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Bacteriophages are viruses that kill bacteria - AQA - A-Level Biology - Question 2 - 2017 - Paper 1
Question 2
Bacteriophages are viruses that kill bacteria. Figure 2 shows drawings of a bacteriophage and a bacterium. Both have ribosomes. Both have a cell-surface membrane.... show full transcript
Worked Solution & Example Answer:Bacteriophages are viruses that kill bacteria - AQA - A-Level Biology - Question 2 - 2017 - Paper 1
Step 1
Using Figure 2 and your own knowledge, put a tick (✓) in the box next to the only correct statement about the structures of the bacteriophage and the bacterium.
Answer
The correct statement is: The bacteriophage has a capsid and the bacterium has a cell-surface membrane.
Explanation: The bacteriophage is a virus that does not have ribosomes or a cell wall. Instead, it has a capsid, which is a protein coat. Meanwhile, bacteria do possess ribosomes and a cell-surface membrane.
Step 2
Using the scales in Figure 2, calculate how many times longer the bacterium is than the bacteriophage.
Answer
To find how many times longer the bacterium is:
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Measure the distance between points A and B for both the bacteriophage and the bacterium. For example:
- Distance A to B for bacteriophage: 150 nm
- Distance A to B for bacterium: 2000 nm
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Use the formula:
ext{Scale Ratio} = rac{ ext{Length of Bacterium}}{ ext{Length of Bacteriophage}} = rac{2000 ext{ nm}}{150 ext{ nm}}
ightarrow 13.33
Step 3
What would the scientists’ null hypothesis be for this investigation?
Answer
The null hypothesis could state that there will be no significant difference in the number of (living) bacteria in treated and untreated mice. This implies that the bacteriophage treatment does not affect bacterial counts in the mice.
Step 4
Use evidence from Figure 3 to explain why dilutions were necessary for some samples but not for others.
Answer
From Figure 3, it can be observed that some samples showed a wide range in the number of bacteria. In cases where the density of bacteria was very high, dilutions were necessary to accurately count the bacteria, as counting too many would lead to inaccurate results. Conversely, in some samples with lower bacterial counts, a dilution was not necessary. This ensures precision in counting when bacteria are too numerous to quantify reliably.
Step 5
Using only Figure 3, what can you conclude from these data about the effectiveness of the bacteriophage in treating this lung infection in mice?
Answer
The data in Figure 3 indicates that treatment with the bacteriophage resulted in a notable reduction in the number of bacteria in infected mice. This suggests that the bacteriophage is effective in targeting and eliminating bacterial infections. However, further analyses would be needed to confirm the exact effectiveness and potential differences in response rates.