EXCHANGE QUESTIONS
a. The amoeba which is a single celled organism does not have a specialised system for gaseous exchange. Explain why this organism has no need of such a system and why humans need a complex system involving specialised surfaces and mechanisms of ventilation  
     
     
     
     
     
     
     
     
     
    (6)
b. How does a molecule of oxygen reach and then enter ther cells of the spongy mesophyll in a dicotoledonous leaf  
     
     
     
     
     
     
     
     
     
     
     
(6)