chapter22 - 1 Food provides the raw materials for growth...

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1 Food provides the raw materials for growth and the fuel to make it happen. 22.1 Why do organisms need food? 22.2 What’s on the menu? Organisms have a variety of diets. 22.3 Calories count: organisms need sufficient energy. 2 Nutrients are grouped into six categories. 22.4 Water is an essential nutrient. 22.5 Proteins in food are broken down to build proteins in the body. 22.6 Carbohydrates and lipids provide bodies with energy and more . 22.7 Vitamins and minerals are necessary for good health. 22.8 How do organisms “know” what to eat? 3 We extract energy and nutrients from food. 22.9 We convert food into nutrients in four steps. 22.10 Ingestion is the first step in the breakdown of food. 22.11 Digestion dismantles food into usable parts. 22.12 Absorption moves nutrients from your gut to your cells. 22.13 Elimination removes unusable material from your body. 22.14 Animals have some alternative means for processing their food. 4 What we eat profoundly affects our health. 22.15 What constitutes a healthy diet? 22.16 Obesity can result from too much of a good thing. 22.17 Weight-loss diets are a losing proposition. 22.18 Diabetes is caused by the body’s inability to regulate blood sugar effectively. 22.19 Food and infection: spicy foods are natural antibiotics.
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At rest and at play: optimizing human physiological functioning 22 Nutrition and Digestion
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1 Food provides the raw materials for growth and the fuel to make it happen. 22 •  1-±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±±- Why do organisms need food? 22-2 CHAPTER 22 NUTRITION AND DIGESTION Food for Energy and Growth Nutrients Digestion and Absorption Diet and Health Lamb roulade with leek basil stuffing and a red wine sauce. Chili fries. Lime-marinated tofu kabobs. A big vanilla milkshake. We dress food up in an almost infinite variety of combinations. We garnish it, we heap on condiments, we daydream about it, and we even write books about it. But despite all the fuss, it really boils down to two simple biological needs: raw materials and fuel. Just as a carpenter needs wood and a car needs fuel, living organisms need raw materials and fuel to function. Here’s why: every second of every day, chemical reactions are occurring inside us. We build complex molecules. We reproduce. We respond to stimuli. And just as a car won’t roll uphill without a push, most of these chemical reactions won’t occur spontaneously. With a little fuel in the motor, however, the car can easily be driven up a hill. So, too, can we, and all the other animals, do things that are energetically costly. Our need for fuel is one of the two reasons why we must eat: building a body, moving around, reproducing, and just staying alive all require energy. Food provides that energy. And the other reason is that to grow and build the myriad complex molecules required for life, we need raw materials: molecules of carbon and nitrogen and phosphorus, to name just a few.
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chapter22 - 1 Food provides the raw materials for growth...

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