OCR A Level Biology B (Advancing) Scientific literacy in biology November 2021 question paper H422/02

This question is based on the Advance Notice article ‘Do Pathogens Gain Virulence as Hosts Become More Resistant?’ on the Insert.

The myxoma virus (MYXV) is a pathogen that causes myxomatosis in its hosts.

Describe how a virus replicates.

Explain why myxomatosis could not be described as endemic in Australia before 1950.

Explain why the myxomatosis outbreak in the 1950s could be described as an epidemic.

HIV is a retrovirus but MYXV is not.

Use this information and your knowledge to complete the following table by placing a tick (if the feature is found in HIV or MYXV.

The graph shows how the virulence of MYXV changed over the period from 1950 to 1990.

Describe how the virulence of MYXV strains varied during the period 1950 to 1990.

The article describes the interactions between pathogen virulence and host resistance to infection.

Explain how immunological and genetic factors would allow a population of wild rabbits to become more resistant to infection by MYXV.

The article discusses how resistance to infection can be affected by two common agricultural practices: vaccination and selective breeding.

Explain how vaccination is used to protect poultry against pathogens such as Marek’s disease virus (MDV).

Explain why vaccination might not prevent epidemics of Marek’s disease in poultry.

Evaluate the suggestion that birds should be bred for susceptibility to MDV rather than resistance.

The faecal occult blood test (FOBT) is a screening method that is now used routinely in people over the age of 65 years.

The presence of blood in faeces (a positive result) is thought to be caused by chronic inflammation of the gut and indicates an increased risk of developing colorectal cancer (CRC).

A Scottish study looked at 133 921 individuals who were tested with FOBT and then followed for up to 16 years.

• 131 207 had a negative FOBT

• 2714 had a positive FOBT

Outline a method that a doctor could use to confirm that a person with a positive FOBT has CRC.

An FOBT kit is sent to everyone in England between 60 and 74 years of age.

Using your own knowledge and the data in the graphs, evaluate the effectiveness of FOBT in screening for CRC.

* CRC is one of more than 100 forms of cancer.

Describe, with examples, how mutations in genes that control cell division can lead to cancer.

Additional answer space if required.

Fig. 3.1 is a diagram of a section through the human brain.

The following table contains statements about areas of the brain shown in Fig. 3.1.

Complete the table using the most appropriate letter from Fig. 3.1. Each letter may be used once, more than once, or not at all.

The brain contains the structures responsible for coordination of the control of body temperature.

An 80-year-old man was found in an unheated room when the outside temperature was below 0º C. The man had a weak pulse. A paramedic measured the man’s core body temperature as 34.2 ºC.

Explain how the paramedic could obtain an accurate measurement of core body temperature.

* The paramedic concluded that the man was suffering from hypothermia.

Describe the biological processes that lead to hypothermia and the treatment for hypothermia.

Additional answer space if required.

Fig. 3.2 shows monthly data for the treatment of cases of hypothermia (Fig. 3.2a) and hyperthermia (Fig. 3.2b) in the United States over a two-year period.

Some patients were treated as outpatients in a clinic or Emergency Department. Others required admission to hospital as inpatients.

Describe and explain the seasonal trends shown in the two graphs in Fig. 3.2.

Suggest why the proportion of inpatient hospital admissions was different for hypothermia and hyperthermia.

A student looked at the data for hyperthermia and concluded that this was evidence for climate change.

Discuss the student’s conclusion.

Fig. 4.1 shows a graph of rate of reaction plotted against substrate concentration for an enzyme that converts a colourless substrate into a coloured product.

V_max represents the maximum rate of reaction.

Describe how you could obtain the data for this graph.

Explain why the experiments you have described should be carried out with excess enzyme.

The Michaelis constant, K_M, is defined as the substrate concentration that gives half the

Use Fig. 4.1 to obtain a value for K_M for this enzyme, including units.

Suggest why it is often difficult to determine a value for V_max experimentally.

Because of the difficulty in determining a value for V_max, a double reciprocal plot can be used instead.

To prepare this plot, the rate of reaction, V, is measured at different substrate concentrations, [S].

Then, a plot of 1 / V against 1 / [S] is made, as shown in Fig. 4.2.

The equation for the graph in Fig. 4.2 is:

This equation is of the form y = mx + c where

• 1 / V represents y

• K_M / V_max represents m

• 1 / [S] represents x

• 1 / V_max represents c

The double reciprocal plot therefore produces a straight line graph.

Use Fig. 4.2 to determine the gradient of the line.

Write an expression that connects the gradient of the line, K_M and V_max.

A student used Fig. 4.2 to determine that V_max = 5.

Use this value and your answer to part (i) to determine K_M for this enzyme.

K_M =........ (units not required)

The following passage describes aspects of epigenetics.

Complete the passage using the most appropriate terms.

A mutation causes a change in the nucleotide sequence of DNA. Epigenetic changes do

not change the nucleotide sequence. Instead, they change the extent to which genes are

One epigenetic mechanism involves acetylation of ………………………., which makes the

genes more accessible. Another mechanism involves …………………………. of the DNA.

Some epigenetic changes can be inherited if they are present in …………………………...

Twenty zebrafish were exposed to hypoxia (oxygen deprivation) by keeping them in water with a low oxygen concentration for 4 weeks.

All the offspring of these fish had greater resistance to hypoxia than offspring whose parents were kept in well-oxygenated water.

The researchers concluded that this showed evidence for inheritance of epigenetic changes rather than being the result of a mutation.

Evaluate this conclusion.

Drosophila simulans and Drosophila mauritiana are two closely related species of fruit fly.

The OdsH gene in Drosophila is described as a speciation gene. It causes epigenetic changes to the DNA that regulates the condensation of chromosomes.

Name the stage of the cell cycle in which condensation of chromosomes occurs.

The OdsH gene causes male sterility in D. simulans – D. mauritiana hybrids.

Based on the information provided, suggest how the OdsH gene has caused D. simulans and D. mauritiana to become and remain separate species.

Barley is a widely grown cereal in the UK. The production of barley malt involves germinating the barley grains (seeds) and then drying them.

The graph shows the results of an investigation into changes in respiratory quotient (RQ) of barley seeds during the first 30 days of germination.

Name the apparatus that could have been used to measure RQ in this investigation.

Barley grains contain about 12% by mass of storage proteins. A student stated that the graph was evidence that these proteins are used as respiratory substrates throughout germination.

Suggest whether the student’s statement is likely to be correct.

Describe how you could extend this experiment to test the student’s hypothesis.

What can you conclude from the graph about the respiratory substrates, other than protein, that are used during germination?

After being used in brewing, spent grain can be used as an animal feed.

Approximately 50% by mass of the fatty acids in spent grain are linoleic acid, C₁₈H₃₂O₂.

Calculate the respiratory quotient, RQ, of linoleic acid when respired aerobically.

State the effect on RQ if the linoleic acid were respired by a mixture of aerobic and anaerobic respiration. Explain your answer.

Immunity can be categorised as

• active or passive

• natural or artificial.

Complete the following table by putting ticks (✓) in the correct boxes to show whether each example is active or passive and natural or artificial.

Scientists investigated the link between breastfeeding in mice and the risk of offspring developing asthma.

They used a model system of asthma called allergic airway disease (AAD).

Two groups of mice were compared:

• Group I: mice who were born to normal mothers (no AAD) and then breastfed by their own mothers.

• Group II: mice who were born to normal mothers but then breastfed by foster mothers with AAD.

After 4 weeks the offspring were exposed to a protein to induce AAD.

The concentration of IgE in the blood of the offspring was determined. IgE is a type of antibody that increases in concentration during allergic reactions. The results are shown in the graph.

Name a statistical test the scientists could have used to compare the results of the two groups. Give a reason for your choice.

State which group of offspring showed more AAD. Give a reason for your choice.

The statistical analysis showed there was a significant difference in the concentrations of IgE antibodies in the two groups.

Breastfeeding is associated with a reduced risk of asthma in children.

Explain whether the results support the conclusion that breastfeeding could reduce the risk of asthma in children.