Disease and immune defence

Learning objectives

• Distinguish a pathogen from a symptom.
• Explain barriers and immune responses.
• Describe vaccination as immune preparation.

The big idea

Pathogens can spread through several routes, including contaminated food, droplets and vectors. Physical barriers, mucus and stomach acid reduce entry; phagocytes and lymphocytes contribute different defences.

Antibodies recognise particular antigens, while immune memory can support a faster later response. Vaccination exposes the immune system to suitable antigens without causing the target disease in the usual way. Antibiotics treat susceptible bacterial infections, not viruses themselves.

Investigate and explain

Using the worked example as supplied data, predict the effect of changing one condition. Draw a labelled model, record your reasoning and identify a variable that would need controlling. No human, animal or microbial experiment is required.

No exact PhET model is claimed for this topic. Use diagrams and supplied-data reasoning instead.

Open the interactive investigation

Check your understanding