Edexcel GCSE Biology: Health, Disease and the Development of Medicines

A child is given a vaccine against the measles virus. Some weeks later the child is exposed to the live measles virus but does not become ill.

Explain how the vaccine made the child immune to measles. In your answer you should refer to antigens, antibodies and memory cells. (6 marks)

Before a new medicine can be sold, it must pass through pre-clinical testing and then clinical trials.

(a) In pre-clinical testing, the drug is first tested on cells and tissues, and then on live animals. Give one thing that pre-clinical testing checks for. (1 mark)

(b) In the first phase of a clinical trial, the drug is given to a small number of healthy volunteers. State what this phase is mainly testing for. (1 mark)

(c) Many clinical trials are "double-blind" and use a placebo. Explain why using a placebo in a double-blind trial makes the results more valid. (2 marks)

Phagocytes are white blood cells that defend the body against pathogens by phagocytosis.

Describe how a phagocyte destroys a pathogen by phagocytosis. (3 marks)

A person was infected with the same pathogen on two occasions. The concentration of the specific antibody in their blood was measured after each infection. The data are shown below.

Days after infection	Antibody concentration after 1st infection / arbitrary units	Antibody concentration after 2nd infection / arbitrary units
0	0	0
5	2	25
10	8	60
15	12	55

(a) State two ways in which the antibody response to the 2nd infection differs from the response to the 1st infection. (2 marks)

(b) Explain why the person did not become ill after the 2nd infection. (1 mark)

A patient has a viral infection (influenza). A doctor explains that prescribing antibiotics would not help.

Explain why antibiotics are not effective against viruses. (2 marks)

Every type of pathogen carries unique molecules on its surface that the immune system can recognise as "foreign".

Name these surface molecules that trigger an immune response. (1 mark)