Digestion

Digestion - 50 50 Nutrient Requirements Animals are...

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50 Nutrition, Digestion, and Absorption 50 • Animals are heterotrophs : They must obtain their nutrition by eating other organisms. • Most plants, some bacteria, and some protists are autotrophs : They trap solar energy through photosynthesis and use that energy to synthesize all of their components. • Heterotrophs depend on the organic synthesis carried out by autotrophs. Nutrient Requirements 50 Measuring energy • A calorie is the amount of heat needed to raise the temperature of 1 g of water by 1°C. • 1 kilocalorie (kcal) = 1,000 calories • Nutritionists refer to the kilocalorie as the Calorie (Cal) , which is capitalized to distinguish it from the single calorie. • Scientists are abandoning the calorie in favor of the International System of Units measure of energy called the joule (1 joule = 0.239 calories).
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50 Nutrient Requirements • An animal’s metabolic rate is the measure of the overall energy needs that must be met by the animal’s food. Fats , carbohydrates , and proteins are the components of food that provide that energy. Basal metabolic rate is the metabolic rate resulting from all of the essential physiological functions that take place in a resting state. • Physical activity adds to the basal energy requirement. Figure 50.2 Food Energy and How We Use It ...the time it takes to burn off these foods 50 Energy Stores • Most animals store fuel molecules that can be released as needed between meals. • Carbohydrates are stored in liver and muscle cells as glycogen . The total glycogen store is about one day’s energy requirements. • The most important form of stored energy in animals is fat . Fat has more energy per gram than glycogen, and it is stored with little associated water, making it more compact. Protein is not used to store energy, but it can be metabolized as a last resort. 50 Nutrient Requirements • Animals that do not take in enough food to meet their energy requirements are undernourished . • They must metabolize molecules of their own body to provide the energy they need. • The first storage compounds to be metabolized in this state are glycogen and fat, so that protein loss is minimized for as long as possible. • Eventually, a starving animal must use its own proteins for fuel. • This impairs body functions and eventually leads to death (also: remember diabetes mellitus).
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Figure 50.3 The Course of Starvation Glycogen Fat Protein 50 Nutrient Requirements • Animals that take in more food than is necessary to meet their energy demands are overnourished . • Excess nutrients are stored as increased body mass. • Glycogen reserves are built up, and then additional carbohydrates, proteins, and fats are converted to body fat. • Some species use seasonal overnourishment to survive
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This note was uploaded on 03/01/2009 for the course MCDB 1B taught by Professor Weimbs during the Spring '08 term at UCSB.

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Digestion - 50 50 Nutrient Requirements Animals are...

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