IBBiologySLExam QuestionsInteraction & InterdependenceDefence Against Disease

Syllabus Edition

First teaching 2023

First exams 2025

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Defence Against Disease (SL IB Biology)

Exam Questions

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Defence Against Disease

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Defence Against Disease

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1
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Which component of blood has a role in preventing pathogens from entering the body?

  • Red blood cells

  • Blood plasma

  • Platelets

  • White blood cells

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2
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What is the principle purpose of sebum secretions onto the surface of the skin?

  • To prevent microorganisms from sticking to the skin.

  • To lower skin pH, which slows down the growth rate of microorganisms.

  • To provide a surface texture to the skin that aids the evaporation of sweat. 

  • To assist in the formation of blood clots as a way of sealing wounds after a cut or graze. 

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3
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This question is about the proteins involved in blood clotting. 

Which shows the 3 boxes on the left joined to the appropriate one on the right?

fibrin-mcq

  • E4Y3ewux_e-3a

  • vaLVpSxr_e-3b

  • Fw4r7nNz_e-3c

  • x~nGGbA3_e-3d

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4
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Which phrase best fits into the gap in the following sentence?

The shape of antibody molecules gives each one a particular 3-D configuration. This allows each antibody to be ______________ each individual pathogen. 

  • ...well suited to...

  • ...specific to...

  • ...functional against...

  • ...the same shape as...

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51 mark

Antibodies can protect the body from pathogens in several ways.

Which of the options below will not occur following antigen-antibody binding?

  • Increased susceptibility to phagocytosis.

  • Neutralisation of toxins to make them harmless.

  • Clonal expansion of T-lymphocytes

  • Agglutination of bacteria to reduce their spread.

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61 mark

A child is given a vaccine for a viral disease. A few months later she is in contact with the same virus.

What is the expected response to the second contact with the virus?

  • Increased number of T-lymphocytes.

  • Large numbers of antibodies are released.

  • Large numbers of antigens are released.

  • Increased number of B-lymphocytes.

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71 mark

When a B-lymphocyte is activated by an antigen, what action is taken?

  • It engulfs the infected body cell which displays a complementary antigen.

  • It secretes signalling proteins that stimulate T-lymphocytes to produce plasma cells.

  • It divides repeatedly to form clones of genetically identical plasma cells.

  • It attaches to the infected cell displaying the antigen and destroys it.

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81 mark

Which type of molecule is most important to directly identify a cell as non-self?

  • Proteins

  • Phospholipids

  • Carbohydrates

  • Nucleic acids

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91 mark

The amount of antibody produced in response to an antigen in a vaccine is shown in the graph below.

unnamed

Which statement about the graph is correct?

  • The second exposure to the antigen occurred at 25 days.

  • T-helper lymphocytes are activated on day 12.

  • Memory cells for this antigen are present in the body within 20 days.

  • The secondary immune response begins at around day 35.

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10
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Scientists use theories to explain observed phenomena. Which of the following combinations of observed phenomenon and explanation shows how scientists developed the theory that explains antibiotic resistance in bacteria?

  Observed phenomenon Explanation
A. Resistance to an antibiotic appears soon after an antibiotic is first used Bacteria respond to a new antibiotic by developing resistance
B. Resistance to an antibiotic appears soon after an antibiotic is first used Bacteria with alleles that provide resistance to the antibiotic survive treatment and pass on their alleles
C. Bacteria with alleles that provide resistance to the antibiotic survive treatment and pass on their alleles The frequency of resistant alleles increases in a bacterial population
D. Antibiotic resistance in bacteria is on the increase in hospitals Patients in hospitals are more susceptible to infection than the general population.

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    1
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    Which of the following are considered primary defence against infectious disease?

    • Skin and mucous membranes.

    • Hair and skin.

    • Phagocytes and fever.

    • Lymphocyte production of antibodies.

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    2
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    Bacteria and viruses are the main pathogens in humans. Antibiotics can be used to treat bacterial infections but not viral infections.

    Which of the following statements explains why?

    • Viruses need a host to survive.

    • Viruses consist of just nucleic acid and a protein coat.

    • Bacteria have peptidoglycan cell walls.

    • Viruses are significantly smaller than bacteria.

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    3
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    An antibiotic sensitivity test was performed on bacteria isolated from a patient’s throat.

    The diagram shows the results of the four antibiotics tested.

    dy6mBDIT_1

    Which one should be used to treat the disease?

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      4
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      When a phagocyte responds to the presence of a pathogen the following events happen:

      1. Enzymatic digestion. 
      2. Endocytosis.
      3. Phagocyte membrane extends out.
      4. Vacuole formation.

      Which of the following would be the correct order of events?

       

      first

      →

      →

      last

      A

      III

      I

      IV

      II

      B

      III

      II

      IV

      I

      C

      II

      IV

      I

      III

      D

      II

      III

      IV

      I

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        5
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        Which of these statements correctly describes a lymphocyte?

        • They have many mitochondria to produce ATP to allow endocytosis of pathogens.

        • They have many lysosomes containing hydrolytic enzymes to digest pathogens.

        • They provide specific defence against disease-causing organisms.

        • They are white blood cells with a lobed nucleus.

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        6
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        The diagram represents the process of blood clot formation.

        9kfxWIkU_2

        What is the correct sequence of events 

          I II III IV
        A Prothrombin Thrombin Fibrin Fibrinogen
        B Clotting factors Thrombin Fibrinogen Fibrin
        C Fibrin Fibrinogen Thrombin Clotting factors
        D Clotting factors Thrombin Fibrin Fibrinogen

         

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          71 mark

          What is adaptive immunity?

          • Treating a specific disease through use of antibiotics.

          • Production of monoclonal antibodies.

          • Production of antibodies by lymphocytes.

          • Endocytosis of pathogens by phagocytes.

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          8
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          Which of the following is not a contributing factor towards the development of antibiotic resistance in bacteria?

          • Stopping a course of antibiotics once symptoms improve.

          • Development of new antibiotics.

          • Natural selection which favours mutations in bacteria.

          • Overuse of antibiotics in agriculture

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          9
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          The following statements are about people infected with HIV/AIDS.

          1. They will have symptoms.
          2. They can be treated and completely cured.
          3. They may live for many years after infection.

          Which ones are correct?

          • I only

          • I and II

          • I and III

          • III only

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          101 mark

          The bacterium Staphylococcus aureus (S. aureus) is one of the main human pathogens and can cause many serious infectious diseases. Mutations in the mec A gene has allowed S.aureus to become resistant to many antibiotics. The table below shows a (Clustal W) partial nucleotide sequence alignment of mec A for different isolates of S. aureus. The drug resistant strain has a base substitution mutation (shown in bold) which changes the amino acid residue from serine to threonine.

          S. aureus isolate 1

          AAC GGA ACC GGT AAG GAC GCG ATC ACC AGC

          S. aureus isolate 2

          AAC GGA ACC GGT AAG GAC GCG ATC ACC AGC

          S. aureus isolate 3

          AAC GGA ACC GGT AAG GAC GCG ATC ACC AGC

          Drug resistant strain

          AAC GGA ACC GGT AAG GAC GCG ATC ACC ACC

          Which of the following statements most likely explains how an amino acid change can cause antibiotic resistance?

          • Alteration of the drug target site which prevents binding

          • Prevents the bacterial cell from synthesising the target protein

          • Bacteria produce less of the target protein 

          • Can introduce a stop codon

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          111 mark

          Which of the following statements are true for antigens?

          1. Antigens are proteins, glycolipids or glycoproteins found on the surface of the cell membrane
          2. The symptoms of allergies, such as a runny nose or itchy eyes, are directly caused by antigens
          3. Blood cells have antigens which determine blood type

          • All of the above

          • I and II only

          • I and III only

          • II only

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          121 mark

          Identify which of the combinations of blood types are compatible for a blood transfusion from donor to recipient.

           

          Donor

          Recipient
          A

          A

          B
          B

          AB

          B
          C

          O

          AB
          D

          A

          O

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            131 mark

            What is required to initiate a specific immune response?

            • Phagocytes engulf pathogens

            • T-helper cells are activated

            • B-cells mature

            • Signalling proteins are released

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            141 mark

            Which of the following statements about plasma cells is incorrect?

            • Plasma cells contain large amounts of rough endoplasmic reticulum

            • Plasma cells originate from B-cells

            • Plasma cells divide by mitosis to produce memory cells

            • Plasma cells produce specific antibodies

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            151 mark

            Which words or phrases can be used to fill spaces (I) and (II) in the following sentence?

            Scientists have particular concerns about the spread of diseases in animals that may result in …....(I)....... transfer of pathogens to humans. Examples of these diseases include tuberculosis and .......(II)........

             

            I

            II
            A

            Zoonotic

            Rabies
            B

            Species-specific

            COVID-19
            C

            Zoonotic

            		 Measles
            D

            Mutated

            		 Japanese encephalitis

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              161 mark

              Which of the following would reduce the likelihood of antibiotic resistance evolving?

              1.  Reducing the use of antibiotics.
              2. Taking measures to reduce the spread of infectious bacteria.
              3. Researching new antibiotics.

              • I only

              • I and II only

              • I and III only

              • I, II, and III

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              171 mark

              Research was carried out into the emergence of antibiotic resistance in the antibiotics used to treat infection X between the years 2000-2016.

              Different antibiotics were recommended during different time periods due to concerns about developing resistance. Note that ciprofloxacin is used to treat a range of infections and not just infection X, while tetracycline is not used to treat infection X but is used to treat many other mild infections.

              Some of the results of the research are shown below.

              6yLkOdKd_4

               What conclusion can be drawn from these results?

              • Resistance evolves when the use of an antibiotic increases.

              • Ceftriaxone should be used to treat all infections.

              • Infection X should not be treated with antibiotics.

              • Tetracycline should no longer be used.

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              1
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              Routine use of antibiotics in animal feed has been common practice in livestock farming, but is now no longer widely practised.

              Which statements best explain why?

              1. Use of antibiotics allows sub-standard hygiene conditions for farm animals to be kept in
              2. It encourages antibiotic resistance
              3. It is expensive
              4. Farm animals get more nutrition from antibiotic-free feed

              • II. and III.

              • I. and II.

              • I. II. and III.

              • All of them

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              2
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              The image below shows a petri dish viewed from above. A lawn of bacteria is growing across the whole surface of the agar. 

              Different antibiotics, X and Y were applied to the agar before inoculating it with bacteria. Both antibiotics were applied to the discs of filter paper at the same concentration. 

              The plates were then incubated for 24 hours at 25°C. Zones of inhibition (areas of the dish with no bacterial growth) are shown on the diagram. cNjoDURL_h-2

              After growth, the following results were obtained. 

              Antibiotic Diameter of zone of inhibition / cm
              X 2.0
              Y 6.0

              How many times more effective was antibiotic Y versus antibiotic X in this study? 

              • 3×

              • 9×

              • 12×

              • 18×

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              3
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              Which is a reason why fungi such as Penicillium have evolved to produce antibiotics?

              • To destroy bacteria that could otherwise feed on Penicillium

              • To destroy bacteria that could otherwise harm the fungus's host organisms

              • To destroy saprophytic bacteria as a way of Penicillium out-competing bacterial competitors for food

              • To kill viruses that may otherwise be pathogenic to the fungus

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              4
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              Some bacteria develop resistance to antibiotics by forming biofilms, which are large colonies of bacteria clumped together.

              Which statement best explains how forming a biofilm might give a bacterial species resistance to antibiotics?

              • Antibiotic molecules are physically unable to reach all bacterial cells in a biofilm

              • Biofilms secrete chemicals which break down the antibiotic

              • Biofilms remain in a host organism for many years

              • Bacterial cells in a biofilm go into a suspended state but can become infectious again at a later stage

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              5
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              Lefamulinâ„¢ is a newly-developed antibiotic that binds to the 50S bacterial ribosomal subunit.

              It was approved by the US Food and Drug Administration (FDA) in August 2019 for the treatment of pneumonia.

              Which is the mode of action of Lefamulinâ„¢?

              • Inhibits bacterial protein synthesis

              • Perforates the bacterial cell membrane

              • Prevents the bacterial cell wall forming

              • Inhibits replication of bacterial DNA

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              61 mark

              If a patient is given a transfusion of the wrong blood type, an immune response results. This response involves agglutination followed by haemolysis, where red blood cells are destroyed and blood may then coagulate. Blood typing involves mixing blood samples with antibodies. The diagram below shows the results of a blood typing test, showing the reactions between blood types (rows) and antibody serums (columns). The first column shows the appearance of each blood sample before testing occurred.11-1_q3h

              Identify the row in the table below that correctly identifies the blood type of blood samples I - IV.

                I II III IV
              A O O O AB
              B A B AB O
              C AB AB AB O
              D B A AB O

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                71 mark

                When a phagocyte responds to the presence of a pathogen, the following events happen:

                1. Enzymatic digestion
                2. Exocytosis
                3. Phagocytosis
                4. Vacuole formation
                5. Endocytosis

                Which of the following would be the correct order of events?

                  Step 1 Step 2 Step 3 Step 4
                A V I IV III
                B V IV I II
                C III II V I
                D III V I IV

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                  8
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                  The pneumococcal conjugate vaccine (PCV13) provides protection against infection caused by the bacterium Streptococcus pneumoniae. The graph shows the number of cases of invasive pneumococcal disease (IPD) caused by antibiotic resistant S. pneumoniae before and after the introduction of PCV13.

                  h-4-2

                  Which statement correctly explains the number of cases of IPD caused by antibiotic resistant S. pneumoniae after the introduction of PCV13?

                  • The vaccine is killing the bacteria that cause the infections.

                  • The vaccine has reduced the use of antibiotics, meaning that resistance alleles are no longer advantageous.

                  • The vaccine has reduced the use of antibiotics and the bacteria respond by becoming less resistant.

                  • The vaccine has reduced the use of antibiotics, preventing resistance alleles from being passed on when bacteria divide. 

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