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

Exam questions on Barriers and non-specific defences

1. Public health officers investigated three illnesses in a rural village. The first patient had drunk untreated stream water, the second had cut her hand on a rusty tool while mending a gate, and the third had breathed in droplets from a coughing neighbour.
   Explain how intact skin helps to prevent pathogens from entering the body.2 marks
2. A student pushes a splinter into her finger. Within an hour the area is red, hot, swollen and tender. Mast cells in the damaged tissue have released histamine.
   Explain why the area around the splinter becomes red and feels hot.2 marks
3. Researchers studied how the body resists infection by Salmonella bacteria. Germ-free mice, bred with no gut flora, became severely ill after a small dose of Salmonella, whereas normal mice given the same dose showed no symptoms. In a separate experiment, adding lysozyme to a cloudy suspension of bacteria made the suspension clear within minutes.
   Explain how gut flora help to protect normal mice from infection by Salmonella.3 marks