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Bacteriophages are viruses that kill bacteria - AQA - A-Level Biology - Question 2 - 2017 - Paper 3
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 3
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. This highlights the structural differences between the two organisms.
Step 2
Using the scales in Figure 2, calculate how many times longer the bacterium is than the bacteriophage. Show your working.
Answer
To find how many times longer the bacterium is than the bacteriophage, we need to use the given scale:
- Distance from A to B for the bacteriophage is approximately 200 nm.
- Distance from A to B for the bacterium is approximately 2 µm (2000 nm).
Now we calculate:
Thus, the bacterium is 10 times longer than the bacteriophage.
Step 3
What would the scientists’ null hypothesis be for this investigation?
Answer
The scientists’ null hypothesis could be: 'There is no difference in the number of live pathogenic bacteria in the mice treated with bacteriophages compared to those not treated with bacteriophages.' This hypothesis establishes a baseline for statistical testing.
Step 4
Use evidence from Figure 3 to explain why dilutions were necessary for some samples but not for others.
Answer
In Figure 3, it shows the mean number of live bacteria for both groups, A and B. The results indicate a significantly higher mean number of bacteria in group A (not treated) than in group B (treated). Dilutions were necessary for group A samples where the number of bacteria was high to ensure accurate counting. In contrast, for group B, the lower bacterial load permitted accurate counting without dilution, facilitating analysis.
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
Figure 3 indicates that the mean number of live bacteria is significantly lower in mice treated with bacteriophage compared to those not treated. This suggests that bacteriophages are effective in reducing the number of pathogenic bacteria in infected mice and underscores their potential therapeutic applications.