Becker's World of the Cell 9th Edition by Lewis Kleinsmith, Jeff Hardin, Gregory Paul Bertoni

Exercise 1

Solar Energy. Although we sometimes hear concerns about a global energy crisis, we actually live on a planet that is flooded continuously with an extravagant amount of energy in the form of solar radiation. Every day, year in and year out, solar energy arrives at the upper surface of the Earths atmosphere at the rate of 1.94 cal/min/cm 2 of cross-sectional area (the solar energy constant ).
(a)Assuming the cross-sectional area of the Earth to be about 1.28 × 10 18 cm 2 , what is the total annual amount of incoming energy
(b)A substantial portion of that energy, particularly in the wavelength ranges below 300 nm and above 800 nm, never reaches the Earths surface. Can you suggest what happens to it
(c)Of the radiation that reaches the Earths surface, only a small proportion is actually trapped photosynthetically by phototrophs. (You can calculate the actual value in Problem 5-2.)Why do you think the efficiency of utilization is so low