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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) can reduce the transmission of dengue by introducing large numbers of sterile male Aedes aegypti into the population. These sterile males compete for mates with fertile males, but since they are sterile, they do not reproduce. As a result, the overall population of mosquitoes declines due to a reduction in successful mating, leading to fewer offspring and ultimately reducing the number of mosquitoes capable of transmitting the dengue virus.
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
To use the mark-release-recapture method, researchers first capture a sample of Aedes aegypti mosquitoes and mark them with a non-toxic identifier. After marking, they release the mosquitoes and allow them some time to disperse and interbreed. Later, a second sample is captured, and the number of marked mosquitoes within this second sample is recorded. The population of A. aegypti can be estimated using the formula:
ext{Population} = rac{ ext{Number in first sample} imes ext{Number in second sample}}{ ext{Number marked in second sample}}
Step 3
Suggest one reason why.
Answer
One reason the release of radiation-sterilized A. aegypti has not been very successful is that radiation may impair their mating abilities or survival, meaning fewer sterile males are able to effectively compete for mates or live long enough to mate.
Step 4
Suggest why the scientists released more transgenic males every week.
Answer
Scientists likely released more transgenic males every week to maintain a sufficient population of these mosquitoes in the habitat, ensuring continued competition with the fertile males. This consistent release also helps counteract the natural death rate of mosquitoes in the population, ensuring the control measures remain effective.
Step 5
Describe how the results in Figure 2 support this conclusion.
Answer
The results in Figure 2 support the conclusion by demonstrating a marked decline in the population of Aedes aegypti mosquitoes in the treated area after the release of transgenic males. If the number of mosquitoes was significantly lower compared to untreated areas over time, it suggests that the introduction of sterile males was effective in reducing overall mosquito numbers and thereby decreasing the potential for dengue transmission.