infection and response

Pathogen

"A microorganism that causes disease."

Types of pathogens

"Bacteria

Bacteria

"Small living cells that reproduce rapidly and release toxins."

Viruses

"Non-living particles that replicate inside host cells and cause cell damage."

Fungi

"Organisms that grow hyphae which penetrate tissue and release spores."

Protists

"Single-celled eukaryotes; some cause disease (e.g.

How pathogens spread

"Direct contact

Preventing spread

"Hand washing

Immune system role

"Protects body against pathogens using white blood cells."

Phagocytosis

"White blood cell engulfs and digests pathogens."

Lymphocytes

"Produce antibodies and antitoxins."

Antibodies

"Proteins that bind to specific antigens on pathogens."

Antigens

"Unique proteins on pathogen surface triggering immune response."

Memory cells

"Long-lived cells that provide immunity after infection."

Vaccination

"Introduction of dead or inactive pathogens to stimulate immunity."

How vaccines work

"Trigger antibody production so immune system responds faster in future."

Herd immunity

"When enough people are vaccinated

Antibiotics

"Drugs that kill bacteria but not viruses."

Painkillers

"Relieve symptoms but do not kill pathogens."

Antibiotic resistance

"Bacteria evolve to survive antibiotics due to overuse or misuse."

MRSA

"Antibiotic-resistant strain of bacteria."

Why antibiotics do not treat viruses

"Viruses replicate inside host cells

Drug discovery sources

"Plants

Aspirin source

"Willow bark."

Penicillin discovery

"Alexander Fleming found mould (Penicillium) producing penicillin."

Modern drug testing

"Preclinical testing (cells/animals)

Preclinical testing

"Tests safety

Clinical trials

"Tests on humans for safety

Double-blind trial

"Neither patient nor doctor knows who has placebo to avoid bias."

Placebo

"Inactive substance used for comparison in trials."

Monoclonal antibodies

"Identical antibodies produced from a single cloned B-lymphocyte."

How monoclonal antibodies are made

"Mouse lymphocyte + tumour cell → hybridoma → divides to produce antibodies."

Uses of monoclonal antibodies

"Pregnancy tests

Monoclonals in pregnancy tests

"Bind to hCG hormone in urine to show positive result."

Advantages of monoclonal antibodies

"Specific

Disadvantages of monoclonal antibodies

"Side effects

Measles cause

"Virus spread by droplets."

Measles symptoms

"Fever

HIV cause

"Virus attacking immune cells."

HIV transmission

"Sexual contact

AIDS

"Final stage of HIV when immune system is severely damaged."

Tobacco mosaic virus (TMV)

"Virus causing mosaic leaf pattern and reduced photosynthesis."

Salmonella

"Bacterial food poisoning causing fever

Salmonella prevention

"Poultry vaccinated; proper cooking; good hygiene."

Gonorrhoea

"Bacterial STD causing discharge and pain when urinating."

Gonorrhoea treatment

"Antibiotics (but resistance increasing)."

Malaria cause

"Protist spread by mosquito vector."

Malaria prevention

"Mosquito nets

Malaria symptoms

"Recurring fever

Plant diseases

"Caused by viruses

Signs of plant disease

"Stunted growth

Identifying plant disease

"Garden manuals

Plant defence — physical

"Cellulose cell wall; tough waxy cuticle; bark; leaf fall removing infected leaves."

Plant defence — chemical

"Antibacterial chemicals; poisons to deter herbivores."

Plant defence — mechanical

"Thorns

Required practical: growing bacteria

"Investigate effect of antibiotics or antiseptics on bacteria using agar plates."

Aseptic technique

"Sterilise equipment

Why incubate at 25°C in school

"Lower temperature reduces growth of harmful bacteria."

Zone of inhibition

"Area where bacteria do not grow around an antibiotic disc."

Calculating inhibition area

"Area = πr²."

How vaccines reduce epidemics

"Fewer infected → less transmission → protects vulnerable people."

Why viruses mutate quickly

"High replication rate and no proofreading during copying."

Antibiotic stewardship

"Using antibiotics only when needed to slow resistance."

Toxin

"Poison released by bacteria causing symptoms."

Antitoxin

"Chemical made by lymphocytes to neutralise toxins."

Why boosters are needed

"Immunity decreases over time as memory cells decline."

Why viruses cause cell damage

"They reproduce inside cells causing them to burst."

Why fungus infections spread quickly

"Spores easily carried by wind or water."

Herd immunity threshold

"Percentage of population needed vaccinated to stop spread."

Why malaria is hard to eradicate

"Mosquito vector widespread; life cycle complex."