Paper 3

Question 1

Describe the effect of smoking on lungs

Answer 1

. Smoking decreases amount of antioxidants (protect cells from damage) in blood.
. Fewer antioxidants - more cell damage in artery walls
. Atheroma formation –> increased CVD risk.
. Nicotine makes platelets sticky, so increased the risk of blood clots.
. Carbon monoxide in cigarette smoke binds to haemoglobin and reduces oxygen transported in the blood.

Question 2

Describe the evasion mechanisms of HIV

Answer 2

. HIV kills the immune system cells it infects.
. Reduces immune cells in the body - less chance of being detected
. HIV has a high rate of mutation in antigen protein genes - changes antigen structure, so new virus strains (antigenic variation)
. Memory cells for one strain of HIV won’t recognize other strains, the immune system has to produce a primary response for each strain
. HIV disrupts antigen presentation in infected cells so immune system cells can’t recognize and kill them.

Question 3

TB evasion mechanisms

Answer 3

. When they infect the lungs, they’re engulfed by phagocytes, and produce substances that prevent lysosome fusing with phagocytic vacuole so bacteria aren’t broken down and multiply undetected in phagocytes.
. Disrupt antigen presentation, so immune system cells don’t recognise and kill infected phagocytes.