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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 - AQA - A-Level Biology - Question 2 - 2017 - Paper 3
Question 2
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. Bot... show full transcript
Worked Solution & Example Answer: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 - 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 that the bacteriophage has a capsid and the bacterium has a cell-surface membrane. This reflects the structural differences between these two entities, where the bacteriophage is a virus and lacks cellular structures like ribosomes and cell walls.
Step 2
Using the scales in Figure 2, calculate how many times longer the bacterium is than the bacteriophage.
Answer
To calculate how many times longer the bacterium is than the bacteriophage, we measure the length from point A to point B for both structures using the provided scale. For the bacterium, the length is approximately 2 µm, and for the bacteriophage, it is approximately 0.1 µm. Therefore, the calculation is as follows:
ext{Length ratio} = rac{ ext{Length of bacterium}}{ ext{Length of bacteriophage}} = rac{2~ ext{µm}}{0.1~ ext{µm}} = 20
Thus, the bacterium is 20 times longer than the bacteriophage.
Step 3
What would the scientists' null hypothesis be for this investigation?
Answer
The null hypothesis for this investigation could be stated as: There is no significant difference in the number of live bacteria in the lungs of mice treated with bacteriophage compared to those not treated with bacteriophage.
Step 4
Use evidence from Figure 3 to explain why dilutions were necessary for some samples but not for others.
Answer
Figure 3 demonstrates a broad range of bacterial counts among the groups. Some samples may contain an excessively high concentration of bacteria, thereby making accurate counting difficult without dilutions. The scientists employed dilutions to ensure that the concentration of bacteria was low enough to enable precise counting, particularly in the case of high counts which can lead to clumping and inaccuracies. Conversely, if a sample has a count low enough already, no dilutions are required.
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
From Figure 3, it can be concluded that the bacteriophage reduces the number of pathogenic bacteria in the lungs of treated mice compared to untreated mice. The mean number of bacteria present in group B (treated with bacteriophage) is significantly lower than that in group A (not treated), indicating that the treatment is effective in reducing bacterial counts in this experimental setup.