K.C.S.E Biology Q & A - MODEL 2014PP2QN03

K.C.S.E Biology Q & A - MODEL 2014PP2QN03

​(a) Describe the mechanism of gaseous exchange in plants through the lenticels. 
(b) Explain each of the following:
(i) the tracheoles lack spiral bands of chitin; 
(ii) the floor of the mouth is lowered during inhalation in a bony fish.

answers

​(a) O2, concentration is higher outside than inside the lenticels; O2, diffuses into lenticels; then  into the cells; CO2 concentration is higher inside the lenticels than on the outside CO2 diffuses out of the lenticels into the atmosphere;  
(b) (i) To provide a large surface area! make them thin; for gaseous exchange to reduce diffussion distance for respiratory gases;
(ii) This increases the volume of the buccal cavity while decreasing the pressure; which forces water to rush into the mouth;