Questions 
Q1.
 
The effect of three different antibiotics, P, Q and R, on one strain of bacteria, was investigated.
Small discs of filter paper were each soaked in a different antibiotic and dried. These discs were used in this investigation.
The flow chart below shows the procedures used in this investigation.

Explain why the Petri dishes were incubated at 30°C.
(2)
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(Total for question = 2 marks)

Q2) Explain why there are more risks involved in the procedures used for Petri dish 1 than the procedures used for Petri dish 2.
(2)
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(Total for question = 2 marks)

Q5.
 
Antibiotics are used to treat bacterial infections in eukaryotic organisms.
(a) The table below describes some of the structures that are found in cells. Complete the table by writing the name of each of the structures described and stating whether it is found in prokaryotic cells only (P), eukaryotic cells only (E) or both types of cell (B).
(3)

(b) Vancomycin is an antibiotic that kills bacterial cells by preventing the synthesis of peptidoglycan, a component of bacterial cell walls.
(i) State the term used to describe antibiotics, such as vancomycin, that kill bacterial cells.
(1)
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(ii) Suggest how bacterial cells are killed by vancomycin.
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(iii) Explain why doctors have been advised to limit the prescription of antibiotics.
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(c) Describe how you could investigate the effect of different antibiotics on bacteria.
(4)
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(Total for question = 12 marks)

Q6.
 
Blowfly larvae can be used by a forensic scientist to help determine the time of death of a body.
The diagram shows a Petri dish used by a student to investigate whether young and old blowfly larvae show a preference for light or dark conditions.

In the first trial, the left side was dark and the right side was light.
Five blowfly larvae were added to each side of the chamber.
After five minutes, the number of larvae on each side of the Petri dish was recorded.
In the second trial, the same experiment was repeated but this time the right side was dark and the left side was light.
The table shows the results of the trials.

(a)  Give a null hypothesis for this investigation.
(1)
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(b)  The Chi squared test can be used to determine whether the results of this investigation indicate a significant difference in the distribution of young larvae between the light and the dark side.

(i)  Use the formula to calculate the Chi-squared value for young larvae.
(3)

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(ii)  The table below gives some critical values for Chi-squared.

Use your calculated value to determine whether the difference between the observed and expected results is significant.
(1)
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(c)  Forensic scientists measure the length of larvae found in the tissues of a dead person to help them determine time of death. Older larvae are longer than younger larvae.
The growth of insect larvae can be affected by a number of factors including toxins.
Explain a procedure that you could use to find out if the presence of a toxin in a sample of dead tissue could affect the accuracy of estimating time of death.
(5)
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(Total for question = 10 marks)