What You Need to Know

Key Concept Diagram

The immune system has non-specific defences (skin, mucus) and specific immune responses (antibodies)

White blood cells (lymphocytes) produce antibodies that are specific to each pathogen's antigens

Memory cells remain after infection or vaccination, enabling a faster response if the pathogen returns

Herd immunity occurs when enough of a population is immune to protect vulnerable individuals

Key Vocabulary

Antigen

A molecule on a pathogen's surface that triggers an immune response

Antibody

A protein produced by white blood cells that binds specifically to a matching antigen

Vaccination

Introducing a weakened or inactive pathogen (or its antigens) to stimulate immunity without disease

Memory cells

Long-lived immune cells that remain after infection to enable a faster response to future exposure

Knowledge Check

Select the correct answer for each question. Click "Check Answer" to see if you are right.

Question 1

How do vaccines protect against disease without causing it?

They kill all bacteria in the body They replace the immune system They make the body too acidic for viruses They contain antigens that stimulate the immune system to produce antibodies and memory cells without causing disease

Question 2

Why can the immune system respond faster to a second infection by the same pathogen?

Memory cells from the first infection recognise the antigen and trigger a rapid antibody response The body produces more blood during infection The pathogen is weaker the second time The body becomes allergic to the pathogen

Question 3

Herd immunity protects people who cannot be vaccinated. This works because:

The vaccine spreads from vaccinated to unvaccinated people When enough people are immune, pathogens cannot spread through the population easily Unvaccinated people develop natural immunity over time Vaccines are not necessary if most people are healthy

Immune System and Vaccines