3.7.6Additional lessons
Adaptive Immune Response — IB Biology HL Revision Notes & Topical Questions
5 min read 4 parts Lesson 5 of 101
Curriculum Equation Key قوانين الرقم الهيدروجيني والاتزان الأيوني - pH & Acid-Base Equilibrium FormulasFast Exam Solution
pH = -log[H⁺] | pOH = -log[OH⁻] | pH + pOH = 14 | [H⁺][OH⁻] = 10⁻¹⁴
Word Equation & Conditions: الرقم الهيدروجيني = -لوغاريتم تركيز أيون الهيدروجين | pH + pOH = 14
Location & Specifications: الاتزان الأيوني، كيمياء 3 ثانوي، التحصيلي، و AP Chemistry.
Part 1 of 4Antigens and Self Recognition
The adaptive response begins when the body detects an antigen it does not recognise as its own.
Antigen
- Antigen An antigen is a molecule, usually a protein or glycoprotein, that the immune system can recognise and that triggers a response.
Self markers
- Self markers Every cell carries surface molecules unique to the individual,
- and lymphocytes that react to these are normally removed during development.
Non-self
- Non-self Molecules on pathogens, transplanted tissue or mismatched blood are not recognised as part of the body and provoke a response.
Blood groups
- Blood groups Red blood cells carry A and B antigens,
- and a person makes antibodies against the antigens they lack,
- which is why transfusions must be matched.
Part 2 of 4B Cell Activation and Antibody Production
1
A helper T cell and a B cell each have receptors specific to the same antigen, and the helper T cell is first activated by an antigen-presenting cell.
2
The T helper cell binds to the B cell and releases signalling proteins that activate it.
3
The activated B cell divides by mitosis, producing a clone of cells with identical antibody specificity.
4
Many clone cells differentiate into plasma cells, which secrete thousands of antibody molecules into the blood and tissue fluid.
5
Antibodies bind to antigens on the pathogen, helping phagocytes engulf it or preventing it from entering cells.
6
Some clone cells become memory cells that persist for years and provide long-term protection.
Part 3 of 4Primary and Secondary Responses
Primary and Secondary Responses
Primary response
- Primary response On first contact the matching B cells are rare, so antibody level rises slowly over several days, and the person usually feels ill.
Secondary response
- Secondary response Memory cells divide rapidly into plasma cells on re-exposure,
- so antibody appears within hours to days and reaches a much higher level.
Immunological memory
- Immunological memory Memory cells are the reason that a second infection with the same pathogen is often cleared before any symptoms appear.
Antigen variation
- Antigen variation Some pathogens, such as influenza viruses, change their surface antigens, so existing memory cells may no longer fit the new strain.
| Feature | Primary response | Secondary response |
|---|---|---|
| Lag before antibody | Several days | Hours to a few days |
| Peak antibody level | Lower | Much higher |
| Cells responsible | Naive B and T cells | Memory cells |
| Symptoms | Usually present | Usually absent |
Part 4 of 4Exam Checklist & Tips
3.7.6 – Key Points for the Exam
- Antibody A Y-shaped protein made by plasma cells that binds to a specific antigen.
- Clonal selection Activation and multiplication of only the lymphocytes that match the antigen.
- Memory cell A long-lived cell that gives a faster response on re-exposure.
- Primary response The slow, small response to a first encounter with an antigen.
- Secondary response The rapid, large response to a repeat encounter.
Common Mistakes
- Saying antibodies are made by T cells, when they are secreted by plasma cells derived from B cells.
- Stating that the body makes antibodies in advance against every pathogen;
- only a few B cells of each type exist before exposure.
- Believing memory cells make antibodies constantly; they only produce them after meeting the antigen again.
- Confusing the primary and secondary responses on a graph, forgetting that the secondary one rises faster and higher.
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