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Dengue is a serious disease that is caused by a virus - AQA - A-Level Biology - Question 2 - 2017 - Paper 1
Question 2
Dengue is a serious disease that is caused by a virus. The virus is carried from one person to another by a mosquito, Aedes aegypti. One method used to try to reduce... show full transcript
Worked Solution & Example Answer:Dengue is a serious disease that is caused by a virus - AQA - A-Level Biology - Question 2 - 2017 - Paper 1
Step 1
Explain how using the SIT could reduce transmission of dengue.
Answer
The Sterile Insect Technique (SIT) reduces the transmission of dengue by introducing sterile males into the mosquito population. These sterile males compete with fertile males for mating opportunities. As a result, the number of successful matings decreases, leading to fewer offspring. Consequently, the overall mosquito population declines, which in turn reduces the spread of dengue.
Step 2
Describe how the mark-release-recapture method could be used to determine the population of A. aegypti at the start of the investigation.
Answer
The mark-release-recapture method involves several key steps:
- Capture a sample of A. aegypti mosquitoes from the habitat.
- Mark the captured mosquitoes in a way that does not affect their survival or behavior and then release them back into their environment.
- Allow time for the marked mosquitoes to disperse and mix within the population.
- In a second sampling event, capture another group of mosquitoes. Count how many of these mosquitoes are marked. The population can be estimated with the equation:
.
Step 3
Suggest one reason why.
Answer
One reason the release of radiation-sterilized A. aegypti has not been very successful is that radiation can affect the mosquitoes' attractiveness, courtship behavior, or survival rates. If the sterilized males cannot effectively compete for mates or if their shortened lifespan results in fewer opportunities to mate, the population control will be less effective.
Step 4
Suggest why the scientists released more transgenic males every week.
Answer
Scientists released more transgenic males weekly to maintain pressure on the existing mosquito population and prevent it from recovering. By continuously introducing sterile males, they ensure that the mating opportunities for fertile females remain low, leading to decreased reproduction and further reduction of the mosquito population.
Step 5
Describe how the results in Figure 2 support this conclusion.
Answer
The results in Figure 2 likely show a decrease in the number of A. aegypti over time in areas where transgenic males were released. If there is a clear trend in the reduction of mosquito populations correlating with the frequency of transgenic male releases, it provides strong evidence that this method is effective in decreasing mosquito numbers. Additionally, data indicating lower mosquito densities over time would directly support the success of the transgenic males in controlling the A. aegypti population, thereby reducing the transmission of dengue.