Biology · Interaction and interdependence

C3.2 — Defence against disease

Biology · SL / HL · syllabus-mapped notes

1. C3.2.1

   Pathogens as the cause of infectious diseases

   Define pathogen, name examples from each group, and place viruses and parasites correctly.

2. C3.2.2

   Skin and mucous membranes as a primary defence

   Explain how skin and mucous membranes prevent pathogens entering.

3. C3.2.3

   Sealing of cuts in skin by blood clotting

   Explain the clotting cascade and why clots matter for infection as well as blood loss.

4. C3.2.4

   Differences between the innate immune system and the adaptive immune system

   Contrast the innate and adaptive immune systems.

5. C3.2.5

   Infection control by phagocytes

   Explain how phagocytes engulf and digest pathogens.

6. C3.2.6

   Lymphocytes as cells in the adaptive immune system that cooperate to produce antibodies

   Explain antibodies' two functional parts, and why one lymphocyte makes only one type.

7. C3.2.7

   Antigens as recognition molecules that trigger antibody production

   Define antigen, state where antigens are found, and explain antibody-antigen binding.

8. C3.2.8

   Activation of B-lymphocytes by helper T-lymphocytes

   Explain how macrophages and helper T-lymphocytes activate the correct B-lymphocytes.

9. C3.2.9

   Multiplication of activated B-lymphocytes to form clones of antibody-secreting plasma cells

   Explain why activated B-lymphocytes clone before secreting antibody.

10. C3.2.10

    Immunity as a consequence of retaining memory cells

    Explain why long-term immunity depends on memory cells rather than antibodies.

11. C3.2.11

    Transmission of HIV in body fluids

    State the body fluids and routes by which HIV is transmitted.

12. C3.2.12

    Infection of lymphocytes by HIV with AIDS as a consequence

    Explain how HIV destroys helper T-cells, and how AIDS follows.

13. C3.2.13

    Antibiotics as chemicals that block processes occurring in bacteria but not in eukaryotic cells

    Explain how antibiotics target prokaryotes, and why they do not work against viruses.

14. C3.2.14

    Evolution of resistance to several antibiotics in strains of pathogenic bacteria

    Explain how multiple antibiotic resistance spreads, and the four measures needed.

15. C3.2.15

    Zoonoses as infectious diseases that can transfer from other species to humans

    Define zoonosis, give examples, and explain why they are a growing concern.

16. C3.2.16

    Vaccines and immunization

    Explain how vaccines produce immunity, and contrast primary with secondary responses.

17. C3.2.17

    Herd immunity and the prevention of epidemics

    Explain herd immunity and who it protects.

18. C3.2.18

    Evaluation of data related to the COVID-19 pandemic

    Evaluate pandemic data using rates rather than totals, and calculate percentage change.