Infection and Response
Map Your Gaps
Card 1 of 10
Swipe right if you know it, left if you don't
✔ Know
✖ Don't know
Types of pathogen
Pathogens are microorganisms that cause infectious disease. There are four types.
Not all microorganisms are pathogens — most are harmless or beneficial.
Types of pathogen — Key Knowledge
- Bacteria reproduce rapidly in the body, may produce toxins that damage cells and tissues
- Viruses reproduce inside cells, damage the cell when they burst out to release new virus particles
- Fungi cause disease in plants and humans, e.g. rose black spot, athlete's foot
- Protists cause diseases like malaria, often spread by vectors
How diseases spread
Communicable diseases spread between organisms by several routes.
Knowing how a disease spreads determines how to prevent it — nets for vectors, hygiene for food-borne, isolation for droplet.
How diseases spread — Key Knowledge
- Direct contact touching an infected person or surface
- Droplet infection pathogens carried in tiny water droplets from coughing or sneezing
- Contaminated food or water ingesting pathogens, e.g. Salmonella
- Vectors animals that carry pathogens between hosts, e.g. mosquitoes spreading malaria
Specific diseases
You need to know the cause, symptoms, and transmission of several named diseases.
Each disease links to one of the four pathogen types — a common exam question is matching disease to pathogen type.
Specific diseases — Key Knowledge
- Measles virus — fever and rash, spread by droplets
- HIV virus — attacks immune cells, leads to AIDS if untreated, spread by body fluids
- Tobacco mosaic virus plant virus — mosaic pattern on leaves, reduces photosynthesis
- Salmonella bacterium — food poisoning with fever and cramps, spread by contaminated food
- Gonorrhoea bacterium — STI, antibiotic resistance increasing
- Rose black spot fungus — purple/black spots on leaves, spread by wind and water
- Malaria protist — spread by mosquito bites, prevented by nets and insecticides
Non-specific defences
The body has physical and chemical barriers that protect against all pathogens — the first line of defence.
These defences are non-specific — they work the same way regardless of which pathogen is encountered.
Non-specific defences — Key Knowledge
- Skin continuous physical barrier
- Nose hairs and mucus trap particles before they reach the lungs
- Cilia and mucus in trachea and bronchi cilia sweep mucus and trapped pathogens up and away
- Stomach acid hydrochloric acid kills most pathogens that are swallowed
White blood cells
If pathogens get past the first line of defence, white blood cells mount an immune response.
Antibodies are proteins made by white blood cells — do not confuse them with antibiotics, which are medicines.
White blood cells — Key Knowledge
- Phagocytosis white blood cells engulf and digest pathogens
- Antibody production white blood cells produce antibodies specific to the antigens on the pathogen's surface
- Antitoxin production white blood cells produce antitoxins to neutralise toxins released by bacteria
- Antigens unique molecules on the surface of pathogens that trigger the immune response
Vaccination
Vaccines introduce a small quantity of dead or inactive pathogen to stimulate the immune system without causing disease.
Vaccines prevent disease — they do not contain live, dangerous pathogens that can give you the disease.
Vaccination — Key Knowledge
- Dead or inactive pathogen injected to trigger immune response safely
- White blood cells produce antibodies specific to the pathogen's antigens
- Memory cells remain in the body after vaccination
- Rapid response if the same pathogen enters again, antibodies are produced much more quickly
- Herd immunity if a large proportion of the population is vaccinated, spread of the pathogen is greatly reduced
Antibiotics and painkillers
Antibiotics kill bacteria but cannot treat viral infections. Painkillers treat symptoms but do not kill pathogens.
The distinction between treating symptoms and curing disease is a key exam concept.
Antibiotics and painkillers — Key Knowledge
- Antibiotics kill bacteria or prevent them from reproducing
- Cannot treat viruses viruses reproduce inside host cells — antibiotics cannot reach them there
- Painkillers relieve symptoms such as pain and fever but do not cure disease
Antibiotic resistance
Overuse of antibiotics leads to the natural selection of resistant bacterial strains.
It is the bacteria that become resistant, not the human body — a common misconception.
Antibiotic resistance — Key Knowledge
- Random mutations some bacteria naturally develop resistance
- Natural selection resistant bacteria survive antibiotic treatment and reproduce
- Resistant strains spread e.g. MRSA
- Reducing resistance complete the full course of antibiotics, do not overprescribe, do not use antibiotics for viral infections
Drug development
New drugs go through a long testing process before they can be prescribed to patients.
This process takes years and ensures drugs are safe and effective before reaching patients.
Drug development — Key Knowledge
- Preclinical testing tested on cells and tissues in the lab, then on animals — checks toxicity, efficacy, and dose
- Clinical trials on healthy volunteers checks for safety and side effects
- Clinical trials on patients checks efficacy at treating the disease
- Placebos inactive substance given to a control group to compare results
- Double-blind trials neither patient nor doctor knows who receives the drug or placebo
- Peer review results are reviewed by other scientists before publication
Monoclonal antibodies (4.3.4) — Biology Only
Monoclonal antibodies are identical antibodies produced from a single clone of cells. Each targets one specific antigen.
The key idea is specificity — each monoclonal antibody binds to one particular antigen and no other.
Monoclonal antibodies (4.3.4) — Biology Only — Key Knowledge
- Production mouse lymphocytes fused with tumour cells to create hybridoma cells that divide rapidly and produce the desired antibody
- Pregnancy tests detect specific hormones using monoclonal antibodies
- Lab diagnosis identifying specific molecules in blood or other samples
- Cancer treatment carry drugs or radioactive substances directly to cancer cells by targeting tumour antigens
- Limitations more side effects than expected, not as widely used in treatment as initially hoped