Chapter 41 Animal NutritionLecture OutlineOverview: The Need to Feed- All animals eat other organisms—dead or alive, whole or by the piece (including parasites).- In general, animals fit into one of three dietary categories.1. Herbivores, such as gorillas, cows, hares, and many snails, eat mainly autotrophs (plants and algae).2. Carnivores, such as sharks, hawks, spiders, and snakes, eat other animals.3. Omnivores, such as cockroaches, bears, raccoons, and humans, consume animal and plant or algal matter.- Humans evolved as hunters, scavengers, and gatherers.- While the terms herbivore, carnivore, and omnivore represent the kinds of food that an animal usually eats, most animals are opportunistic, eating foods that are outside their main dietary category when these foods are available.- For example, cattle and deer, which are herbivores, may occasionally eat small animals or bird eggs.- Most carnivores obtain some nutrients from plant materials that remain in the digestive tract of the prey that they eat.- All animals consume bacteria along with other types of food.- For any animal, a nutritionally adequate diet must satisfy three nutritional needs:1. A balanced diet must provide fuel for cellular work.2. It must supply the organic raw materials needed toconstruct organic molecules.3. Essential nutrients that the animal cannot make from raw materials must be provided in its food.Concept 41.1 Homeostatic mechanisms manage an animal’s energy budget- The flow of food energy into and out of an animal can be viewed as a “budget,” with the production of ATP accounting for the largest fraction by far of the energy budget of most animals.Lecture Outline for Campbell/Reece Biology, 7th Edition, © Pearson Education, Inc. 41-1- ATP powers basal or resting metabolism, as well as activity and, in endothermic animals, thermoregulation.- Nearly all ATP generation is based on the oxidation of organic fuel molecules—carbohydrates, proteins, and fats—in cellular respiration.- The monomers of any of these substances can be used as fuel.- Fats are especially rich in energy, liberating about twicethe energy liberated from an equal amount of carbohydrate or protein during oxidation.- When an animal takes in more calories than it needs to produce ATP, the excess can be used for biosynthesis.- This biosynthesis can be used to grow in size or for reproduction, or it can be stored in energy depots.- In humans, the liver and muscle cells store energy as glycogen, a polymer made up of many glucose units. Glucose is a major fuel molecule for cells, and its metabolism, regulated by hormone action, is an important aspect of homeostasis. If glycogen stores are full and caloric intake still exceeds caloric expenditure, the excess is usually stored as fat. When fewer calories are taken in than are expended—perhaps because of sustained heavy exercise or lack of food—fuel is taken out of storage depots and oxidized. The human body expends liver glycogen first and then draws on muscle glycogen and fat.- Most healthy people—even if they are not obese—have enough stored fat to sustain them through several weeks of starvation. The average human’s energy needs can be fueled bythe oxidation of only 0.3 kg of fat per day.- Severe problems occur if the energy budget remains out of balance for long periods.- If the diet of a person or other animal is chronically deficient in calories, undernourishment results.- The stores of glycogen and fat are used up, the body begins breaking down its own proteins for fuel, muscles begin to decrease in size, and the brain can become protein-deficient.- If energy intake remains less than energy expenditure, death will eventually result, and even if a seriously undernourished person survives, some damage may be irreversible.- Because a diet of a single staple such as rice or corn can often provide sufficient calories, undernourishment is Lecture Outline for Campbell/Reece Biology, 7th Edition, © Pearson Education, Inc. 41-2generally common only where drought, war, or some other crisis has severely disrupted the food supply.- Another cause of undernourishment is anorexia nervosa, an eating disorder associated with a compulsive aversion to body fat. Obesity is a global health problem.- Overnourishment, or obesity, the result of excessive food intake, is a common problem in the United States and other affluent nations.- The human body tends to store any excess fat molecules obtained from food instead of using them for fuel. In contrast, when we eat an excess of carbohydrates,the body tends to increase its rate of carbohydrate oxidation.- Thus, the amount of fat in the diet can have a more direct effect on weight gain than the amount of dietary carbohydrates.- While fat hoarding can be a liability today, it probably provided a fitness advantage for our hunting-and-gathering ancestors, enabling individuals with genes promoting the storage of high-energy molecules during feasts to survive the eventual famines.- The World Health Organization now recognizes obesity as a major global health problem.- The increased availability of fattening foods in many countries combines with more sedentary lifestyles to put excess weight on bodies.- In the United States, the percentage of obese people has doubled to 30% over the past 20 years, and another 35% are overweight.- Obesity contributes to health problems, including diabetes, cancer of the colon and breast, and cardiovascular disease.- Research on the causes and possible treatments for weight-control problems continues.- Over the long term, feedback circuits control the body’sstorage and metabolism of fat.- Several hormones regulate long-term and short-term appetite by affecting a “satiety center” in the brain.- Inheritance is a major factor in obesity.- Most of the weight-regulating hormones are polypeptides.- Dozens of genes that code for these hormones have been identified.Lecture Outline for Campbell/Reece Biology, 7th Edition, © Pearson Education, Inc. 41-3- In mammals, a hormone called leptin, produced by adipose cells, is a key player in a complex feedback mechanism regulating fat storage and use.- As adipose tissue increases, high leptin levels cue the brain to depress appetite and to increase energy-consuming muscular activity and body-heat production.- Conversely, loss of body fat decreases leptin levels in the blood, signaling the brain to increase appetite and weight gain.- Mice that