Defence Against Disease (DP IB Biology: HL): Exam Questions

Describe how mucous membranes form a primary defence against pathogens.

When the skin is cut microorganisms may enter the body. One defence against this is blood clotting.

Outline the cascade of events that results in blood clotting.

When a blood clot forms in the coronary arteries it is called a coronary thrombosis.

The table shows data on the number of deaths from coronary thrombosis in the UK.

Describe the trend in the number of deaths between 2012 and 2020.

Distinguish between antibodies and antigens.

The human immunodeficiency virus (HIV) can cause an immune response in its host.

Describe and explain the effect of HIV on the immune system.

Rhinoviruses cause the common cold. These viruses may be destroyed by phagocytosis when they enter a human body.

Describe phagocytosis.

Vaccinations often contain antigens. Scientists investigated whether having a fourth COVID-19 vaccination booster could increase antibody production by the immune system.

•  They divided 100 mice into five groups

• They injected the mice in each group with a different dose of COVID-19 antigens

• They then measured mean antibody production in the mice

 The graph below shows their results.

Describe the effect of COVID-19 antigen dose on mean antibody production.

Scientists investigated antibiotic resistant bacteria in poultry and in poultry farmers. They looked for Escherichia coli cells that were resistant to the antibiotic tetracycline.

The scientists took samples of faeces from the poultry and the farmers. The bacteria were grown on nutrient agar containing tetracycline. Resistant bacteria grew and were visible as colonies on the agar plates.

The results are shown in the table below.

 Turkey farmers often fed their birds food containing tetracycline, whereas chicken farmers did not.

Suggest a hypothesis that could have been tested in this investigation.

Describe the results of the investigation described in part (a).

Scientists investigated treatment of a bacterial respiratory infection that occurs in humans. The bacterial pathogen is often resistant to the antibiotics currently used for treatment.

The scientists investigated the use of a new antibiotic to treat the respiratory infection. The new antibiotic blocks DNA replication in bacterial cells.

They tested the new antibiotic on mice with the same respiratory infection.  The antibiotics were given to the mice at a dose of 25 mg kg⁻¹ per day.

Calculate the dose of antibiotic that would be given to a 33 g mouse each day.

The antibiotic tetracycline is used to treat human bacterial infections, such as pneumonia and other respiratory tract infections.  This antibiotic is safe to use in humans as it does not inhibit or block processes such as DNA replication, ribosome function, transcription or translation.

Suggest why these processes are not inhibited in humans but can be in bacteria.

The diagram shows a human immunodeficiency virus (HIV).

Suggest, with a reason, which labelled component of the virus is most likely to act as an antigen.

Antibiotics are not used to treat viral infections, such as infection with HIV.

Explain why.

Misuse of antibiotics can increase the chance that antibiotic resistant bacterial strains will develop.

Outline two ways to reduce the risk of antibiotic resistance developing.

Define the term antigen.

In humans the ABO system of blood typing is based on red blood cell antigens. The table below contains some information about the antigens involved in ABO blood types.

Identify the groups marked 1 and 2 from which blood groups B and AB could safely receive a blood transfusion.

Explain the blood transfusion options, shown in the table in part (b), available to a person with type O blood.

A medical researcher vaccinated a group of adult patients against human papillomavirus (HPV). He gave each patient two doses of vaccine five months apart. The researcher tested three samples of blood from each of the patients for antibodies against HPV.

Sample 1: taken 3 week before the first dose of vaccine

Sample 2: taken 3 weeks after the first dose of vaccine

Sample 3: taken 3 weeks after the second dose of vaccine

The results are shown in the graph below.

Calculate the percentage increase in the mean concentration of antibodies in the blood between samples 2 and 3.

Explain the differences in antibody concentration between the three blood samples in the graph in part (a).

In a trial for a new, improved version of the vaccine in part (a) a doctor gave the new vaccine to a group of adult volunteers, following the same procedures.

Suggest two factors the doctor should have considered when selecting adult volunteers for this trial.

Haemophilia B is a rare genetic disorder that reduces or prevents production of factor IX, a protein that is responsible for a cascade of reactions that occur during the blood clotting process.

Suggest how insufficient levels of factor IX are likely to affect blood clotting.

Haemophilia B cannot be cured but one form of treatment involves injecting patients with factor IX, which is derived either from donated blood or artificially produced using genetic engineering.

Suggest why it is important to determine the correct dose of factor IX before injecting patients.

In certain rare cases the body may produce antibodies against therapeutic factor IX injections.

Suggest how these antibodies may affect the treatment.

T-cells are another type of white blood cell that can help the body fight against infections. T-cells can bind to the surface of infected cells and destroy them directly. This ability has been harnessed in a new type of cancer treatment known as chimeric antigen receptor (CAR) T cell therapy.

During CAR T cell therapy, T cells from the patient's blood are modified to enable them to bind to the cell surface receptors on cancer cells. The diagram shows the process of CAR T cell therapy.

Distinguish between a patient T cell (stage 1 of the diagram) and a CAR T cell.

Using the information in part (a), suggest how CAR T cell therapy functions as a cancer treatment.

One limitation of CAR T cell therapy is that it is more effective in treating blood cancers than cancers with solid tumours. The structure of such a tumour is shown in the diagram.

Use information in the diagram to suggest why CAR T cell therapy is more effective in treating blood cancers than cancers with solid tumours.

B lymphocytes are a type of white blood cell. These lymphocytes produce antibodies in response to activation.

The diagram below shows the appearance of a B lymphocyte before and after it has been activated.

Explain how the changes that occur within the B lymphocyte when it is activated allow it to carry out its function.

Rituximab is a type of antibody that is used to treat certain B lymphocyte cancers (e.g. leukaemia). It binds to the cell surface protein CD20 on B-lymphocytes. Once the antibody binds to the protein it triggers cell death in the cancerous B-lymphocyte.

Patients are given rituximab through a drip into a vein on a regular basis for the duration of their cancer treatment.

Based on your knowledge of the immune system, explain why patients would need regular infusions with rituximab.

When treating more aggressive forms of B lymphocyte cancer, rituximab is often combined with more traditional chemotherapies.

The graph below shows the results of a trial looking at the effects of several different treatments, alone and in combination, on B lymphocytes grown in the laboratory.

Rituximab on its own killed 23% of the B lymphocytes, and when combined with hydroxyurea it killed 82% of the B lymphocytes.

Calculate the percentage increase in effectiveness of rituximab in combination with hydroxyurea, compared to rituximab on its own. Give your answer to three significant figures.

A medical student concluded that drug combinations are a more effective cancer treatment for human patients than any of the drugs used alone.

Use the information from part (c) to evaluate this conclusion.

Phagocytes and lymphocytes play an important role in the immune system.

Compare and contrast the role of phagocytes and lymphocytes in the immune system.

Bacteria may develop resistance to antibiotics over time.

Outline the development of antibiotic resistance in a bacterial population.

This image shows a type of phagocyte called a neutrophil.

• N1-N4: multi-lobed nucleus

• A: lysosomes

• G: glycogen granules

Use the image to explain how neutrophils are adapted for their role.

When pathogens enter the body phagocytes carry out phagocytosis.

(i) Outline the process of phagocytosis.

[3]

(ii) After phagocytosis, some phagocytes may display parts of the pathogen on their cell surface.

Explain how this may lead to a specific immune response in the infected individual.

[2]

The image shows the progress of infection when damaged human skin comes into contact with Human Papillomavirus, or HPV.

It can be 6-12 months before HPV antibodies can be detected in the blood of an individual with a HPV infection.

Use the information in the image to suggest why this is the case.

The vaccination for HPV is routinely given to teenage girls in order to provide future protection against cervical cancer. The standard procedure is for each girl to receive three doses of the vaccine for full immunity, although there is some discussion about the optimum number of doses.

The graph below shows antibody production after different doses of the HPV vaccine.

A student concluded from the data that it didn’t matter whether girls were given two doses of vaccine or three.

Evaluate this conclusion.

HPV vaccines provide protection against cancer by preventing the virus from causing mutations in infected cells.

Current medical advances in vaccine technology mean that researchers hope that it will soon be possible to vaccinate people against cancer cells themselves.

The image shows some of the changes that can take place when a cell becomes cancerous.

Use the image to suggest how a vaccine could be effective against the development of cancer.

The graph below shows the events that take place during the progression of a vaccination program

Suggest an explanation for the changes in vaccine coverage seen in stage 3 of the vaccination program.

Towards the end of stage 4 in the graph in (a), the disease incidence drops to zero.

Explain what needs to happen within the vaccination programme to reach a disease incidence of zero.

In the 1850s a law was passed in the UK to make vaccination against smallpox compulsory in infants.

At this time there was an estimated population of 27 368 800 and the birth rate was 35 births per 1000 individuals.

The table shows the herd immunity thresholds for some different diseases.

Of the diseases listed, only smallpox has been fully eradicated.

Calculate the minimum number of babies that needed to be vaccinated to reach the herd immunity threshold suggested in the table.

The image shows the evolutionary links between the simian immunodefficiency virus (SIV) and the human immunodefficiency virus (HIV).

Note that the image shows the evolution of two strains of SIV, one in chimpanzees (cpzPtt) and one in gorillas (gor).

Suggest what the image indicates about the emergence of HIV in human populations.

The graph shows some of the changes that take place in the blood after infection by HIV.

After 2 year, HIV leads to the development of Acquired Immunodeficiency Syndrome (AIDS).

Use the information in the graph and your knowledge of the immune system to explain this.

HIV infects human T-cells by binding to a cell surface receptor called CD4. This binding causes a shape change in the viral surface glycoproteins, enabling the virus to enter the host cell.

A new treatment for HIV involves a monoclonal antibody called Ibalizumab, the action of which is shown in the diagram below.

Suggest how Ibalizumab works as a treatment for HIV

A trial looking at the efficacy of Ibalizumab investigated its impact on CD4 cell (also known as helper T cell) count after 25 weeks of treatment.

The results are shown in the graph.

• Each bar represents the mean increase in CD4 count from the baseline level before treatment

• <50 cells/μl = patient group who all started the trial with fewer than 50 CD4 cells per μl

• ≥50 cells/μl = patient group who all started the trial with more than or equal to 50 CD4 cells per μl

• Error bars represent the standard deviations for each group of patients

State and explain what can be concluded about the efficacy of Ibalizumab from the results shown.