How does the body defend itself against pathogens, and how do vaccines and antibiotics help?
Option A Immunology and disease: pathogens and disease transmission; non-specific defences; the specific immune response; antibodies; active and passive immunity; vaccination; and antibiotics.
A focused answer to the Eduqas Component 3 Option A on immunology and disease. Covers pathogens, non-specific defences, the specific cellular and humoral immune response, antibodies, active and passive immunity, vaccination, herd immunity, and antibiotics.
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What this dot point is asking
Eduqas Option A wants you to describe pathogens and how disease spreads, explain non-specific and specific defences, explain antibodies, distinguish active and passive immunity, explain vaccination and herd immunity, and explain how antibiotics work. This is one of the three Section B options; study it if your school has chosen it.
Pathogens and transmission
A pathogen is a microorganism that causes disease: bacteria (for example tuberculosis), viruses (for example influenza), fungi and protoctists (for example the malaria parasite). Diseases spread by droplet infection, direct contact, contaminated food or water, vectors (such as mosquitoes) and body fluids. Pathogens cause harm by damaging cells or releasing toxins.
Non-specific defences
The specific immune response
The specific (adaptive) response targets a particular antigen:
- Antigen presentation: a phagocyte (antigen-presenting cell) displays the pathogen's antigen.
- T helper cells with a complementary receptor bind the antigen, become activated, and release cytokines that stimulate other cells.
- Clonal selection and expansion: B lymphocytes with complementary antibodies are selected and divide by mitosis into plasma cells and memory cells.
- Plasma cells secrete large amounts of specific antibody; memory cells persist for a faster secondary response.
- T cytotoxic (killer) cells destroy infected body cells directly.
The secondary response (on re-exposure) is faster and stronger because memory cells respond quickly.
Antibodies
Active and passive immunity, and vaccination
- Active immunity: the body makes its own antibodies after meeting an antigen, natural (after infection) or artificial (after vaccination). It is long-lasting because memory cells are made.
- Passive immunity: antibodies made by another organism are received, natural (mother to baby via the placenta or breast milk) or artificial (an injection of antibodies). It is short-lived (no memory cells).
A vaccine contains a harmless form of the antigen, triggering an active immune response and memory cells without disease. Herd immunity occurs when enough of a population is immune that the pathogen cannot spread easily, protecting those who are not immune.
Antibiotics
Antibiotics kill bacteria or stop them reproducing, often by targeting structures bacteria have but human cells lack (such as the peptidoglycan cell wall). They do not work on viruses. Overuse and misuse drive antibiotic resistance by natural selection, which is why courses should be completed and use limited.
Examples in context
Example 1. Why a vaccine needs a booster. Some vaccines need boosters to top up memory cells and keep antibody levels high enough, applying immunological memory to public-health practice.
Example 2. Anti-venom as passive immunity. A snakebite victim is given pre-made antibodies (anti-venom) for immediate protection, a fast but short-lived passive immunity because no memory cells are made.
Try this
Q1. State two non-specific defences of the body. [2 marks]
- Cue. Any two: the skin barrier; mucus; stomach acid; the inflammatory response; phagocytosis.
Q2. Explain why active immunity lasts longer than passive immunity. [2 marks]
- Cue. Active immunity produces memory cells, giving a rapid secondary response; passive immunity provides antibodies but no memory cells, and the antibodies are broken down.
Q3. Explain why antibiotics do not work against viral infections. [2 marks]
- Cue. Antibiotics target structures such as the bacterial cell wall and ribosomes; viruses lack these structures and replicate inside host cells.
Exam-style practice questions
Practice questions written in the style of WJEC Eduqas exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
Eduqas 20196 marksDescribe the role of B lymphocytes and T lymphocytes in the specific immune response to a bacterial infection.Show worked answer →
An antigen-presenting cell (for example a macrophage) displays the bacterial antigen on its surface.
A T helper cell with a complementary receptor binds the antigen and is activated; it releases cytokines that stimulate other cells.
This activates B lymphocytes with complementary antibodies (clonal selection); the B cell divides by mitosis (clonal expansion) into plasma cells and memory cells.
Plasma cells secrete large amounts of specific antibody that binds the antigen (agglutination, marking pathogens for destruction); memory cells remain for a faster secondary response.
T cytotoxic (killer) cells destroy infected cells directly.
Markers reward antigen presentation, T helper cells activating the response, B cells dividing into plasma and memory cells, plasma cells secreting specific antibody, and memory cells giving a secondary response.
Eduqas 20215 marksExplain the difference between active and passive immunity, giving an example of each, and state which provides longer-lasting protection.Show worked answer →
Active immunity is when the body makes its own antibodies after exposure to an antigen; it can be natural (after an infection) or artificial (after a vaccination).
Passive immunity is when antibodies made by another organism are introduced into the body; it can be natural (antibodies passed from mother to baby across the placenta or in breast milk) or artificial (an injection of antibodies, for example anti-tetanus serum).
Active immunity is longer lasting because the body produces memory cells, which give a rapid secondary response; passive immunity is short-lived because no memory cells are made and the introduced antibodies are broken down.
Markers reward active immunity making its own antibodies (with an example), passive immunity receiving antibodies from elsewhere (with an example), and active immunity lasting longer because of memory cells.
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Sources & how we know this
- Eduqas A Level Biology Specification (A400) — Eduqas (2015)