Lines of defence, the immune response and memory
Answers are for parents and teachers.
1
Explain how the stomach and the airways each help to keep microbes out.
The stomach lining makes hydrochloric acid, which kills microbes that arrive with food. In the airways, mucus traps microbes and the cilia sweep the mucus out of the body.
2
Compare humoral and cell-mediated immunity: name the main weapon of each.
Humoral immunity uses antibodies against pathogens and toxins in plasma and lymph. Cell-mediated immunity uses T cells, which act with perforin and lymphotoxins.
3
An activated helper T cell divides 5 times in a row. How many cells does it make? If 8 are memory helper T cells, how many are active helper T cells?
2 × 2 × 2 × 2 × 2 = 32 cells. 32 − 8 = 24 active helper T cells (invented numbers).
4
A student says: “If you have had an infection once, you never need a doctor about infections again.” Is that right?
No. Memory cells give fast protection against that same pathogen, but they do not protect against other pathogens, and a doctor decides about any health problem.
5
Using memory cells, explain why a person who has had measles is usually protected from measles later.
Memory cells stay for tens of years. If the measles pathogen returns, they answer at once, so it is usually destroyed before symptoms appear.