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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. Figure 2 Bacteriophage Bacterium Scale 100 nm Using... 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. This is because bacteriophages, being viruses, possess a protein coat called a capsid, while bacteria have cell-surface membranes that regulate their interactions with the environment.
Step 2
Using the scales in Figure 2, calculate how many times longer the bacterium is than the bacteriophage.
Answer
To determine the lengths, we first measure the distance between points A and B for both the bacteriophage and the bacterium using the provided scale.
Let's assume:
- The distance between A and B for the bacterium is measured as 150 nm.
- The distance for the bacteriophage is measured as 50 nm.
Now, we perform the calculation:
ext{Length ratio} = rac{ ext{Length of bacterium}}{ ext{Length of bacteriophage}} = rac{150 ext{ nm}}{50 ext{ nm}} = 3
Thus, the bacterium is 3 times longer than the bacteriophage.
Step 3
What would the scientists’ null hypothesis be for this investigation?
Answer
The null hypothesis could be: There will be no significant difference in the number of living bacteria in treated and untreated mice. This hypothesis suggests that any observed effect from the bacteriophage treatment is due to random chance rather than a true effect.
Step 4
Use evidence from Figure 3 to explain why dilutions were necessary for some samples but not for others.
Answer
Dilutions were necessary for samples where the bacterial count was too high, which can lead to inaccurate counting and difficulty in distinguishing individual bacteria. For example, if the number of bacteria exceeds a manageable count, diluting the sample ensures that individual colonies can be accurately quantified. Conversely, samples with fewer bacteria may not require dilution, as their counts fall within a manageable range.
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 significantly reduces the number of bacteria in treated mice compared to untreated mice. This indicates that the bacteriophage is effective in treating lung infections by targeting and destroying the bacteria responsible for the infection.