IB Biology Quiz: Understand Defence Against Disease
20 questions · exam conditions
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Understand Defence Against DiseaseQuestion 1 of 20

A patient bitten by a venomous snake receives an injection of antivenom, which contains antibodies from an immunized animal. Which statement accurately describes the type and duration of the resulting immunity?

It is artificial active immunity, providing long-lasting protection against future bites.
It is natural active immunity, as the patient's body learns to produce its own antivenom.
It is artificial passive immunity, providing immediate but temporary protection.
It is natural passive immunity, as the antibodies are from a biological source.
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IB Biology Quiz

IB Biology Quiz: Understand Defence Against Disease

Practice Understand Defence Against Disease in IB Biology with focused quiz questions that help you check what you know, review explanations, and build confidence with test-style prompts.

What this quiz covers

This quiz focuses on Understand Defence Against Disease, giving you a quick way to practice the rules, question types, and explanations that matter most for IB Biology.

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Try each quiz question before looking at the correct answer. Use the explanations to review missed ideas, then come back to similar questions until the pattern feels familiar.

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Question 1

A patient bitten by a venomous snake receives an injection of antivenom, which contains antibodies from an immunized animal. Which statement accurately describes the type and duration of the resulting immunity?

  1. It is artificial active immunity, providing long-lasting protection against future bites.
  2. It is natural active immunity, as the patient's body learns to produce its own antivenom.
  3. It is artificial passive immunity, providing immediate but temporary protection. (correct answer)
  4. It is natural passive immunity, as the antibodies are from a biological source.
Explanation: This is artificial passive immunity. It is 'artificial' because it is administered medically, and 'passive' because the recipient is given pre-made antibodies rather than producing their own. The protection is immediate because the antibodies can neutralize the venom right away, but it is temporary because no memory cells are formed, and the foreign antibodies are eventually cleared from the body.

Question 2

A cancer therapy uses monoclonal antibodies that bind specifically to a protein found only on the surface of tumor cells. What is a primary mechanism by which these antibodies can lead to the destruction of tumor cells?

  1. They enter the tumor cells and use reverse transcriptase to block the expression of oncogenes.
  2. They act as opsonins, marking the tumor cells for recognition and destruction by phagocytes like macrophages. (correct answer)
  3. They bind to all rapidly dividing cells, causing lysis through the activation of the complement system.
  4. They deliver a payload of antiviral medication that infects and kills the targeted tumor cells.
Explanation: One of the key functions of antibodies is opsonization. By binding to antigens on a cell's surface, they can act as a flag or marker. Phagocytic cells have receptors for the constant region of antibodies, allowing them to efficiently identify and engulf the marked cell. A is incorrect; antibodies are proteins that do not enter cells to affect transcription. C is incorrect because the antibodies are specific to the tumor protein, not all rapidly dividing cells. D describes an antibody-drug conjugate, but opsonization is a more fundamental antibody mechanism.

Question 3

An individual develops a severe allergy to pollen. What is the correct sequence of events that occurs upon a second exposure to the pollen that triggers an allergic reaction?

  1. Pollen binds to helper T-cells, which directly release large quantities of histamine.
  2. Macrophages phagocytose the pollen and signal B-cells to immediately degranulate and release histamine.
  3. Pollen antigens cross-link IgE antibodies bound to the surface of mast cells, causing degranulation. (correct answer)
  4. Pollen is neutralized by circulating IgG antibodies, which in turn triggers mast cells to release cytokines.
Explanation: In a previously sensitized person, IgE antibodies specific to the allergen (pollen) are attached to the surface of mast cells. Upon re-exposure, the allergen binds to and cross-links these IgE antibodies, triggering the mast cell to release histamine and other inflammatory mediators, causing allergy symptoms. A and B incorrectly identify the cells that release histamine. D incorrectly identifies IgG as the primary antibody type in allergy (it is IgE).

Question 4

The Human Immunodeficiency Virus (HIV) primarily infects and destroys helper T-cells. Why does the loss of this specific cell type lead to the collapse of adaptive immunity seen in AIDS?

  1. Helper T-cells are the primary producers of antibodies, so their loss prevents humoral immunity.
  2. Helper T-cells are phagocytes that are essential for the initial clearance of all invading pathogens.
  3. Helper T-cells are responsible for the immunological memory of all previous infections.
  4. Helper T-cells are required to activate B-cells and cytotoxic T-cells, coordinating most adaptive responses. (correct answer)
Explanation: Helper T-cells are the central coordinators of the adaptive immune response. They are activated by antigen-presenting cells and, in turn, release cytokines that provide the necessary signals to activate B-cells (for antibody production) and cytotoxic T-cells (for killing infected cells). Without them, both major arms of the adaptive immune system fail to function effectively. A is incorrect (plasma cells produce antibodies). B is incorrect (macrophages are primary phagocytes). C is incorrect (memory B and T cells hold memory).

Question 5

Cytokines, such as interleukins, are crucial for a coordinated immune response. What is the primary biochemical function of these molecules?

  1. They are enzymes that directly digest the cell walls of bacterial pathogens.
  2. They are cell-surface receptors that bind directly to foreign antigens.
  3. They are signalling proteins that regulate the activity and proliferation of immune cells. (correct answer)
  4. They are pore-forming proteins that lyse virus-infected host cells.
Explanation: Cytokines are a broad category of small proteins that act as chemical messengers between immune cells. They bind to specific receptors on target cells, triggering signal transduction pathways that can induce responses like cell proliferation, differentiation, activation, or apoptosis. They are essential for communication and coordination within the immune system. A, B, and D describe the functions of other molecules (e.g., lysozyme, antibodies, perforin).

Question 6

Autoimmune diseases like multiple sclerosis and rheumatoid arthritis are caused by a fundamental failure in the immune system's ability to maintain self-tolerance. What does this failure entail?

  1. The body's phagocytes lose the ability to engulf and destroy pathogens, leading to chronic infections that trigger autoimmunity.
  2. The immune system fails to produce memory cells, resulting in a constant, low-level activation against the body's own tissues.
  3. Lymphocytes that are reactive to the body's own antigens are not properly eliminated or inactivated, and they subsequently become activated. (correct answer)
  4. The production of all antibody classes is upregulated, leading to non-specific binding to self-tissues and widespread inflammation.
Explanation: Self-tolerance is the mechanism that prevents the immune system from attacking the body's own cells. It involves deleting or inactivating self-reactive T and B-cells during their maturation. In autoimmunity, this process fails, allowing these self-reactive cells to persist, become activated, and mount an immune attack against self-antigens, causing tissue damage. A, B, and D describe other types of immune dysfunction, not the core cause of autoimmunity.

Question 7

An individual who recovers from chickenpox has lifelong immunity to that specific virus but can still be infected by the influenza virus. What is the fundamental principle of adaptive immunity that explains this observation?

  1. Phagocytes activated during the chickenpox infection are only effective against the chickenpox virus.
  2. Antibodies have broad reactivity but the influenza virus has a protective coat that resists them.
  3. Immunological memory is highly specific; memory cells produced against chickenpox do not recognize influenza antigens. (correct answer)
  4. The innate immune system develops a specific, long-lasting barrier against chickenpox but not influenza.
Explanation: A core principle of adaptive immunity is specificity. The lymphocytes (B and T cells) that are selected and activated during an infection have receptors that recognize specific antigens from that particular pathogen. The resulting memory cells are also specific to that pathogen. Therefore, memory cells for chickenpox provide no protection against the antigenically distinct influenza virus. A and D are incorrect as they misattribute specificity and memory to the innate system. B is incorrect as antibodies are highly specific.

Question 8

A 'sandwich' ELISA test uses two different monoclonal antibodies to detect a target antigen. One antibody is fixed to a surface as a 'capture' antibody, and the other is linked to an enzyme as a 'detection' antibody. For a positive result, what must be true about the antigen?

  1. The antigen must have at least two different epitopes that can be bound simultaneously by the capture and detection antibodies. (correct answer)
  2. The antigen must be an enzyme that can activate the detection antibody, causing a color change.
  3. The antigen must be small enough to bind within a single antibody's antigen-binding site.
  4. The antigen must be able to denature the capture antibody, allowing the detection antibody to bind in its place.
Explanation: The principle of a sandwich ELISA relies on the antigen being 'sandwiched' between two antibodies. This requires the antigen to be large enough to have at least two distinct binding sites (epitopes). The capture antibody binds to one epitope, immobilizing the antigen, and the detection antibody binds to another epitope, bringing the enzyme along to generate a signal. If the antigen had only one epitope, both antibodies could not bind at the same time.

Question 9

A child receives a vaccine containing inactivated viral antigens. Months later, they are exposed to the live virus but show no symptoms. Which statement provides the most accurate immunological explanation?

  1. The vaccine triggered a primary response and the formation of memory cells, which then mounted a rapid and effective secondary response to the live virus. (correct answer)
  2. The inactivated antigens from the vaccine remain in the circulation, immediately neutralizing any live virus that enters the body.
  3. The vaccine contained a high concentration of monoclonal antibodies that provide long-term passive immunity against the virus.
  4. The vaccine permanently modified the child's innate immune cells to recognize the live virus with high specificity.
Explanation: Vaccination works by safely inducing a primary adaptive immune response. This leads to the production of a large pool of specific memory B and T-cells. Upon subsequent exposure to the live pathogen, these memory cells are quickly activated, launching a secondary response that is much faster and more potent than a primary response, eliminating the pathogen before it can cause disease. B is incorrect. C describes passive immunity, not vaccination. D is incorrect as vaccines generate specific memory in the adaptive, not innate, immune system.

Question 10

A significant decrease in vaccination coverage within a community leads to a measles outbreak. Which statement best explains the immunological principle behind this outbreak?

  1. The measles virus rapidly mutates when vaccination rates drop, rendering the existing vaccine ineffective for everyone.
  2. A decline in herd immunity increases the pathogen's circulation, raising the probability of exposure for all individuals, including those in whom the vaccine was not fully effective. (correct answer)
  3. Unvaccinated individuals develop an atypical immune response that actively suppresses the memory cells of vaccinated individuals nearby.
  4. The measles vaccine provides only passive immunity, which wanes over time and requires constant boosting from a highly vaccinated population.
Explanation: Herd immunity protects a community by reducing the circulation of a pathogen, which shields vulnerable individuals (infants, immunocompromised, and the small percentage for whom vaccines are not 100% effective). When vaccination rates fall, herd immunity weakens, the pathogen spreads more easily, and the risk of infection increases for everyone. A is a possibility for viruses but not the primary principle of herd immunity failure. C is biologically incorrect. D is incorrect as vaccines stimulate active, not passive, immunity.

Question 11

Which of the following processes is a characteristic of the adaptive immune system but NOT the innate immune system?

  1. Recognition of pathogen-associated molecular patterns (PAMPs).
  2. Recruitment of phagocytic cells to the site of an infection.
  3. Production of memory cells that provide long-term immunity. (correct answer)
  4. Release of inflammatory mediators such as histamine.
Explanation: The defining feature of the adaptive immune system is the generation of immunological memory through the creation of memory B and T-lymphocytes. The innate immune system is non-specific and does not generate memory; its response is the same upon every encounter with a pathogen. A, B, and D are all characteristic features of the innate immune response (though some overlap with adaptive responses).

Question 12

During a primary immune response, which event is the direct trigger for the clonal selection of a specific B-lymphocyte?

  1. The binding of a specific free-floating antigen to the B-lymphocyte's surface antibodies. (correct answer)
  2. The secretion of interleukins by an activated helper T-cell that has recognized the same antigen.
  3. The rapid proliferation of the B-lymphocyte into a clone of antibody-secreting plasma cells.
  4. The differentiation of a B-lymphocyte into a memory cell to prepare for future infections.
Explanation: Clonal selection is the process by which a specific antigen 'selects' a lymphocyte by binding to its complementary surface receptors. This binding event is the initial trigger that singles out the B-cell for activation. The other steps, such as receiving help from T-cells (B) and proliferating or differentiating (C and D), occur after the initial selection by the antigen.

Question 13

In the production of monoclonal antibodies, B-lymphocytes are fused with myeloma cells. What is the essential contribution of the myeloma cell to the resulting hybridoma?

  1. The genetic information for producing the highly specific target antibody.
  2. The ability to divide indefinitely in culture, ensuring a continuous supply of antibodies. (correct answer)
  3. Surface receptors that allow the hybridoma to be easily activated by antigens.
  4. The machinery for secreting large quantities of antibodies of various specificities.
Explanation: The B-lymphocyte provides the genetic code for the specific antibody of interest, but it has a finite lifespan. The myeloma cell is a cancerous plasma cell that has been selected for its ability to divide endlessly (immortality) but has lost its own antibody-producing ability. The fusion combines the specificity of the B-cell with the immortality of the myeloma cell. A describes the B-cell's contribution. C is not the primary purpose. D is incorrect as the goal is a monoclonal (single specificity) antibody.

Question 14

During a viral infection, which immune cell is primarily responsible for identifying and destroying host cells that have become virus factories?

  1. Plasma cells, which secrete antibodies that can penetrate infected cells and trigger lysis.
  2. Helper T-lymphocytes, which directly bind to and induce apoptosis in virus-infected cells.
  3. Macrophages, which can distinguish infected from uninfected cells and selectively phagocytose them.
  4. Cytotoxic T-lymphocytes, which recognize viral antigens presented on the surface of infected cells. (correct answer)
Explanation: The key role of cytotoxic T-cells (TC cells or CD8+ T-cells) is to monitor the body's cells for signs of intracellular infection. They recognize foreign peptides (like viral proteins) presented on MHC class I molecules on the surface of infected cells and eliminate these cells by inducing apoptosis. A is incorrect as antibodies act on extracellular pathogens. C is less specific than T-cell recognition. D is incorrect as helper T-cells coordinate the response but do not directly kill infected cells.

Question 15

The release of histamine from mast cells during an inflammatory response causes localized redness and swelling. What are the physiological effects of histamine that lead directly to these symptoms?

  1. Vasoconstriction of arterioles and decreased permeability of capillaries to trap pathogens.
  2. Activation of B-cells and T-cells in the local area to initiate an adaptive immune response.
  3. Stimulation of nerve endings and inhibition of local blood clotting to increase pain.
  4. Vasodilation of arterioles and increased permeability of capillaries to allow fluid and cell leakage. (correct answer)
Explanation: Histamine causes vasodilation (widening of blood vessels), which increases blood flow to the area, resulting in redness and heat. It also increases the permeability of capillaries, allowing plasma fluid and immune cells to move from the bloodstream into the surrounding tissue, which causes swelling (edema). A describes the opposite effects. C and D are not the direct effects of histamine that cause redness and swelling.

Question 16

A virus infects a human liver cell. For the immune system to eliminate this cell, which molecular presentation must occur on the liver cell's surface?

  1. The liver cell presents viral peptide fragments on MHC class I molecules to cytotoxic T-cells. (correct answer)
  2. The liver cell presents viral peptide fragments on MHC class II molecules to helper T-cells.
  3. The liver cell secretes whole virus particles that are presented by B-cells to cytotoxic T-cells.
  4. The liver cell presents intact viral proteins on its surface, which are recognized by antibodies.
Explanation: All nucleated somatic cells (like liver cells) use MHC class I molecules to display fragments of proteins being made inside the cell (endogenous antigens). When a cell is infected with a virus, it presents viral peptides on MHC class I. This complex is recognized by cytotoxic T-cells, which then kill the infected cell. MHC class II is used by antigen-presenting cells for exogenous antigens. B, C, and D describe incorrect pathways for the cell-mediated response to an infected host cell.

Question 17

A bacterium is coated with antibodies. This coating enhances the ability of a macrophage to bind to and engulf the bacterium. This process is known as:

  1. Neutralization
  2. Agglutination
  3. Opsonization (correct answer)
  4. Inflammation
Explanation: Opsonization is the process of marking a pathogen for phagocytosis. Antibodies act as opsonins by binding to the pathogen's surface; phagocytes have receptors for the antibody's constant region, which greatly facilitates binding and engulfment. Neutralization is blocking a pathogen or toxin's function. Agglutination is clumping pathogens together. Inflammation is a broader response to injury or infection.

Question 18

The secondary immune response to an antigen is significantly faster and stronger than the primary response. Which factor is most directly responsible for this difference?

  1. The innate immune system develops antigen-specific memory after the first exposure.
  2. A large population of antigen-specific memory lymphocytes persists after the primary response. (correct answer)
  3. The high level of antibodies produced during the primary response remains in circulation indefinitely.
  4. The pathogen is generally less virulent during a second infection, giving the immune system more time.
Explanation: The basis of immunological memory is the population of long-lived memory B and T-cells created during the primary response. These cells are more numerous and more easily activated than the naive lymphocytes that initiated the primary response, leading to a much faster and greater production of antibodies and effector T-cells upon re-exposure. A is incorrect; the innate system has no memory. C is incorrect; antibody levels decline after the infection is cleared. D is an assumption about the pathogen, not a feature of the immune system.

Question 19

An antibody molecule is highly specific to one antigenic determinant. Which feature of the antibody's quaternary structure is directly responsible for this specificity?

  1. The amino acid sequence of the constant region of the heavy chains, which determines the antibody's class.
  2. The unique three-dimensional shape of the antigen-binding sites formed by the variable regions of a heavy and light chain. (correct answer)
  3. The number and position of disulfide bonds that link the four polypeptide chains into a stable Y-shape.
  4. The flexible hinge region that allows the two arms of the antibody to bind epitopes at various distances apart.
Explanation: The specificity of an antibody is determined by the variable regions at the tips of the 'Y' arms. The unique sequence of amino acids in these regions folds to create a specific 3D shape, the antigen-binding site, which is complementary to a single epitope. A determines the antibody's effector function. C is crucial for structural integrity but not specificity. D enhances binding efficiency (avidity) but does not determine what antigen is recognized (specificity).

Question 20

A novel virus emerges from a wildlife reservoir and causes a severe pandemic in humans. From an immunological standpoint, what best explains the high susceptibility of the human population?

  1. The virus has a lipid envelope that makes it invisible to all human phagocytes.
  2. The human population lacks any pre-existing immunological memory to the novel viral antigens. (correct answer)
  3. The virus primarily infects cells of the innate immune system, disabling the first line of defense.
  4. Human antibodies are structurally incapable of binding to antigens from a non-human virus.
Explanation: When a pathogen is novel to a species, no individuals have prior exposure, and therefore no one possesses adaptive immunological memory (memory B and T-cells). This means every single infection requires a slow and often less effective primary immune response, allowing the virus to replicate and cause disease before it is controlled. A is incorrect; phagocytes can recognize enveloped viruses. C is possible for some viruses but the lack of adaptive memory is the key population-level issue. D is incorrect; the immune system is capable of responding to any foreign antigen.