Metabolism is a generic term for all of the chemical reactions that break down a

Question

Metabolism is a generic term for all of the chemical reactions that break down and "burn" food, thereby releasing energy. The following table shows data for metabolism and gas exchange in humans: This table gives the energy released, the oxygen consumed, and the carbon dioxide released upon metabolizing a given food, per gram of food. a. Calculate the energy yield per liter of oxygen consumed for each food type. These numbers should be roughly constant, therefore we can determine a person's metabolic rate simply by measuring his or her rate of oxygen consumption. In contrast, the CO_2/O_2 ratios are different for the different food groups. This circumstance allows us to estimate what is actually being used as the energy source by comparing oxygen intake to carbon dioxide output. b. An average adult at rest uses about 16 liters of O_2 per hour. The corresponding heat release is called the "basal metabolic rate" (BMR or the energy per time liberated by metabolizing food). Find it, in kcal/hour and kcal/day. c. What power output does this correspond to in watts? d. Typically, a person's CO2 output might be 13.4 liters/hour. What, if anything can you say about the type of food materials being consumed? e. During exercise, the metabolic rate increases. Someone performing hard labor for 10 hours/day might need about 3500 kcal of food per day. Suppose a person does mechanical work at a steady rate of 50 watts over 10 hours. We can define the body's efficiency as the ratio of mechanical work done the excess energy intake (beyond the BMR calculated in b). Find this efficiency.

Explanation / Answer

a. For carbohydrate,

Oxygen usage = 0.81 litre/g

0.81 litre oxygen burns = 1 g carbohydrate

1 litre will burn = 1/0.81 = 1.2345 g carbohydrate

Hence energy released = 4.1 x 1.2345 = 5.0617 kcal/litre oxygen

For fay,

1.96 litre oxygen for 1 g fat

1 litte oxygen for = 1/1.96 = 0.51 g fat

Hence, energy released = 0.51 x 9.3 = 4.744 kcal/litre oxygen

For protein,

One litte oxygen burns = 1/0.94 = 1.0638 g protein

Hence energy released = 4.0 x 1.0638 = 4.255 kcal/litre oxygen

For alcohal,

One litre alcohal burns = 1/1.46 = 0.6849 litre alcohal

Energy released = 0.6849 x 7.1 = 4.86 kcal/litre oxygen

b) hence average energy released per litre oxygen intake is = (5.0617 + 4.744 + 4.255 + 4.86)/4

= 4.73 kcal/litre oxygen

Hence for 16 litre oxygen, enegy released = 4.73 x 16 = 75.68 kcal/hr

And for whole day 24 hours = 75.68 x 24 = 1816.38 kcal/day

c. As energy released = 75.68 kcal/hour = 4.18 x 75.68 x 1000/3600 watt

= 87.87 watt

d. CO2 emitted = 13.4 litre per hour

Hence food consumed per hour

If carbohydrate = 13.4/0.81 = 16.54 g

Energy = 16.54 x 4.1= 67.87 kcal

If fat = 13.4/1.39 = 9.64 g

Energy = 9.64 x 9.3 = 89.695 kcal

If protein = 13.4/0.75 = 17.87 g

Energy = 17.87 x 4.0 = 71.47 kcal

If alcohal = 13.4/0.97 = 13.81 g

Energy = 13.81 x 7.1 = 98.08 kcal

Hence we can say that protein is being burnt at that timeas energy output matches with output energy average per hour.

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