Immunity, antibodies and vaccination

Learning objectives

• Compare innate and adaptive defences.
• Explain clonal selection and memory.
• Distinguish active and passive immunity.

The big idea

Phagocytes and other innate defences respond broadly, while adaptive responses involve antigen-specific lymphocytes. Antigen recognition stimulates suitable clones; plasma cells secrete antibodies and memory cells support later responses.

Active immunity follows an individual’s own immune response, whereas passive immunity involves transferred antibodies and does not create the same memory by that transfer alone. Vaccination programmes depend on efficacy, coverage, pathogen behaviour and access. Antibody structure links specificity with binding.

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