IB Biology SL C3.2 Defence Against Disease Questions

Practise IB Biology SL C3.2 by explaining blood clotting and immune responses, interpreting infection and vaccine evidence, and tracing antibiotic-resistance patterns.

Exam points

Define pathogens and relate named infectious-disease examples to symptoms, transmission, or disease effects.
Trace clotting-factor release and the thrombin conversion of fibrinogen into a fibrin mesh that seals a wound.
Distinguish innate from adaptive immunity and explain how phagocytes detect, engulf, and digest pathogens.
Explain antigen-specific lymphocyte responses, including antibody production, B-cell cloning, and helper-T-cell roles.
Use prior exposure or antibody-response evidence to explain memory-cell protection on reinfection.
Explain how HIV infection damages lymphocytes and reduces antibody production in AIDS.
Explain why antibiotics block bacterial targets but do not treat viral infections.
Use mutation, selection, and resistance data to explain how antibiotic-resistant bacteria survive and spread.
Identify zoonoses and use animal-to-human transmission examples such as rabies or Japanese encephalitis.
Interpret vaccination or antibody-response evidence to distinguish prior immunity and vaccine-induced responses.

Covered syllabus points

C3.2.1—Pathogens cause infectious diseases C3.2.2—Skin and mucous membranes C3.2.3—Blood clotting C3.2.4—Innate vs. adaptive immune system C3.2.5—Phagocytes C3.2.6—Lymphocytes C3.2.7—Antigens C3.2.8—B-lymphocyte activation C3.2.9—Clones of plasma cells C3.2.10—Immunity from memory cells C3.2.11—HIV transmission C3.2.12—HIV infection and AIDS C3.2.13—Antibiotics C3.2.14—Antibiotic resistance evolution C3.2.15—Zoonoses C3.2.16—Vaccines and immunization C3.2.17—Herd immunity C3.2.18—COVID-19 pandemic data evaluation

[Maximum number: 3]

(a)

Define pathogen.

[ 1 ]

(b)

Explain why antibiotics are effective against bacterial diseases but not against viral diseases.

[ 2 ]

[Maximum number: 7]

According to the cell theory, living organisms are composed of cells.

Explain the role of cells in the defence against infectious disease.

[Maximum number: 7]

People with the inherited disease hemophilia have a deficiency in one of the proteins that act as clotting factors in blood.

Explain how blood clotting occurs and the consequence for a person who has hemophilia.

Clotting process:
Blood clotting seals cuts in the skin.
Clotting factors are released from platelets.
Thrombin is activated.
A cascade reaction occurs with thrombin.
Thrombin causes fibrinogen to be converted to fibrin.
Fibrin forms a clot/blocks the cut/prevents blood from being lost.

Consequences of hemophilia:
If a person does not have enough clotting factors/has hemophilia, the clot will not form.
Pathogens can enter the body more easily.
Blood will be lost from a cut, affecting blood pressure / causing bleeding to death.
Loss of blood affects the amount of hemoglobin/ $\mathrm{O}_{2}$ carried around the body.
Reference to lifestyle / menstrual/birth problems, e.g. surgery or contact sports.

[Maximum number: 1]

Define pathogen.

[Maximum number: 1]

Which cell type is part of the innate immune system?

Phagocytes

B-lymphocytes

T-lymphocytes

Helper T-cells

[Maximum number: 2]

The structure of part of the digestive system is shown in the diagram below.

Cells defend the body against pathogens. Outline how some of these cells ingest pathogens in the blood and in body tissues.

[Maximum number: 2]

Outline the role of lymphocytes in defence against disease.

[Maximum number: 1]

What is a characteristic of antigens?

They recognize foreign substances

They are produced in bone marrow

They cause disease in humans

They stimulate the production of antibodies

[Maximum number: 7]

Tuberculosis (TB) is an infectious disease caused by the bacterium Mycobacterium tuberculosis.

Explain the production of antibodies when a patient is infected with the TB bacterium.

[Maximum number: 6]

Describe the production of antibodies.

[Maximum number: 1]

A person was infected with a pathogen and then later in life they were re-infected with the same pathogen. The graph shows the concentration of antibodies found in the blood that were produced in response to these two infections.

Antibody concentration plotted against days after first infection and, following a delay, second infection. The first response has a smaller, later peak; the second response has a larger, earlier peak.

Time / days
What is the reason for the faster rise in antibody concentration after the second infection?

The patient had previously been vaccinated with the antibody.

Antibodies had been stored after the first exposure.

Lymphocytes rapidly reproduced to form plasma cells.

The second exposure was more infectious.

[Maximum number: 8]

Discuss the transmission and social implications of AIDS.

[Maximum number: 1]

The graph shows changes in the relative amount of one blood component and the number of HIV RNA copies in blood plasma of an infected person over time.

Key: - Blood component

HIV RNA copies

Which statement explains a likely symptom nine years after the initial infection?

The patient feels tired, as there would be fewer red blood cells to transport oxygen.

The patient has difficulty recovering from infectious diseases due to a lack of antibodies.

The risk of bleeding and blood infections increases due to a lack of clotting factors.

Opportunistic infections spread, as there are few phagocytes to destroy bacteria.

[Maximum number: 2]

Outline why antibiotics are effective against bacteria but not against viruses.

[Maximum number: 5]

Tuberculosis (TB) is an infectious disease caused by the bacterium Mycobacterium tuberculosis.

Describe the risk to the human population of indiscriminate use of antibiotics.

[Maximum number: 1]

The electron micrograph shows the Japanese encephalitis virus.

Why are some diseases, such as Japanese encephalitis, known as zoonoses?

They can be directly transferred from an animal to humans.

They are transferred from human to human.

They are only found in animals in captivity (zoos).

They can directly transfer antigens into animal cells.

[Maximum number: 2]

The image shows a castor bean tick (Ixodes ricinus) which is commonly found in woodlands or forest areas. This tick can carry bacteria that cause Lyme disease in humans.

Close-up photograph of a tick, showing an oval patterned body, projecting mouthparts and four pairs of jointed legs.

(a)

A vaccine has been developed to protect people against the symptoms of Lyme disease.
The graph shows the relative number of antibodies specific to these bacteria in the blood of a person before vaccination.

Graph of relative antibody number in blood against time in years. A curve declines towards the point marked vaccination; the horizontal axis includes a break labelled many years.

Graph of relative antibody number in blood against time in years. The existing curve declines before the point marked vaccination; a broken horizontal axis extends towards many years later.

[ 2 ]

(i)

Suggest what can be concluded from the graph about the person before they were vaccinated.

[ 1 ]

(ii)

Sketch a line on the graph to show how the number of antibodies would change over time after vaccination.

[ 1 ]

All question bank results loaded

a	produce antibodies;
b	memory cells confer immunity;
c	specific immunity results from production of antibodies specific to a particular antigen;
d	recognize pathogens;
e	destroy foreign cells/cancer cells;

a	phagocytes/lymphocytes are white blood cells;
b	TB bacterium has a specific antigen;
c	this antigen is recognised by white blood cells;
d	a clone of lymphocytes/plasma cells/B cells are produced;
e	antibodies are produced by lymphocytes;
f	each lymphocyte produces just one type of antibody;
g	(this is) specific immunity;
h	(part of the) antibody/immunoglobulin binds to the antigen / specific antibody binds to the specific antigen;
i	antibodies are proteins/immunoglobulins;
j	some activated B lymphocytes differentiate into memory B cells;
k	memory cells reproduce quickly;
l	memory cells prevent infection in the future;

a	antibiotics block bacterial processes;
b	example of bacterial process, e.g. cell wall formation;
c	variations exist naturally in a population / some are naturally resistant to the antibiotic;
d	bacteria that are not resistant to this antibiotic will die / only resistant will survive (when antibiotic given);
e	this characteristic could be passed to next generation;
f	(natural selection) leads to changes in the proportions/frequency in the population;
g	human population will be exposed to antibiotic resistant bacteria and will not have antibiotic to kill them;
h	(antibiotic resistant bacteria) may pass resistance to other bacteria species/types by means of plasmids (so other bacteria species turn resistant too);

a	(person had been) previously infected / have immunity / have memory cells (to the bacterium);
b	had been bitten by an (infected) tick before;
c	their immunity is diminishing/reducing;

Covered syllabus points

Question 1

Question (a)

Question (b)

Question 2

Question 3

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Question 5

Question 6

Question 7

Question 8

Question 9

Question 10

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Question 17

Question (a)

Question (i)

Question (ii)