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Dengue is a serious disease that is caused by a virus - AQA - A-Level Biology - Question 2 - 2017 - Paper 2
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 reduce transm... 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 2
Step 1
Explain how using the SIT could reduce transmission of dengue.
Answer
The Sterile Insect Technique (SIT) reduces dengue transmission by introducing sterile male Aedes aegypti into the population. When these sterile males mate with fertile females, they produce no offspring, leading to a decline in the mosquito population over time. This reduces the number of mosquitoes capable of transmitting the dengue virus, thereby minimizing the incidence of the disease.
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 determine the population of Aedes aegypti, researchers would capture a sample of mosquitoes from a designated area and mark them. After releasing these marked mosquitoes back into the environment, they would allow time for the population to mix. Subsequently, another capture would occur, and the number of marked mosquitoes in this second sample could indicate the total population size using the formula:
where:
- N = total population size
- M = number of marked mosquitoes released
- C = total number of mosquitoes captured in the second sample
- R = number of marked mosquitoes recaptured.
Step 3
Suggest one reason why the release of radiation-sterilised A. aegypti has not been very successful in controlling the transmission of dengue.
Answer
One reason for the limited success of radiation-sterilised A. aegypti in controlling dengue could be that these males may still attract females due to their courtship behavior, yet they do not produce viable offspring. Additionally, if a significant number of fertile males are still present in the population, they can continue mating with females, leading to population sustainability.
Step 4
Suggest why the scientists released more transgenic males every week.
Answer
The scientists likely released more transgenic males every week to maintain a consistent and high ratio of transgenic males to wild males in the population. This strategy would enhance the likelihood of mating between transgenic males and wild females, ultimately increasing the effectiveness of the lethal gene in reducing the number of Aedes aegypti.
Step 5
Explain how the results in Figure 2 support this conclusion.
Answer
The results shown in Figure 2 indicate a significant decrease in the number of Aedes aegypti per km² in the treated area compared to the control area over the weeks. This decline suggests that the released transgenic males effectively reduced the population of A. aegypti, supporting the conclusion that the release of transgenic males with a lethal gene is a successful method for controlling dengue transmission.