Barriers and non-specific defencesEdexcel A-Level Biology A: Mind map

Exam questions on Barriers and non-specific defences

1. Pathogens can enter the body by several routes and the body has barriers against each one. In hospital, patient 1 has taken a broad-spectrum antibiotic for ten days and has developed severe diarrhoea caused by Clostridium difficile in the gut. Patient 2 takes a drug that raises the pH of the stomach contents from about pH 2 to about pH 5.
   Explain why taking a broad-spectrum antibiotic could lead to the infection in patient 1.2 marks
2. A student cuts her finger on broken glass. Within a few minutes the area around the cut becomes red, warm, swollen and painful, although the cut was cleaned straight away.
   Explain how inflammation helps the body to fight an infection in the cut.2 marks
3. Interferon is released by cells infected with a virus. In an experiment, two dishes of cultured cells were exposed to the same dose of influenza virus. One dish had been treated with interferon for six hours beforehand and one was untreated. After 48 hours the untreated dish had 120 plaques (areas of dead cells) and the interferon-treated dish had 18 plaques.
   Describe how interferon protects cells from viral infection.3 marks