MYP Biology sample question: Vaccination and herd immunity

Vaccination programmes have greatly reduced the number of cases of diseases such as measles.

1. (a)Explain how a vaccine gives a person immunity to a disease.[3]
   Show the mark scheme for (a)

   • • The vaccine contains a weakened or dead pathogen, or its antigens (1)
   • • This stimulates white blood cells to make antibodies and memory cells (1)
   • • If the real pathogen enters later, the response is faster and stronger (1)
2. (b)Explain what is meant by herd immunity.[2]
   Show the mark scheme for (b)

   • • When a large proportion of the population is immune, the pathogen spreads less (1)
   • • which also protects people who cannot be vaccinated, such as babies (1)

Mention antigens, antibodies and memory cells in that order. Herd immunity protects people who are not vaccinated.