Tis estimated that there are approximately 1 × 1014 cells in the human body. which of the following represents this amount in standard notation? 100,000,000,000,000 14,000,000,000,000 10,000,000,000,000 1,000,000,000,000,000

Well, the biggest reason is that cells have such large numbers so to write them out in standard notions would surely make you exhausted.  Scientific notation helps because it makes you able to write very large numbers in a smaller format.  That being said, the other reasons could include to get more accurate counts, to get the counts complete before the cells change/grow/die, and to tract large numbers of cells at one time.  It all comes down to the fact that cells are constantly reproducing and expanding.  There are way to many to count in standard notation.  The most important reason is to track the different types of cells.  You have to be able to separate them from one another and rather quickly before you lose track.  You need to count RBC, WBC, Platelets, etc.  Scientific notation allows you to do so in a way that makes a better representation of factual numbers.  Another reason would be to make sure that people understand the data and it's readable.  Scientific notation at times, can prove to be more legible to anyone observing your work. 

d is ur answer hopes this i dont really know how to explain it to u.