allow the addition of 50 mm³ of cinnamon oil. Use the following equation in your calculation:

Use 3.14 as the value for π.

Show your working.

The student kept the plates at 25 °C for 24 hours.

Figure 5 shows what one of her plates looked like after 24 hours.

The student measured the diameter of the clear zone with no bacterial growth around each well. She made these measurements to the nearest whole mm

Table 1 shows her results.

Suggest exactly what the student added to the wells to get the positive control and negative control results.

Complete Table 1 to show the median and mean diameters.

The mean ± 2 standard deviations includes over 95% of the data.

Use this information to consider whether the standard deviations suggest the differences in means are likely to be due to chance.

Explain your answer, including at least one calculation.

Define genome and proteome.

The classification system used in the early 20th century grouped different species of bacteria according to the position and shape of flagella on bacterial cells and by the number of flagella per cell. These were observed using an optical microscope. Each species of bacterium has a characteristic cell shape and arrangement of flagella. These characteristics may be shared with other species within a genus. Flagella are fragile, difficult to stain and may extend from the cell at any angle.

Consider the accuracy and limitations of the early classification of bacteria using the arrangement of flagella.

Suggest why several bacterial species have been renamed in recent years.

Figure 6 shows an image from an optical microscope of a single bacterial cell.

This bacterial cell is 2.3 μm long (excluding the flagellum).

Calculate the magnification of this image.

Show your working.

Carbon monoxide (CO) is released during incomplete combustion of fossil fuels.

Figure 7 shows the dissociation curve for oxyhaemoglobin when:

• not exposed to CO

• exposed to CO such that 50% of the oxygen binding sites are occupied by CO (50% COHb).

Using Figure 7, what can you conclude about how exposure to CO affects the loading and unloading of oxygen by haemoglobin?

Explain your answer.

The World Health Organisation (WHO) suggests that to avoid long-term health effects, COHb concentrations should be kept below 2.5%.

WHO recommends that people should not be exposed to:

• air with > 10 mg m^–3 CO for more than 8 hours

• air with > 30 mg m^–3 CO for more than 1 hour.

Scientists have used a mathematical model to calculate the exposure to carbon monoxide that would result in 2.5% COHb in both adults and children.

Table 2 shows the scientists’ results.

The scientists suggest that the WHO recommendations for carbon monoxide concentrations resulting in 2.5% COHb should be reduced.

Evaluate the scientists’ conclusion.

Scientists investigated a drug called MiTMAB as a treatment for cancer. MiTMAB inhibits cytokinesis.

Figure 8 shows drawings of cancer cells seen with an optical microscope from a:

• sample treated with MiTMAB

• control sample.

Figure 8

The cells in drawing A can be identified as those treated with MiTMAB.

Explain why.

MiTMAB acts as a non-competitive inhibitor of an enzyme called dynamin.

Suggest how MiTMAB can cause dynamin to become inactive.

When active, dynamin has two functions:

it stimulates cytokinesis

it inhibits cell death.

The scientists treated actively growing cultures of cancer cells with MiTMAB.

They incubated:

• one sample of 2500 cells without MiTMAB as a control

• eight samples, each with 2500 cells and a different concentration of MiTMAB.

After 72 hours, the scientists measured the number of cells in each sample.

Figure 9 shows the scientists’ results.

A negative value for proportion of control growth means that fewer than 2500 cells were counted after 72 hours.

Use all the information given to explain the results shown in Figure 9.

0.01 dm³ of MiTMAB solution was added to the treated cells.

Calculate the increase in mass of MiTMAB (in μg) added to the cells to reduce the cell growth from equal to the control to 0.0 of the control.

Show your working.

Dengue fever is a human disease caused by the dengue virus.

Scientists designed an ELISA test to detect antibodies to the dengue virus in a patient’s blood sample.

Figure 10 shows a diagram of this test and some information about how it works.

Figure 11 shows the negative and positive results that were produced 20 minutes after the use of the test shown in Figure 10.

Suggest what is on the test at line T and explain what causes the line to appear in a positive test.

A line at C shows that the test has worked.

Suggest one reason why a line at C shows the test has worked.

Figure 12 shows a flowchart of how the anti-human antibodies with enzyme attached are produced.

Suggest why the fused cells allow continuous production of monoclonal antibodies.

Evaluate the ethics of the production process shown in Figure 12.

Early identification of dengue fever can be difficult as many other diseases produce

the same symptoms. Early identification is important because people suffering with dengue fever can become ill very quickly and may need hospital treatment.

Scientists compared the effectiveness of three diagnostic tests for dengue fever.

• Laboratory-based test – a patient’s blood sample is sent from the doctor’s clinic to a laboratory for testing.

• Current test used in the doctor’s clinic.

• New test to be used in the doctor’s clinic – the ELISA test shown in Figures 10 and 11 (on page 24).

The scientists’ results are shown in Table 3.

A blood sample from each patient with confirmed dengue fever at each time after onset of symptoms was tested with all three diagnostic tests.

The scientists recommend that the new test is used for the identification of dengue fever in all countries around the world.

Discuss this recommendation. Use all the information given.

The dengue virus causes damage to capillaries so that blood proteins move out of the capillaries into the tissue fluid.

Explain how this would affect the return of tissue fluid into the capillaries.

Describe how a quaternary protein is formed from its monomers.

Do not include the process of translation in your answer.

Describe the structure of DNA and the structure of a chromosome.

Mutation can result in an increase in genetic variation within a species.

Describe and explain the other processes that result in increases in genetic variation within a species.