GCSE Biology Infection & Response

What is a pathogen?

A microorganism that causes disease (bacteria, viruses, fungi or protists)

Name the four main types of pathogen

Bacteria, viruses, fungi and protists

How do bacteria cause disease?

They reproduce rapidly and produce toxins that damage cells and tissues

How do viruses cause disease?

They invade cells and use them to reproduce, destroying the cells in the process

Give one example of a bacterial disease

Salmonella (or gonorrhoea, tuberculosis)

Give one example of a viral disease

Measles (or HIV, tobacco mosaic virus, influenza)

Give one example of a fungal disease

Athlete’s foot (or rose black spot in plants)

Give one example of a disease caused by a protist

Malaria

How is malaria transmitted?

By the bite of an infected female Anopheles mosquito (vector)

What are the three main ways pathogens can be spread?

By air (droplets), by water, and by direct contact

Name three ways the body prevents pathogens from entering

Skin (barrier), mucus and cilia in the airways, hydrochloric acid in the stomach, tears/saliva (lysozyme)

What are the three main ways white blood cells defend against pathogens?

Phagocytosis (engulfing), producing antibodies, producing antitoxins

What is phagocytosis?

When a white blood cell engulfs and digests a pathogen

What are antibodies?

Proteins produced by white blood cells that bind to specific antigens on pathogens and help destroy them

What are antitoxins?

Proteins produced by white blood cells that neutralise the toxins produced by pathogens

What is a vaccine?

A dead or inactive form of a pathogen (or antigen) that stimulates the body to produce antibodies and memory cells

How does vaccination protect against future infection?

Memory cells remain in the blood and can produce antibodies quickly if the same pathogen is encountered again

What is herd immunity?

When a large proportion of the population is vaccinated, making it harder for the pathogen to spread

What are antibiotics used for?

To kill bacteria or stop them reproducing (they do not work on viruses)

Why don’t antibiotics work on viruses?

Viruses live and reproduce inside cells, so antibiotics cannot target them without damaging the host cells

What is antibiotic resistance?

When bacteria evolve so that antibiotics no longer kill them (caused by mutations and overuse of antibiotics)

Name one way to reduce the spread of antibiotic resistance

Only use antibiotics when necessary; complete the full course; do not use them for viral infections

What are painkillers used for?

To relieve the symptoms of a disease (e.g. paracetamol) – they do not kill the pathogen

How are new drugs traditionally discovered?

From plants or microorganisms (e.g. aspirin from willow bark, penicillin from the Penicillium mould)

What are the three main stages of drug testing?

1. Tested on cells/tissues in the lab  2. Tested on animals  3. Clinical trials on humans

What is a double-blind trial?

Neither the patient nor the doctor knows who is receiving the real drug or the placebo – reduces bias

What is a placebo?

A dummy medicine that does not contain the active drug (used in clinical trials)

Name two plant defence responses against pathogens

Cell walls thickened with cellulose, production of antibacterial chemicals, waxy cuticle, stomata can close

What is the difference between a communicable and a non-communicable disease?

Communicable (infectious) diseases can be passed from person to person; non-communicable cannot (e.g. cancer, heart disease)