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IMSO 2006 Science – Taiwan Selection First Round Theory Question 15

IMSO Science · IMSO 2006 Science – Taiwan Selection First Round Theory

Question 15

Base your answers to questions 40 and 41 on the information below and on your knowledge of biology. A small village was heavily infested with mosquitoes. The village was sprayed weekly with an insecticide for a period of several months. The results of daily counts of the mosquito population are shown in the graph below.

*Editorial note: the source labels this passage 40 and 41; it applies to questions 14 and 15 here.*

Question illustration

Which statement best explains the decreased effectiveness of the insecticide?
  1. The insecticide caused mutations that resulted in immunity in the mosquito.
  2. Mosquitoes resistant to the insecticide lived and produced offspring.
  3. The insecticide reacted chemically with the DNA of the mosquitoes and was destroyed.
  4. All of the mosquitoes produced antibodies that activated the insecticide.