Lesson 1 of 24
Why is the human body described as a host?
Cram notes for Option A, Immunology and disease, in WJEC A level Biology Unit 4.
Many organisms live in or on the body, so it is their : gut bacteria such as E. coli, skin flora, mites and parasites such as tapeworms. Most are harmless or useful; disease follows when the balance is upset.
Lesson 2 of 24
What do the key terms about disease mean?BioWelsh recommended
We recommend revising this because it has appeared regularly in past papers. Asked in 5 of 7 WJEC exam series (2017 to 2025), 8 marks in total. This is a revision priority, not a prediction of your exam.
We recommend revising this because it has appeared regularly in past papers. Asked in 5 of 7 WJEC exam series (2017 to 2025), 8 marks in total. This is a revision priority, not a prediction of your exam.
- : causes disease. : can be passed between individuals.
- : infected, no symptoms, can pass it on. : long-term that is a constant source of infection.
- : always present at a steady level. : a large, rapid rise in cases. : an across many countries.
- : an organism that transmits a , such as a mosquito. : a damaging molecule made by a .
- : triggers an immune response. : a protein that binds one specific . : forms with different surface .
- : weakened or killed , or toxoids that give . : kills or stops bacteria. : the drug no longer works.
We recommend revising this because it has appeared regularly in past papers. Asked in 5 of 7 WJEC exam series (2017 to 2025), 8 marks in total. This is a revision priority, not a prediction of your exam.
Lesson 3 of 24
How is cholera caught, prevented and treated?
: the bacterium cholerae infects the small intestine. It spreads by the faecal-oral route in contaminated water. Its makes cells lose chloride ions and water follows, causing severe watery diarrhoea and dehydration.
We recommend revising this because it has appeared regularly in past papers. Asked in 3 of 7 WJEC exam series (2017 to 2025), 6 marks in total. This is a revision priority, not a prediction of your exam.
Prevention: clean water, sewage treatment, hygiene, and an oral in two doses. Treatment: oral rehydration solution or a drip, plus . Rehydration rate = (volume per kg × body mass) ÷ hours.
Lesson 4 of 24
How does tuberculosis spread and how is it controlled?
: the bacterium Mycobacterium tuberculosis infects the lungs. It spreads in airborne droplets, most in crowded, poorly ventilated housing and in people with weakened immunity, such as with HIV.
We recommend revising this because it has appeared regularly in past papers. Asked in 2 of 7 WJEC exam series (2017 to 2025), 9 marks in total. This is a revision priority, not a prediction of your exam.
Prevention: (weakened M. bovis), and contact tracing. Treatment: several together for at least six months, so is unlikely.
Lesson 5 of 24
How was smallpox wiped out?
: variola virus (DNA), spread by droplets and contact, causing a blistering rash. Eradicated in 1980 by with vaccinia virus and ring , because it had one stable , no animal , no and an easily recognised rash.
Lesson 6 of 24
Why does influenza keep coming back?
: an RNA virus infecting the airway epithelium, spread by droplets and surfaces. Its are (H) and (N). Birds and pigs are .
The diagram below shows and shift.
We recommend revising this because it has appeared regularly in past papers. Asked in 4 of 7 WJEC exam series (2017 to 2025), 9 marks in total. This is a revision priority, not a prediction of your exam.
- : small change H and N a little each year, so a new is needed every year.
- Shift: two subtypes in one cell swap RNA pieces, giving a new H and N combination that can cause a .
Lesson 7 of 24
How is malaria transmitted and controlled?
: the protoctist Plasmodium, carried by the female Anopheles mosquito (the ). in the tropics, in wet seasons.
The diagram below shows the life cycle of Plasmodium.
- injected when the mosquito feeds; they reproduce asexually in liver cells, making .
- reproduce asexually in red blood cells, which burst every few days, causing fever.
- Some become , taken in by a mosquito; gametes fuse in its gut and form in the salivary glands.
Prevention: bed nets, insecticide, draining water, fish or oil for larvae, sterile males, drugs for travellers. Treatment: artemisinin combinations. give only partial protection: many , change between stages, parasite hidden inside cells.
Lesson 8 of 24
How do the five named diseases compare?BioWelsh recommended
We recommend revising this because it has appeared regularly in past papers. Asked in 3 of 7 WJEC exam series (2017 to 2025), 8 marks in total. This is a revision priority, not a prediction of your exam.
We recommend revising this because it has appeared regularly in past papers. Asked in 3 of 7 WJEC exam series (2017 to 2025), 8 marks in total. This is a revision priority, not a prediction of your exam.
| Disease | Organism | Spread by | Key control |
|---|---|---|---|
| Bacterium | Contaminated water | Clean water, sewage treatment, rehydration | |
| Tuberculosis | Bacterium | Airborne droplets | , long course |
| Virus (DNA) | Droplets and contact | ; eradicated | |
| Virus (RNA) | Droplets and surfaces | Annual , hygiene | |
| Protoctist | Mosquito | Nets, insecticide, antimalarial drugs |
Lesson 9 of 24
How do viruses reproduce and cause disease?
The diagram below shows the and cycles.
- : the virus attaches, injects its nucleic acid, the copies it and makes proteins, new particles assemble and leave by or budding.
- : viral DNA joins a chromosome and is copied with it, with no symptoms, until a trigger starts the (herpes, HIV).
Viruses cause disease by lysing cells, by toxic effects on metabolism, by transforming cells into cancer cells (HPV) and by suppressing the immune system (HIV destroys ). Cells infected after n cycles = burst size to the power n.
Lesson 10 of 24
What are antibiotics, and how are they classified?BioWelsh recommended
We recommend revising this because it has appeared regularly in past papers. Asked in 3 of 7 WJEC exam series (2017 to 2025), 13 marks in total. This is a revision priority, not a prediction of your exam.
We recommend revising this because it has appeared regularly in past papers. Asked in 3 of 7 WJEC exam series (2017 to 2025), 13 marks in total. This is a revision priority, not a prediction of your exam.
kill bacteria (); ones stop them dividing (tetracycline). many kinds of bacteria; a few. do not affect viruses.
The graph below shows the effect of each type on living bacteria.
- No : numbers keep rising.
- : the line goes flat.
- : the line falls.
Lesson 11 of 24
How does the cell wall of Gram-negative bacteria protect them?
The diagram below compares and walls.
We recommend revising this because it has appeared regularly in past papers. Asked in 3 of 7 WJEC exam series (2017 to 2025), 13 marks in total. This is a revision priority, not a prediction of your exam.
- : thick , stains purple, more easily reached by and .
- : thin inside an outer membrane of lipid and , stains red.
- The outer membrane keeps out many and .
Lesson 12 of 24
How do penicillin and tetracycline work?BioWelsh recommended
We recommend revising this because it has appeared regularly in past papers. Asked in 3 of 7 WJEC exam series (2017 to 2025), 13 marks in total. This is a revision priority, not a prediction of your exam.
The diagram below shows how kills a growing bacterium.
We recommend revising this because it has appeared regularly in past papers. Asked in 3 of 7 WJEC exam series (2017 to 2025), 13 marks in total. This is a revision priority, not a prediction of your exam.
- binds to the of , so cross-links cannot form.
- The wall weakens, water enters by and the cell bursts: .
The diagram below shows tetracycline at a .
We recommend revising this because it has appeared regularly in past papers. Asked in 3 of 7 WJEC exam series (2017 to 2025), 13 marks in total. This is a revision priority, not a prediction of your exam.
- Tetracycline binds to the 30S subunit and blocks the A site, so tRNA cannot attach.
- Protein synthesis stops; it binds reversibly, so it is and .
Lesson 13 of 24
How do you find out which antibiotic works best?BioWelsh recommended
We recommend revising this because it has appeared regularly in past papers. Asked in 3 of 7 WJEC exam series (2017 to 2025), 10 marks in total. This is a revision priority, not a prediction of your exam.
The diagram below shows disc and gradient-strip tests.
We recommend revising this because it has appeared regularly in past papers. Asked in 3 of 7 WJEC exam series (2017 to 2025), 10 marks in total. This is a revision priority, not a prediction of your exam.
- Discs of on a lawn of bacteria: the bigger the , the more effective the . No zone .
- A gradient strip gives the where the meets the strip.
We recommend revising this because it has appeared regularly in past papers. Asked in 3 of 7 WJEC exam series (2017 to 2025), 10 marks in total. This is a revision priority, not a prediction of your exam.
Use and at about 25 °C in school. Zone area = πr², assuming a perfect circle. Dose = mg per kg × body mass; volume = dose ÷ concentration.
Lesson 14 of 24
How has the overuse of antibiotics spread resistance?
The diagram below shows selection for .
- A random gives one bacterium .
- The kills the susceptible bacteria; the one survives, reproduces and passes on the .
- can also spread on between bacteria.
Overuse: for viral infections, not taking them as prescribed, use in farming. Examples: , C. difficile, drug- . : , changed , fewer . Tetracycline : pumping it out, protecting the .
Lesson 15 of 24
How does the body keep pathogens out?
Non-specific barriers: skin (keratin, in ), skin flora, mucus and cilia, in tears and saliva, stomach acid, clotting, and .
The diagram below shows .
- The recognises the bacterium's and engulfs it into a phagosome.
- Lysosomes fuse with it and their digest the bacterium; then present its .
Lesson 16 of 24
How does the body recognise a foreign antigen?
The immune system ignores self molecules and responds to non-self . come from bone marrow : B cells mature in the bone marrow and T cells in the thymus. present to , whose activate B cells, and .
Lesson 17 of 24
How do B cells and antibodies fight infection?BioWelsh recommended
We recommend revising this because it has appeared regularly in past papers. Asked in 4 of 7 WJEC exam series (2017 to 2025), 13 marks in total. This is a revision priority, not a prediction of your exam.
The diagram below shows the .
We recommend revising this because it has appeared regularly in past papers. Asked in 4 of 7 WJEC exam series (2017 to 2025), 13 marks in total. This is a revision priority, not a prediction of your exam.
- by a ; a binds and releases .
- of the B cell with a complementary , then by mitosis.
- secrete ; memory B cells remain.
The diagram below shows an .
We recommend revising this because it has appeared regularly in past papers. Asked in 2 of 7 WJEC exam series (2017 to 2025), 8 marks in total. This is a revision priority, not a prediction of your exam.
- Two heavy and two light polypeptide chains held by disulphide bridges.
- form two binding sites complementary to one ; the constant region is the same across the class.
- Two binding sites let agglutinate bacteria, so engulf them in clumps.
Lesson 18 of 24
How do T cells destroy infected cells?BioWelsh recommended
We recommend revising this because it has appeared regularly in past papers. Asked in 4 of 7 WJEC exam series (2017 to 2025), 13 marks in total. This is a revision priority, not a prediction of your exam.
The diagram below shows the .
We recommend revising this because it has appeared regularly in past papers. Asked in 4 of 7 WJEC exam series (2017 to 2025), 13 marks in total. This is a revision priority, not a prediction of your exam.
- Infected or cancer cells display foreign on their surface.
- A with a complementary binds; T helper make it divide.
- It releases , which makes holes in the membrane, and the cell dies. Memory T cells remain.
Lesson 19 of 24
Why is the second response to an antigen faster and bigger?BioWelsh recommended
We recommend revising this because it has appeared regularly in past papers. Asked in 5 of 7 WJEC exam series (2017 to 2025), 15 marks in total. This is a revision priority, not a prediction of your exam.
The graph below compares the primary and secondary responses.
We recommend revising this because it has appeared regularly in past papers. Asked in 5 of 7 WJEC exam series (2017 to 2025), 15 marks in total. This is a revision priority, not a prediction of your exam.
- Primary: a long (, and expansion), then a small peak of . Symptoms appear.
- Secondary: respond at once, so a short , faster production and a much higher concentration that lasts longer. No symptoms.
We recommend revising this because it has appeared regularly in past papers. Asked in 5 of 7 WJEC exam series (2017 to 2025), 15 marks in total. This is a revision priority, not a prediction of your exam.
Lesson 20 of 24
What is the difference between active and passive immunity?
Active: you make your own and ; slow to start, long-lasting (natural: infection; artificial: ). Passive: you receive ; immediate but short-lived, no (natural: , breast milk; artificial: injected ).
The graph below shows levels after a bite from a rabid animal.
- Injected protect at once but are broken down within weeks.
- The gives no for about a week, then a high, lasting level with .
Lesson 21 of 24
How does vaccination protect against disease?
A gives the without the disease, so a makes . Types: live (MMR, ), killed, toxoid (tetanus), (HPV), mRNA. protects unborn babies. Boosters cause a and top up .
Lesson 22 of 24
Why do some vaccination programmes work better than others?BioWelsh recommended
We recommend revising this because it has appeared regularly in past papers. Asked in 4 of 7 WJEC exam series (2017 to 2025), 9 marks in total. This is a revision priority, not a prediction of your exam.
We recommend revising this because it has appeared regularly in past papers. Asked in 4 of 7 WJEC exam series (2017 to 2025), 9 marks in total. This is a revision priority, not a prediction of your exam.
A works best when it is highly , the has one stable , it does not hide inside cells, there is no animal and uptake is high.
The diagram below shows .
- With low uptake, infection passes through the many unvaccinated people.
- With high uptake, it soon meets only immune people and dies out, protecting those who cannot be vaccinated.
Lesson 23 of 24
What ethical issues must vaccination programmes consider?BioWelsh recommended
We recommend revising this because it has appeared regularly in past papers. Asked in 3 of 7 WJEC exam series (2017 to 2025), 7 marks in total. This is a revision priority, not a prediction of your exam.
We recommend revising this because it has appeared regularly in past papers. Asked in 3 of 7 WJEC exam series (2017 to 2025), 7 marks in total. This is a revision priority, not a prediction of your exam.
Issues: safety and rare side effects, testing on animals and volunteers, the right to choose ( is voluntary in the UK), protecting others, cost-effectiveness and fair access. Some people cannot be vaccinated (weakened immunity, chemotherapy); others refuse for religious reasons or from mistrust. The discredited 1998 MMR claim cut uptake and measles returned.
Lesson 24 of 24
Putting Option A together
- Five diseases: and (bacteria), and (viruses), (protoctist).
- stops cell wall cross-links (); tetracycline blocks the A site ().
- : random , then selection by the .
- Specific response: presentation, , and expansion, plasma and .
- : faster, bigger, longer, thanks to .
- lasts; is immediate but brief.
Worksheets
Worksheet 1: Option A Immunology and disease (160 marks)
15 exam-style questions, 160 marks
Written by BioWelsh in the style of the WJEC A level Biology examination. Not an official WJEC paper.
Check your understanding.
62 questions. Practise in a focused view, with your answers kept while this page is open.
Related learning
- Microbiology
The , bacterial cell walls, culturing and are the basis of action and testing.
- Human reproduction
cross the , giving natural to the foetus.
- Variation & evolution
is an example of .
- Applied genetics
projects on Anopheles and Plasmodium aim to improve .
Specification & sources
- https://www.wjec.co.uk/media/mxbh1zaf/wjec-gce-biology-spec-from-2015-e-101025.pdf
- https://openstax.org/books/biology-2e/pages/42-1-innate-immune-response
- https://openstax.org/books/biology-2e/pages/42-2-adaptive-immune-response
- https://openstax.org/books/biology-2e/pages/42-3-antibodies
- https://openstax.org/books/biology-2e/pages/21-2-virus-infections-and-hosts
- https://openstax.org/books/microbiology/pages/14-2-fundamentals-of-antimicrobial-chemotherapy
- https://openstax.org/books/microbiology/pages/14-3-mechanisms-of-antibacterial-drugs
- https://openstax.org/books/microbiology/pages/14-5-drug-resistance
- https://openstax.org/books/microbiology/pages/14-6-testing-the-effectiveness-of-antimicrobials
- https://openstax.org/books/microbiology/pages/16-1-the-language-of-epidemiologists
- https://openstax.org/books/microbiology/pages/18-5-vaccines
- https://openstax.org/books/microbiology/pages/22-2-bacterial-infections-of-the-respiratory-tract
- https://openstax.org/books/microbiology/pages/24-3-bacterial-infections-of-the-gastrointestinal-tract
- https://openstax.org/books/microbiology/pages/25-4-parasitic-infections-of-the-circulatory-and-lymphatic-systems
- https://openstax.org/books/microbiology/pages/22-3-viral-infections-of-the-respiratory-tract
- https://openstax.org/books/microbiology/pages/21-3-viral-infections-of-the-skin-and-eyes
- https://openstax.org/books/microbiology/pages/3-3-unique-characteristics-of-prokaryotic-cells
- https://openstax.org/books/microbiology/pages/18-1-overview-of-specific-adaptive-immunity
- WJEC GCE A Level Biology Unit 4 mark schemes and examiner reports, Option A: Summer 2017 (Q7), 2018 (Q6), 2019 (Q8), 2023 (Q7), 2024 (Q7) and 2025 (Q7): depth, exam wording and rejected answers
- images/u4.immunology__photo-vibrio.jpg · Ronald Taylor, Tom Kirn and Louisa Howard, Dartmouth Electron Microscope Facility · Copyrighted free use · https://commons.wikimedia.org/wiki/File:Cholera_bacteria_SEM.jpg
- images/u4.immunology__photo-tb.jpg · CDC/Dr. George P. Kubica · Public domain · https://commons.wikimedia.org/wiki/File:Mycobacterium_tuberculosis_Ziehl-Neelsen_stain_02.jpg
- images/u4.immunology__photo-smallpox.jpg · CDC/Dr. Fred Murphy and Sylvia Whitfield · Public domain · https://commons.wikimedia.org/wiki/File:Smallpox_virus_virions_TEM_PHIL_1849.JPG
- images/u4.immunology__photo-flu.jpg · CDC/F. A. Murphy · Public domain · https://commons.wikimedia.org/wiki/File:Influenza_A_virus_-_negative_stain_image_TEM.JPG
- images/u4.immunology__photo-anopheles.jpg · Edward McClellan, CDC · CC0 · https://commons.wikimedia.org/wiki/File:A._quadrimaculatus.jpg
- images/u4.immunology__photo-malaria-rings.jpg · CDC/Dr. Greene · Public domain · https://commons.wikimedia.org/wiki/File:Plasmodium_falciparum_rings_form_parasites4885_lores.jpg
- images/u4.immunology__photo-gametocytes.jpg · CDC/Dr. Mae Melvin · Public domain · https://commons.wikimedia.org/wiki/File:Plasmodium_falciparum_01.png
- images/u4.immunology__photo-antibiogram.jpg · Ajay Kumar Chaurasiya · CC0 · https://commons.wikimedia.org/wiki/File:Lactococcus_garvieae_antibiogram_pattern_on_blood_agar.jpg
- https://creativecommons.org/publicdomain/zero/1.0/
- https://creativecommons.org/publicdomain/mark/1.0/