4.3Body Systems and Plants
The Immune System — EST 2 Biology Revision Notes & Topical Questions
5 min read 8 parts Lesson 3 of 8 1 quiz
Lesson summary
The Immune System EST Biology notes: Describe nonspecific defenses of the body.Antibodies have two heavy and two light chains; variable regions bind antigen.Antibodies neutralize, agglutinate (clump) and tag pathogens for phagocytosis.The secondary response is faster, larger and …
- ABO blood groups
- Innate defenses
- Inflammation
- Humoral response
- Cell-mediated response
- Self vs non-self
Section 1 of 8The Immune System
Essential knowledge
Innate defenses
Innate defenses act immediately against any invader: skin and mucous membranes block entry, cilia sweep mucus, lysozyme digests bacterial walls, and stomach acid kills microbes. Neutrophils and macrophages engulf invaders; natural killer cells destroy virus-infected cells; interferons warn neighboring cells.
Inflammation
Inflammation damaged cells and mast cells release histamine, causing vasodilation and leaky capillaries; phagocytes move to the site. Pus contains dead white cells and bacteria.
Humoral response
Humoral response each B cell has a unique receptor. When a B cell binds its antigen and receives help from a helper T cell, it undergoes clonal selection and expansion, producing plasma cells that secrete antibodies into blood and lymph.
Cell-mediated response
Cell-mediated response cytotoxic T cells recognize antigens on MHC I of infected or cancer cells and kill them with perforin. Helper T cells coordinate both responses. Transplant rejection is largely T-cell mediated.
Self vs non-self
Self vs non-self lymphocytes that react strongly to self are eliminated during development. Failure leads to autoimmunity (multiple sclerosis, rheumatoid arthritis).
Immunological memory
Immunological memory after first exposure, memory B and T cells persist. On second exposure, antibody levels rise sooner and much higher. Vaccines exploit this; herd immunity protects those who cannot be vaccinated.
Blood types
Blood types red cells carry A, B, both or no antigens; plasma carries antibodies against absent antigens. Mismatched transfusion causes agglutination. Rh incompatibility can harm a second Rh+ fetus of an Rh- mother.
Pathogens
Pathogens viruses are nonliving particles of nucleic acid and a protein coat that replicate inside host cells (lytic or lysogenic cycles); bacteria are cells, some release toxins. Lymphatic organs include lymph nodes, spleen, thymus, tonsils and bone marrow.
Section 2 of 8Process & sequence
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Pathogen breaches barriers and enters tissues.
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Macrophages engulf it and present antigen on MHC proteins.
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Helper T cells recognize the antigen and release cytokines.
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B cells with matching receptors divide (clonal selection) into plasma cells and memory cells.
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Plasma cells secrete antibodies; cytotoxic T cells kill infected cells.
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Pathogen is cleared; memory cells remain for future protection.
Specific immune responsewrite these steps in this order; each step is a marking point.
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Antigen enters body
2
Macrophage presents antigen
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Helper T cell activated
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B and T cells cloned
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Antibodies and killer cells act
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Memory cells remain
Section 3 of 8Compare
| Line | Type | Examples |
|---|---|---|
| First | Nonspecific barriers | Skin, mucus, cilia, stomach acid, lysozyme in tears |
| Second | Nonspecific internal | Phagocytes, inflammation, fever, interferons, complement |
| Third | Specific (adaptive) | B cells and antibodies, T cells, memory cells |
| Type | How obtained | Memory cells? | Example |
|---|---|---|---|
| Natural active | Infection | Yes | Recovering from chickenpox |
| Artificial active | Vaccination | Yes | Measles vaccine |
| Natural passive | Antibodies from mother | No | Via placenta or breast milk |
| Artificial passive | Injected antibodies | No | Antivenom |
Passive immunity is immediate but short-lived.
Section 4 of 8Worked examples
Worked examples
A graph shows antibody levels after two exposures to the same antigen 4 weeks apart. Describe and explain the difference.
- After the first exposure there is a lag of about a week and a low peak of antibody: naive B cells must be selected and cloned.
- After the second exposure antibody rises within days to a far higher and more sustained level because memory B cells rapidly divide into plasma cells.
- This is the secondary response.
Why can a person with type A blood not receive type B blood?
- Type A plasma contains anti-B antibodies.
- Donated type B red cells carry B antigens,
- so the antibodies bind them, causing agglutination and destruction of the donated cells,
- which can block vessels and be fatal.
Section 5 of 8Keep going
The Immune System EST Biology: what to do next
These The Immune System EST Biology notes covered the key ideas, worked examples and exam technique for this topic. Check your The Immune System EST Biology understanding with the practice questions below, then reread any The Immune System EST Biology point you were unsure about before moving on.
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Previous lesson: 4.2 Circulation and gas exchange
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Next lesson: 4.4 Excretion and homeostasis
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Course: EST 2 Biology — all units
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Official syllabus: OpenStax free science textbooks
Section 6 of 8Key terms
Section 7 of 8Command terms
Command terms
Identify / Describe (FRQ)
A short, specific statement; describing requires relevant characteristics, not a single word.
Explain / Justify (FRQ)
Give the cause-and-effect reasoning or evidence; a restated fact does not score.
Calculate
Show setup, substitution and the answer with units.
Predict
State the expected outcome; add a reason only if asked to justify.
MCQ technique
Read every option; eliminate distractors that are true statements but do not answer the question; watch for NOT/EXCEPT.
Section 8 of 8Exam technique
Keywords the mark scheme looks for in this lesson
Keywords the mark scheme looks for in this lesson
Pathogen · Antigen · Antibody · Phagocytosis · B lymphocyte · T lymphocyte · Memory cell · Vaccine · Inflammation · MHC
Learn each definition in the Key words tab exactly; a missing keyword in a definition usually loses the mark.
How to get full marks (examiner guidance)
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Answer exactly what is asked; extra correct material does not earn credit, and contradictory statements can cancel credit (AP FRQ).
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Use precise vocabulary (e.g. “active site”, “concentration gradient”, “allele”), never “it/stuff/things”.
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Show units and working in calculations.
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In MCQs, predict the answer before reading the options, then eliminate.
Marked practiceQuizzes for this lesson
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