Disease and immunity Cambridge IGCSE Biology (9–1) revision
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In plain words
Some diseases are caught: a microbe gets in, multiplies and makes you ill. Your body has walls to keep microbes out and an army of white blood cells for the ones that get through. That army also remembers, which is why you usually catch chickenpox only once, and why vaccines work.
Three things to know
- A pathogen is an organism that causes disease. A transmissible disease is one in which the pathogen can pass from one host to another: by direct contact (blood, body fluids) or indirectly (air, food, water, surfaces, animals).
- Defences: skin, hairs in the nose, mucus, stomach acid, and white blood cells. Clean water, hygienic food preparation, hand-washing and sewage treatment stop diseases spreading.
- Every pathogen has its own antigens. Lymphocytes make antibodies with the shape to fit them. Memory cells stay behind, so a second infection is dealt with quickly: this is active immunity. A vaccine contains a harmless form of the pathogen that produces the same memory cells.
Tips and tricks
- Antigen: on the pathogen. Antibody: made by you. Antibiotic: a medicine. Three different words.
- A vaccine doesn't contain antibodies. It makes your body produce its own, and the memory cells to make more.
It lands in your notebook with its questions as flashcards.
Disease and immunity: 5 questions and answers
These are the quiz’s questions. Do the quiz first, then come back here for the ones that got you.
What is a pathogen?
Bacteria, viruses, fungi and protoctists can all be pathogens.
Which is a barrier that stops pathogens entering the body?
Unbroken skin is hard for microbes to cross.
What do antibodies attach to?
Each antibody fits one kind of antigen.
What does a vaccine contain?
It triggers the body to make its own antibodies and memory cells.
Why does a second infection by the same pathogen usually cause no illness?
The response is fast enough to destroy the pathogen before symptoms appear.
Quiz
5 questions
Tap an answer and you’ll see straight away whether it’s right, and why.
Worksheet
3 questions, 8 marks. Write your answers on paper, then check them.
Disease and immunity
Cambridge IGCSE Biology (9–1) 0970 · 8 marks · papermunch.org
Name ______________________________ Date ______________
State what is meant by a pathogen and by a transmissible disease.[2]
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A pathogen is a disease-causing organism. A transmissible disease is one in which the pathogen can be passed from one host to another.
Give three ways in which the body is defended against pathogens.[3]
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Any three: skin as a barrier; hairs in the nose; mucus; stomach acid; white blood cells (phagocytosis, antibodies).
Explain how vaccination protects a person against a disease.[3]
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A harmless (dead or weakened) form of the pathogen, with its antigens, is given. Lymphocytes make antibodies and memory cells. If the real pathogen arrives later, the memory cells make antibodies quickly, before the person becomes ill.
Answers: Disease and immunity
- 1. A pathogen is a disease-causing organism. A transmissible disease is one in which the pathogen can be passed from one host to another.
- 2. Any three: skin as a barrier; hairs in the nose; mucus; stomach acid; white blood cells (phagocytosis, antibodies).
- 3. A harmless (dead or weakened) form of the pathogen, with its antigens, is given. Lymphocytes make antibodies and memory cells. If the real pathogen arrives later, the memory cells make antibodies quickly, before the person becomes ill.