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Food and Nutrition A Science A–Z Life Series Word Count: 2,328 Food and Nutrition Written by Barb Davis Visit www.sciencea-z.com www.sciencea-z.com Food and Nutrition Written by Barb Davis www.sciencea-z.com Key elements Used in This Book The Big Idea: Humans are like other organisms in that we need food to survive. Food is the fuel that powers us. Plants use photosynthesis to make their own food, while animals eat plants, other animals, or both. Plants and animals both use the process of respiration to convert food into energy. In animals—including humans—food breaks down as it travels through the digestive system, releasing nutrients and energy. To be healthy, we need to consume a balance of various organic and inorganic nutrients. Knowing which nutrients the body needs and in what proportions in our diet, as well as which foods contain those nutrients, are all important for maintaining our health. Key words: agriculture, breathe, carbohydrate, carbon dioxide, carnivore, cell, chlorophyll, cholesterol, consumer, cud, decomposer, diet, digestion, digestive system, energy, enzyme, esophagus, fiber, food, food chain, glucose, herbivore, inorganic, lipid, liver, mineral, molecule, nutrient, nutrition, omnivore, organic, organism, oxygen, pancreas, photosynthesis, plants, producer, protein, respiration, ruminant, saliva, small intestine, soil, stomach, stomata, sugar, sunlight, trans fat, transpiration, villi, vitamin, water, water vapor Key comprehension skills: Compare and contrast Other suitable comprehension skills: Cause and effect; classify information; main idea and details; identify facts; elements of a genre; interpret graphs, charts, and diagrams Key reading strategy: Retell Other suitable reading strategies: Ask and answer questions; connect to prior knowledge; summarize; visualize; using a table of contents and headings; using a glossary and boldfaced terms Photo Credits: Front cover: © iStockphoto.com/Elena Schweitzer; back cover (tl): © iStockphoto.com/Purdue9394; back cover (tr), page 24 (l): © iStockphoto.com/Yin Yang; back cover (b): © iStockphoto.com/ Linda Kloosterhof; title page: © iStockphoto.com/Andreas Prott; page 3: © iStockphoto.com/ Catherine Yeulet; page 4 (l): © iStockphoto.com/Jim Kruger; page 4 (tr): © iStockphoto.com/ Maria Gritcai; page 4 (br): © iStockphoto.com/Robert Plotz; page 5: © iStockphoto.com/Dane Steffes; page 6 (top inset): © iStockphoto.com/Julie Macpherson; page 6 (bottom inset): © iStockphoto.com/ Karl Dolenc; page 6 (bottom main): © iStockphoto.com/Redmal; pages 6 (top main), 9 (c), 11 (l), 12, 18 (br), 19 (6, 7), 21 (tl): © Jupiterimages Corporation; page 8: © Learning A–Z; page 9 (t): © Xavier Marchant/Dreamstime.com; page 9 (b): © iStockphoto.com/Klaas Lingbeek-van Kranen; page 11 (c): © iStockphoto.com/Ivan Burmistrov; page 11 (r): © iStockphoto.com/Grafissimo; page 13 (t): © iStockphoto.com/Suprijono Suharjoto; page 14 (b): © iStockphoto.com/Aesthesia; page 15 (t): MedicalRF.com/Getty Images; page 15 (c): © iStockphoto.com/Emrah Oztas; page 15 (b): © iStockphoto.com/Marty Eby; page 16 (t): © iStockphoto.com/Robert Churchill; page 16 (b): © Dorling Kindersley/Getty Images; page 17 (tl): © iStockphoto.com/Jesús Arias; page 17 (tr): © iStockphoto.com/Peter Baxter; page 17 (bl): © iStockphoto.com/Katarina Drpic; pages 17 (br), 20 (tc): © iStockphoto.com/Kelly Cline; page 18 (tl): © iStockphoto.com/Michael Flippo; page 18 (tr): © iStockphoto.com/Dennis DeSilva; page 18 (bl): © iStockphoto.com/Matthew Cole; page 19 (2): © iStockphoto.com/Joe Potato; page 19 (5): © iStockphoto.com/Nataliya Peregudova; page 20 (tl): © iStockphoto.com/James McQuillan; page 20 (tr): © iStockphoto.com/Larry Sherer; page 20 (b): © iStockphoto.com/Nina Shannon; page 21 (tr): © iStockphoto.com/Morgan L; page 21 (bc): © iStockphoto.com/Denis Pepin; page 21 (cr): © iStockphoto.com/Mark Gillow; page 22 (c): © iStockphoto.com/Valentyn Vokov; page 22 (b): © iStockphoto.com/DNY59; page 23: © iStockphoto.com/Vikram Raghuvanshi; page 24 (r): © iStockphoto.com/Wojciech Gajda; pages 19 (1, 3, 4), 21 (bl): © Hemera Technologies/Jupiterimages Corporation; page 21 (br): © Olga Miltsova/123RF; page 22 (t): © Miltonia/123RF Illustration Credits: Pages 10, 13 (bottom), 14 (top), 15 (top): Cende Hill/© Learning A–Z Food and Nutrition / © Learning A–Z / Written by Barb Davis All rights reserved. / www.sciencea-z.com lipids fats and oils (p. 19) mineralsinorganic nutrients required in small amounts for health and normal growth (p. 22) nutrientssubstances in food or soil that organisms need to live, stay healthy, and grow (p. 17) omnivorean animal that eats both plants and animals (p. 9) oxygenan invisible, odorless gas essential for life that makes up part of the air (p. 7) Table of Contents photosynthesisthe process by which plants convert energy from the Sun into food (p. 5) What Needs Food?.................................................... 4 proteinorganic nutrients used by the body to grow and to repair cells (p. 20) How Do Plants Get Food?....................................... 5 respirationthe process by which cells produce energy from stored sugars (p. 7) How Do Plants Use Food for Energy?................... 7 vitaminsorganic nutrients required in small amounts for health and normal growth (p. 22) Index agriculture, 11 digestion, 12–16, 18, 19, 21 energy, 4–8, 10, 12, 14–20, 24 food chain, 10 photosynthesis, 5–8, 10 respiration, 7, 8, 12, 15, 18 ruminant, 16 26 small intestine, 13–15 stomach, 13, 14, 16 stomata, 5–7 villi, 15 water, 5–8, 23 water vapor, 7, 8, 12, 15 How Do Animals Get Food?................................... 9 How Do Animals Use Food for Energy?............. 12 Food’s Journey Through the Human Body......... 13 Food, Nutrition, and Health.................................. 17 Organic Nutrients................................................. 18 Inorganic Nutrients............................................... 22 Conclusion............................................................... 24 Glossary.................................................................... 25 Index......................................................................... 26 3 What Needs Food? All living things, or organisms, need energy in order to live, complete their daily activities, and remain healthy. This energy comes from food. This book explains two life-sustaining processes: how organisms get food and how food goes through changes inside organisms so they can use the food for energy. Before reading on, think about how plants get food and how they turn the food into energy. Glossary carbohydrates organic nutrients, including sugars and starches, that can provide an organism with energy (p. 18) carbon dioxidean invisible, odorless gas that is used during photosynthesis and given off as a waste product during respiration (p. 5) carnivorean animal that only eats other animals (p. 9) chlorophyll a material in green plants that can turn water, air, and sunlight into food (p. 5) digestion a series of chemical reactions that break food down into forms that the body can use (p. 12) energy the power to do work, make a change, or move objects (p. 4) All living things need food to survive. enzymes proteins that speed up a chemical reaction in the body (p. 13) fibera food substance that cannot be digested but which helps the process of digestion (p. 21) glucose a simple sugar made by plants during photosynthesis that is an important source of energy for all living things (p. 5) herbivorean animal that only eats plants (p. 9) 4 25 Conclusion How Do Plants Get Food? You have learned that both plants and animals convert food into the energy they need. Plants make their own food, while animals must consume food. Luckily, you don’t have to control the process of turning food into energy in your own body. But you do have some important responsibilities when it comes to deciding what to eat. As you know, animals get the energy they need to survive by eating many kinds of food found in their environment. But plants don’t eat food. Unlike other living things, they have the ability to make their own food. Plants produce food through a chemical process called photosynthesis. Proteins, carbohydrates, lipids . . . your body needs many things to produce energy and to stay healthy. In fact, your body needs a balance of nutrients. So how do you select what to eat when you’re hungry? Choosing foods by flavor, texture, or appearance will not guarantee you a healthy diet. The most important thing to do is to make sure you eat a variety of foods. Try to avoid foods that have too much fat and cholesterol. Limit the amount of red meat, fried foods, butter, and artificial ingredients you eat. Use healthier fats and eat plenty of great-tasting fruits and vegetables, which have the nutrients your body needs. 24 During photosynthesis, plants make a simple kind of sugar, called glucose, which becomes their food source. You may have thought that plants get their food from the soil, but this is not the case. Green plants contain chlorophyll, a pigment that absorbs sunlight and converts the light energy into glucose. During photosynthesis, plants also use a gas called carbon dioxide, which is found in the air. The carbon dioxide gets absorbed through tiny holes called stomata, which are mostly found on the underside of a plant’s leaves. Although soil does not provide plants with their food, it does supply plants with water and minerals, both of which are absorbed through the roots. Water and minerals aid in the process of photosynthesis. The diagram on page 6 reviews the process of photosynthesis. 5 Photosynthesis in Green Plants 5 4 3 6 2 Clearly, eating a good combination of foods is extremely important. Actually, your body might be able to go without any food for a month. However, you could only survive for about a week without water, and even less time in a hot, dry place or while being active. Almost every chemical reaction that takes place in your body requires water. Your saliva is mostly water. Blood, which is about 83 percent water, carries nutrients to cells and carries away waste materials. More than half your body mass is water. Experts say you need about two liters (10.5 glasses) of water a day to stay healthy. You get a lot of water from the foods you eat. But there’s no better way to stay hydrated than by simply drinking clean water, especially when its hot and when you exercise. 1 1Roots absorb water and minerals, and transport them to the plant’s cells. 2A green pigment in plant cells, called chlorophyll, captures the Sun’s light energy and turns it into chemical energy. 3Carbon dioxide from air enters the leaf through tiny holes called stomata. 6 4The energy from the Sun helps carbon dioxide molecules react with water molecules to make a simple sugar called glucose. 5The plant uses some of the glucose it makes and stores the rest. 6Oxygen, a waste product from the food-making process, passes out of the leaf and enters the air. 23 Vitamins assist with many jobs in your body. They can support good eyesight, strong teeth, and healthy skin. Many foods and drinks contain vitamins. Carrots, for example, contain vitamin A, while oranges supply you with vitamin C. Although you don’t need large amounts of vitamins, you can become ill without adequate amounts. Inorganic Nutrients The left side of the formula below explains what plants use during photosynthesis. The right side explains what plants produce during photosynthesis. Photosynthesis Formula water + carbon dioxide + light → sugar (food) + oxygen How Do Plants Use Food for Energy? Minerals are inorganic nutrients that are important to your health. Calcium is one of the many minerals your body needs. A lack of calcium can cause bone problems. Other minerals found in foods include salt, zinc, iron, copper, magnesium, and potassium. Your blood uses iron to carry oxygen, and salt is used in your sweat, blood, and tears. Your body only needs small amounts of these minerals for good health. However, your body does not manufacture minerals, Some people take so you must get them pills to add extra vitamins and minerals from the food you eat. to their diet. 22 Photosynthesis takes place inside the smallest parts of a plant—its cells. Much like bricks in a building, cells join together to make up most living things. Some of the glucose (sugar) that a plant makes during photosynthesis remains stored in its leaves, fruit, stem, roots, and other parts. To use the rest of the food for energy, the plant must break down the glucose in its cells. This involves a different chemical process, called respiration. During respiration, glucose reacts with oxygen to release energy that plants need to live. Respiration also forms carbon dioxide and water vapor as waste products. These waste products exit the plant through the stomata. The left side of the next formula explains what plants use during respiration. The right side explains what plants produce during respiration. 7 Respiration Formula sugar (food) + oxygen → energy + carbon dioxide + water vapor To review, photosynthesis is how plants make their own food. Respiration is how plants use that food for energy. While photosynthesis occurs in sunlight, respiration can occur in the dark or the light. All organisms use respiration, but plants also use photosynthesis. Use the chart below to compare these two important processes. Photosynthesis Respiration produces food uses food stores energy releases energy uses water uses glucose uses carbon dioxide uses oxygen produces glucose produces water vapor produces oxygen produces carbon dioxide occurs in sunlight occurs in the dark or light used primarily by plants used by all organisms When plants lose water vapor through their leaves, it is called transpiration. To prove that plants give off water, try sealing a few leaves of a living plant in a bag for a few days and watch what happens! 8 There are many kinds of protein, and your body needs a variety. You can get some of these proteins from foods such as eggs, cheese, milk, meat, and fish. You can get other proteins from nuts, seeds, dried peas, beans, and grains such as wheat, rice, and oats. Vegetarians, who don’t eat meat, rely on foods from plants to get the protein they need. Eat meat, cheese, milk, eggs, and nuts for protein. Another important part of a healthy diet is fiber. Fiber is a substance that your body cannot digest. Why would you need something you cannot digest? Fiber helps food pass through your intestines quickly and easily. Fresh fruits and vegetables, beans and peas, and whole-grain cereals are all good sources of fiber. Scientists believe that eating a diet high in fiber helps prevent cancer and other health problems. 21 How Do Animals Get Food? Animals get food in three ways. Before you read on, can you guess what these ways might be? These foods are tasty, but they are often high in unhealthy fats, and they do not provide many healthy nutrients. Lipids also create the fat under your skin that keeps you warm as well as the oil that makes your hair shiny. All healthy bodies need a certain amount of fat. However, too much fat is unhealthy. Certain fats are good for you if eaten in the right balance, including omega-3 and omega-6 fatty acids. Some foods contain a particular type of fat, called trans fat, which can increase the amount of cholesterol in the blood. Too much cholesterol can lead to heart disease. While carbohydrates are the main source of your body’s energy, protein is useful in another way. Your body uses protein to build and repair cells. Protein is essential for building and strengthening your bones, muscles, skin, and the rest of your body. 20 Milk is a good source of protein. Some animals only eat plants; a zebra is considered an herbivore because it only eats plants. Some animals eat other animals; a lion that eats zebras and other animals is a carnivore, or meat eater. Finally, an animal may eat both plants and animals, which makes it an omnivore; warthogs are omnivores. Think of ten wild animals. How would you classify them as herbivores, carnivores, or omnivores? herbivore carnivore omnivore 9 A Desert Food Chain primary consumer secondary consumer producer decomposer tertiary consumer All living things are part of one or more food chains. Almost all food chains begin with food producers. This group includes green plants— which produce energy through photosynthesis— as well as algae, and other organisms that can make their own food. Primary consumers (herbivores and omnivores) eat the producers, getting energy in the process. Then secondary consumers (carnivores and omnivores) eat primary consumers. Tertiary consumers (mostly carnivores) eat secondary consumers. Finally, decomposers break down any leftover living matter. This step completes the food chain. In this way, energy flows through the food chain. Since plants are organisms that make food, they are where most of the food production begins. 10 Complex carbohydrates consist of long chains of glucose molecules, called starches. Foods such as potatoes, rice, whole grains, beans, corn, and some other vegetables are starches. These complex “carbs” take longer for your body to digest, so they keep your energy steadier throughout the day than simple carbohydrates do. Which category of carbohydrates do you suppose doctors suggest you eat more of? Vegetables, cereal, whole-grain breads, and rice are carbohydrates. Lipids, which are fats and oils, are another type of nutrient. Rub a peanut on a paper bag and you get an oily stain. Nuts, meats, and other foods contain lipids. Your body uses lipids to store energy. Ounce for ounce, lipids supply more than twice as much energy as carbohydrates do. Some foods, like these, contain healthy fats. 19 Organic Nutrients Your body gets most of its energy from carbohydrates. These important organic nutrients are found in many common foods. How do they give you energy? Just as in plants, animals use the process of respiration to convert food into energy. After you eat foods that contain carbohydrates, your body breaks them down into glucose molecules (a simple sugar) and combines them with oxygen. Do you remember what happens next? Energy is released! Refer to the formula on page 8 to review the process of respiration. Carbohydrates are generally described as one of two types: simple or complex. Simple carbohydrates are small molecules of sugars that come in foods such as doughnuts, candy, fruit, and soda pop. You can digest them very quickly to get a short-term spike in energy. But if you don’t use this energy by being active, it often gets stored as fat. Eating too much sugar for many years may also result in disease. 18 Agriculture How do you get the foods you eat? Do you go into nature to collect plants and hunt wild animals? Probably not. Someone else has grown the plants and raised the animals for you, and then they sold the food to you in a nearby store or restaurant. Agriculture is the science of growing crops and raising livestock. For most of human history, agriculture involved backbreaking labor. People planted seeds by hand and harvested the crops with handheld tools. Harnessing animals to pull a heavy plow was extremely hard work, too. In 1830, it took 250 to 300 hours of labor to produce 100 bushels of wheat. By 1890, mechanical planters, tractors, and other inventions had cut that time to about 50 hours. Today, advanced technology helps farmers harvest that same100 bushels of wheat in much less time. Plus, the wheat requires fewer acres of land now because scientists have found ways to alter plants so they yield more food than they used to. In other words, agriculture has become much more efficient since the time when people used handheld tools to dig holes in the soil and plant one seed at a time. 11 How Do Animals Use Food for Energy? There it sits—a nice, juicy apple loaded with energy, ready to help you walk, run, and breathe. How does your body get the energy contained in that apple? Remember the plant and its chemical-processing factory? Animals also process chemicals to make energy. This process is called digestion. The digestive system in animals works like a “disassembly line.” It takes food apart, piece by piece, in a series of chemical reactions that break food down into tiny particles. These particles, called molecules, are distributed to the body’s cells by blood, which circulates throughout the body. Food, Nutrition, and Health Foods contain chemicals that provide you— and all organisms—with the energy to move, grow, and heal. These chemicals and substances in food are called nutrients. You need a variety of nutrients to maintain good health. Not all foods contain the same nutrients, so it is important to eat foods that give you the right balance of nutrients. There are six main types of nutrients. We classify them into two main groups: organic and inorganic. Organic nutrients—essential chemicals found in living things—come from foods such as meat, fruits, grains, and vegetables. Inorganic nutrients are chemicals not produced by living things. As you read on, think about whether the foods you eat provide all of these important nutrients. You’ve learned that plant cells use the respiration process to convert glucose to energy. A similar thing happens inside the cells of animals. During breathing, oxygen is delivered to blood cells. Then glucose molecules from the animal’s food combine with oxygen in the animal’s cells. When glucose and oxygen combine in a chemical reaction, they release—you guessed it—energy! Just as plants do, animals give off water vapor and carbon dioxide during respiration. The water vapor is what makes an animal’s breath feel wet. 12 17 So Many Stomachs! What do cows, camels, and giraffes have in common? They all have very unusual stomachs! These animals, called ruminants, have up to four chambers in their stomach that each act as a separate stomach. Why so many? Whether it is three chambers or four, the main purpose of these stomachs is the same: eat now, digest later. Ruminants eat on the run, grabbing as much food as they can before some hungry predator starts to chase them. The ruminants store a large quantity of food in the first chamber of their stomach. Here, it begins the breakdown process with the help of digestive enzymes. Later on, the animal can bring up the partially digested food, called cud, from the first stomach and chew it some more. Have you ever seen cows comfortably lying around, looking as though they’re chewing gum? That’s not gum they’re chewing! This second chewing helps break down grasses that are hard to digest. Then the cud passes into the other chambers of the stomach, where enzymes continue to launch chemical reactions to extract Stomach energy from the food. chambers 16 Food’s Journey Through the Human Body Now let’s look at the digestive system of the human body. When you eat an apple, the food begins a long journey. It starts with your teeth, which tear off a piece of the apple. The saliva in your mouth adds moisture and enzymes. Enzymes are chemicals found throughout your digestive system. They speed up the chemical reactions that take place during digestion. At this stage of your food’s journey, the enzymes soften the apple as your teeth grind it into smaller bits of food so you can swallow it. Next, your tongue pushes the softened apple bits to the back of your mouth, and you swallow. The food travels down your esophagus, the long tube that connects your throat to your stomach. The circular muscles in this tube contract to push the food down toward your stomach. mouth esophagus stomach liver pancreas large intestine small intestine 13 What was once a bite of a tasty apple has reached your stomach. The lining of your stomach makes two types of chemicals: gastric juices and enzymes. Did you ever eat a piece of lemon? It’s so sour! Gastric juices in your stomach are acidic, like lemon juice, but much stronger. As the apple bits reach your stomach, gastric juices mix with the food and break it down even further. Stomach enzymes launch chemical reactions that break down the food into even tinier pieces. Then your stomach moves the food around. Your food is unrecognizable at this point. It is being turned into energy. Even though your stomach mixes food and enzymes, most digestion takes place in your small intestine. As the food travels from your stomach to the small intestine, other organs, such as the liver and pancreas, add more enzymes and other digestive chemicals. 14 In some people, the pancreas doesn’t work. So they use manufactured enzymes from a pig’s pancreas to help break down their food for them! The digested molecules of food are now in a form that the body can use for energy. They leave the small intestine through villi—tiny fingerlike structures lining its walls. Blood moves through the villi to pick up the molecules so they can circulate to other cells in your body. villi Now you have completely digested that apple you ate hours ago. Digestion has turned the fruit into molecules of sugar. The sugar molecules carry stored energy from the apple. These molecules are transported by the blood to your body’s cells, where respiration changes most of the molecules into energy. You use this energy for all of your body’s activities. The blood carries the waste products of water vapor and carbon dioxide to your lungs, where you breathe them out. Any leftovers from the food you ate will leave the body as waste. The small intestine is only called “small” because it’s narrow. It can be 7 meters (23 ft.) long—as long as a truck! 15