This mini-lesson walks you through Cambridge IGCSE Diseases & immunity: pathogens and transmissible disease, the body's defences, active vs passive immunity, vaccination, and antibiotics.
Make a guess: how can a dead or inactive germ keep you safe?
Mission 1How does a vaccine protect you?
Mission 2Why can't antibiotics cure a cold?
Work through each screen, answer the questions as you go (some wordy, some calculations) and collect ⭐ stars. Watch for the Key term flags. Press Start when you're ready.
Disease · pathogens
Pathogens & transmissible disease
A pathogen is a disease-causing organism — usually a microorganism. A transmissible disease is one where a pathogen can be passed from one host to another.
Pathogens can be bacteria, viruses, fungi or protoctists.
They spread by direct contact (e.g. touching, blood, body fluids) and indirect contact (e.g. contaminated food or water, droplets in the air).
Good hygiene, clean water, safe food handling and covering coughs all reduce transmission.
Body barriers: the skin, hairs in the nose, mucus (moved by cilia in the airways) and stomach acid all help stop pathogens entering in the first place.
Quick check
What is a pathogen?
?Which of these best describes a pathogen?
Disease · body defences
The body's defences
If a pathogen does get in, white blood cells defend the body in two main ways:
Phagocytosis — phagocytes engulf and digest pathogens.
Antibody production — lymphocytes make antibodies, special proteins that lock onto antigens on the pathogen, destroying it or marking it for phagocytes to engulf.
Antibodies are specific — each type fits only one antigen, like a key in a lock.
Memory cells: after an infection, some lymphocytes stay as memory cells. If the same pathogen returns, they make antibodies faster and in greater numbers, so you don't get ill — this is immunity.
Sort it
Barrier, phagocyte, or antibody?
Tap a defence, then tap which kind it is.
🛡️ Barrier (keeps out)
😋 Phagocyte
🔑 Antibody
Key term · immunity
Active vs passive immunity
There are two kinds of immunity, and the difference is who makes the antibodies:
Active immunity — your own body makes the antibodies (and memory cells) after meeting an antigen — either by catching the disease or by vaccination. It is long-lasting.
Passive immunity — antibodies are given to you ready-made, e.g. across the placenta or in breast milk from mother to baby. It gives quick but short-lived protection, with no memory cells.
Vaccination gives active immunity; a baby getting antibodies in breast milk gets passive immunity.Quick check
Active or passive?
?A newborn baby receives antibodies from its mother through breast milk. What type of immunity is this?
Disease · vaccination
Vaccination
A vaccine contains a weakened or dead pathogen (or its antigens). It trains the immune system without making you ill:
The antigens in the vaccine make lymphocytes produce antibodies.
The body also makes memory cells.
If the real pathogen ever enters, memory cells make antibodies quickly and in large amounts, destroying it before you become ill.
Herd immunity: if enough people in a population are vaccinated, the pathogen cannot spread easily, protecting even those who are not vaccinated.
Careful: a vaccine does not "kill" the pathogen directly. It prepares your immune system so it can respond fast in future.
Calculate
Your turn — vaccine uptake
1In a town of 500 children, 420 have been vaccinated against measles. Calculate the percentage of children vaccinated.
?A child is given a vaccine containing a dead form of a virus. Later, the live virus gets into her body, but she does not become ill. Why not?
Mission 2 of 2
Why can't antibiotics cure a cold?
Make a guess: why won't antibiotics cure a cold?
Disease · antibiotics
Antibiotics
Antibiotics are drugs that kill bacteria (or stop them growing) inside the body, without harming your own cells. Penicillin was the first.
Very important: antibiotics work on bacteria only. They do not work against viruses (like colds and flu), because viruses reproduce inside your own cells.
Antibiotic resistance: overusing antibiotics has let some bacteria become resistant. To slow this down, you should:
Only take antibiotics when they are really needed (not for viral infections).
Always finish the whole course, even if you feel better.
Mission 2 check
Why can't antibiotics cure a cold?
?Sam has a cold. He takes some antibiotics. A week later his cold is no better. What is the best explanation?
Match it
Match each term to its meaning
Tap a meaning on the left, then its matching term on the right.
Meaning
Term
Quick check
Will antibiotics help?
?A patient has flu, which is caused by a virus. Why won't antibiotics cure it?
Quick check
Why don't you catch it twice?
?After recovering from chickenpox, a child does not get it again. What best explains this?