In Chapters 6 and 7, we learned that energy in the chemical bonds of food molecules is transferred to the high-energy phosphate bonds of ATP. ATP provides animals with energy for cellular work. Each conversion of energy from food molecules to ATP and from ATP to cellular work is inefficient, however; in fact, most of the energy that was in the food is lost as heat. Even the energy the animal uses is eventually reduced to heat, as molecules that were synthesized are broken
(a) Ailuropoda melanoleuca down and the energy of movement is dissipated by friction. Therefore, we can talk about the energy requirements of animals and the energy content of food in terms of a measure of heat energy: the calorie.
A calorie is the amount of heat necessary to raise the temperature of 1 gram of water 1°C. Since this value is a tiny amount of energy compared with the energy requirements of many animals, physiologists commonly use the kilocalo-rie (kcal) as a unit of measure (1 kcal = 1,000 calories). Nutritionists also use the kilocalorie as a standard unit of energy, but they traditionally refer to it as the Calorie (Cal), which is always capitalized to distinguish it from the single calorie. (Scientists are gradually abandoning the calorie as an energy unit as they switch to the International System of Units. In this system, the basic unit of energy is the joule: 1 joule = 0.239 calories.)
The metabolic rate of an animal (see Chapter 41) is a measure of the overall energy needs that must be met by the animal's ingestion and digestion of food. The basal metabolic rate of a human is about 1,300-1,500 kcal/day for an adult female and 1,600-1,800 kcal/day for an adult male. Physical activity adds to this basal energy requirement. For a person doing sedentary work, about 30 percent of total energy consumption is due to skeletal muscle activity, and for a person doing heavy physical labor, 80 percent or more of total caloric expenditure is due to skeletal muscle activity. The components of food that provide energy are fats, carbohydrates,
50.1 Heterotrophs Get Energy from Autotrophs (a) Herbivores get their energy directly from autotrophs. Large herbivores such as the giant panda must consume huge amounts of plant matter (this particular animal eats only bamboo plants) to fulfill their nutritional needs. (b) Polar bears are carnivores, and ferocious predators. A carnivore's energy is indirectly obtained from autotrophs, since the energy stored in a prey animal was originally obtained from autotrophs.
(a) Ailuropoda melanoleuca
(b) Ursus maritimus
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This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.