CIE iGCSE Biology- 10.1 Diseases and immunity- Study Notes- New Syllabus
CIE iGCSE Biology-10.1 Diseases and immunity- Study Notes – New syllabus
CIE iGCSE Biology-10.1 Diseases and immunity- Study Notes -CIE iGCSE Biology – 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, 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)
Supplement
- 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
- Explain that passive immunity is a short-term defence against a pathogen by antibodies acquired from another individual, including across the placenta and in breast milk
- Explain the importance of breast-feeding for the development of passive immunity in infants
- State that memory cells are not produced in passive immunity
- Describe cholera as a disease caused by a bacterium which is transmitted in contaminated water
- Explain that the cholera bacterium produces a toxin that causes secretion of chloride ions into the small intestine, causing osmotic movement of water into the gut, causing diarrhoea, dehydration and loss of ions from the blood
What is a Pathogen?
A pathogen is a disease-causing microorganism. It can invade the body, disrupt normal functions, and cause illness.
🔬 Types of Pathogens
Pathogens come in various forms, including bacteria, viruses, fungi, and protozoa.
| Type of Pathogen | Example Disease | Example Organism |
|---|---|---|
| Bacteria | Tuberculosis (TB) | Mycobacterium tuberculosis |
| Viruses | Influenza, COVID-19 | Influenza virus, Coronavirus |
| Fungi | Athlete’s foot | Trichophyton |
| Protozoa | Malaria | Plasmodium species |
A pathogen is any microorganism or agent that can cause disease when it infects a host (like a human, plant, or animal).
What is a Transmissible Disease?
A transmissible disease is a type of infectious disease that can be passed from one host to another. This means the pathogen (such as bacteria, viruses, or fungi) can move from an infected person, animal, or surface to a new individual and cause illness.
🔁 How Can Transmissible Diseases Spread?
| Method of Transmission | Examples |
|---|---|
| Direct contact | Touching infected people, cuts, or fluids (e.g. athlete’s foot, HIV) |
| Indirect contact | Contaminated surfaces, food, water (e.g. cholera) |
| Droplet infection | Coughing, sneezing (e.g. flu, COVID-19) |
| Vectors | Animals that carry pathogens (e.g. mosquitoes in malaria) |
A transmissible disease is one where the pathogen can be transferred from an infected host to a healthy one, causing the disease to spread.
How Pathogens Are Transmitted
Pathogens (like bacteria, viruses, or fungi) are disease-causing organisms. They can be transmitted from one host to another in two main ways:
(a) Direct Contact Transmission
This occurs when a pathogen is passed directly from an infected person to another person.
Examples include:
- Through blood (e.g. sharing needles, cuts, transfusions)
- Through other body fluids such as:
- Saliva
- Semen
- Vaginal fluids
- Breast milk
Diseases spread this way: HIV/AIDS, Hepatitis B and C, STIs
(b) Indirect Transmission
This occurs without direct person-to-person contact. The pathogen is passed via another route, such as:
| Mode of Indirect Transmission | Examples |
|---|---|
| Contaminated surfaces | Touching infected doorknobs, objects |
| Contaminated food or water | Cholera, food poisoning |
| Animals (vectors) | Malaria (via mosquito), plague |
| Airborne particles | Coughing/sneezing – flu, COVID-19 |
📌 Summary:
Pathogens can be transmitted either directly, through contact with infected body fluids, or indirectly, through contaminated food, air, surfaces, or animals.
Body Defences Against Pathogens
Our body has several ways to protect itself from harmful microbes like bacteria and viruses. These defences stop pathogens from entering or help destroy them if they get in. They can be grouped into physical barriers, chemical defences, and the immune system.
(a) Skin – First Line of Defence
The skin acts as a tough outer barrier. It protects us by:
- Blocking the entry of microbes
- Producing natural oils (sebum) that kill bacteria
- Having friendly microbes on the surface that compete with harmful ones
- If the skin is cut, blood clots quickly to seal the gap
(b) Nose – Hairs and Mucus Trap Microbes
The nose helps filter out microbes in the air:
- Tiny hairs trap dust and large particles
- Sticky mucus traps bacteria and viruses
- These trapped microbes are either sneezed out or swallowed
(c) Mucus and Cilia in Airways
The lining of the trachea and bronchi (airways) also protect us:
- Goblet cells make mucus to trap microbes
- Cilia (tiny hair-like structures) move the mucus up to the throat
- We usually cough it out or swallow it. This keeps the lungs clean
(d) Stomach Acid – Kills Swallowed Pathogens
The stomach makes hydrochloric acid, which:
- Kills most bacteria and viruses we swallow
- Helps protect us from infections in food and water
(e) White Blood Cells – The Immune Defence
If microbes get inside, white blood cells in the blood help fight them. There are 3 main ways:
| Defence Method | What It Does |
|---|---|
| Phagocytosis | Some white blood cells swallow and digest the pathogen |
| Antibodies | Others make antibodies that lock onto and destroy specific microbes |
| Antitoxins | Some release antitoxins to neutralize toxins made by bacteria |
The body protects itself with:
- Physical barriers (skin, nose hairs)
- Chemical defences (mucus, stomach acid)
- White blood cells that kill microbes inside the body
Preventing the Spread of Disease
Infectious diseases can spread quickly, especially in poor living conditions. To stop this, it’s important to break the chain of infection by maintaining clean environments and healthy habits.
Here are five keyways to help control the spread of disease:
(a) Clean Water Supply
- Safe drinking water is essential for health.
- Dirty or contaminated water can carry bacteria, viruses, and parasites.
- Diseases like cholera, typhoid, and dysentery are often spread this way.
- Having a clean water supply prevents waterborne diseases and helps communities stay healthy.
(b) Hygienic Food Preparation
- The way food is handled affects how safe it is to eat.
- Unwashed hands, dirty utensils, or undercooked meat can spread microbes.
- Salmonella and E. coli infections can result from poor food hygiene.
- Cooking food properly and preparing it in a clean space helps stop the spread of disease.
(c) Good Personal Hygiene
- Personal hygiene is a key defence, especially against everyday infections.
- Important habits include:
- Washing hands before eating or after using the toilet
- Bathing regularly and keeping nails trimmed
- Covering the mouth when coughing or sneezing
- These small actions stop microbes from spreading between people.
(d) Waste Disposal
- If waste (especially human waste and rubbish) is not managed well:
- It becomes a breeding ground for flies and rats.
- Can lead to the spread of diseases like plague, cholera, and diarrhoeal infections.
- Proper bins, toilets, and waste collection systems help keep living areas safe.
(e) Sewage Treatment
- Even though details aren’t needed, it’s important to know why sewage treatment matters:
- Untreated sewage contains harmful pathogens.
- If released into rivers or land, it can pollute water and soil.
- This can lead to serious outbreaks of disease in the community.
- Sewage treatment ensures waste is made safe before being released, protecting both people and the environment.
Clean water, safe food, personal hygiene, waste management, and sewage treatment all help block the spread of harmful microbes – keeping individuals and whole communities healthy.
Active Immunity – How the Body Fights Pathogens
When a pathogen enters the body, our immune system responds by producing antibodies. This response is called active immunity, and it helps us fight the infection and also prevents future illness from the same microbe.
🧪What Is Active Immunity?
- Active immunity is when the body makes its own antibodies to fight a pathogen.
- It usually happens in two situations:
- After catching a natural infection
- After getting a vaccination
- In both cases, the body learns to recognize the pathogen and prepares to fight it if it comes again.
How It Works
- Pathogen enters the body (through infection or vaccine)
- White blood cells detect antigens (proteins) on the pathogen
- They produce specific antibodies to destroy it
- Some white blood cells turn into memory cells
- If the same pathogen enters again, the immune system responds faster and stronger
Key Features of Active Immunity
| Feature | Description |
|---|---|
| Long-term protection | Memory cells stay in the body for years or life |
| Takes time to develop | Antibodies aren’t made instantly – can take days |
| Natural or artificial | Can be from infection or from a vaccine |
Example:
- If someone recovers from measles, their body keeps memory cells, so they are unlikely to get measles again.
- A measles vaccine gives the same protection by triggering antibody production without causing illness.
In active immunity, the body makes its own antibodies after infection or vaccination. It provides long-lasting protection and helps stop the same disease from coming back.
Antigens Are Unique to Each Pathogen
Pathogens like bacteria and viruses have special markers on their surfaces called antigens. These play a key role in how the body detects and fights infections.
🔬 What Are Antigens?
- Antigens are proteins (or molecules) found on the surface of pathogens.
- They act like “ID tags” that help the immune system recognise the invader.
- Each pathogen (like the flu virus, HIV, or salmonella) has its own unique antigens.
🧩 Specific Shape Matters
- Every antigen has a specific shape, like a key.
- The immune system makes antibodies that match this shape – like a lock and key.
- This is why the body needs to produce different antibodies for different diseases.
🎯 Why This Is Important
- The immune system can only attack a pathogen if it recognizes the antigens.
- If a new pathogen enters, the body takes time to identify its antigen shape before making the right antibody.
- This is also why vaccines must match the specific antigen of the pathogen they’re protecting against.
Each pathogen has its own antigens with a unique shape.
The immune system uses this shape to produce the correct antibody and fight off infection.
Antibodies
🧪 What Are Antibodies?
- Antibodies are special proteins made by white blood cells (lymphocytes) when the body detects harmful pathogens like bacteria or viruses.
- Their job is to identify and help destroy these invaders.
🔐 How Antibodies Work
- Each antibody is shaped to match one specific antigen on a pathogen’s surface – like a lock and key.
- When an antibody binds to an antigen, it forms an antigen–antibody complex.
- This helps the body neutralize or remove the threat.
🛡️ Two Main Ways Antibodies Help Defend the Body
| Mechanism | What Happens |
|---|---|
| Direct destruction | Some antibodies kill the pathogen directly, e.g. by bursting it or stopping its function |
| Marking for destruction | Others label the pathogen, so phagocytes (a type of white blood cell) can easily find and destroy it |
This teamwork between antibodies and phagocytes helps clear infections faster.
Antibodies are proteins made by white blood cells. They bind to antigens with a matching shape, and either destroy the pathogen directly or mark it so phagocytes can eliminate it.
How Antibodies Fit Specific Antigens
The immune system is incredibly clever. It doesn’t just attack anything – it targets pathogens based on their unique surface markers, called antigens. To do this, the body produces special proteins called antibodies, which are shaped to match specific antigens.
🔍 What Does “Specific” Mean?
- Each pathogen (like bacteria or viruses) has its own unique antigens on its surface.
- These antigens act like ID tags, telling the immune system what the pathogen is.
- In response, the body produces antibodies that are custom-designed to attach to those antigens.
- This is what scientists mean when they say antibodies are specific each one is made to match a particular antigen.
🔐 Lock-and-Key Relationship
- The shape of an antibody is exactly complementary to the shape of the antigen it targets.
- Think of it like a lock and key: the antibody is the key, and the antigen is the lock.
- Only the correct antibody can bind to the matching antigen.
- If the shapes don’t match, the antibody simply won’t bind, and the immune response won’t work.
🧠 Why This Is Important
- This shape-based match allows the immune system to be highly accurate.
- It ensures that only harmful microbes are attacked not the body’s own cells.
- It also explains why we need new antibodies for new infections: different pathogens have different-shaped antigens.
Every antibody has a specific shape that fits only one type of antigen.
This complementary fit allows antibodies to recognize, bind to, and help destroy the correct pathogens just like a key fits a particular lock.
How Active Immunity Is Gained
Active immunity is a type of protection that your body develops after fighting off an infection or after getting a vaccine. It’s part of how your immune system learns to recognise and remember specific pathogens – so it can defend you faster in the future.
Gained After an Infection
- When a pathogen (like a virus or bacterium) enters the body, it has unique antigens on its surface.
- In response, your white blood cells make antibodies that are shaped to match those antigens.
- These antibodies help destroy the pathogen.
- After the infection is gone, memory cells stay in your body.
- If the same pathogen enters again, your immune system remembers it and responds quickly.
- This is why people often don’t get the same disease twice – the body has developed active immunity.
Gained Through Vaccination
- A vaccine contains a weakened or inactive form of a pathogen – or just its antigens.
- It’s safe and doesn’t make you ill, but it stimulates the immune system.
- Just like a real infection, your body makes antibodies and memory cells.
- So, if the real pathogen shows up later, your body is ready to fight it immediately.
- This is how vaccines protect you without making you sick and give you long-lasting active immunity.
In both cases infection or vaccination, the body produces its own antibodies and memory cells. That’s what makes it “active” immunity: your immune system does the work itself.
Active immunity is gained when your body is exposed to a pathogen – either through natural infection or vaccination.
In both cases, your immune system makes its own antibodies and memory cells, giving you long-term protection from future infections.
How Vaccination Works?
Vaccination is a way of training the immune system without causing illness. It prepares your body to fight real infections by creating immunity in advance.
(a) Weakened Pathogens or Antigens Are Introduced
- A vaccine contains either:
- A weakened or dead pathogen, or
- Just the antigens (surface proteins) from the pathogen
- These are not harmful and do not cause disease, but they are enough to alert the immune system
- This step “tricks” the body into thinking it’s under attack.
(b) Antigens Trigger an Immune Response
- The lymphocytes (a type of white blood cell) detect the antigens
- In response, they produce antibodies that are specific to the antigen
- These antibodies bind to the antigen and help destroy it
- Even though there’s no real infection, the body behaves as if there is one and starts building a defence.
(c) Memory Cells Are Made – Long-Term Protection
- Some lymphocytes become memory cells
- These stay in the body for a long time – sometimes for life
- If the real pathogen enters the body in the future:
- The memory cells recognise it immediately
- Antibodies are made quickly and in large amounts
- The infection is stopped before it causes illness
- This is what gives long-term immunity – the body is now prepared.
Vaccination introduces harmless antigens into the body.
This triggers an immune response, leading to the production of antibodies and memory cells.
If the real infection happens later, the immune system responds faster and stronger, often preventing illness entirely.
How Vaccination Helps Control the Spread of Disease
Vaccination doesn’t just protect individuals – it plays a major role in protecting entire communities. When enough people are vaccinated, it becomes much harder for diseases to spread.
🛡️ Protecting the Individual
- A vaccinated person develops active immunity without getting sick.
- Their immune system produces antibodies and memory cells.
- If they encounter the real pathogen later, they can fight it off quickly.
- This makes them less likely to get sick and also less likely to spread the disease to others.
🌍 Herd Immunity – Protecting the Community
- When most of the population is vaccinated, the disease has fewer people to infect.
- Even those who can’t be vaccinated (e.g. babies, the elderly, or immunocompromised individuals) are still protected.
- This effect is called herd immunity.
- Example: If 95% of people are vaccinated against measles, the virus cannot spread easily, so even unvaccinated people are protected.
🚫 Slowing and Stopping Outbreaks
- Widespread vaccination reduces the number of infections over time.
- Some diseases can be completely eliminated through strong vaccination programmes.
- Example: Smallpox was globally eradicated through vaccination.
- It also reduces the pressure on hospitals during outbreaks (e.g. COVID-19 or seasonal flu).
📌 Summary
Vaccination helps control disease spread by:
- Giving individuals immunity
- Reducing transmission in the population
- Creating herd immunity
- Preventing outbreaks and saving lives
It is one of the most powerful tools in public health and disease prevention.
Passive Immunity
🧪 What Is Passive Immunity?
- Passive immunity is a type of protection where a person receives ready-made antibodies from another individual.
- Unlike active immunity (where your body makes its own antibodies), passive immunity is temporary but can provide immediate defence.
🕒 Short-Term Protection
- Passive immunity works quickly – the antibodies are already made.
- But the protection doesn’t last long because:
- The body doesn’t produce its own memory cells.
- The borrowed antibodies eventually break down and disappear.
Natural Examples – From Mother to Baby
| Source | How Antibodies Are Passed |
|---|---|
| Placenta (before birth) | Antibodies from the mother’s blood pass to the baby, giving protection in the womb |
| Breast milk (after birth) | The mother’s antibodies in milk protect the baby’s gut and help fight infections |
This is especially important in the early months, when a baby’s immune system is still developing.
💉 Artificial Passive Immunity
- Passive immunity can also be given medically, such as:
- Antibody injections after exposure to dangerous diseases (e.g. rabies, tetanus).
- These give fast protection when it’s too late to wait for the body to make its own antibodies.
- However, this protection is short-term and does not lead to long-lasting immunity.
📌 Summary
Passive immunity is when antibodies come from another person, not made by your own body.
It gives quick but temporary protection, such as:
- From mother to baby (via placenta or breast milk)
- Through antibody injections in emergencies
It helps defend the body when time is short or when someone can’t produce their own immune response.
Breastfeeding and Passive Immunity in Babies
In the first few months after birth, a baby’s immune system is still developing and is not strong enough to fight off infections on its own. Breastfeeding plays a key role in protecting infants during this vulnerable time by providing them with passive immunity.
🧪 What Is Passive Immunity in Infants?
Passive immunity means the baby receives ready-made antibodies from the mother.
- These antibodies don’t come from the baby’s own immune system.
- They are transferred from the mother, offering immediate but short-term protection.
🍼 How Breast Milk Helps
Breast milk (especially colostrum, the first milk produced after birth) contains:
- Antibodies, especially IgA, which line the baby’s gut and prevent pathogens from entering
- Enzymes and white blood cells that provide additional protection
This help protect against:
- Diarrhoea
- Ear infections
- Respiratory infections
- Other early-life illnesses
Why This Is Important?
- A baby’s immune system is immature at birth and takes time to develop.
- Breast milk fills the gap by defending the baby from harmful microbes in the environment.
- This is especially important where access to clean water and healthcare is limited.
🧠 Extra Benefit
- Although passive immunity from breast milk is temporary, it buys time for the baby’s immune system to grow.
- Breastfed babies often have fewer infections in early life, supporting their overall health and development.
📌 Summary
Breastfeeding provides passive immunity by transferring the mother’s antibodies to the baby through milk.
This gives the baby short-term protection from infections during the first few months of life, when their immune system is still developing.
Why Passive Immunity Doesn’t Produce Memory Cells
Passive immunity gives the body ready-made antibodies from another person (like a mother or through medical injection). While this provides quick protection, it does not lead to long-term immunity and here’s why:
🚫 No Memory Cells Are Made
- In passive immunity, the body is not exposed to the pathogen’s antigens in a way that activates its own immune system.
- The body doesn’t make its own antibodies, so it also doesn’t produce memory cells.
- Without memory cells, the immune system doesn’t “learn” or remember how to fight the pathogen in the future.
🔁 What Happens Instead
- The borrowed antibodies give temporary protection.
- After a few weeks or months, these antibodies break down and disappear.
- If the same pathogen infects the body again, the immune system must start from scratch.
📌 Summary
In passive immunity, no memory cells are made because the body doesn’t actively respond to the pathogen.
This means the protection is short-term only and doesn’t result in long-lasting immunity.
Cholera: A Waterborne Bacterial Disease
🦠What is Cholera?
- Cholera is an infectious disease caused by a bacterium called Vibrio cholerae.
- It affects the digestive system, especially the small intestine, leading to severe diarrhoea and dehydration.
Cause of Cholera
The disease is caused by Vibrio cholerae which produces a toxin in the small intestine that interferes with the normal absorption of water.
🌊 How is Cholera Transmitted?
Cholera is mainly spread through contaminated water and sometimes contaminated food.
| Source of Infection | How it Happens |
|---|---|
| Drinking water | Water contaminated with human faeces containing the bacteria |
| Food washed in dirty water | Raw vegetables, fruits, or seafood from infected areas |
| Poor sanitation | Open defecation and lack of clean toilets increase the spread |
⚠️ Symptoms of Cholera
- Profuse watery diarrhoea
- Vomiting
- Severe dehydration
- Rapid weight loss
- If untreated, it can lead to shock or death
✅ Prevention of Cholera
- Drink boiled or purified water
- Improve sanitation and hygiene
- Wash hands before eating or preparing food
- Avoid raw or undercooked food in affected areas
- Vaccination is available in some countries
🧠 Summary
Cholera is a bacterial disease spread through contaminated water and causes severe diarrhoea.
It is preventable with clean water, good hygiene, and proper sanitation.
How Cholera Causes Diarrhoea and Dehydration
Cholera is not just any bacterial infection – it’s dangerous because of how the Vibrio cholerae bacterium disrupts normal body function at the cellular level. Here’s what happens inside the small intestine:
🔬 Step-by-Step: How the Cholera Bacterium Affects the Body
Toxin Production:
- The cholera bacterium enters the small intestine after a person drink contaminated water.
- Once there, it produces a harmful toxin (called cholera toxin).
Disruption of Ion Balance:
- This toxin causes the cells lining the small intestine to secrete chloride ions (Cl⁻) into the gut lumen.
Osmosis and Water Loss:
- As chloride ions build up, water moves out of the body’s cells by osmosis to balance concentrations.
- This causes a massive water outflow into the gut.
Result: Severe Diarrhoea
- The excess water in the gut causes watery diarrhoea.
- Along with water, essential salts (like sodium and potassium) are lost too.
Dangerous Consequences:
- The body becomes quickly dehydrated.
- There’s major ion (electrolyte) loss, which may lead to muscle cramps, organ failure, or death if untreated.
💡 Why Rehydration Is Essential
The main treatment for cholera is rapid oral rehydration therapy (ORT) or IV fluids. This help replace lost water and salts, preventing life-threatening complications.
The cholera bacterium releases a toxin in the small intestine that forces chloride ions out of intestinal cells.
Water follows by osmosis, causing diarrhoea, dehydration, and ion loss, making cholera a medical emergency if untreated.