2007 solution

2007 solution - ER 102 Spring 2007 Solutions to the 2007...

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ER 102 Solutions to the 2007 Midterm Examination J. Harte Spring 2007 1. a. A micron is 10 -4 cm, and water has a density of 1 g/cm 3 and thus a cubic micron has a mass of approximately 10 -12 grams. b. Taking a typical person to have a mass of 5 x 10 4 g, we get metabolic rate of bacterium = 100 Watts(10 -12 /5 x 10 4 ) 3/4 = 0.3 x 10 -10 Watts. c. Assuming 75 Gt(C)/y for annual NPP, and using 1 Gt = 10 15 g, we get a total annual energy release of 40 kJ/g(C) x 75 x 10 15 g(C)/y = 3 x 10 21 J/y ~ 10 14 Watts . Dividing by the wattage of a bacterium, we get a total population size of 10 14 / (0.3 x 10 -10 ) ~ 3 x 10 24 bacteria . d. Total bacteria mass: total bacteria (part c) x mass per bacteria (part a) = (3 x 10 24 bacteria)(10 -12 g/bacteria) = 3 x 10 12 grams of bacteria Total human mass: total humans (6.9 x 10 9 humans) x mass per human (5 x 10 4 g/human) = 3 x 10 14 grams of humans The mass of all bacteria is about one hundred times smaller as the mass of all living humans today. e.
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2007 solution - ER 102 Spring 2007 Solutions to the 2007...

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