Drug testing and antibioticsEdexcel A-Level Biology A: Subtopic test

1. 1
   In 1785 the doctor William Withering published an account of treating patients who had dropsy (swelling caused by fluid retention) with a herbal remedy later known as digitalis soup. By testing the plants in the mixture separately he showed that foxglove was the active ingredient, and he adjusted the dose according to the response of more than 100 of his patients. He recorded the doses and the outcomes, but all of the patients knew they were being given the remedy.

   (a)

   Which is a weakness of Withering's method when compared with a modern drug trial?

   [1 mark]

   • AHe tested the remedy on patients who had the disease
   • BHe recorded the doses given and the outcomes
   • CHe tested the plants in the mixture separately
   • DHe had no control group and the patients knew they were receiving the remedy

   (b)

   A modern trial of a similar drug gives some patients a placebo. What is a placebo?

   [1 mark]

   • AAn inactive substance that looks the same as the drug
   • BA lower dose of the same drug
   • CA drug that is already licensed for use
   • DA drug with known side effects

   (c)

   Explain why modern drug trials are double blind.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A pharmaceutical company has developed a new drug to lower blood pressure. After testing on cells and animals, it must pass three phases of clinical trials before it can be licensed for use.

   (a)

   Which statement correctly describes phase 1 of a clinical trial?

   [1 mark]

   • AA large number of patients are given the drug or a placebo to compare effectiveness
   • BA small number of healthy volunteers are given the drug to test its safety and side effects
   • CThe drug is tested on cultured cells to see if it is toxic
   • DThe drug is given to the public so that rare side effects can be found

   (b)

   Which is the main reason for using a large number of patients in phase 3?

   [1 mark]

   • ATo find the highest dose that healthy people can tolerate
   • BTo check that the drug is absorbed by animals
   • CTo compare the effectiveness with a placebo or existing treatment and to detect less common side effects
   • DTo reduce the cost of the trial

   (c)

   Suggest why phase 1 uses healthy volunteers rather than patients with high blood pressure.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A student cultures bacteria on nutrient agar in a school laboratory to find out how well the bacteria grow. The student must give the bacteria the conditions they need and must not allow microorganisms from the environment to get into the plates.

   (a)

   Explain three conditions that the student must provide to allow the bacteria to grow on the agar.

   [3 marks]

   (b)

   Explain why the student (i) flames the inoculating loop before use, (ii) lifts the lid of the dish only slightly and for a short time, (iii) tapes the lid on with two short pieces of tape and (iv) incubates the plate at 25 °C rather than 37 °C.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A student investigates whether extracts from garlic, ginger and mint can stop the growth of Escherichia coli. A lawn of the bacteria is spread on nutrient agar. Paper discs (diameter 6 mm) soaked in each extract are placed on the lawn, together with a disc soaked in an antibiotic and a disc soaked in sterile water. The plate is incubated for 48 hours at 25 °C. The diameters of the clear zones, including the 6 mm disc, are: garlic 18 mm, ginger 6 mm, mint 11 mm, antibiotic 26 mm and sterile water 6 mm.

   (a)

   Describe how the student should carry out this investigation so that the plate is not contaminated and the results are valid.

   [6 marks]

   (b)

   Use the results to evaluate the antibacterial activity of the extracts. Include a calculation of the area of the clear zone around the garlic disc.

   [6 marks]

   Total for question 4: 12 marks

End of questions