It is estimated that photosynthesis fixes 120 Gt of carbon per year (carbon, not
ID: 1553196 • Letter: I
Question
It is estimated that photosynthesis fixes 120 Gt of carbon per year (carbon, not CO2). This portion of the carbon cycle represents the world's capacity for generating biofuels (in addition to supplying food). If transportation needs could be met via biofuels, what fraction of the world's photosynthesis would have to be used to supply this biofuel assuming that 1/3 of the world's 540 EJ total energy use is devoted to transportation. [Assume that biofuel is glucose; use 15.6 kJ/g as the energy density of glucose.]
a) Less than 2%Explanation / Answer
Answer is (d)
Energy due to photosynethesis =15.6x120x1018 joule
= 1872x1018 joule
Total Energy = 540x1018 joule
Transport = 1/3x540x1018 joule
= 180x1018 joule
fraction = 1872x1018 / 180x1018
= 10.4 Answer
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