C3.2  Defense Against Disease

Guiding Questions:  
Guiding questions help students view the content of the syllabus through the conceptual lenses of both the themes and the levels of biological organization.

• How do body systems recognize pathogens and fight infections?
• What factors influence the incidence of disease in populations?

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​Linking Questions:  
Linking questions strengthen students’ understanding by making connections between topics.  The ideal outcome of the linking questions is networked knowledge.

• How do animals protect themselves from threats? 
• How can false-positive and false-negative results be avoided in diagnostic tests? 

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Resources:

• At SHS, Topic C3.2 is taught in the Natural Selection, Pathogens and Innate Immunity and Adaptive Immunity units. 
• Quizlet study set for this topic.  Coming soon!
• View the general sequence of the SHS course
• View the SHS units mapped to the IB Biology curriculum roadmap

C3.2.1— Pathogens as the cause of infectious diseases.

• List three major types of cause of disease.
• Define “pathogen.”
• List major pathogen types.​

​C3.2.2— Skin and mucous membranes as a primary defense.

• Define “primary defense.”
• Outline the role of skin, sebaceous glands and mucous membranes in the defense against pathogens.

C3.2.3— Sealing of cuts in skin by blood clotting.

• State two benefits of blood clotting when skin is cut.
• Outline two roles of platelets in the blood clotting cascade.
• Describe the blood clotting cascade, including the role of platelets, clotting factors, prothrombin, thrombin, fibrinogen and fibrin.

C3.2.4— Differences between the innate immune system and the adaptive immune system.

• Distinguish between innate and adaptive immunity, including the types of cells and timing of response to infection.​

​C3.2.5-- Infection control by phagocytes.

• Outline the function of phagocytic white blood cells in defense against pathogens.
• Describe the process by which a macrophage destroys a pathogen.​​​

​C3.2.6- Lymphocytes as cells in the adaptive immune system that cooperate to produce antibodies.

• Outline the structure and function of  lymphocyte cells. 
• State the location of lymphocytes in the body.
• Define “specific” in relation to an immune response.
• Define “antibody.”
• Outline the role of lymphocytes in producing antibodies to a specific pathogen.

C3.2.7- Antigens as recognition molecules that trigger antibody production.

• Define antigen.
• Describe the structure of antigens.
• Describe the cause and consequence of an antibody binding to an antigen. 
• Outline the difference between the ABO blood antigens.
• State the four human ABO blood types.
• Describe the consequence of mismatched blood transfusions, including agglutination and hemolysis.

​C3.2.8- Activation of B-lymphocytes by helper T-lymphocytes.

• Describe activation of helper T lymphocytes by a macrophage cell. 
• Outline the role of the helper T lymphocytes in the activation of B lymphocytes.
• State that B-cells secrete antibodies only when they have been activated by a helper T-cell. 

C3.2.9- Multiplication of activated B-lymphocytes to form clones of antibody-secreting plasma cells.

• Describe clonal selection of plasma B cells.
• State the plasma B-cells produce antibodies only after they have grown and differentiated for protein synthesis.

C3.2.10- Immunity as a consequence of retaining memory cells.

• Define immunity.
• Outline the role of memory B cells in maintaining immunity.
• Compare the primary and secondary immune responses to a specific pathogen in regards to magnitude, speed and duration.
  

C3.2.11-  Transmission of HIV in body fluids.

• List mechanisms of HIV transmission. ​

C3.2.12- Infection of lymphocytes by HIV with AIDS as a consequence.

• Describe the consequences of HIV on the immune system.
• Outline the relationship between HIV and AIDS.

C3.2.13-  Antibiotics as chemicals that block processes occurring in bacteria but not in eukaryotic cells.

• Outline the natural function of antibiotics when secreted from saprotrophic fungi. 
• Outline the function of antibiotics when used in medical treatment. 
• State why antibiotics fail to control viral infections.

C3.2.14- Evolution of resistance to several antibiotics in strains of pathogenic bacteria.

• Describe how natural selection leads to the development of antibiotic resistance in bacteria.
• Discuss the medical cause and consequences of evolution of antibiotic resistance.

C3.2.15- Zoonoses as infectious diseases that can transfer from other species to humans.

• Outline the major routes of pathogen transmission.
• Outline the reason why most infectious agents are species specific. 
• Define zoonosis.
• List an example of a zoonotic pathogen. 
• List two reasons that will lead to an increase in appearance of zoonotic diseases in humans.​

C3.2.16- Vaccines and immunization.

• Define immunization.
• Outline the different classes of vaccine active ingredients.
• Explain the principle of vaccination, with reference to the primary and secondary immune response. ​

​​​​C3.2.17- Herd immunity and the prevention of epidemics.

• Define herd immunity.
• Explain how herd immunity limits the potential of disease transmission. 
• Define Ro (pronounced 'R-nought”). 
• Given an Ro value, estimate the percentage of people in a population who must be immune to reach herd immunity.​

 ​​​​C3.2.18- Evaluation of data related to the COVID-19 pandemic.

• State how to express one number as a percentage of a second number. 
• State how to calculate percentage change.
• State how to calculate percentage difference.
• Evaluate data related to the COVID-19 pandemic using percentage change and percentage difference. ​