Barriers and non-specific defencesEdexcel International A Level Biology: Subtopic test

1. 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.

   (a)

   The second patient's bacteria entered the body through the cut. Which route of entry does this describe?

   [1 mark]

   • AInhalation through the gas exchange system
   • BIngestion through the digestive system
   • CDirect entry through a break in the skin
   • DEntry through the urinary and reproductive tract

   (b)

   Which defence is most likely to kill many of the pathogens swallowed by the first patient in the stream water?

   [1 mark]

   • AKeratin in the outer layer of the skin
   • BHydrochloric acid in the stomach
   • CMucus lining the trachea
   • DInterferon released by infected cells

   (c)

   Explain how intact skin helps to prevent pathogens from entering the body.

   [2 marks]

   Total for question 1: 4 marks

2. 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.

   (a)

   What is the effect of histamine on the blood vessels near the splinter?

   [1 mark]

   • AArterioles constrict, reducing blood flow to the area
   • BCapillaries constrict so that less fluid leaves the blood
   • CVeins become more permeable but their diameter does not change
   • DArterioles dilate and capillaries become more permeable

   (b)

   Which statement best explains why the finger is swollen?

   [1 mark]

   • APlasma leaks from permeable capillaries into the tissue spaces
   • BLymph vessels dilate and fill with phagocytes
   • CPhagocytes divide by mitosis inside the capillaries
   • DPlatelets swell as they seal the damaged tissue

   (c)

   Explain why the area around the splinter becomes red and feels hot.

   [2 marks]

   Total for question 2: 4 marks

3. 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.

   (a)

   Explain how gut flora help to protect normal mice from infection by Salmonella.

   [3 marks]

   (b)

   Explain how lysozyme caused the suspension of bacteria to become clear.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A patient is admitted to hospital with burns covering 30% of his body surface. Over the next few days he develops a bacterial infection in the damaged tissue, and the area is inflamed and full of neutrophils. He is also given a course of broad-spectrum antibiotics, which reduces the numbers of bacteria in his gut.

   (a)

   Explain why the patient is at high risk of infection, and why his burned tissue becomes inflamed.

   [6 marks]

   (b)

   Describe how neutrophils at the site of infection destroy bacteria by phagocytosis, and explain how this helps to clear the infection.

   [6 marks]

   Total for question 4: 12 marks

End of questions