Explain how a vaccination can prevent an illness.
Resposta curta
A vaccine contains a dead, inactive or weakened form of a pathogen, or parts of it, carrying its antigens. White blood cells (lymphocytes) respond by making specific antibodies and memory cells. If the real pathogen enters the body later, memory cells recognise it and antibodies are produced much faster and in larger amounts, so the pathogen is destroyed before it causes illness.
Passo a passo
- The vaccine introduces antigens from a harmless form of the pathogen.
- Lymphocytes recognise the antigens as foreign.
- They produce antibodies that are specific to those antigens.
- Memory cells are made and stay in the blood.
- On a later infection, the secondary response is faster and stronger, so symptoms do not develop.
Exemplo resolvido
A strong 4-mark answer includes
- Dead or inactive pathogen, or its antigens
- Lymphocytes produce specific antibodies
- Memory cells are formed
- Rapid production of antibodies on reinfection
Erros comuns
- Saying the vaccine contains antibodies. It contains antigens; the body makes the antibodies.
- Saying vaccines kill bacteria. That is what antibiotics do, and they do not work on viruses.
- Leaving out memory cells, which earn a mark on almost every mark scheme.
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