Malaria is caused by single-celled parasitic organisms belonging to the protist kingdom.
The most common organisms to cause malaria are Plasmodium falciparum, Plasmodium vivax, Plasmodium
ovale and Plasmodium malariae.
The Plasmodium life cycle takes place in mosquitos and humans. The organisms cause no negative effects to
mosquitos; in humans, however, they go through several growth stages while located in the liver cells and
red blood cells, leading to severe health effects.
The drug chloroquine was first discovered by German chemists and from the 1950s was widely used as a
successful treatment for malaria.
However, in the 1990s, health workers and scientists documented a gradual increase in the number of
malaria cases in which chloroquine was ineffective as a treatment.
Which of the following is the most likely explanation?
A. Malaria sufferers were now excreting chloroquine before it could kill the parasite.
B. Mutations conferring chloroquine resistance were now arising more frequently in Plasmodium
organisms.
C. The use of chloroquine favoured the survival and reproduction of resistant parasites.
D. A new species of Plasmodium had emerged.
Answer is C
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