Living Environment - January 2011


Base your answers to questions 51 through 53 on the passage below and on your knowledge of biology.

A New Theory on Malaria Transmission
Plasmodium falciparum, one parasite that causes malaria, spreads rapidly, infecting up to 500 million people every year. Malaria spreads when an infected mosquito bites an uninfected human, who then becomes infected. This infected human is bitten by an uninfected mosquito, which then becomes infected. This infected mosquito then
bites and infects an uninfected human. Malaria transmission is illustrated below.

Scientists have a new idea about how this disease spreads. When the malaria parasite is passed to humans through the bite of an infected mosquito, there is a great possibility that this action alters the chemical scent of the human. The altered human body scent then attracts more uninfected mosquitoes, which bite the infected person, thus spreading the disease.

To test this hypothesis, an experiment was conducted on humans infected with malaria. The results indicate that malaria gametocytes (a stage of the parasite) may trigger the production of chemicals that change the scent of the human. The change in human scent makes humans more appealing to mosquitoes. Scientists are now studying ways to copy this chemical scent for use in traps that would attract mosquitoes.

51 Which statement best describes the role of gametocytes in the spread of malaria?

(1) They give off a scent that attracts infected mosquitoes.
(2) They absorb human body scents that attract mosquitoes.
(3) They release a scent into the human body.
(4) They cause a chemical reaction that alters human scent

52 Malaria is easily spread because uninfected mosquitoes are attracted to

(1) humans without malaria
(2) humans infected with gametocytes
(3) gametocytes in other mosquitoes
(4) mosquitoes that are uninfected

53 State one reason why the use of synthetic scents in traps is a better way to lower
mosquito populations than spraying with pesticides. [1]

Base your answers to questions 54 and 55 on the information below and on your knowledge of biology.

The graph below shows the effect of substrate concentration on the action of enzyme X. This enzyme is functioning at its optimal temperature, 36C, and at its optimal pH, 5.5.

54 When the substrate concentration increases from 0.4% to 0.5%, the rate of the

(1) decreases
(2) increases
(3) remains the same
(4) increases, then decreases

55 State what would most likely happen to the rate of enzyme action if the temperature
were reduced by 10 degrees. Support your answer. [1]

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