Answers

2015-06-09T17:11:37+05:30
Because human beings also need some molecules to move from place of lower concentration to higher for example sodium-potassium pumpĀ 
so this type of movement is known as active transportĀ 
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2015-06-09T17:28:15+05:30
Because inside human beings there are so many cells. If transport will be done through simple diffusion then oxygen will be tranported to every cell which will take 3 years of time.
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