An interesting recent development is a growing awareness of bacteria. It\'s now

Question

An interesting recent development is a growing awareness of bacteria. It's now realized that the total biomass of bacteria on earth far outweighs all animals, plants, and other complex living beings put together. A recent claim is that "there are 10 times as many bacterial cells in a typical human body as there are human cells." If we don't count blood and bone (about 20% of your mass) estimate the fraction of your mass that is bacterial and not "you". (A set of approximate biological scales is shown below.) Be sure to clearly state your assumptions and how you came to the numbers you estimated, since grading on this problem will be mostly based on your reasoning, not on your answer.

Explanation / Answer

The volume of human cell is 10um×10um×10um , while the volume of the bacterium cell is 1um×1um×0.6um(counting the number of grids in bacterium cell in vertical direction) therefore if we consider the density of both cells to be same then mass ratio of human cell to bacterium cell is 1000÷0.6 = 1666.67 . Now if no. Of bacterium is 10 times no. Of human cells in body if we assume total mass of human cells in our body be x then mass of bacterium cells in our body is 10x/1666.67 . Now mass of human cells excludong bones and blood is 0.8x . Therefore mass percentage of bacterium cells to total mass is : (10x/1666.67)÷(0.8x+10x/1666.67) = 0.00744

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