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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.

Syllabus
First assessment 2025
Course
Biology SL
Level
SL

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 diseasesC3.2.2—Skin and mucous membranesC3.2.3—Blood clottingC3.2.4—Innate vs. adaptive immune systemC3.2.5—PhagocytesC3.2.6—LymphocytesC3.2.7—AntigensC3.2.8—B-lymphocyte activationC3.2.9—Clones of plasma cellsC3.2.10—Immunity from memory cellsC3.2.11—HIV transmissionC3.2.12—HIV infection and AIDSC3.2.13—AntibioticsC3.2.14—Antibiotic resistance evolutionC3.2.15—ZoonosesC3.2.16—Vaccines and immunizationC3.2.17—Herd immunityC3.2.18—COVID-19 pandemic data evaluation

Question 1

[Maximum number: 3]

Question (a)

(a)

Define pathogen.

[ 1 ]

Question (b)

(b)

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

[ 2 ]

Question 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.

Question 3

[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.

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