Infection & response
Communicable diseases and pathogens, the body’s defences, the immune system, vaccination and the development of drugs.
Learn
Infection & response, explained point by point
Everything the GCSE specification expects you to be able to do, and how to actually do it - the same lesson a signed-in student studies from.
Describe pathogens and the four types of disease-causing microbe
Pathogens are microbes that cause communicable (catching) disease, and they come in four types: bacteria, viruses, fungi and protists. Bacteria and viruses reproduce rapidly - bacteria release toxins, while viruses take over your cells to copy themselves. Measles (virus), salmonella (bacterium), rose black spot (fungus) and malaria (protist) are the named examples to know.
Explain how diseases spread and how spread can be reduced
Pathogens pass on through the air, in water or food, by direct contact, or via a vector like a mosquito. Knowing the route tells you how to break it: washing hands and food hygiene stop many bacteria, vaccination protects individuals, and controlling mosquitoes cuts malaria. Isolating infected people stops person-to-person spread.
Describe the body's defences against pathogens
Your first line of defence keeps pathogens out: skin, the nose's hairs and mucus, and stomach acid that kills swallowed microbes. If they get in, white blood cells take over - some engulf and digest pathogens (phagocytosis), others produce antibodies and antitoxins. This is the immune system doing its job before you even notice.
Explain how the immune system and vaccination give immunity
When white blood cells meet a new pathogen they make antibodies that lock onto it, and afterwards they remember it, responding faster next time - that is immunity. A vaccine uses a dead or weakened form to trigger this memory safely, so you are protected without getting ill. When enough people are vaccinated, spread slows for everyone.
Describe antibiotics, painkillers and the problem of resistance
Antibiotics kill bacteria inside the body and have hugely reduced deaths from bacterial disease, but they do not affect viruses. Painkillers ease symptoms without killing the pathogen. Overusing antibiotics lets resistant bacteria (like MRSA) survive and multiply, so doctors prescribe them carefully and patients should finish the whole course.
Describe how new drugs are discovered, developed and tested
Traditional medicines often came from plants - aspirin from willow, digitalis from foxgloves - while most new drugs are now made in the lab. New drugs are tested for toxicity, effectiveness and dose, first on cells and animals (preclinical), then on healthy volunteers and patients (clinical trials). Double-blind trials, where neither patient nor doctor knows who gets the placebo, keep the results fair.
Infection & response key terms
The words the specification and the mark schemes use, each defined the way an examiner wants it.
- Pathogen
- A microorganism that causes infectious disease. Pathogens may be viruses, bacteria, protists or fungi.
- Communicable disease
- A disease that can be passed from one organism to another, for example by direct contact, water, air or vectors.
- Antibody
- A protein produced by white blood cells that binds to the specific antigens on a pathogen, helping to destroy it.
- Antitoxin
- A protein produced by white blood cells that neutralises the toxins released by some bacteria.
- Antibiotic
- A medicine, such as penicillin, that kills bacteria inside the body. Antibiotics do not work on viruses.
- Vaccination
- Introducing a small amount of a dead or inactive form of a pathogen so the immune system learns to make the right antibodies quickly if the real pathogen ever arrives.
- Toxin
- A poison produced by some pathogens, particularly bacteria, that damages tissues and makes us feel ill.
Practice
Try a Infection & response question
A GCSE-style original question from this topic. Have a go before you open the working - deciding on an answer first is what makes the working stick.
Which statement best describes how vaccination protects a person from a disease?
- a dead or inactive pathogen makes white blood cells produce antibodies and memory cells
- antibiotics are injected to kill the pathogen in advance, so it is destroyed before it can ever cause symptoms
- ready-made antibodies are added and stay active forever
- the pathogen is made stronger so the body gets used to it, building up its tolerance with each dose given
Show the answer and the working
Answer: a dead or inactive pathogen makes white blood cells produce antibodies and memory cells
A vaccine primes the immune system so memory cells can respond rapidly to a future infection.
- A vaccine contains a dead or inactive pathogen.
- White blood cells respond by making antibodies against its antigens.
- Memory cells stay in the blood, so a future infection is dealt with quickly.