Chapter 7, Problem 84RPP

BIO Metabolic rate Energy for our activities is provided by the chemical energy of the foods we eat. The absolute value of the rate of conversion of this chemical energy into other forms of energy (ΔE/Δt) is called the metabolic rate. The metabolic rate depends on many factors-a person’s weight, physical activity, the efficiency of bodily processes, and the fat-muscle ratio. Table 7.9 lists the metabolic rates of people under several different conditions and in several different units of measure:

1 kcal = 1000 calories = 4186 J. Dieticians call a kcal simply a Cal. A piece of bread provides about 70 kcal of metabolic energy.

Type of activity	ΔE/Δt (watts)	ΔE/Δt(kcal/h)	ΔE/Δt(kcal/day)
45-kg person at rest	80	70	1600
68-kg person at rest	100	90	2100
90-kg person at rest	120	110	2600
68-kg person walking 3 mph	280	240	5800
68-kg person moderate exercise	470	400	10,000
68-kg person heavy exercise	700	600	14,000

In 1 hour of heavy exercise a 68-kg person metabolizes 600 kcal – 90 kcal = 510 kcal more energy than when at rest. Typically, reducing kilocalorie intake by 3500 kcal (either by burning it in exercise or not consuming it in the first place) results in a loss of 0.45 kg og body mass (the mass is lost through exhaling carbon dioxide-the product of metabolism).

A 50-kg mountain climber moves 30 m up a vertical slope. If the muscles in her body convert chemical energy into gravitational potential energy with an efficiency of no more than 5%, what is the chemical energy used to climb the slope?

a. 7 kcal

b. 3000 J

c. 70 kcal

d. 300,000 J