AQA A Level Biology Paper 2 June 2022 question paper 7402/2

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

carbon, such as carbohydrates, lipids and proteins. Most of the sugars synthesised

per given time. The chemical energy store in dry biomass can be estimated

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

Describe the light-independent reaction of photosynthesis.

I represents the chemical energy store in ingested food F represents the chemical energy lost to the environment in faeces and urine R represents the respiratory losses to the environment.

In the UK, some female cattle are only used for breeding. This female breeding herd has dairy cows and beef cows.

Table 1 shows data on dairy cows and beef cows in the UK female breeding herd in December 2013 and December 2017.

In December 2017, the female breeding herd was 48% of all female cattle in the UK. Use Table 1 to calculate the percentage of all female cattle that were beef cows in the UK in December 2017.

Use Table 1 to calculate the increase in the number of dairy cows in the UK female breeding herd between December 2013 and December 2017.

Show your working.

Farming cattle for humans to eat is less efficient than farming crops because of energy transfer. Explain why.

Nitrogen-fixing bacteria such as Azotobacter chroococcum use the enzyme nitrogenase to produce ammonia from nitrogen gas in the air. A. chroococcum can use ammonium chloride as a direct source of ammonia. When a source of ammonia is not available this bacterium uses nitrogen fixation.

A scientist investigated the effect of an increase in the concentration of ammonium chloride on the activity of nitrogenase in this bacterium. He prepared several liquid medium cultures of the bacterium. Each liquid culture had the same volume. He grew each culture in a different concentration of ammonium chloride.

In each culture:

• he recorded the nitrogenase activity in arbitrary units

• he removed the bacteria and then recorded the concentration of ammonium chloride remaining in each liquid medium.

Table 2 shows the scientist’s results.

Apart from temperature and pH, give two variables the scientist would have controlled when preparing the liquid medium cultures.

A student concluded that this investigation showed that ammonia inhibits nitrogenase activity in nitrogen-fixing bacteria. Use all the information to evaluate the student’s conclusion.

Nitrogenase catalyses the reduction of nitrogen during nitrogen fixation. The reaction requires 16 molecules of ATP for each molecule of nitrogen that is reduced. When ammonia inhibits nitrogenase activity, nitrogen-fixing bacteria may benefit. Explain how.

A student used the apparatus shown in Figure 1 to measure the rate of aerobic respiration of seeds for 48 hours.

During the 48 hours, the coloured liquid moved to the left.

Explain why.

Apart from time, give two measurements the student would have to make to determine the rate of aerobic respiration of these seeds in cm³ hour^–1

The student used the same apparatus to determine the volume of carbon dioxide the seeds produced during 48 hours.

Give the change the student would need to make to the contents of the apparatus and describe how he could calculate the volume of carbon dioxide produced.

The student calculated that during the 48 hours, 6.2 × 10^–4 cm³ of oxygen was absorbed by 40 g of seeds.

Calculate the oxygen uptake in cm³ g^–1 hour^–1

Lemurs are small mammals. Lemurs live in trees and feed on leaves and fruit. Scientists used a computer program to predict the expected distribution of two species of lemur, Eulemur rufus and Eulemur rufifrons, on the island of Madagascar. These predictions were based on the environmental needs of each species. Then, the scientists determined the actual distribution of these two species of lemur on the island of Madagascar.

Figure 2 shows the scientists’ results.

Using Figure 2, give three conclusions you can make about the distribution of these lemur species.

Using all the information, suggest how speciation happened to produce two species of lemur.

The scientists used the mark-release-recapture method to determine the number of lemurs in one area of forest. They captured, marked and released a first sample of 30 lemurs. A week later, they captured a second sample of 25 lemurs from the same area of forest. The scientists calculated that there were 250 lemurs in that area of forest.

Suggest one precaution needed when marking the lemurs to make sure the estimate of the number of lemurs is valid.

Using the information provided, calculate how many lemurs in the second sample were marked.

In humans, the ABO blood groups and Rhesus blood groups are under genetic control. The inheritance of the ABO blood groups is controlled by three alleles of a single gene, I^A, I^B and I^O. The alleles I^A and I^B are codominant, and the allele I^O is recessive to I^A and recessive to I^B.

There are four ABO phenotypes, A, B, AB and O.

The gene for the Rhesus blood groups has two alleles. The allele for Rhesus positive, R, is dominant to the allele for Rhesus negative, r.

The genes for the ABO and Rhesus blood groups are not sex-linked and are not on the same chromosome.

Figure 3 shows the phenotypes in a family tree for the ABO and Rhesus blood groups.

Give the genotypes of the ABO blood groups for individuals 1 and 2.

Do not include the genotypes for the Rhesus blood groups in your answer.

Explain one piece of evidence from Figure 3 that the allele for Rhesus positive is dominant.

Calculate the probability of individuals 1 and 2 producing a Rhesus positive son with blood group A (individual 3). You can assume that individual 1 is heterozygous for the Rhesus blood group.

Show your working.

Scientists determined the frequencies of the ABO alleles and ABO phenotypes in a large population. They then used a statistical test to determine if the frequencies of the four phenotypes differed significantly from the frequencies expected according to the Hardy–Weinberg equation.

The frequencies of the I^A and I^O alleles were 0.15 and 0.65. What is the frequency of

Name the statistical test you should use to determine if the observed frequencies of the four phenotypes differed significantly from the frequencies expected according to the Hardy–Weinberg equation.

State how many degrees of freedom should apply.

Number of degrees of freedom

The scientists concluded that the observed frequencies of the four phenotypes differed significantly from the expected frequencies. Use your knowledge of the Hardy–Weinberg principle to suggest two reasons why.

Give two reasons why transmission across a cholinergic synapse is unidirectional.

Figure 4 shows the changes in membrane potential in a postsynaptic neurone after repeated stimulation from a single presynaptic neurone.

Name and explain the type of summation shown in Figure 4.

Type of summation

Myasthenia gravis (MG) is an autoimmune disease caused when antibodies bind to the sarcolemma (postsynaptic membrane) of neuromuscular junctions. This can weaken contraction of muscles.

Mestinon is a drug that inhibits the enzyme acetylcholinesterase. Mestinon can help in the treatment of MG.

Suggest and explain how MG can weaken contraction of muscles.

Do not include details of myofibril or muscle contraction in your answer.

Mestinon can help in the treatment of MG. Explain how.

Scientists investigated the production of laboratory rats with the characteristics of type II diabetes. The scientists used the following method.

• They divided the rats into two groups, A and B, and fed them different diets for 2 weeks.

• They fed the rats in group A the normal diet containing 12% fat.

• They fed the rats in group B a high-fat diet containing 56% fat.

• After 2 weeks, they injected both groups of rats with 35 mg kg^–1 of the drug streptozotocin (STZ) to induce diabetes.

1 week later, the scientists determined the mean body mass and mean blood glucose concentration for each group.

Table 3 shows the results.

Table 3

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

Calculate how many grams of STZ should be injected into a rat with a mass of 230.45 g. Show your working.

Give your answer in standard form.

Suggest and explain why STZ was injected per unit of body mass.

The scientists concluded that group B rats could be used for studying type II diabetes in humans.

Use all the information and your knowledge of type II diabetes to evaluate this conclusion.

The scientists repeated the investigation using much higher doses of STZ. This led to destruction of pancreatic cells. The scientists concluded that these rats would not be suitable for studying type II diabetes.

Give two reasons why the scientists made this conclusion.

Name the part of the body which releases antidiuretic hormone (ADH) into the blood.

Alcohol decreases the release of ADH into the blood.

Suggest two signs or symptoms which may result from a decrease in ADH.

Describe the effect of ADH on the collecting ducts in kidneys.

BRCA1 and BRCA2 are human genes that code for tumour suppressor proteins. Mutations in BRCA1 and BRCA2 can cause cancer (lines 1–2). Explain how.

Genetic testing, using DNA from saliva, can screen for all known harmful mutations in both genes (lines 5–6). Describe how this DNA could be screened for all known harmful mutations in both genes.

Effective treatment of ER-positive breast cancers often involves the use of drugs which have a similar structure to oestrogen (lines 9–10).

Suggest and explain how these drugs are an effective treatment of ER-positive breast cancers.

Blood tests can be used to test for cancers (line 11). However, the results of blood tests may not be conclusive when testing for prostate cancer. Explain why.

Treatment with drugs might be able to reverse the epigenetic changes that cause cancers (lines 16–17). Suggest and explain how.