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Alzheimer's disease (AD) is a non-reversible brain disorder that develops over a number of years - AQA - A-Level Biology - Question 10 - 2017 - Paper 1
Question 10
Alzheimer's disease (AD) is a non-reversible brain disorder that develops over a number of years. At the start of 2014 the number of Americans with AD was estimated ... show full transcript
Worked Solution & Example Answer:Alzheimer's disease (AD) is a non-reversible brain disorder that develops over a number of years - AQA - A-Level Biology - Question 10 - 2017 - Paper 1
Step 1
Assuming one with AD died in 2014, calculate the annual percentage increase in AD cases in America for 2014 (lines 2–4).
Answer
To find the annual percentage increase, we use the formula:
ext{Percentage Increase} = rac{ ext{New Value} - ext{Old Value}}{ ext{Old Value}} imes 100Let the number of cases in 2014 be 5.4 million, and assume the old value was 5.3 million.
So,
ext{Percentage Increase} = rac{5.4 - 5.3}{5.3} imes 100 \\ ext{Percentage Increase} = rac{0.1}{5.3} imes 100 \\ ext{Percentage Increase} ext{≈ } 1.89 ext{%}If you were to take the numbers more precisely as 5.4 million (i.e., 5,400,000) and calculate based on whatever the previous year's calculated value, the percentage might slightly vary,
Step 2
Explain how donepezil could improve communication between nerve cells (lines 7–9).
Answer
Donepezil improves communication between nerve cells by inhibiting the enzyme acetylcholinesterase. This enzyme breaks down acetylcholine, a neurotransmitter essential for memory and learning. By inhibiting this enzyme, donepezil allows for increased levels of acetylcholine in the synaptic cleft, enhancing neurotransmission, which can help mitigate symptoms of Alzheimer’s disease.
Step 3
Suggest and explain two reasons why there is a high frequency of the E280A mutation in Yaramul (lines 13–15).
Answer
- Founder Effect: The E280A mutation may have originated from a small ancestor population. As the population expanded, the mutation frequency increased due to the limited genetic diversity.
- Inbreeding: Due to the isolated nature of Yaramul, interbreeding among the population can raise the frequency of the E280A mutation because offspring are more likely to inherit the same alleles from a common ancestor.
Step 4
Explain why natural selection has not reduced the frequency of the E280A mutation in the population (lines 16–17).
Answer
Natural selection has not reduced the frequency of the E280A mutation because it leads to early-onset Alzheimer’s disease, which may not significantly affect reproductive success. Therefore, individuals with the mutation may still reproduce before symptoms appear, allowing the mutation to persist in the gene pool.
Step 5
The age at which the E280A mutation is expressed to cause AD can vary. Suggest one reason for this (lines 11–12).
Answer
One reason for the variation in the age of onset can be genetic factors, such as the presence of other alleles that may influence the expression of the E280A mutation. Environmental factors such as lifestyle and diet can also play a role in determining the age at which AD symptoms develop.
Step 6
Suggest explanations for the figures the scientists recorded (lines 19–21).
Answer
The discrepancy between the number of E280A mutations detected (75) and the potential AD cases (74) suggests that not all individuals with the mutation will develop Alzheimer's. This could be due to factors such as incomplete penetrance, environmental influences, or the presence of protective alleles that mitigate the effects of the E280A mutation.
Step 7
Suggest why a DNA probe for the mutated triplet was not considered a suitable method for detection of the E280A mutation (lines 23–23).
Answer
A DNA probe for the mutated triplet may not be suitable for detection because the mutation could be common or found in other places, leading to false positives. Additionally, non-specific binding may occur, making it difficult to accurately identify individuals with the E280A mutation.