Question 1
A patient develops fever and diarrhoea after drinking contaminated water. A microscopic investigation detects a unicellular eukaryote multiplying in the intestine.
What type of pathogen is most likely responsible?
A.
Virus
B.
Archaeon
C.
Protist
D.
Bacterium
Question 2
Mucous membranes line passages that are exposed to the external environment.
What is a role of mucus in defence against disease?
A.
It converts fibrinogen into insoluble fibrin threads.
B.
It divides by mitosis to form memory lymphocytes.
C.
It traps pathogens so they can be removed from the body.
D.
It produces specific antibodies against pathogen antigens.
Question 3
The flow chart summarizes part of the blood clotting process after a cut in the skin.
Platelets release clotting factors thrombin is produced X is converted to Y erythrocytes are trapped.
What are X and Y?
A.
X: fibrin; Y: fibrinogen
B.
X: erythrocyte; Y: platelet
C.
X: antibody; Y: antigen
D.
X: fibrinogen; Y: fibrin
Question 4
A phagocyte moves from the blood into infected tissue and surrounds a bacterium with extensions of its plasma membrane.
What process brings the bacterium into the phagocyte?
A.
Facilitated diffusion
B.
Osmosis
C.
Endocytosis
D.
Exocytosis
Build a Practice Exam — Biology HL
Test your knowledge with a custom paper containing questions from selected topics.
Question 5
During a nineteenth-century epidemic, a physician recorded where cases occurred and compared them with the activities of people before they became ill.
Define pathogen.
[1]
Outline how careful observation of patterns in cases can lead to control of an infectious disease.
[2]
Question 6
A defence response is rapid, recognizes broad categories of pathogen and does not become more effective after previous exposure to the same pathogen.
What type of immune response is described?
A.
Herd immune response
B.
Adaptive immune response
C.
Secondary antibody response
D.
Innate immune response
Question 7
An individual recovers from an infection. Several years later, exposure to the same pathogen produces a much faster antibody response.
What best explains this faster response?
A.
Memory lymphocytes specific to the antigen survived after the first infection.
B.
Phagocytes change permanently to recognize only that pathogen.
C.
Antibiotics remain in the blood and kill the pathogen directly.
D.
Platelets release clotting factors more rapidly after the first infection.
Question 8
A B-lymphocyte has a receptor that binds antigen P. A helper T-lymphocyte has been activated by antigen Q.
What is the expected outcome for the B-lymphocyte if only these two cells make contact?
A.
It is activated because it has directly bound its specific antigen.
B.
It differentiates immediately into phagocytes that digest antigen Q.
C.
It is not activated because the helper T-lymphocyte was activated by a different antigen.
D.
It is activated because any helper T-lymphocyte can activate any B-lymphocyte.
Build a Practice Exam — Biology HL
Test your knowledge with a custom paper containing questions from selected topics.
Question 9
Untreated HIV infection can progress to AIDS.
Why does the loss of certain lymphocytes in HIV infection increase susceptibility to opportunistic infections?
A.
Fewer helper T-lymphocytes are available to activate B-lymphocytes for antibody production.
B.
Fewer skin cells are available to secrete antibiotics against viruses.
C.
Fewer erythrocytes are available to trap pathogens in fibrin during clotting.
D.
Fewer platelets are available to produce antigens on pathogen surfaces.
Question 10
A virus circulates naturally in wild birds. Mosquitoes feeding on infected birds later transmit the virus to humans, causing encephalitis.
What term best describes this disease?
A.
Autoimmune disease
B.
Zoonosis
C.
Genetic disease
D.
Deficiency disease
Question 11
The skin and mucous membranes are primary defences against pathogens.
State what is meant by a primary defence.
[1]
Explain how skin acts as both a physical and chemical barrier.
[2]
Outline one way in which mucus helps defend body openings or exposed passages.
[1]
Question 12
The diagram shows events at a small cut in the skin soon after damage to a blood vessel.
State the role of platelets in blood clotting.
[1]
Explain how fibrin is produced during blood clotting.
[2]
Outline why rapid clot formation reduces the chance of infection.
[1]
Build a Practice Exam — Biology HL
Test your knowledge with a custom paper containing questions from selected topics.
Question 13
A patient develops a bacterial infection after bacteria enter through a wound.
Compare the innate immune system with the adaptive immune system.
[2]
Outline how a phagocyte controls infection at the wound.
[2]
Question 14
Rabies and Japanese encephalitis are examples of diseases that can be transmitted from other animal species to humans. HIV is transmitted between humans in specific body fluids.
Define zoonosis.
[1]
State one mode by which a zoonotic pathogen may be transmitted to humans.
[1]
Explain how HIV can be transmitted in body fluids, and why ordinary social contact is not a transmission route.
[2]
Question 15
During a cholera outbreak in a city, investigators recorded the number of households supplied by different water pumps and the number of households in which at least one cholera case occurred.
Water pump | Households supplied (households) | Households with cholera case (households) |
|---|---|---|
Marlborough pump | 180 | 7 |
Oxford pump | 220 | 6 |
Broad Street pump | 200 | 162 |
Cambridge pump | 150 | 5 |
Regent pump | 170 | 4 |
Identify the pump most strongly associated with cholera transmission.
[1]
Calculate the number of affected households per 100 households supplied by the Broad Street pump.
[1]
Explain how observations of disease distribution can lead to control of infectious disease before the pathogen is fully understood.
[2]
Question 16
Samples of airway mucus were collected from healthy volunteers. Bacterial growth was measured after incubation with untreated mucus, mucus treated to remove lysozyme, and a nutrient solution with no mucus.
Describe the effect of untreated mucus on bacterial growth compared with the nutrient solution.
[2]
Suggest why removing lysozyme from mucus changes bacterial growth.
[1]
State one way in which mucous membranes act as a primary defence other than by lysozyme activity.
[1]
Build a Practice Exam — Biology HL
Test your knowledge with a custom paper containing questions from selected topics.
Question 17
A bacterial infection is treated with antibiotic X. After treatment begins, most bacteria die but a few survive and reproduce. The infection later contains a high proportion of bacteria resistant to antibiotic X.
What is the best explanation for this change?
A.
The antibiotic stimulated antibody production against only susceptible bacteria.
B.
Resistant bacteria were selected because susceptible bacteria were killed or inhibited.
C.
Antibiotic X caused every bacterium to mutate in the same way.
D.
Susceptible bacteria became eukaryotic cells that were no longer affected by the drug.
Question 18
The estimated herd immunity threshold can be calculated using , where is the average number of secondary infections caused by one infected person in a fully susceptible population.
What is the estimated herd immunity threshold when ?
A.
B.
C.
D.
Question 19
A comparison of two countries during a COVID-19 wave uses only the total number of confirmed deaths in each country.
What is the most important limitation of this comparison?
A.
The totals prove that vaccination had no effect in either country.
B.
The totals are invalid because deaths cannot be expressed as percentages.
C.
The totals do not account for differences in population size or data collection methods.
D.
The totals remove the need to consider age structure or access to healthcare.
Question 20
A patient with influenza requests antibiotics from a doctor. Influenza is caused by a virus.
State one bacterial process or structure that can be blocked by antibiotics.
[1]
Explain why antibiotics do not control influenza virus infection.
[2]
Suggest why unnecessary antibiotic prescriptions should be avoided.
[1]
Build a Practice Exam — Biology HL
Test your knowledge with a custom paper containing questions from selected topics.
Question 21
Only a small number of B-lymphocytes in the body can respond to a particular antigen on a pathogen.
Outline the two conditions required for activation of a specific B-lymphocyte.
[2]
Explain how activated B-lymphocytes produce enough antibody to help control an infection.
[2]
Question 22
The diagram represents antibodies interacting with molecules on the outer surface of a pathogen. Similar recognition can occur with antigens on erythrocytes during an incompatible blood transfusion.
Define antigen.
[1]
Explain why one antibody type binds to one antigen but not equally well to every pathogen.
[2]
Suggest why erythrocyte antigens can cause a problem in an incompatible blood transfusion.
[1]
Question 23
The graph shows antibody concentration after vaccination and after later exposure to the same pathogen.
State one type of material that may be present in a vaccine.
[1]
Compare the antibody responses after vaccination and after later exposure to the same pathogen.
[2]
Explain the role of memory cells in immunity after vaccination.
[1]
Question 24
The graph shows changes in HIV concentration and helper T-lymphocyte number during an untreated HIV infection.
State the type of lymphocyte especially infected and killed by HIV.
[1]
Explain why a reduction in these lymphocytes limits the ability to produce antibodies.
[2]
Define opportunistic infection.
[1]
Build a Practice Exam — Biology HL
Test your knowledge with a custom paper containing questions from selected topics.
Question 25
Researchers compared clot formation in normal blood and in blood with a greatly reduced platelet concentration after a small standardized cut in a capillary tube.
State the dependent variable measured in the investigation.
[1]
Compare the time taken for a visible clot to form in the two blood samples.
[1]
Explain the role of platelets in sealing a cut in the skin.
[2]
Question 26
A sample of phagocytes was mixed with fluorescently labelled bacteria. Microscopy was used to record the mean number of bacteria inside each phagocyte and the proportion of bacteria still intact.
Time / min | Mean bacteria inside each phagocyte | Bacteria still intact / % |
|---|---|---|
0 | 0.0 | 100 |
10 | 1.7 | 86 |
20 | 4.0 | 69 |
30 | 6.4 | 53 |
40 | 7.5 | 35 |
50 | 8.1 | 21 |
60 | 8.3 | 12 |
Identify the process by which bacteria enter the phagocyte.
[1]
State the mean number of bacteria inside each phagocyte after .
[1]
Explain how phagocytes control infection after bacteria have entered a wound.
[2]
Question 27
A volunteer was exposed to the same harmless antigen twice, several weeks apart. The concentration of a specific antibody in blood plasma was measured after each exposure.
Compare the peak antibody concentrations after the first and second exposures.
[2]
Explain why the second antibody response is faster.
[2]
State why the antibody response is specific to this antigen.
[1]
Question 28
Public health records were used to classify selected infectious diseases according to the usual animal reservoir and the main route by which humans become infected.
Disease | Usual animal reservoir | Main route of infection to humans |
|---|---|---|
Japanese encephalitis | Pigs and birds | Mosquito vector bites an infected person |
Zoonotic tuberculosis | Cattle | Inhalation of droplets or consumption of unpasteurised milk |
Rabies | Infected mammals, especially dogs | Bites or scratches from infected animals |
Plague | Rodents | Flea bites |
Identify the disease in the table that is mainly transmitted to humans by a mosquito vector.
[1]
Compare the transmission of zoonotic tuberculosis and rabies to humans.
[2]
Suggest why close contact between humans and wildlife can increase the risk of new zoonotic disease outbreaks.
[1]
Build a Practice Exam — Biology HL
Test your knowledge with a custom paper containing questions from selected topics.
Question 29
A hospital monitors a pathogenic bacterial strain during repeated use of an antibiotic. The graph shows the percentage of isolates resistant to the antibiotic over several years.
Explain how the percentage of resistant bacteria can increase when an antibiotic is used repeatedly.
[3]
Suggest one practice that can slow the emergence of multiresistant bacteria.
[1]
Question 30
A report compares COVID-19 data from two countries using confirmed case totals, death totals, testing rates and population size. The herd immunity threshold can be estimated using , where is the average number of secondary infections caused by one infected person in a fully susceptible population.
Country | Confirmed cases / people | Deaths / people | Tests / 1000 people | Population / people |
|---|---|---|---|---|
Country A | 1,200,000 | 24,000 | 600 | 60,000,000 |
Country B | 900,000 | 18,000 | 180 | 20,000,000 |
Calculate the herd immunity threshold when .
[1]
Explain how herd immunity shows interdependence among members of a population.
[1]
Evaluate the use of raw confirmed case totals alone to compare the severity of the pandemic in the two countries.
[2]
Question 31
Bacteria isolated from patients in a hospital ward were tested with paper discs containing four antibiotics. The diameter of the zone of inhibition was measured for each antibiotic in isolates collected at the start and end of a treatment period.
Identify the antibiotic that was most effective against the bacteria at the end of the treatment period.
[1]
Calculate the percentage decrease in the zone of inhibition for tetracycline during the treatment period.
[1]
Suggest how use of antibiotics can lead to an increase in resistant bacteria.
[2]
State why antibiotics are not expected to control a viral infection.
[1]
Question 32
A longitudinal study followed untreated individuals infected with HIV. Helper T-lymphocyte concentration and the frequency of opportunistic infections were recorded over several years.
Year / years | Helper T-lymphocytes / cells | Opportunistic infections / episodes per year |
|---|---|---|
0 | 820 | 0 |
1 | 780 | 0 |
2 | 740 | 1 |
3 | 700 | 1 |
4 | 640 | 2 |
5 | 560 | 3 |
6 | 460 | 5 |
7 | 300 | 12 |
8 | 190 | 20 |
Describe the relationship between helper T-lymphocyte concentration and opportunistic infections.
[2]
Calculate the percentage decrease in helper T-lymphocyte concentration from the start of the study to year 8.
[1]
Explain why loss of helper T-lymphocytes can lead to AIDS.
[2]
Build a Practice Exam — Biology HL
Test your knowledge with a custom paper containing questions from selected topics.
Question 33
B-lymphocytes specific to one antigen were cultured under four conditions. After three days, the number of antibody-secreting plasma cells was counted.
Identify the culture condition that produced the greatest number of plasma cells.
[1]
Explain why antigen alone caused little plasma cell formation.
[2]
State why one activated B-lymphocyte can give rise to many plasma cells with the same antibody specificity.
[1]
Question 34
A model was used to estimate the effect of vaccination coverage on transmission of a respiratory virus. The basic reproduction number, , for the virus in a fully susceptible population was estimated to be .
Calculate the herd immunity threshold using .
[1]
A community has vaccination coverage. Use the model to suggest whether this community is likely to have herd immunity.
[2]
Explain how vaccination can contribute to herd immunity.
[2]
Question 35
In a maternity hospital, two wards had different rates of fever after childbirth. Doctors moved directly from examining bodies in the morgue to delivering babies in Ward A. Midwives in Ward B did not work in the morgue. After handwashing with an antiseptic solution was introduced for doctors entering Ward A, the rate of fever decreased.
I.
Identify the evidence in the graph that supports hand contamination as a cause of fever in Ward A.
[1]
II.
Explain why the observations can support a conclusion about infectious disease even if the pathogen was not identified.
[2]
Explain how skin and mucous membranes act as primary defences against pathogens.
[2]
Evaluate one limitation of using these observations alone to establish the cause of the disease.
[1]
Question 36
A student cuts a finger while handling soil-contaminated plant material. Within minutes, bleeding slows and a clot begins to form at the wound surface. Later, white blood cells accumulate around the wound.
I.
Explain the sequence of events that forms a blood clot at the wound.
[3]
II.
Explain how clotting reduces the risk of infection.
[1]
Compare and contrast the innate immune system and the adaptive immune system.
[2]
Explain how phagocytes help control infection at the wound.
[1]
Build a Practice Exam — Biology HL
Test your knowledge with a custom paper containing questions from selected topics.
Question 37
Public health workers are preparing advice for teenagers about HIV. The advice must explain both how transmission occurs and why untreated HIV can lead to AIDS.
I.
Outline two mechanisms by which HIV can be transmitted.
[2]
II.
Explain why HIV is not transmitted by ordinary social contact such as sharing a classroom.
[1]
Explain how HIV infection of lymphocytes can lead to opportunistic infections in AIDS.
[3]
Suggest one public health measure that reduces HIV transmission and explain its effect.
[1]
Question 38
COVID-19 surveillance data from three countries were compared during the same month. The countries differed in population size, number of tests performed and vaccination coverage.
Country | Population / million | Tests performed | Vaccination coverage / % | Confirmed cases | Recorded deaths | New cases before measure | New cases after measure |
|---|---|---|---|---|---|---|---|
A | 25.0 | 3,000,000 | 78 | 2,500,000 | 75,000 | n/a | n/a |
B | 40.0 | 900,000 | 60 | 1,200,000 | 29,000 | 40,000 | 22,000 |
C | 8.0 | 1,200,000 | 91 | 350,000 | 7,000 | n/a | n/a |
Calculate recorded deaths as a percentage of confirmed cases for country A.
[1]
Calculate the percentage change in new cases in country B after the public health measure was introduced.
[1]
Suggest three reasons why raw numbers of recorded COVID-19 deaths may not allow a fair comparison of the impact of the pandemic between countries.
[3]
Question 39
A diagnostic test for a viral infection was evaluated in a population screening programme. The test has a sensitivity of and a specificity of . In the screened population, people were infected and people were not infected.
Group | Number of people | Relevant test measure | Value / % |
|---|---|---|---|
Infected | 200 | Sensitivity | |
Not infected | 9800 | Specificity |
Calculate the expected number of false-negative results.
[1]
Calculate the expected number of false-positive results.
[1]
Explain one way in which laboratories can reduce the risk of false results in diagnostic testing.
[2]
Suggest why false-positive results can still be a significant problem when infection prevalence is low.
[1]
Question 40
A new vaccine contains a purified surface protein from a bacterial pathogen. Only a very small number of B-lymphocytes in a person are able to bind this protein before vaccination.
I.
Explain why only some B-lymphocytes respond to the vaccine antigen.
[2]
II.
Explain the role of helper T-lymphocytes in activation of these B-lymphocytes.
[2]
Explain why clonal expansion is necessary before a high antibody concentration is reached.
[2]
Discuss how memory cells produced after vaccination can provide immunity without causing the bacterial disease.
[2]
Build a Practice Exam — Biology HL
Test your knowledge with a custom paper containing questions from selected topics.
Question 41
A clinic monitored a pathogenic strain of Staphylococcus aureus isolated from skin infections. The strain was exposed to three antibiotics in agar plates over several years. Larger zones of inhibition indicate greater susceptibility to the antibiotic.
Year | Antibiotic A zone / mm | Antibiotic B zone / mm | Antibiotic C zone / mm | Penicillin-resistant isolates / % |
|---|---|---|---|---|
1 | 24 | 22 | 20 | 10 |
2 | 23 | 19 | 15 | 14 |
3 | 22 | 16 | 11 | 18 |
4 | 20 | 13 | 7 | 25 |
5 | 18 | 11 | 4 | 32 |
I.
Identify the antibiotic to which the bacterial strain shows the greatest resistance at the end of the monitoring period. Give a reason.
[1]
II.
Calculate the percentage change in resistant isolates during the monitoring period. Show your working.
[2]
Explain why antibiotics used against this bacterial strain would not control an infection caused only by a virus.
[2]
Discuss how multiresistant bacterial strains can evolve and why careful antibiotic use is needed.
[3]
Question 42
A respiratory virus has an estimated average transmission value in a fully susceptible population. A vaccine is available for the virus. Some individuals in the population cannot be vaccinated for medical reasons.
Community | Vaccination coverage / % | People unable to be vaccinated / people |
|---|---|---|
Community A | 68 | 24 |
Community B | 80 | 17 |
Community C | 93 | 9 |
I.
Calculate the estimated herd immunity threshold for this virus.
[1]
II.
Using the threshold, identify which community or communities in the visual are expected to have transmission greatly impeded.
[1]
Explain how vaccination can lead to immunization against a specific pathogen.
[3]
Discuss why herd immunity shows interdependence between members of a population.
[3]
Question 43
A volunteer received two doses of a vaccine containing RNA that codes for a viral surface antigen. The second dose was given several weeks after the first dose. Antibody concentration was measured over time.
I.
Identify two features of the antibody response after the second dose that show it is a secondary immune response.
[2]
II.
Explain the cellular basis of the faster response after the second dose.
[2]
Explain how an RNA vaccine can stimulate production of antibodies specific to a viral antigen.
[2]
Discuss why a booster containing a modified antigen from a new viral variant may improve protection but may not give complete certainty of protection.
[2]
Question 44
Researchers screened a chemical library for new antibacterial compounds. Candidate compounds were tested against a pathogenic bacterium and against cultured human cells. A useful antibiotic should inhibit bacterial growth at low concentration while causing little harm to human cells.
Compound | Bacterial IC50 / µM | Human-cell survival at 10 µM / % |
|---|---|---|
A | 0.05 | 97 |
B | 0.20 | 88 |
C | 0.10 | 56 |
D | 0.75 | 93 |
E | 0.35 | 79 |
I.
Identify the most promising compound from the visual and justify your choice.
[2]
II.
Explain why targeting bacterial cell wall synthesis can make an antibiotic selectively toxic.
[2]
Discuss why a newly discovered antibiotic should still be used carefully if it becomes available clinically.
[2]
Evaluate one limitation of screening chemical libraries using inhibition of bacterial growth in culture.
[2]
Build a Practice Exam — Biology HL
Test your knowledge with a custom paper containing questions from selected topics.
Question 45
A patient requires a blood transfusion. Erythrocytes from potential donors differ in their surface antigens. If incompatible erythrocytes are transfused, the patient may produce antibodies that bind to donor erythrocyte antigens.
Donor | Donor erythrocyte antigens | Patient plasma antibodies | Antibody binding? |
|---|---|---|---|
Donor 1 | A | anti-A and anti-B | Yes |
Donor 2 | B | anti-A and anti-B | Yes |
Donor 3 | A and B | anti-A and anti-B | Yes |
Donor 4 | none | anti-A and anti-B | No |
I.
Predict what could happen if erythrocytes with an antigen recognized as foreign are transfused.
[2]
II.
Using the visual, identify a compatible donor for the patient and justify your choice.
[1]
Explain how antigens act as recognition molecules in an adaptive immune response.
[2]
Compare and contrast immune responses to erythrocyte antigens and pathogen antigens.
[2]
Question 46
Two countries reported COVID-19 data over the same six-month period. The countries differed in population size, testing rate, median age and vaccination coverage.
Country | Population / people | Confirmed cases | Deaths | Tests / 1,000 people | Median age / years | Vaccination coverage / % |
|---|---|---|---|---|---|---|
Country A | 12,000,000 | 36,000 | 360 | 720 | 30 | 85 |
Country B | 50,000,000 | 160,000 | 2,000 | 250 | 44 | 67 |
I.
Calculate deaths per population for one named country in the visual. Show your working.
[2]
II.
Calculate deaths as a percentage of confirmed cases for the same country.
[1]
Analyse why raw totals of confirmed cases and deaths may be misleading when comparing the two countries.
[3]
Evaluate the claim that the country with fewer deaths had a more effective vaccination programme.
[2]
Question 47
A rapid diagnostic test for a viral infection is being considered for use at the entrance to a large event. The test has high specificity but lower sensitivity when samples are taken early after infection.
Parameter | Value |
|---|---|
Expected attendance | 10,000 people |
Estimated infection prevalence among attendees | 1.0% |
Test sensitivity when taken early after infection | 80% |
Test specificity | 99% |
I.
Calculate the expected number of false-negative results at the event. Show your working.
[2]
II.
Suggest one method to reduce the risk caused by false-negative results.
[1]
Explain how false-negative and false-positive results can affect infectious disease control.
[2]
Evaluate whether this test should be used as the only control measure for the event.
[2]
Question 48
Cases of a viral encephalitis increased in villages near rice fields where pigs and wading birds are common. Mosquito larvae were found in standing water near the villages. A control programme combined mosquito control, vaccination of at-risk people and public advice to reduce bites.
Survey item | Result |
|---|---|
Rice fields nearby | Present |
Pigs near villages | Common |
Wading birds near villages | Common |
Mosquito larvae in standing water | Found |
Human encephalitis cases before control | 40 |
Human encephalitis cases after control | 10 |
I.
Use the information to identify two pieces of evidence that the disease may be a zoonosis transmitted by a vector.
[2]
II.
Calculate the percentage change in human cases after the control programme. Show your working.
[1]
Discuss how different control measures could reduce transmission of this zoonotic disease.
[3]
Evaluate whether vaccination alone would be sufficient to prevent an epidemic in this situation.
[2]
Build a Practice Exam — Biology HL
Test your knowledge with a custom paper containing questions from selected topics.
The Ultimate All-in-One
IB Platform
All content on this website has been developed independently from and is not endorsed by the International Baccalaureate Organization. International Baccalaureate and IB are registered trademarks owned by the International Baccalaureate Organization.