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Name CHAPTER 11 Class Date The Chemistry of Living Things SECTION 2 Compounds of Living Things California Science Standards BEFORE YOU READ After you read this section, you should be able to answer these questions: 8.3.c, 8.6.c • Why is water important for living things? • How does salt help your body cells function? • What are four complex organic compounds needed by living things? Why Is Water Important for Living Things? Water is one of the simplest compounds that all living things need. In fact, about 70% of your body weight is due to water. Water is found everywhere in your body. It is inside your cells. It surrounds your tissues and joints, and it is inside your blood vessels. Although you may not realize it, the water you drink helps your body do many important things. "RAINÈ "ONEÈ +IDNEYÈ The percentage of water is not the same in different parts of your body. -USCLEÈ "LOODÈ Water helps you control your body temperature. It stores heat and insulates your body in cold surroundings. On a hot day, water cools your body. It does this by evaporating from your skin in the form of sweat. Water make the joints in your body move more easily. Water surrounds your bones and joints and delicate organs such as the eyes and brain. Water cushions these parts from shock. Water has other functions in your body. It transports many nutrients and other substances around your body. As your body produces waste, water also helps dilute the waste and remove it. In addition, water is needed by your cells to make the molecules you use for energy. STUDY TIP Memorize When you come across new vocabulary words, create flashcards to help you remember their meanings. Write each word on one side of an index card. Then, write its definition (and other important facts) on the other side. Math Focus 1. Analyze Data If a human body has about 10 pounds of blood, how much does the water in the blood weigh? Show your work. READING CHECK 2. Identify Name five ways that your body needs water in order to function properly. Copyright © by Holt, Rinehart and Winston. All rights reserved. Interactive Reader and Study Guide 157 The Chemistry of Living Things Name Class SECTION 2 Date Compounds of Living Things continued Animals have salt in their bodies. Therefore, they need to have a certain amount of salt in their diets. CALIFORNIA STANDARDS CHECK 8.6.c Students know that living organisms have many different kinds of molecules, including small ones, such as water and salt, and very large ones, such as carbohydrates, fats, proteins, and DNA. 3. Explain When athletes exercise very hard, it is important for them to replace salts lost from their bodies. How can low amounts of salts affect electrical signals in your body? Why Do Living Things Need Salt? Why is the deer licking salt in the figure above? The deer must replace the salt that is lost from its body. If you’ve ever tasted sweat or tears, you know that your body also contains salt. There are different types of salt. The salt you usually eat is sodium chloride. There are other salts that are made of elements such as potassium and calcium. All of these salts are present in your body and have vital functions. Salts help transport materials in and out of the cells. Cells use a difference in electrical charge inside and outside the cell membrane to move materials in and out. Cells use the charges carried by salt ions to do this. Salts are also used to conduct electrical signals throughout your body. This is especially important for nerve cells, muscle cells, and heart cells. What Organic Compounds Do Living Things Need? READING CHECK 4. Identify What four complex compounds are needed by the human body? Living things require simple compounds such as water and salts. They also need large complex compounds. Can you think of some examples? You may have read about carbohydrates and proteins on food labels. Cells need carbohydrates, lipids, proteins, and nucleic acids in order to function. Eating well-balanced meals is important for your body. Carbohydrates, proteins, and lipids come from different foods. Copyright © by Holt, Rinehart and Winston. All rights reserved. Interactive Reader and Study Guide 158 The Chemistry of Living Things Name Class Date Compounds of Living Things continued SECTION 2 CARBOHYDRATES Compounds made of one or more molecules of simple sugar are called carbohydrates. Small sugar molecules can join together to form complex carbohydrates. The figure below shows a glucose (simple sugar) molecule and a sucrose (table sugar) molecule. You can see that the sucrose is made of two simple sugars joined together. Glucose is a simple sugar. Sucrose is a more-complex sugar. #(/( ( # # (/ (/ / /( ( /( ( # # # ( ( /( Glucose molecule (/ #( / /( #( TAKE A LOOK / /( / #( /( /( /( /( 5. Identify How many simple sugar molecules make up one molecule of sucrose? Sucrose molecule A complex carbohydrate can be made of thousands of simple sugars arranged in a long chain of repeating units. This chain is called a polymer. Cells use carbohydrates as an energy source. For example, your body breaks down carbohydrates and stores some of the energy in muscle cells in the form of molecules called glycogen. Carbohydrates also have other uses in cells. Cellulose, a type of carbohydrate, forms cell walls that give plants their rigid structure. READING CHECK 6. Describe What is a polymer? LIPIDS Lipids are organic compounds that do not dissolve in water. Lipids are fat-soluble; that is, they dissolve in fats. Examples of lipids include fats, oils, and waxes. Like carbohydrates, they are required by living things. Though too much fat in your diet is unhealthful, some fat is important to help you maintain good health. Lipids are large molecules made mostly of carbon and hydrogen atoms. Saturated fats are lipids with only single bonds between the carbon atoms. Unsaturated fats are lipids that contain double bonds. Lipids have many roles in living things. One role is to store energy. When carbohydrates or glycogen are not available, cells use energy stored in your body fat. Fat layers under your skin and around your organs also protect and insulate your body. The vitamins A, D, E, and K are necessary for good health. They are fat-soluble, so they need fat to work properly. They are also stored in your body fat. Critical Thinking 7. Infer Vitamins A, D, E, and K can reach dangerous levels in a person’s body if he or she takes too many vitamin supplements. What do you think is the reason? Copyright © by Holt, Rinehart and Winston. All rights reserved. Interactive Reader and Study Guide 159 The Chemistry of Living Things Name SECTION 2 Class Date Compounds of Living Things continued PROTEINS READING CHECK Proteins are organic compounds made of building blocks called amino acids. Most proteins are large molecules made of long-chain polymers of amino acids. Each type of protein in a cell has its own special structure. This structure depends on the way the amino acid chains fold together. Think of folding a shirt while doing laundry. There are different ways to fold it. With proteins, the way one is folded affects its function in the body. There are only 20 different types of amino acids, the protein building blocks. However, the possible combinations of amino acids are almost limitless. For example, a simple prokaryotic bacteria such as Escherichia coli has over 1,000 different proteins. 8. Identify What are proteins made of? Human hair Peanuts Red blood cells Proteins play a variety of important roles in living organisms. READING CHECK 9. Identify What is the protein that carries oxygen to your body cells? Proteins have a wide range of important functions in living things. The figure above shows some examples of different proteins. Keratin protein in hair is strong and lightweight. Nuts are foods dense in proteins that store energy. Your body has other unique proteins that help keep you healthy. One important protein in red blood cells is hemoglobin. Hemoglobin carries oxygen to all the cells in your body. It also carries away carbon dioxide. Many hormones are proteins. For example, insulin is a protein hormone that helps control the level of sugar in your blood. This is important for maintaining a steady flow of energy. Antibodies in your body are also made of proteins. Antibodies attach to and destroy bacteria. Copyright © by Holt, Rinehart and Winston. All rights reserved. Interactive Reader and Study Guide 160 The Chemistry of Living Things Name SECTION 2 Class Date Compounds of Living Things continued NUCLEIC ACIDS The largest organic compounds made by living things are nucleic acids. Nucleic acids are made up of sugars, phosphates, and nucleotides. Nucleotides are molecules made of carbon, oxygen, hydrogen, nitrogen, and phosphorus. Four different nucleotides are found in the nucleic acid known as DNA. They are adenine, thymine, guanine, and cytosine. ' # 10. Identify What are nucleic acids made of? "ASEPAIR ' # 4 ! !DENINE ! 4 ' # 4HYMINE 4 ! ! 4 'UANINE 3UGARPHOSPHATE BACKBONE READING CHECK ' # 4 ! ! 4 ' # 4 ! ! 4 DNA is a complex molecule that looks like a twisted ladder. The bases are found in pairs between the two sides of the DNA ladder. #YTOSINE Nucleic acids store genetic information. They are sometimes called “the blueprints of life.” This is because they carry all the information needed for a cell to make all of its proteins. If the protein code in a nucleic acid is changed, the proteins it affects will not function normally. Think of the differences in eye color between you and your friends. They are due to differences in the nucleotide patterns for proteins that make up the eye. The differences in nucleotide sequences result in different traits and different species. TAKE A LOOK 11. Identify Which base is always paired with thymine? Say It Predict Report to the class on what might happen if there were a change in the nucleic acids needed to make hemoglobin. DNA AND RNA There are two different types of nucleic acids: DNA and RNA. A model of DNA is shown above. DNA is the genetic material found in the nuclei of your cells. DNA exists in long-chain polymers. If you stretched out the DNA in a human cell, it would stretch about six feet! When a cell needs to make a certain protein, it copies a small part of the DNA onto another type of nucleic acid called RNA. The RNA is moved out of the nucleus and into the cytoplasm. The RNA directs the organization of amino acids into a specific protein. READING CHECK 12. Describe What instructions does RNA contain? Copyright © by Holt, Rinehart and Winston. All rights reserved. Interactive Reader and Study Guide 161 The Chemistry of Living Things Name Class Section 2 Review Date 8.3.c, 8.6.c SECTION VOCABULARY carbohydrate a class of energy-giving nutrients that includes sugars, starches, and fiber; contains carbon, hydrogen, and oxygen lipid a type of biochemical that does not dissolve in water; fats and steroids are lipids Wordwise The root lip means “fat.” nucleic acid a molecule made up of subunits called nucleotides protein a molecule that is made up of amino acids and that is needed to build and repair body structures and to regulate processes in the body 1. Infer How does water act as your body’s “shock cushion” ? 2. Fill In Complete the Spider Map of the compounds discussed in this section that are vital for living things. Below each compound, tell if it is a small molecule or a large molecule. Compounds living things depend on 3. Identify Long-chain proteins and long-chain carbohydrates are examples of the type of molecule called a . 4. Classify What can both carbohydrates and lipids provide for the body? Copyright © by Holt, Rinehart and Winston. All rights reserved. Interactive Reader and Study Guide 162 The Chemistry of Living Things