CIE iGCSE Co-ordinated Sciences-B10. Diseases and immunity- Study Notes- New Syllabus
CIE iGCSE Co-ordinated Sciences-Diseases and immunity – Study Notes
CIE iGCSE Co-ordinated Sciences-Diseases and immunity – Study Notes -CIE iGCSE Co-ordinated Sciences – per latest Syllabus.
Key Concepts:
Core
- Describe a pathogen as a disease-causing organism
- Describe a transmissible disease as a disease in which the pathogen can be passed from one host to another
- State that a pathogen is transmitted:
(a) by direct contact, including through blood and other body fluids
(b) indirectly, including from contaminated surfaces, food, animals and air - Describe the body defences against pathogens, limited to: skin, hairs in the nose, mucus, stomach acid and white blood cells
- Explain the importance of the following in controlling the spread of disease:
(a) a clean water supply
(b) hygienic food preparation
(c) good personal hygiene
(d) waste disposal
(e) sewage treatment (details of the stages of sewage treatment are not required) - State that vaccinations are available for some pathogens to help control the spread of diseases
Supplement
- State the features of viruses, limited to a protein coat and genetic material
- Describe active immunity as defence against a pathogen by antibody production in the body
- State that each pathogen has its own antigens, which have specific shapes
- Describe antibodies as proteins that bind to antigens leading to direct destruction of pathogens or marking of pathogens for destruction by phagocytes
- State that specific antibodies have complementary shapes which fit specific antigens
- Explain that active immunity is gained after an infection by a pathogen or by vaccination
- Outline the process of vaccination:
(a) weakened pathogens or their antigens are put into the body
(b) the antigens stimulate an immune response by lymphocytes which produce antibodies
(c) memory cells are produced that give long-term immunity - Explain the role of vaccination in controlling the spread of diseases
CIE iGCSE Co-Ordinated Sciences-Concise Summary Notes- All Topics
Pathogens
📌 Introduction
Health problems are often caused by pathogens. These are tiny living things (microorganisms) that invade the body and cause disease.
🌱 Definition
A pathogen is a disease-causing organism.
🧬 Main Types of Pathogens
- Bacteria
• Single-celled organisms.
• Cause disease by releasing toxins or directly damaging cells.
• Examples: Mycobacterium tuberculosis → TB, Vibrio cholerae → Cholera. - Viruses
• Much smaller than bacteria.
• Not true cells → made of genetic material + protein coat.
• Reproduce only inside host cells (destroy them).
• Examples: HIV → AIDS, Influenza virus → Flu. - Fungi
• Some are multicellular (moulds), others unicellular (yeast).
• Cause disease by invading tissues or spreading spores.
• Examples: Candida → Thrush, Ringworm. - Protoctists (Protozoa)
• Single-celled eukaryotes.
• Often parasitic → live inside host and damage it.
• Example: Plasmodium → Malaria.
📊 Summary Table
| Pathogen type | Key features | Example disease |
|---|---|---|
| Bacteria | Single-celled, release toxins | Cholera, TB |
| Viruses | Non-cellular, need host cells | HIV/AIDS, Flu |
| Fungi | Some multicellular, spread by spores | Ringworm, Thrush |
| Protoctists | Single-celled parasites | Malaria |
⚡ Quick Recap
Pathogen = disease-causing organism.
Main types = Bacteria, Viruses, Fungi, Protoctists.
They invade the body and disrupt normal cell functions → illness.
👉 Mnemonic: “Bad Viruses Find Prey” (Bacteria, Viruses, Fungi, Protoctists).
Transmissible Disease
📌 Introduction
Not all diseases spread from person to person. The ones that do are called transmissible diseases because their pathogens can move from one host to another.
🌱 Definition
A transmissible disease is a disease in which the pathogen can be passed from one host to another.
🔄 How Pathogens Spread
- Direct Transmission
• From one host straight to another.
• Examples: Blood contact (needles, transfusion), Sexual contact (HIV, syphilis), Touching infected skin (athlete’s foot). - Indirect Transmission
• Pathogen passes via another medium.
• Examples:
– Airborne → coughing/sneezing (TB, influenza)
– Water/food → contaminated sources (cholera, typhoid)
– Vectors → animals carrying pathogens (mosquitoes → malaria, houseflies → dysentery)
📊 Examples
| Disease | Pathogen type | Transmission |
|---|---|---|
| Cholera | Bacteria | Contaminated water/food |
| Influenza (Flu) | Virus | Airborne droplets |
| HIV/AIDS | Virus | Blood/sexual contact |
| Malaria | Protoctist (Plasmodium) | Mosquito vector |
⚡ Quick Recap
Transmissible disease = pathogen spreads from one host to another.
Spread can be:
Direct → blood, sexual contact, touch.
Indirect → air, water, food, vectors.
Examples: HIV, cholera, malaria, flu.
👉 Trick: “DAWV” = Direct, Air, Water, Vectors → main routes of transmission.
Transmission of Pathogens
📌 Introduction
Pathogens can spread in two main ways: directly from one person to another or indirectly through mediums like air, food, water, or animals.
🌱 (a) Direct Transmission
Pathogen moves straight from one host to another.
- Blood → e.g. transfusion with infected blood, sharing needles.
- Body fluids → sexual contact, saliva, breast milk.
- Touch (skin-to-skin) → e.g. athlete’s foot, syphilis.
🌍 (b) Indirect Transmission
Pathogen passes via another medium before reaching a new host.
- Contaminated surfaces → door handles, towels, clothes.
- Food & water → cholera, typhoid.
- Vectors (animals) → mosquitoes (malaria), houseflies (dysentery).
- Airborne droplets → sneezing, coughing (influenza, TB).
📊 Summary Table
| Transmission | How it happens | Example diseases |
|---|---|---|
| Direct | Blood, body fluids, touch | HIV, athlete’s foot |
| Indirect | Surfaces, food/water, vectors, air | Cholera, malaria, TB, influenza |
⚡ Quick Recap
Direct → Blood + Body fluids + Touch.
Indirect → Surfaces + Food/Water + Animals + Air.
Examples: HIV (direct), Cholera (indirect), Malaria (vector), Flu (airborne).
Trick: “B-B-T” = Blood, Body fluids, Touch (Direct)
Trick: “S-F-A-A” = Surfaces, Food, Animals, Air (Indirect)
Body Defences Against Pathogens
📌 Introduction
The human body protects itself from pathogens using barriers that stop entry and white blood cells that destroy those which enter.
🌱 First Line of Defence – Barriers
- Skin → Tough outer layer. Prevents microbe entry. Cuts are sealed by blood clots forming scabs.
- Nose hairs → Trap dust and microbes from inhaled air.
- Mucus → Sticky fluid in nose/airways traps pathogens. Cilia sweep mucus to throat, where it is swallowed.
- Stomach acid (HCl) → Very acidic (pH ~2). Destroys microbes entering with food or mucus.
🧬 Second Line of Defence – White Blood Cells
- Phagocytes → Engulf and digest pathogens (process = phagocytosis).
- Lymphocytes → Produce antibodies that attach to pathogens and antitoxins that neutralise toxins.
📊 Summary Table
| Defence | How it works | Example |
|---|---|---|
| Skin | Physical barrier, sealed by clot/scab | Prevents microbes entering wounds |
| Nose hairs + Mucus | Trap and remove pathogens | Stopped before lungs |
| Stomach acid | Destroys swallowed microbes | HCl pH ~2 |
| Phagocytes | Engulf + digest pathogens | Phagocytosis |
| Lymphocytes | Antibodies + antitoxins | Neutralise pathogens/toxins |
⚡ Quick Recap
Skin = barrier
Nose hairs + Mucus = trap microbes
Stomach acid = kills microbes
White blood cells = destroy pathogens inside
👉 Trick: “SNMS + WBC”
(Skin, Nose hairs, Mucus, Stomach acid + White Blood Cells)
Controlling the Spread of Disease
📌 Introduction
Diseases spread quickly when hygiene is poor. Simple public health measures like clean water, proper food handling, and waste management greatly reduce infections.
(a) 🚰 Clean Water Supply
- Prevents diseases like cholera, typhoid, dysentery.
- Stops people drinking water contaminated with faeces or pathogens.
- Safe water = fewer water-borne diseases.
(b) 🍲 Hygienic Food Preparation
- Cooking food properly kills microbes.
- Washing hands and surfaces prevents cross-contamination.
- Avoids food poisoning from Salmonella, E. coli etc.
(c) 🧼 Good Personal Hygiene
- Handwashing removes pathogens before eating or after toilet use.
- Bathing, brushing teeth, covering mouth when coughing = prevents spread.
- Cuts and wounds cleaned + covered → stops pathogen entry.
(d) 🚮 Proper Waste Disposal
- Household waste left open → attracts flies, rats, and other carriers of pathogens.
- Correct disposal prevents spread by insects and animals.
(e) 💧 Sewage Treatment
- Untreated sewage carries dangerous bacteria, viruses, and parasites.
- Proper treatment prevents contamination of rivers, lakes, and groundwater.
- Greatly reduces water-borne diseases in communities.
📝 Quick Recap
Clean water → no water-borne diseases.
Hygienic food → no food poisoning.
Personal hygiene → blocks direct spread.
Waste disposal → stops flies/rats spreading disease.
Sewage treatment → prevents faecal contamination of water.
Vaccinations and Disease Control
📌 Key Point
Vaccinations are available for some pathogens (not all).
They help to control the spread of diseases by giving immunity to individuals and reducing transmission in the community.
✅ Examples
- Polio vaccine
- Measles, Mumps, Rubella (MMR) vaccine
- COVID-19 vaccines
- Tetanus vaccine
📝 Quick Recap
Vaccines exist for certain diseases only.
They work by protecting individuals + reducing spread.
Large-scale vaccination → fewer outbreaks, possible eradication.
👉 Memory Tip: “Some but not all pathogens” → vaccines are selective!
Features of Viruses
📌 Introduction
Viruses are the smallest disease-causing agents. They are not made of cells and are considered non-living outside a host.
🌱 Key Features
- Protein coat (capsid):
- Protective outer layer.
- Surrounds and protects the genetic material.
- Helps virus attach to host cells.
- Genetic material:
- Can be DNA or RNA, never both.
- Carries instructions for making new viruses.
- Uses host cell machinery to replicate.
📌 Special Note:
- Viruses have no cytoplasm, no cell organelles, no cell membrane.
- Cannot reproduce alone → must infect a host cell (obligate parasites).
📝 Quick Recap
Protein coat → protection + attachment.
Genetic material (DNA/RNA) → codes for making more viruses.
Non-cellular, parasitic, non-living outside host.
👉 Mnemonic: “PG = Protein + Genetic material” (the two main virus features).
Active Immunity
📌 Introduction
Immunity = ability of the body to resist infection. Active immunity is when your own body makes antibodies to fight pathogens.
🌱 Definition
Active immunity is the defence against a pathogen by the production of antibodies in the body.
🔑 Key Points
- Antibodies are made by lymphocytes (a type of white blood cell).
- Active immunity develops in two ways:
- Natural active immunity → after infection (e.g. getting chickenpox).
- Artificial active immunity → after vaccination (weakened or dead pathogen given).
- Provides long-term protection, because memory cells remain in the body.
- On future infection → memory cells produce antibodies faster and stronger.
🌍 Examples
- Recovering from measles = natural active immunity.
- Getting a polio vaccine = artificial active immunity.
📝 Quick Recap
Active immunity → body produces antibodies.
Two types: Natural (infection), Artificial (vaccination).
Gives long-lasting protection due to memory cells.
👉 Trick: Active = Antibodies made by yourself
Antigens on Pathogens
📌 Introduction
When pathogens (bacteria, viruses, fungi) enter the body, the immune system recognizes them by antigens.
🌱 Key Point
- Each pathogen has its own antigens.
- Antigens = special molecules (usually proteins) present on the surface of pathogens.
- They have unique, specific shapes – like a fingerprint for each pathogen.
- The immune system uses these shapes to detect and attack the invader.
🧬 How it works
- White blood cells (lymphocytes) detect the antigen.
- They produce antibodies that are complementary in shape to that antigen.
- Antibody binds to antigen → pathogen destroyed.
🌍 Example
- Influenza virus has different antigens on its surface.
- That’s why flu vaccines are updated regularly, because antigens can change shape (mutation).
📝 Quick Recap
Pathogens carry antigens on their surface.
Each antigen = unique shape.
Antibodies must be complementary to bind.
Antigen shape → key for immune recognition.
👉 Trick: Antigen = “Anti-generator” → generates an immune response.
Antibodies
📌 Introduction
Antibodies are special proteins made by lymphocytes in response to antigens. They are part of the immune defence system.
🌱 Key Points
- Antibodies = proteins with a specific shape.
- They are complementary to the antigen on a pathogen (like lock & key).
- Function: bind to antigens on the surface of pathogens.
🧬 What Happens After Binding
- Direct destruction of pathogens
- Some antibodies can destroy or neutralize the pathogen directly.
- Example: cause bacteria to burst or stop viruses from entering cells.
- Marking pathogens for destruction
- Antibodies “tag” the pathogen.
- Phagocytes then recognize and engulf the tagged pathogen by phagocytosis.
🌍 Example
- Antibodies produced against bacteria may cause them to clump → easier for phagocytes to engulf.
📊 Summary Table
| Feature | Antibodies |
|---|---|
| Nature | Proteins produced by lymphocytes |
| Bind to | Antigens (specific fit) |
| Role 1 | Direct destruction of pathogen |
| Role 2 | Mark pathogen for phagocytes → phagocytosis |
📝 Quick Recap
Antibodies = proteins with specific shapes.
Bind to antigens on pathogens.
Lead to:
– Direct destruction
– Marking for phagocytosis
👉 Memory trick: Antibody = Anti-bodyguard → protects the body by locking onto intruders.
Antigen – Antibody Specificity
📌 Key Point
Specific antibodies have complementary shapes which fit specific antigens.
🧬 Explanation
- Each pathogen has its own unique antigen on its surface.
- Antibodies are proteins made by lymphocytes.
- An antibody has a binding site whose shape is complementary to the shape of one specific antigen (like a lock and key).
- This ensures that an antibody will only bind to the matching antigen → forming an antigen–antibody complex.
📝 Quick Recap
Antigens = unique markers on pathogens.
Antibodies = proteins with complementary binding sites.
Specific match only (lock + key principle).
👉 Trick: “A fits A” → Antibody fits Antigen.
Active Immunity
📌 Introduction
Active immunity is the body’s own protection against pathogens. It develops when the immune system makes antibodies after exposure to an antigen.
🌱 Key Points
- Definition → Active immunity = when the body produces its own antibodies.
- It provides long-term protection (sometimes lifelong).
- Gained in two ways:
- After an Infection
- Pathogen (virus/bacteria) enters → immune system responds.
- Lymphocytes detect antigens → produce specific antibodies.
- Memory cells are formed → faster response if pathogen returns.
- After Vaccination
- Vaccine contains weakened, dead, or harmless form of pathogen (or its antigens).
- Immune system still produces antibodies.
- Memory cells remain → protection without suffering the disease.
🌍 Examples
- Infection: Chickenpox → once recovered, usually lifelong immunity.
- Vaccination: Polio, measles, COVID-19 vaccines.
📊 Summary Table
| Type of Exposure | How Antibodies Are Produced | Example |
|---|---|---|
| Natural infection | Pathogen invades, immune system fights | Chickenpox |
| Vaccination | Harmless antigens introduced | Polio vaccine |
📝 Quick Recap
Active immunity = body makes its own antibodies.
Occurs after infection or vaccination.
Leaves behind memory cells → long-term protection.
👉 Trick: Active = Antibodies made by you (A = A)
Vaccination
📌 Introduction
Vaccination is a way of giving the body immunity without causing the disease. It trains the immune system to recognise and fight a pathogen quickly if it ever enters.
🌱 Process of Vaccination
- Weakened / Harmless Pathogen or Antigen Introduced
- Vaccine contains dead, weakened, or harmless pathogens OR just their antigens.
- Safe → cannot cause the full disease.
- Immune Response Triggered
- Lymphocytes detect the antigens.
- They produce specific antibodies.
- Memory Cells Formed
- Some lymphocytes turn into memory cells.
- These remain in the blood for years (sometimes lifelong).
- Long-term Immunity
- If the real pathogen enters later → memory cells respond quickly and strongly.
- Pathogen destroyed before symptoms appear → person stays healthy.
🌍 Examples of Vaccines
- Polio vaccine
- Measles, Mumps, Rubella (MMR) vaccine
- COVID-19 vaccines
📊 Summary Table
| Step | What Happens | Why It’s Important |
|---|---|---|
| 1 | Weakened pathogen/antigen injected | Safe exposure |
| 2 | Lymphocytes make antibodies | Immune response |
| 3 | Memory cells stored | Future protection |
| 4 | Rapid response on reinfection | Long-term immunity |
📝 Quick Recap
Vaccine = antigen without disease.
Stimulates antibodies + memory cells.
Provides long-term immunity.
👉 Memory Trick: V-A-M → Vaccine → Antibodies → Memory cells
Role of Vaccination in Controlling the Spread of Diseases
📌 Introduction
Vaccination is one of the most effective methods to prevent infectious diseases. Instead of curing people after infection, it works by stopping the disease from spreading in the first place.
🌱 How Vaccination Helps
- Immunity in Individuals
- Vaccinated person develops active immunity (antibodies + memory cells).
- If exposed later, pathogen destroyed quickly → no disease develops.
- Reduces Transmission
- Fewer infected people = fewer chances of passing pathogen to others.
- Breaks the chain of infection.
- Herd Immunity
- When a large proportion of the population is vaccinated → even unvaccinated people (newborns, elderly, immunocompromised) are protected.
- Pathogen struggles to spread → outbreak risk drops sharply.
- Disease Eradication
- If vaccination is widespread + continuous → diseases can be eliminated.
- Example: smallpox eradicated, polio nearly eradicated.
📊 Summary Table
| Role of Vaccination | Explanation |
|---|---|
| Protects individual | Person gains long-term immunity |
| Reduces spread | Fewer hosts for pathogen |
| Herd immunity | Protects unvaccinated people |
| Eradication | Possible if global coverage is achieved |
📝 Quick Recap
Vaccine = immunity without disease.
Protects individuals + communities.
Herd immunity stops major outbreaks.
Can eradicate diseases if coverage is high.