Disease and response · GCSE Biology
Infection and response
Pathogens, transmission, white blood cells, vaccination, antibiotics and why viruses cannot be treated with antibiotics.
Pathogens cause communicable disease. White blood cells ingest, produce antibodies and produce antitoxins. Vaccines teach memory cells. Antibiotics kill bacteria — they do nothing to viruses.
The important bits
What you need to know
- 1
Pathogens are microorganisms that cause disease: bacteria, viruses, fungi and protists. Communicable diseases can be transmitted from one organism to another.
- 2
Bacteria such as Salmonella and gonorrhoea produce toxins. Viruses such as measles and HIV live and reproduce inside cells, damaging them. Malaria is caused by a protist transmitted by mosquitoes. Rose black spot is a fungal plant disease.
- 3
The body defends itself with the skin, mucus, cilia and stomach acid, then with white blood cells: phagocytosis, antibody production and antitoxin production.
- 4
A vaccine contains a dead or inactive form of a pathogen. White blood cells produce antibodies and memory cells, so a later infection is destroyed before symptoms develop. Herd immunity protects people who cannot be vaccinated.
- 5
Antibiotics kill bacteria or inhibit their growth. They do not affect viruses. Painkillers treat symptoms, not the pathogen. Overuse of antibiotics selects for resistant strains such as MRSA.
- 6
New drugs are tested in preclinical trials on cells and animals, then in clinical trials on healthy volunteers and patients. Double-blind trials with placebos reduce bias.
- 7
HIV infects white blood cells and can lead to AIDS when the immune system cannot fight other infections. Antiviral drugs can stop the virus multiplying but do not cure it.
Go deeper
Name the pathogen type, then the damage
Marks sit in the category. Bacteria are prokaryotic cells that often release toxins. Viruses are not cells; they hijack host cells to copy themselves, which is why antibiotics cannot reach a target cell wall. Fungi such as rose black spot destroy leaves and cut photosynthesis. Protists such as Plasmodium cause malaria and need a vector. Transmission questions want a route: airborne droplets, sexual contact, contaminated food, vector bite, dirty water. Prevention then matches the route: vaccination, condoms, cooking food thoroughly, mosquito nets, sanitation. A vague “hygiene” scores poorly unless you specify the action.
Go deeper
Immunity is memory, not a force field
On first infection, white blood cells that recognise the antigen clone and make antibodies. That takes time, so you feel ill. Memory cells remain. On reinfection they produce the matching antibodies far faster, so the pathogen is destroyed before symptoms. A vaccine fakes the first infection safely. Explain herd immunity as a reduced chance of meeting the pathogen because most people are immune, which protects infants and people with weak immune systems. Antibiotic resistance is natural selection: random mutations, antibiotics kill non-resistant bacteria, resistant bacteria survive and reproduce. Finish a course, do not use antibiotics for viral colds, and do not treat farm animals routinely if the question asks how to reduce resistance.
See the idea in action
Measles is viral and spreads in droplets. A child who is vaccinated receives inactive pathogen. White blood cells make antibodies and memory cells. Later exposure meets a rapid secondary response, so the child does not develop measles. Antibiotics would not treat measles because they do not affect viruses. A bacterial infection such as gonorrhoea can be treated with antibiotics, though resistant strains are a growing problem.
Exam technique
Turn knowledge into marks
State whether the pathogen is a bacterium, virus, fungus or protist before you describe treatment. Vaccination questions need antigens, antibodies and memory cells. Never say vaccines contain “a bit of the disease”.
Common mistakes
Do not give these marks away
- 01
Saying antibiotics kill viruses, or that vaccines contain live disease that makes you ill in the same way as the infection.
- 02
Confusing antibodies with antibiotics.
- 03
Describing white blood cells only as “fighting disease” without phagocytosis, antibodies or antitoxins.
Why do antibiotics not treat measles?
AMeasles is caused by a fungus
BMeasles is caused by a virus, and antibiotics do not affect viruses
CThe measles pathogen lives only in mosquitoes
DAntibiotics only work on plant diseases
Show the answer
Measles is caused by a virus, and antibiotics do not affect viruses. Antibiotics target bacterial processes. Viruses reproduce inside host cells and do not have those targets, so measles needs vaccination and supportive care, not antibiotics.
Quick questions
If this is the bit you searched
How do vaccines work?
They introduce a dead or inactive pathogen. White blood cells produce antibodies and memory cells, so a later infection is dealt with before symptoms develop.
What is the difference between antibiotics and antibodies?
Antibiotics are drugs that kill bacteria. Antibodies are proteins made by white blood cells that bind to specific antigens on a pathogen.