3.7.4Additional lessons
The Immune System — IB Biology HL Revision Notes & Topical Questions
5 min read 4 parts Lesson 3 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.
Section 1 of 4Innate Immunity
The innate system is the body's rapid first response to anything foreign.
Non-specific
- Non-specific The innate system recognises 'non-self' material in general and responds in the same way whatever the invader is.
Immediate
- Immediate Its responses begin within minutes to hours of an infection because no learning step is needed beforehand.
Present from birth
- Present from birth Everyone inherits innate defences, and they do not change in strength over a lifetime of exposure.
Barriers and chemicals
- Barriers and chemicals Skin, mucus, lysozyme and stomach acid act as first-line defences that keep many pathogens out.
Phagocytes
- Phagocytes White blood cells such as macrophages and neutrophils engulf and digest microbes that cross the barriers.
Section 2 of 4Adaptive Immunity
Adaptive Immunity
Specific
- Specific Lymphocytes respond to one particular antigen, so each pathogen is attacked by cells made for it.
Slower first response
- Slower first response On first exposure it takes days to select and multiply the right lymphocytes,
- so symptoms may appear before the pathogen is cleared.
Memory
- Memory Memory cells remain after infection, so a second exposure gives a much faster and larger response that often prevents symptoms.
Acquired during life
- Acquired during life The set of antigens a person can respond to grows with each infection or vaccination.
Cell types
- Cell types B lymphocytes make antibodies, and T lymphocytes either help other cells or destroy infected body cells.
Section 3 of 4Working Together
1
A pathogen passes the barriers and is detected by cells of the innate system, which respond at once.
2
Phagocytes engulf the pathogen and display some of its antigens on their surface membranes.
3
Lymphocytes with matching receptors bind these antigens and are activated, then divide to form clones.
4
Antibodies and cytotoxic cells eliminate the pathogen, and memory cells are kept for protection later.
| Feature | Innate | Adaptive |
|---|---|---|
| Specificity | Non-specific | Specific to one antigen |
| Speed of first response | Minutes to hours | Days |
| Memory | None | Yes, memory cells |
| Main cells | Phagocytes | B and T lymphocytes |
| Present at birth | Yes | Develops during life |
Section 4 of 4Exam Checklist & Tips
3.7.4 – Key Points for the Exam
- Innate immunity Fast, non-specific defence present from birth.
- Adaptive immunity Slower, specific defence involving lymphocytes and memory.
- Antigen A molecule that triggers an immune response.
- Non-self Any molecule or cell not recognised as part of the body.
- Memory cell A long-lived lymphocyte that allows a rapid response to a repeat infection.
Common Mistakes
- Thinking the innate system has memory; it responds equally strongly each time.
- Stating that the adaptive system acts first, when the innate system reacts earlier.
- Calling antibodies cells; they are proteins made by plasma cells.
- Treating the two systems as separate, although phagocytes activate lymphocytes.
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