Diseases & Immunity

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Notes

Pathogens & Barriers

A **pathogen** is a disease-causing organism (e.g. bacterium, virus, fungus).
Diseases caused by pathogens are **transmissible** – passed from host to host.
Transmission can be **direct** (body fluids: HIV, gonorrhoea) or **indirect** (air droplets, contaminated food/water, vectors like mosquitoes).
**Mechanical barriers**: skin (blocks entry, heals with scab), hairs in nose (trap pathogens).
**Chemical barriers**: mucus (traps pathogens, removed by coughing/swallowing), stomach acid (HCl kills pathogens).
**Cellular defences**: white blood cells – phagocytes engulf pathogens (**phagocytosis**); lymphocytes produce **antibodies**.

Controlling the Spread of Disease

**Clean water supply** prevents waterborne diseases like cholera.
**Hygienic food preparation** (washing hands, proper cooking) reduces contamination.
**Personal hygiene** (soap, tissues for sneezes/coughs) limits colds and flu.
**Waste disposal** (sealed bins) reduces vectors like flies.
**Sewage treatment** removes pathogens before release into environment.

Active Immunity (Extended)

**Active immunity**: body makes its own antibodies and **memory cells** after exposure to a pathogen or vaccination.
Slow-acting but provides **long-lasting** protection.
Can be acquired naturally (infection) or artificially (vaccination).

Antigens & Antibodies (Extended)

**Antigens** are molecules (e.g. proteins) on cell surfaces; they are unique to each individual/pathogen.
**Lymphocytes** recognise foreign antigens and produce **antibodies** – proteins complementary in shape to the antigen.
Antibodies cause **agglutination** (clumping) of pathogens, making them easier for phagocytes to engulf.
**Memory cells** remain after infection; on reinfection, they trigger rapid antibody production – person is immune.
Some pathogens mutate and change antigens, so memory cells may not recognise them.

Vaccination (Extended)

Vaccines contain a **dead or weakened form** of a pathogen (with antigens) that cannot cause disease.
They stimulate lymphocytes to produce antibodies and **memory cells** without causing illness.
Vaccination gives **active immunity** – long-lasting protection.
**Herd immunity**: when a high % of the population is vaccinated, the pathogen has few hosts, protecting the unvaccinated.
Smallpox was **eradicated** in 1980 by a global vaccination programme.

Passive Immunity & Breastfeeding

**Passive immunity**: antibodies are acquired from another individual – fast-acting but **short-term** (no memory cells).
Antibodies pass from mother to infant via **breast milk** (colostrum), protecting the baby until its own immune system matures.
The body does **not** produce its own antibodies or memory cells in passive immunity.

Cholera

Cholera is caused by **Vibrio cholerae** bacteria, transmitted via contaminated water/food.
Bacteria attach to the small intestine and produce a **toxin**.
The toxin stimulates intestinal cells to release **chloride ions** into the gut lumen.
Lower water potential in the gut causes water to move out of cells by **osmosis**, leading to severe **diarrhoea**.
Loss of water and ions can be fatal; treated with **oral rehydration therapy** (salt and sugar solution).

Cellular defences: phagocytes engulf pathogens; lymphocytes produce antibodies.

Vaccination introduces antigens, stimulating antibody production and memory cells.

Cholera bacteria attach to the intestine, release toxin, causing Cl- secretion and osmotic water loss.

Practice questions

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1.What is a pathogen?
Easy
- AA disease-causing organism
- BA transmissible disease
- CA phagocyte that engulfs bacteria
- DA bacterial cell
2.The immune system recognises which part of a pathogen?
Easy
- AAntibiotic
- BAntigen
- CActive site
- DAntibody
3.Which body defence listed below acts as a chemical barrier?
Easy
- AMucus lining the airways
- BAntibody production
- CHairs in the nose
- DPhagocytosis
4.Which of the options below is an example of a transmissible disease?
Easy
- AObesity
- BTooth decay
- CCholera
- DRickets
5.Which cells produce mucus?
Easy
- ACiliated cells
- BGoblet cells
- CNerve cells
- DWhite blood cells
6.The human body has a number of barriers to prevent infection by pathogens. Which of these are examples of mechanical barriers? 1. Skin 2. Mucus 3. Hairs in the nose 4. Antibodies 5. Stomach acid
Medium
- A1 and 3
- B1, 2 and 4
- C2 and 4
- D1, 3 and 5
7.Which of the following diseases listed below are not caused by infectious pathogens? 1. Coronary Heart Disease 2. Cholera 3. AIDS 4. Scurvy
Medium
- A2 only
- B1 and 4
- C2 and 3
- D2, 3 and 4
8.Which of the following is an effect of a cholera infection? 1. Loss of salts from the blood 2. Loss of water from the blood 3. Blockage of the small intestine 4. Persistent diarrhoea
Medium
- A1 and 4
- B1, 2 and 4
- C3 and 4
- DAll 4

More questions

9.Statements 1 to 4 describe stages in the development of cholera. 1. Chloride ions are secreted into the gut. 2. Osmosis causes water to move into the gut. 3. The infected person becomes dehydrated. 4. Toxins are produced by the pathogenic bacteria. What is the correct sequence of the four stages?
Medium
- A1 → 2 → 3 → 4
- B1 → 4 → 3 → 2
- C4 → 1 → 2 → 3
- D4 → 1 → 3 → 2
10.Which of the following is a correct definition for the term transmissible disease?
Medium
- Aa disease caused by a pathogen that can be passed from one host to another
- Ba disease caused by a pathogen that cannot be treated with antibiotics
- Ca disease that is always transmitted through direct contact between individuals
- Da disease caused by unhealthy lifestyle choices that increase the risk of infection
11.Passive and active immunity have which of the following features in common? 1. They are always long-term. 2. They always involve the activity of memory cells. 3. They involve antibodies. 4. They can be acquired by vaccination.
Hard
- A1 and 2
- B3 only
- C2 and 3
- D3 and 4
12.Varicella zoster virus (VZV) causes chickenpox. The graph shows the concentration of antibodies in the blood of a patient after vaccination against VZV. What most likely happened at point X to cause the increase in antibody concentration?
Hard
- Ainfection with a different pathogen
- Bthe vaccine took time to stimulate lymphocytes
- Cantibodies produced earlier were released into the blood
- Dinfection with the VZV
13.A child is vaccinated against measles. A few years later, the child is exposed to the measles virus. The graph shows the concentration of measles antibodies in the child’s blood over time. Which statement is consistent with the information in the graph?
Medium
- AAfter vaccination, the child produced memory cells.
- BThe child had passive immunity against measles.
- CThe measles virus contains antibodies.
- DThe vaccination failed to protect the child against measles.
14.Which row in the table correctly describes the attributes of passive immunity?
Hard
- AA: effective period long term, antibodies made yes, involves production of memory cells no
- BB: effective period long term, antibodies made yes, involves production of memory cells yes
- CC: effective period short term, antibodies made no, involves production of memory cells no
- DD: effective period short term, antibodies made no, involves production of memory cells yes
15.Varicella zoster virus (VZV) causes chickenpox. The graph shows the concentration of antibodies in the blood of a patient after vaccination against VZV. At point X, there is a sharp increase in antibody concentration. What most likely happened at point X?
Hard
- AInfection with a different pathogen
- BThe vaccine took time to stimulate lymphocytes
- CAntibodies produced earlier were released into the blood
- DInfection with the VZV
16.The diagram shows a bacterium with proteins on its surface (X). The diagram also shows proteins made by the human body (Y). Which row shows the correct combination for destroying the bacterium?
Easy
- AX are antigens, Y are antibodies
- BX are antibodies, Y are antigens
- CX are pathogens, Y are phagocytes
- DX are toxins, Y are antitoxins
17.Which of the following diseases can be transmitted by contact with contaminated surfaces?
Medium
- AAthlete's foot and malaria
- BSalmonella and typhoid
- CInfluenza and dengue fever
- DSalmonella and athlete's foot
18.The graph shows the response of the body to vaccination. What should replace the letter X on the y-axis label?
Medium
- AAntibody concentration
- BAntigen concentration
- CPathogen concentration
- DPlatelet concentration
19.A tissue is transplanted from a female donor to a male recipient and is rejected. What is the main cause of this rejection?
Medium
- AThe presence of an X chromosome
- BThe action of platelets
- CThe action of antibiotics
- DAntibody production
20.A population of 1000 people is exposed to a new infectious disease. 800 are vaccinated, 200 are not. The vaccine is 90% effective. If the disease has a basic reproduction number (R0) of 4, what is the approximate percentage of the population that is immune?
Hard
- A72%
- B80%
- C90%
- D100%
21.The diagram shows a bacterium with surface proteins X and human antibodies Y. Which row correctly describes how the antibodies destroy the bacterium?
Medium
- AAntibodies bind to antigens, causing agglutination and signalling phagocytes.
- BAntibodies engulf the bacterium directly.
- CAntibodies produce toxins that kill the bacterium.
- DAntibodies replicate inside the bacterium.
22.A population of 1000 people is exposed to a new infectious disease. 800 are vaccinated, 200 are not. The vaccine is 90% effective. If the disease has a basic reproduction number (R0) of 5, what is the minimum percentage of the population that must be immune to achieve herd immunity?
Hard
- A80%
- B90%
- C70%
- D85%
23.Which of the following is a correct sequence of events in the development of cholera symptoms?
Medium
- ABacteria attach to intestine → produce toxin → chloride ions released into gut → water moves into gut by osmosis → diarrhoea
- BBacteria produce toxin → bacteria attach to intestine → water moves into gut → chloride ions released → diarrhoea
- CChloride ions released → bacteria attach → toxin produced → water moves into gut → diarrhoea
- DWater moves into gut → bacteria attach → toxin produced → chloride ions released → diarrhoea
24.Which of the following is a mechanical barrier to pathogen entry?
Easy
- AHairs in the nose
- BMucus
- CStomach acid
- DAntibodies
25.A student investigates the effect of temperature on the activity of an enzyme. Which of the following would be the most appropriate control variable?
Hard
- ApH of the buffer solution
- BTemperature of the water bath
- CTime taken for the reaction
- DConcentration of the product
26.The graph shows antibody concentration after vaccination. At point X, antibody concentration increases sharply. What is the most likely cause?
Medium
- AInfection with the same pathogen
- BThe vaccine finally taking effect
- CAntibodies from another source entering the blood
- DA second vaccination dose
27.Which disease can be transmitted by contaminated food or water?
Easy
- ACholera
- BInfluenza
- CHIV
- DAthlete's foot
28.A student wants to test a food sample for the presence of starch. Which reagent should be used, and what is the positive result?
Medium
- AIodine solution; blue-black colour
- BBenedict's solution; brick-red precipitate
- CBiuret reagent; purple colour
- DEthanol emulsion; white colour
29.In an experiment to measure the effect of vaccination on antibody production, a group of mice is vaccinated and another group is not. Both groups are later exposed to the pathogen. Which graph would show the expected antibody response?
Hard
- AVaccinated group shows a rapid, high antibody peak; unvaccinated shows a slower, lower peak.
- BBoth groups show identical antibody responses.
- CUnvaccinated group shows a rapid peak; vaccinated shows no response.
- DVaccinated group shows no antibodies; unvaccinated shows a slow rise.
30.Which of the following is a correct definition of passive immunity?
Medium
- AShort-term immunity gained by receiving antibodies from another individual.
- BLong-term immunity gained by producing antibodies after infection.
- CImmunity gained by vaccination with dead pathogens.
- DImmunity that involves memory cell production.
31.A vaccine contains weakened pathogens. Why are weakened pathogens used instead of dead ones?
Hard
- AWeakened pathogens can still replicate slightly, provoking a stronger immune response without causing disease.
- BDead pathogens cannot stimulate antibody production.
- CWeakened pathogens are easier to produce.
- DDead pathogens may mutate and become harmful.
32.Which type of white blood cell is responsible for producing antibodies?
Easy
- ALymphocyte
- BPhagocyte
- CNeutrophil
- DErythrocyte
33.What is the name of the molecule on the surface of a pathogen that triggers an immune response?
Easy
- AAntibody
- BAntigen
- CAntitoxin
- DPathogen
34.Which of the following is an example of a transmissible disease?
Medium
- AObesity
- BCholera
- CRickets
- DCoronary heart disease
35.The diagram shows a bacterium with surface proteins (X) and human antibodies (Y). Which row correctly describes how the antibodies destroy the bacterium? (Diagram: icon_scene with bacterium icon, labels X on surface proteins, Y on Y-shaped antibody icons near bacterium)
Medium
- AAntibodies attach to antigens and cause agglutination
- BAntibodies engulf the bacterium
- CAntibodies produce toxins that kill the bacterium
- DAntibodies stimulate the bacterium to self-destruct
36.Statements 1 to 4 describe stages in the development of cholera. 1. Chloride ions are secreted into the gut. 2. Osmosis causes water to move into the gut. 3. The infected person becomes dehydrated. 4. Toxins are produced by the pathogenic bacteria. What is the correct sequence?
Medium
- A4 → 1 → 2 → 3
- B1 → 2 → 3 → 4
- C4 → 1 → 3 → 2
- D1 → 4 → 3 → 2
37.Which row correctly describes passive immunity?
Hard
- AShort-term, no antibody production by the body, no memory cells
- BLong-term, antibody production by the body, memory cells formed
- CShort-term, antibody production by the body, memory cells formed
- DLong-term, no antibody production by the body, memory cells formed
38.The graph shows antibody concentration after vaccination. At point X, antibody concentration increases sharply. What is the most likely cause? (Diagram: icon_scene showing a line graph with axes: time on x-axis, antibody concentration on y-axis; curve rises after vaccination, then a sharp rise at point X labelled 'second exposure')
Hard
- AInfection with the same pathogen
- BThe vaccine took time to stimulate lymphocytes
- CAntibodies produced earlier were released into the blood
- DInfection with a different pathogen
39.Which of the following is a correct sequence of events in an immune response to a pathogen?
Hard
- ALymphocyte recognises antigen → lymphocyte produces antibody → antibody binds to antigen → phagocyte engulfs pathogen
- BPhagocyte engulfs pathogen → lymphocyte produces antibody → antibody binds to antigen → memory cells formed
- CAntibody binds to antigen → phagocyte engulfs pathogen → lymphocyte produces antibody → memory cells formed
- DLymphocyte produces antibody → antibody binds to antigen → lymphocyte recognises antigen → phagocyte engulfs pathogen
40.Which type of white blood cell engulfs and digests pathogens?
Easy
- ALymphocyte
- BPhagocyte
- CPlatelet
- DRed blood cell

Slides

Pathogens & Barriers

A pathogen is a disease-causing organism.
Pathogens cause transmissible diseases that can be passed from host to host.
Transmission can be direct (e.g., body fluids) or indirect (e.g., air, water, vectors).

What is a pathogen?

A transmissible disease
A phagocyte that engulfs bacteria
A disease-causing organism
A bacterial cell

Body Defences: Mechanical & Chemical Barriers

Mechanical barriers: skin and hairs in the nose physically block pathogens.
Chemical barriers: mucus traps pathogens; stomach acid kills them.
These are first-line defences before the immune system is activated.

Which of these are mechanical barriers?

Skin
Stomach acid
Hairs in the nose
Antibodies

White Blood Cells: Phagocytes & Lymphocytes

Phagocytes engulf and digest pathogens (phagocytosis).
Lymphocytes produce antibodies that clump pathogens together (agglutination).
Chemicals released by lymphocytes attract phagocytes to destroy the clumped pathogens.

The process by which white blood cells engulf and digest pathogens is called ____. The clumping of pathogens by antibodies is called ____.

Antigens & Antibodies (Extended)

Antigens are molecules (e.g., proteins) on the surface of cells.
Lymphocytes recognise foreign antigens and produce complementary antibodies.
Antibodies attach to antigens, causing agglutination and signalling phagocytes.

The immune system recognises which part of a pathogen?

Antibiotic
Antigen
Active site
Antibody

Active Immunity (Extended)

Active immunity: the body makes its own antibodies and memory cells.
It can be acquired by natural infection or by vaccination.
Active immunity is slow-acting but long-lasting.

Which of these are characteristics of active immunity?

Involves production of memory cells
Fast-acting
Long-lasting
Antibodies are made by the body

Vaccination (Extended)

Vaccines contain dead or weakened pathogens with specific antigens.
They stimulate an immune response without causing illness.
Memory cells are produced, providing long-lasting immunity.

What happens when a person is vaccinated against measles?

type of immunity: passive, production of memory cells: yes
type of immunity: passive, production of memory cells: no
type of immunity: active, production of memory cells: yes
type of immunity: active, production of memory cells: no

Herd Immunity (Extended)

When a large percentage of the population is vaccinated, the pathogen has few hosts.
This protects the unvaccinated as well – called herd immunity.
Herd immunity prevents epidemics and can lead to disease eradication (e.g., smallpox).

When a large proportion of the population is vaccinated, it provides protection for the whole population. This is known as ____ immunity.

Passive Immunity & Breastfeeding

Passive immunity: antibodies are acquired from another individual.
It is fast-acting but short-term (no memory cells produced).
Example: antibodies pass from mother to infant via breast milk.

Which of these are true about passive immunity?

The body makes its own antibodies
It is short-term
Memory cells are produced
Antibodies are acquired from another individual

Cholera

Cholera is caused by Vibrio cholerae bacteria, transmitted via contaminated water/food.
Bacteria attach to the small intestine and produce a toxin.
The toxin causes chloride ions to be released into the gut, lowering water potential.
Water moves into the gut by osmosis, causing severe diarrhoea and dehydration.

Which sequence correctly describes the development of cholera?

1 → 2 → 3 → 4
1 → 4 → 3 → 2
4 → 1 → 2 → 3
4 → 1 → 3 → 2

Controlling the Spread of Disease

Clean water supply prevents waterborne diseases like cholera.
Hygienic food preparation and personal hygiene reduce transmission.
Proper waste disposal and sewage treatment remove pathogens from the environment.

Which of these are correct methods to control the spread of disease?

Boiling drinking water reduces risk of waterborne pathogens
Disinfecting surfaces reduces transmission via direct contact
Collecting food waste in sealed bins reduces spread by animals
Treating sewage before release prevents direct transmission between individuals

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