K.C.S.E Biology Q & A - MODEL 2015PP2QN01

K.C.S.E Biology Q & A - MODEL 2015PP2QN01

The diagram below illustrates a blood capillary surrounding a structure for gaseous exchange in human beings.

​(a) Name the gaseous exchange structure. 
(b) Identify the gases labelled Y and Z. 
Y
Z           
(c) How does the gas labelled Y reach the inside of the blood capillary? 
(d) How does cigarette smoking lead to lung cancer?

ANSWERS

​.(a) Alveolus; 
(b) Y - oxygen/O2;
Z - Carbon (IV) Oxide/CO2; 
(c) Oxygen concentration is lower in the blood capillary than in the alveolus; oxygen diffuses; through the epithelium and endothelium of capillary wall, plasma into the red blood cells where it combines with haemoglobin. 
(d) Cigarettes/tobacco contains tar; tar contains carcinogenic substances; which trigger cancer