Biology/Life Sciences Chapter 6 PDF

The Cell Chapter 6 Chemistry in Biology ")' )DEA Atoms are the foundation of biological chemistry and the building blocks of all living organisms. Chapter 7 Cellular Structure and Function Careers ")' )DEA Cells are the structural...

The Cell Chapter 6 Chemistry in Biology ")' )DEA Atoms are the foundation of biological chemistry and the building blocks of all living organisms. Chapter 7 Cellular Structure and Function Careers ")' )DEA Cells are the structural in Biology Forensic Pathologist and functional units of all living Forensic pathologists are organisms. medical specialists who investigate the cause and the manner of human Chapter 8 death. Forensic pathologists work in the Cellular Energy field and in a laboratory to analyze medical ")' )DEA Photosynthesis evidence such as skulls. converts the Sun’s energy into "IOLOGY Visit chemical energy, while cellular biologygmh.com to learn more respiration uses chemical energy about forensic pathology. Then to carry out life functions. write a summary of the classification of the manner of death that forensic Chapter 9 pathologists use. Cellular Reproduction ")' )DEA Cells go through a life cycle that includes interphase, mitosis, and cytokinesis. 144 Louie Psihoyos/CORBIS To read more about forensic pathologists in action, visit biologygmh.com. Unit 2 The Cell 145  Biology/Life Sciences 1.b, 4.c, 4.f, 5.a, 6.d, 6.f, 9.a Chemistry in Biology Section 1 Atoms, Elements, and Compounds -!). )DEA Matter is composed of tiny particles called atoms. Section 2 Chemical Reactions -!). )DEA Chemical reactions allow living things to grow, develop, reproduce, and adapt. Section 3 Water and Solutions -!). )DEA The properties of water make it well suited to help maintain homeostasis in an organism. Section 4 The Building Blocks of Life -!). )DEA Organisms are made up of carbon-based molecules. Multiple collagen fibers BioFacts SEM Magnification: 8000ⴛ Collagen is the most abundant protein in mammals. Collagen can be found in muscle, bone, teeth, skin, and the cornea of the eye. Wrinkles that become visible as people age are the result of collagen breaking down. Single collagen fiber SEM Magnification: Unavailable 146 (t)David M. Phillips/Photo Researchers, (b)BSIP/Photo Researchers, (bkgd)David Young-Wolff/PhotoEdit  Start-Up Activities I&E 1.d LAUNCH Lab Enzymes Make this Foldable to help you organize information about enzyme How does the nutrient content structure and function. of foods compare? STEP 1 Draw a line across the middle Your body’s structure and function depends on chemical of a piece of paper. elements including those found in proteins, carbohy- drates, fats, vitamins, minerals, and water. In this lab, you will investigate nutrients that provide those elements. Procedure 1. Read and complete the lab safety form. 2. Construct a data chart to record grams or percent of each nutrient listed above. Include columns for Serving Size, Calories, and STEP 2 Fold the top and bottom edges Calories from Fat. to meet at the middle of the paper. 3. Study and record data from the Nutrition Facts label on a cereal box. 4. Choose three additional labeled food items. Predict how the nutrients in these items compare with the nutrients in the cereal. Use STEP 3 Fold in half to make four the Nutrition Facts labels to record data. sections as shown. Analysis 1. Evaluate What factors influenced your predictions of the nutrient contents? Were your predictions correct? 2. Analyze Which food item has the greatest STEP 4 Cut along the fold lines of the amount of proteins per serving? The least? top and bottom flaps to form four tabs of equal size. Label the tabs A, B, C, and D as shown.
Visit biologygmh.com to: ▶ study the entire chapter online &/,$!",%3 Use this Foldable with ▶ explore Concepts in Motion, the Section 6.2. As you study the section, Interactive Table, Microscopy Links, record what you learn about enzymes. Virtual Labs, and links to virtual On the front tabs, draw the four general dissections steps of enzyme activity. ▶ access Web links for more information, projects, and activities ▶ review content online with the Inter- active Tutor and take Self-Check Quizzes Section Chapter 1 XXXXXXXXXXXXXXXXXX 6 Chemistry in Biology 147  Biology/Life Sciences 1.b Students know enzymes are proteins that catalyze biochemical reactions without altering the reaction equilibrium and the activities of enzymes depend on the temperature, ionic conditions, and Section 6.1 the pH of the surroundings. Also covers: Biology/Life Sciences 6.d Objectives ◗ Identify the particles that make Atoms, Elements, up atoms. ◗ Diagram the particles that make and Compounds up an atom. ◗ Compare covalent bonds and ionic -!). )DEA Matter is composed of tiny particles called atoms. bonds. Real-World Reading Link Many scientists think that the universe began with ◗ Describe van der Waals forces. a huge explosion billions of years ago. They think that the building blocks that Review Vocabulary make up the amazing diversity of life we see today are a result of that explosion. The study of those building blocks is the science of chemistry. substance: a form of matter that has a uniform and unchanging composition New Vocabulary Atoms atom Chemistry is the study of matter—its composition and properties. nucleus Matter is anything that has mass and takes up space. All of the organ- proton isms you study in biology are made up of matter. Atoms are the build- neutron ing blocks of matter. electron element #ONNECTION TO (ISTORY In the fifth century B.C., the Greek philoso- isotope phers Leucippus and Democritus first proposed the idea that all matter compound is made up of tiny, indivisible particles. It wasn’t until the 1800s that covalent bond molecule scientists began to collect experimental evidence to support the exis- ion tence of atoms. As technology improved over the next two centuries, ionic bond scientists proved not only that atoms exist but also that they are made van der Waals force up of even smaller particles. The structure of atoms An atom is so small that billions of them fit on the head of a pin. Yet, atoms are made up of even smaller particles called neutrons, protons, and electrons, as illustrated in Figure 6.1. Neu- trons and protons are located at the center of the atom, which is called the nucleus. Protons are positively charged particles (p +), and neutrons are particles that have no charge (n 0). Electrons are negatively charged particles that are located outside the nucleus (e⫺). Electrons constantly move around an atom’s nucleus in energy levels. The basic structure of an atom is the result of the attraction between protons and electrons. Atoms contain an equal number of protons and electrons, so the overall charge of an atom is zero..UCLEUS  PROTONS  e  NEUTRONS  c.UCLEUS  PROTON e  NEUTRONS c  ELECTRON E Figure 6.1 Hydrogen has only one proton  ELECTRONS and one electron. Oxygen has eight protons, E eight neutrons, and eight electrons. The electrons move around the nucleus in two energy levels (YDROGEN ATOM /XYGEN ATOM (shown as the darker shaded rings). 148 Chapter 6 Chemistry in Biology  0%2)/$)# 4!",% /& 4(% %,%-%.43 'AS ,IQUID -ETAL  3OLID  -ETALLOID %LEMENT (YDROGEN 3YNTHETIC ELEMENTS (YDROGEN.ONMETAL (ELIUM     !TOMIC NUMBER  3TATE OF MATTER ( 2ECENTLY      (E  3YMBOL ( DISCOVERED  ,ITHIUM "ERYLLIUM "ORON #ARBON.ITROGEN /XYGEN &LUORINE.EON !TOMIC MASS           ,I "E " #. / &.E         3ODIUM -AGNESIUM !LUMINUM 3ILICON 0HOSPHORUS 3ULFUR #HLORINE !RGON         .A -G           !L 3I 0 3 #L !R         0OTASSIUM #ALCIUM 3CANDIUM 4ITANIUM 6ANADIUM #HROMIUM -ANGANESE )RON #OBALT.ICKEL #OPPER :INC 'ALLIUM 'ERMANIUM !RSENIC 3ELENIUM "ROMINE +RYPTON                    + #A 3C 4I 6 #R -N &E #O.I #U :N 'A 'E !S 3E "R +R                   2UBIDIUM 3TRONTIUM 9TTRIUM :IRCONIUM.IOBIUM -OLYBDENUM 4ECHNETIUM 2UTHENIUM 2HODIUM 0ALLADIUM 3ILVER #ADMIUM )NDIUM 4IN !NTIMONY 4ELLURIUM )ODINE 8ENON                    2B 3R 9 :R.B -O 4C 2U 2H 0D !G #D )N 3N 3B 4E ) 8E                   #ESIUM "ARIUM ,ANTHANUM (AFNIUM 4ANTALUM 4UNGSTEN 2HENIUM /SMIUM )RIDIUM 0LATINUM 'OLD -ERCURY 4HALLIUM ,EAD "ISMUTH 0OLONIUM !STATINE 2ADON                    #S "A ,A (F 4A 7 2E /S )R 0T !U (G 4L 0B "I 0O !T 2N                   &RANCIUM 2ADIUM !CTINIUM 2UTHERFORDIUM $UBNIUM 3EABORGIUM "OHRIUM (ASSIUM -EITNERIUM $ARMSTADTIUM 2OENTGENIUM 5NUMBIUM 5NUNQUADIUM               &R 2A !C 2F $B 3G "H (S -T $S 2G 5UB 5UQ              4HE NAMES AND SYMBOLS FOR   ARE TEMPORARY &INAL NAMES WILL BE SELECTED WHEN THE ELEMENTS DISCOVERIES ARE VERIFIED #ERIUM 0RASEODYMIUM.EODYMIUM 0ROMETHIUM 3AMARIUM %UROPIUM 'ADOLINIUM 4ERBIUM $YSPROSIUM (OLMIUM %RBIUM 4HULIUM 9TTERBIUM ,UTETIUM               ,ANTHANIDE SERIES #E 0R.D 0M 3M %U 'D 4B $Y (O %R 4M 9B ,U               4HORIUM 0ROTACTINIUM 5RANIUM.EPTUNIUM 0LUTONIUM !MERICIUM #URIUM "ERKELIUM #ALIFORNIUM %INSTEINIUM &ERMIUM -ENDELEVIUM.OBELIUM ,AWRENCIUM !CTINIDE SERIES               4H 0A 5.P 0U !M #M "K #F %S &M -D.O ,R               Figure 6.2 The periodic table of the elements organizes all of the known elements. Examine the biologists’ guide to the periodic table on the back cover of this book. Elements An element is a pure substance that cannot be broken down into other substances by physical or chemical means. Elements are made of only one type of atom. There are over 100 known elements, 92 of which occur naturally. Scientists have collected a large amount of Figure 6.3 The elements in Earth’s crust and living organisms vary in their abundance. Living things are composed primarily of information about the elements, such as the number of three elements—carbon, hydrogen, and oxygen. protons and electrons each element has and the atomic Interpret What is the most abundant element that exists mass of each element. Also, each element has a unique in living things? name and symbol. All of these data, and more, are col- lected in an organized table called the periodic table of 2ELATIVE #OMPOSITION OF ,IVING V.ONLIVING -ATTER elements.  0ERCENT OF RELATIVE The periodic table of elements As shown in /RGANISMS  ABUNDANCE Figure 6.2, the periodic table is organized into horizon- %ARTHS #RUST tal rows, called periods, and vertical columns, called  groups. Each individual block in the grid represents an  element. The table is called periodic because elements in the same group have similar chemical and physical  properties. This organization even allows scientists to predict elements that have not yet been discovered or  ( # /. #A.A 0 3I /THERS isolated. As shown in Figure 6.3, elements found in liv- AND AND ing organisms also are found in Earth’s crust. -G + Section 1 Atoms, Elements, and Compounds 149  Figure 6.4 Carbon-12 and carbon-13  e  e  e occur naturally in living and nonliving things. All living things also contain a small amount of  c  c  c carbon-14. e c e c e Compare How do the isotopes differ? c e c e c e How are they the same? e e e e c e c e c c c c e c c c e c c e c e e c e c c c #ARBON  #ARBON  #ARBON  NUCLEUS NUCLEUS NUCLEUS Isotopes Although atoms of the same element have the same num- ber of protons and electrons, atoms of an element can have different numbers of neutrons, as shown in Figure 6.4. Atoms of the same ele- ment that have different numbers of neutrons are called isotopes. Iso- Careers In biology topes of an element are identified by adding the number of protons and neutrons in the nucleus. For example, the most abundant form of car- Nuclear Engineer A nuclear bon, carbon-12, has six protons and six neutrons in its nucleus. One engineer develops applications that carbon isotope—carbon-14—has six protons and eight neutrons. Iso- use the radioactive properties of topes of elements have the same chemical characteristics. elements. Nuclear engineers might focus on radiation for medical Radioactive isotopes Previously, you read that neutrons have no diagnostics and treatments, food charge. Changing the number of neutrons in an atom does not change preservation, or electricity generation. the overall charge of the atom (it still has no charge). However, chang- For more information on biology ing the number of neutrons can affect the stability of the nucleus, in careers, visit biologygmh.com. some cases causing the nucleus to decay, or break apart. When a nucleus breaks apart, it gives off radiation that can be detected and used for many applications. Isotopes that give off radiation are called radioactive isotopes. Carbon-14 is a radioactive isotope that is found in all living things. Scientists know the half-life, or the amount of time it takes for half of carbon-14 to decay, so they can calculate the age of an object by finding how much carbon-14 remains in the sample. Other radioactive isotopes have medical uses, such as in radiation therapy to treat cancers, as shown Figure 6.5 Radioactive isotopes are used to help doctors diagnose disease and locate and in Figure 6.5. treat certain types of cancer. 150 Chapter 6 Chemistry in Biology (l)Custom Medical Stock Photography, (r)Neil Borden/Photo Researchers (tl)Peter Bowater/Photo Researchers, (tr)Spencer Jones/Picture Arts/CORBIS, (bl)W. Cody/CORBIS, (br)Charles D. Winters/Photo Researchers Table salt is the compound NaCl. Brilliant fireworks displays depend on compounds containing the metal strontium. Wetlands are sources of living things made of complex compounds and the simple compound methane (CH4 ). Figure 6.6 You and your world are made Compounds of compounds. Elements can combine to form more complex substances. A compound is a pure substance formed when two or more different elements combine. There are millions of known compounds and thousands more discovered each year. Figure 6.6 shows you a few. Each compound has a chemical for- mula made up of the chemical symbols from the periodic table. You might know that water is the compound H2O. Sodium chloride (NaCl) is the compound commonly called table salt. The fuel people use in cars is a mixture of hydrocarbon compounds. Hydrocarbons only have hydrogen and carbon atoms. Methane (CH4) is the simplest hydrocarbon. Bacteria in areas such as the wetlands shown in Figure 6.6 release 76 percent of global Figure 6.7 Electrolysis of water methane from natural sources by decomposing plants and other organ- produces hydrogen gas that can be used for isms. They are made of compounds, too. hydrogen fuel cells. Compounds have several unique characteristics. First, compounds are always formed from a specific combination of elements in a fixed ratio. Water always is formed in a ratio of two hydrogen atoms and one oxygen atom, and each water molecule has the same structure. Second, compounds are chemically and physically different than the elements that comprise them. For example, water has different properties than hydrogen and oxygen. Another characteristic of compounds is that they cannot be broken down into simpler compounds or elements by physical means, such as tearing or crushing. Compounds, however, can be broken down by chemical means into simpler compounds or into their original ele- ments. Consider again the example of water. You cannot pass water through a filter and separate the hydrogen from the oxygen, but a proc- ess called electrolysis, illustrated in Figure 6.7, can break water down into hydrogen gas and oxygen gas. Section 1 Atoms, Elements, and Compounds 151  Chemical Bonds Compounds such as water, salt, and methane are formed when two or more substances combine. The force that holds the substances together is called a chemical bond. Think back to the protons, neutrons, and electrons that make up an atom. The nucleus determines the chemical identity of an atom, and the electrons are involved directly in forming chemical bonds. Electrons travel around the nucleus of an atom in areas called energy levels, as illustrated in Figure 6.8. Each energy level has a specific number of electrons that it can hold at any time. The first energy level, which is the level closest to the nucleus, can hold up to two.UCLEUS electrons. The second can hold up to eight electrons. A partially-filled energy level is not as stable as an energy level that is empty or completely filled. Atoms become more stable by losing elec- %LECTRON ENERGY LEVELS trons or attracting electrons from other atoms. This results in the for- mation of chemical bonds between atoms. It is the forming of chemical Figure 6.8 Electrons are moving bonds that stores energy and the breaking of chemical bonds that pro- constantly within the energy levels vides energy for processes of growth, development, adaptation, and surrounding the nucleus. reproduction in living things. There are two main types of chemical bonds—covalent bonds and ionic bonds. Covalent bonds When you were younger, you probably learned to share. If you had a book that your friend wanted to read as well, you could enjoy the story together. In this way, you both benefited from the book. Similarly, one type of chemical bond happens when atoms share electrons in their outer energy levels. The chemical bond that forms when electrons are shared is called a covalent bond. Figure 6.9 illustrates the covalent bonds between oxygen and hydrogen to form water. Each hydrogen (H) atom has one electron in its outermost energy level and oxygen (O) has six. Because the outermost energy level of oxygen is the second level, which can hold up to eight electrons, oxygen has a strong tendency to fill the energy level by sharing the electrons from the two nearby hydrogen atoms. Hydrogen does not completely give up the electrons, but also has a strong tendency to share electrons with oxygen to fill its outermost energy level. Two covalent bonds form, which creates water. Most compounds in living organisms have covalent bonds holding them together. Water and other substances with covalent bonds are called molecules. A molecule is a compound in which the atoms are held together by covalent bonds. Depending on the number of pairs of electrons that are shared, covalent bonds can be single, double, or tri- ple, as shown in Figure 6.10.  e  c Figure 6.9 In water (H2O), two hydrogen e e atoms each share one electron with one oxygen atom. Because the oxygen atom needs two electrons to fill its outer energy level, it #OVALENT forms two covalent bonds, one with each 7ATER BOND hydrogen atom. MOLECULE 152 Chapter 6 Chemistry in Biology  3INGLE BOND $OUBLE BOND 4RIPLE BOND ( /. Figure 6.10 A single bond has one pair Ionic bonds Recall that atoms are neutral—they do not have an of shared electrons, a double bond has two electric charge. Also recall that for an atom to be most stable, the outer- pairs, and a triple bond has three pairs. most energy level should be either empty or completely filled. Some atoms tend to give up (donate) or obtain (accept) electrons to empty or fill the outer energy level in order to be stable. An atom that has lost or gained one or more electrons becomes an ion and carries an electric charge. For example, sodium has one electron in its outermost energy level. Sodium can become more stable if it gives up this one electron, leaving its outer energy level empty. When it gives away this one nega- tive charge, the neutral sodium atom becomes a positively charged sodium ion (Na⫹). Similarly, chlorine has seven electrons in its outer energy level and needs just one electron to fill it. When chlorine accepts an electron from a donor atom, such as sodium, chlorine becomes a negatively charged ion (Cl⫺). An ionic bond is an electrical attraction between two oppositely charged atoms or groups of atoms called ions. Figure 6.11 shows how an ionic bond forms as a result of the electrical attraction between Na⫹ and Cl⫺ to produce NaCl (sodium chloride). Substances formed by ionic Figure 6.11 To form ions, sodium bonds are called ionic compounds. donates an electron and chlorine gains an Ions in living things include sodium, potassium, calcium, chloride, electron. An ionic bond forms when the oppositely charged ions come close together. and carbonate ions. They help maintain homeostasis as they travel in and out of cells. In addition, ions help transmit signals among cells that allow you to see, taste, hear, feel, and smell. Interactive Figure To see an animation of how ionic bonds form, visit biologygmh.com. )ONIC BOND.A  #L.A #L.A ATOM  e #L ATOM  e.A ION  e #L ION  e  Z  Z  Z  Z 3ODIUM ATOM  #HLORINE ATOM 3ODIUM ION  #HLORIDE ION.A  #L.A#L Section 1 Atoms, Elements, and Compounds 153  Some atoms tend to donate or accept electrons more easily than other atoms. Look at the periodic table of elements inside the back cover of this textbook. The elements identified as metals tend to donate VOCABULARY electrons, and the elements identified as nonmetals tend to accept elec- WORD ORIGIN trons. The resulting ionic compounds have some unique characteris- Atom tics. For example, most dissolve in water. When dissolved in solution, comes from the Greek word atomos, ionic compounds break down into ions and these ions can carry an meaning not divisible. electric current. Most ionic compounds, such as sodium chloride (table salt), are crystalline at room temperature. Ionic compounds generally have higher melting points than molecular compounds formed by covalent bonds. #ONNECTION TO %ARTH 3CIENCE Although most ionic compounds are solid at room temperature, other ionic compounds are liquid at room temperature. Like their solid counterparts, ionic liquids are made up of positively and negatively charged ions. Ionic liquids have important potential in real-world applications as safe and environmentally friendly solvents that can possibly replace other harmful solvents. The key characteristic of ionic liquid solvents is that they typically do not evaporate and release chemicals into the atmosphere. Most ionic liquids are safe to handle and store, and they can be recycled after use. For these reasons, ionic liquids are attractive to industries that are dedi- cated to environmental responsibility. Reading Check Compare ionic solids and liquids. I&E 1.a, 1.d Test for Simple Sugars What common foods contain glucose? Glucose is a simple sugar that provides energy for cells. In this lab, you will use an reagent called Benedict’s solution, which indicates the presence of –CHO (carbon, hydrogen, oxygen) groups. A color change determines the presence of glucose and other simple sugars in common foods. Procedure 1. Read and complete the lab safety form. 2. Create a data table with columns labeled Food Substance, Sugar Prediction, Observations, and Results. 3. Choose four food substances from those provided. Read the food labels and predict the presence of simple sugar in each food. Record your prediction. 4. Prepare a hot water bath with a temperature between 40°–50°C using a hot plate and 1000-mL beaker. 5. Label four test tubes. Obtain a graduated cylinder. Add 10 mL of a different food substance to each test tube. Then add 10 mL distilled water. Swirl gently to mix. 6. Add 5 mL of Benedict’s solution to each tube. Use a clean stirring rod to mix the contents. 7. Using test tube holders, warm the test tubes in the hot water bath for 2–3 min. Record your obser- vations and results. Analysis 1. Interpret Data Did any of the foods contain simple sugars? Explain. 2. Think Critically Could a food labeled “sugar free” test positive using Benedict’s solution as an indicator? Explain. 154 Chapter 6 Chemistry in Biology (inset)Dennis Kunkel/PhotoTake NYC, (bkgd)Zigmund Leszczynski/Animals Animals van der Waals Forces You have learned that positive ions and negative ions form based on the ability of an atom to attract electrons. If the nucleus of the atom has a weak attraction for the electron, it will donate the electron to an atom with a stronger attraction. Similarly, elements in a covalent bond do not always attract electrons equally. Recall also that the electrons in a molecule are in random motion around the nuclei. This movement of electrons can cause an unequal distribution of the electron cloud around the molecule, creating temporary areas of slightly positive and negative charges. When molecules come close together, the attractive forces between these positive and negative regions pull on the molecules and hold them together. These attractions between the molecules are called van der Waals forces, named for the Dutch physicist Johannes van der Waals who first described the phenomenon. The strength of the attrac- tion depends on the size of the molecule, its shape, and its ability to attract electrons. Van der Waals forces are not as strong as covalent and ionic bonds, but they play a key role in biological processes. Scientists have determined that geckos, such as the one shown in Figure 6.12, can climb smooth surfaces due to van der Waals forces between the atoms in the hairlike structures on their toes and the Figure 6.12 Geckos have millions of atoms on the surface they are climbing. microscopic hairs on the bottoms of their feet that are about as long as two widths of a van der Waals forces in water Let’s consider how van der human hair. Each spreads into 1000 smaller Waals forces work in a common substance—water. The areas of slight pads that get close to the surface of an atom. positive and negative charge around the water molecule are attracted to the opposite charge of other nearby water molecules. These forces hold the water molecules together. Without van der Waals forces, water mol- ecules would not form droplets, and droplets would not form a surface of water. It is important to understand that van der Waals forces are the attractive forces between the water molecules, not the forces between the atoms that make up water. Section 6.1 Assessment Biology/Life Sciences 6.d Section Summary Understand Main Ideas Think Scientifically ◗ Atoms consist of protons, neutrons, 1. -!). )DEA Diagram Sodium and electrons. has 11 protons and 11 neutrons in its nucleus. Draw a sodium atom. 5. Explain how the number of ◗ Elements are pure substances made electrons in an energy level affects Be sure to label the particles. up of only one kind of atom. bond formation. 2. Explain why carbon monoxide ◗ Isotopes are forms of the same ele- (CO) is or is not an element. -!4( IN "IOLOGY Beryllium ment that have a different number 6. of neutrons. 3. Explain Are all compounds mol- has four protons in its nucleus. How ecules? Why or why not? many neutrons are in beryllium-9? ◗ Compounds are substances with 4. Compare van der Waals forces, Explain how you calculated your unique properties that are formed ionic bonds, and covalent bonds. answer. when elements combine. ◗ Elements can form covalent and ionic bonds. Self-Check Quiz biologygmh.com Section 1 Atoms, Elements, and Compounds 155  Biology/Life Sciences 1.b Students know enzymes are proteins that catalyze biochemical reactions without altering the reaction equilibrium and the activities of enzymes depend on the temperature, ionic conditions, and Section 6. 2 the pH of the surroundings. Also covers: Biology/Life Sciences 6.f Objectives ◗ Identify the parts of a chemical Chemical Reactions reaction. ◗ Relate energy changes to chemical -!). )DEA Chemical reactions allow living things to grow, reactions. develop, reproduce, and adapt. ◗ Summarize the importance of enzymes in living organisms. Real-World Reading Link When you lie down for the night, you probably think that your body is completely at rest. In fact, you will still be digesting food you ate Review Vocabulary that day, the scrape on your elbow will be healing, and your muscles and bones will process: a series of steps or actions be growing and developing. All of the things that are happening inside your body that produce an end product are the result of chemical reactions. You are a 24-hour reaction factory! New Vocabulary chemical reaction Reactants and Products reactant A new car with its shining chrome and clean appearance is appealing to product many drivers. Over time, however, the car might get rusty and lose some activation energy of its appeal. Rust is a result of a chemical change called a chemical reac- catalyst enzyme tion. A chemical reaction is the process by which atoms or groups of substrate atoms in substances are reorganized into different substances. Chemical active site bonds are broken and/or formed during chemical reactions. The rust on the chain in Figure 6.13 is a compound called iron oxide (Fe2O3), and it was formed when oxygen (O2) in the air reacted with iron (Fe). It is important to know that substances can undergo changes that do not involve chemical reactions. For example, consider the water in Figure 6.13. The water is undergoing a physical change. A physical change alters the substance’s appearance but not its composition. It is water before and after the change. How do you know when a chemical reaction has taken place? Although you might not be aware of all the reactions taking place inside your body, you know the surface of the chain in Figure 6.13 has changed. What was Figure 6.13 After a chemical change, such as once silver and shiny is now dull and orange-brown. Other clues that a rusting, a new substance is formed. During a chemical reaction has taken place include the production of heat or light, physical change such as ice melting or water boiling, and formation of a gas, liquid, or solid. only the appearance of the water has been altered. Chemical Change Physical Change 156 Chapter 6 Chemistry in Biology (l)Julian Calder/CORBIS, (r)Charles D. Winters/Photo Researchers David Young-Wolff/PhotoEdit Chemical equations When scientists write chemical reactions, they express each component of the reaction in a chemical equation. When writing chemical equations, chemical formulas describe the sub- stances in the reaction and arrows indicate the process of change. Reactants and products A chemical equation shows the reactants, the starting substances, on the left side of the arrow and the products, the substances formed during the reaction, on the right side of the arrow. The arrow can be read as “yields” or “react to form.” Reactants → Products Figure 6.14 The process that provides The following chemical equation can be written to describe the your body with energy involves the reaction of reaction that provides energy in Figure 6.14. glucose with oxygen to form carbon dioxide and water. C6H12O6 ⫹ O2 → CO2 ⫹ H2O Glucose and oxygen react to form carbon dioxide and water. Balanced equations In chemical reactions, matter cannot be created or destroyed. This principle is called conservation of mass. Accordingly, all chemical equations must show this balance of mass. This means that the number of atoms of each element on the reactant side must equal the number of atoms of the same element on the product side. Use coefficients to make the number of atoms on each side of the arrow equal. C6H12O6 + 6O2 → 6CO2 + 6H2O VOCABULARY Multiply the coefficient by the subscript for each element. You can see ACADEMIC VOCABULARY in this example that there are six carbon atoms, twelve hydrogen atoms, Coefficient: and eighteen oxygen atoms on each side of the arrow. The equation con- In a chemical equation, the number firms that the number of atoms on each side is equal, and therefore the written in front of a reactant or a equation is balanced. You will study this important reaction further in product. The number 6 in 6Fe2O3 is a coefficient. Chapter 8. Reading Check Explain why chemical equations must be balanced. Energy of Reactions #ONNECTION TO 0HYSICS A sugar cookie is made with flour, sugar, and other ingredients mixed together, but it is not a cookie until you bake it. Something must start the change from cookie dough to cookies. The key to starting a chemical reaction is energy. For the chemical reactions that transform the dough to cookies to happen, energy in the form of heat is needed. Similarly, most compounds in living things cannot undergo chemical reactions without energy. Section 2 Chemical Reactions 157  %NERGY $IAGRAM !CTIVATION 89 ENERGY %NERGY 2EACTANTS %NERGY RELEASED 89 0RODUCT 2EACTION PROGRESS Figure 6.15 The flame of the match provides activation energy—the amount of energy needed to begin a reaction. The reaction gives off energy in the form of heat and light. Activation energy The minimum amount of energy needed Explain Why is the reaction in the graph for reactants to form products in a chemical reaction is called the exothermic? activation energy. For example, you know a candle will not burn until you light its wick. The flame provides the activation energy for the reaction of the substances in the candle wick with oxygen. In this case, once the reaction begins, no further input of energy is needed and the candle continues to burn on its own. Figure 6.15 shows that for the reactants X and Y to form product XY, energy is required to start the reaction. The peak in the graph represents the amount of energy that must be added to the system to make the reaction go. Some reactions do not happen because they have a very high activation energy. Energy change in chemical reactions Compare the progress of the reaction in Figure 6.15 to the progress of the reaction in Figure 6.16. Both reactions require activation energy to get started. However, notice from the graph in Figure 6.15 that the energy of the product is lower than the energy of the reactants. This reaction is exothermic—it released energy in the form of heat. The reaction in Figure 6.16 is endo- thermic—it absorbed heat energy. The energy of the products is higher than the energy of the reactant. In every chemical reaction, there is a change in energy due to the making and breaking of chemical bonds as reactants for products. Your body temperature of about 37°C is evidence that chemical reactions are happening inside your body. Figure 6.16 In an endothermic reaction, the energy of the products is higher than the energy of the reactant. %NERGY $IAGRAM 89 %NERGY !CTIVATION 0RODUCTS ENERGY %NERGY 89 ABSORBED 2EACTANTS 2EACTION PROGRESS 158 Chapter 6 Chemistry in Biology (t)PhotoLink/Getty Images, (b)Matt Meadows  %NERGY $IAGRAM Enzymes All living things are chemical factories driven by chemical reactions. However, these chemical reactions proceed very slowly when carried out in the laboratory because the activation energy is high. To be useful !CTIVATION to living organisms, additional substances must be present where the ENERGY %NERGY 89 chemical reactions occur to reduce the activation energy and allow the reaction to proceed quickly. A catalyst is a substance that lowers the activation energy needed to WITH ENZYME start a chemical reaction. Although a catalyst is important in speeding WITHOUT ENZYME 89 up a chemical reaction, it does not increase how much product is made and it does not get used up in the reaction. Scientists use many types of catalysts to make reactions go thousands of times faster than the reac- 2EACTION PROGRESS tion would be able to go without the catalyst. Figure 6.17 When an enzyme acts as a Special proteins called enzymes are the biological catalysts that biological catalyst, the reaction occurs at a rate speed up the rate of chemical reactions in biological processes. Enzymes that is useful to cells. are essential to life. Compare the progress of the reaction described in Compare the activation energy of the reac- tion without enzyme to the activation energy Figure 6.17 to see the effect of an enzyme on a chemical reaction. Like of the reaction with enzyme. all catalysts, the enzyme is not used up by the chemical reaction. Once it has participated in a chemical reaction, it can be used again. An enzyme’s name describes what it does. For example, amylase is an important enzyme found in saliva. Digestion of food begins in your mouth when amylase speeds the breakdown of amylose, one of the two compo- nents of starch. Like amylase, most enzymes are specific to one reaction. I&E 1.d Investigate Enzymatic Browning What factors affect enzymatic browning? When sliced, an apple’s soft tissue is exposed to oxygen, causing a chemical reaction called oxidation. Enzymes in the apple speed this reaction, producing dark- ened, discolored fruit. In this lab, you will investigate methods used to slow enzymatic browning. Procedure 1. Read and complete the lab safety form. 2. Predict the relative amount of discoloration each of these apple wedges will show when exposed to air. Justify your prediction. Sample 1: Untreated apple wedge Sample 3: Apple wedge submerged in lemon juice Sample 2: Apple wedge submerged Sample 4: Apple wedge submerged in sugar solution in boiling water 3. Prepare 75 mL of each of the following: boiling water, lemon juice, and sugar solution in three 250-mL beakers. 4. Slice an apple into four wedges. Immediately use tongs to submerge each wedge in a different liq- uid. Put one wedge aside. 5. Submerge the wedges for three minutes, then place on a paper towel, skin side down. Observe for 10 min, then record the relative amount of discoloration of each apple wedge. Analysis 1. Analyze How did each treatment affect the chemical reaction that occurred on the fruit’s soft tissue? Why were some of the treatments successful? 2. Think Critically A restaurant owner wants to serve fresh-cut fruit. What factors might be consid- ered in choosing a recipe and preparation method? Section 2 Chemical Reactions 159  Figure 6.18 Substrates interact with Substrate Active Product enzymes at specific places called active sites. sites Only substrates with a specific shape can bind to the active site of an enzyme. Interactive Figure To see an animation of enzyme activity, visit biologygmh.com. Substrate Enzyme Enzyme-substrate Product complex Follow Figure 6.18 to learn how an enzyme works. The reactants that bind to the enzyme are called substrates. The specific location &/,$!",%3 where a substrate binds on an enzyme is called the active site. The Incorporate information active site and the substrate have complementary shapes. This enables from this section into your Foldable. them to interact in a precise manner, similar to the way in which puzzle pieces fit together. As shown in Figure 6.18, only substrates with the same size and shape as the active site will bind to the enzyme. Once the substrates bind to the active site, the active site changes shape and forms the enzyme-substrate complex. The enzyme-substrate complex helps chemical bonds in the reactants to be broken and new bonds to form—the substrates react to form products. The enzyme then releases the products. Factors such as pH, temperature, and other substances affect enzyme activity. For example, most enzymes in human cells are most active at an optimal temperature close to 37°C. However, enzymes in other organisms, such as bacteria, can be active at other temperatures. Enzymes affect many biological processes. When a person is bitten by a poisonous snake, enzymes in the venom break down the mem- branes of that person’s red blood cells. Hard green apples ripen due to the action of enzymes. Photosynthesis and cellular respiration, which you will learn more about in Chapter 8, provide energy for the cell with the help of enzymes. Just as worker bees are important for the survival of a beehive, enzymes are the chemical workers in cells. Section 6. 2 Assessment Biology/Life Sciences 1.b, 6.f Section Summary Understand Main Ideas Think Scientifically ◗ Balanced chemical equations must 1. -!). )DEA Identify the parts show an equal number of atoms for of this chemical reaction: each element on both sides. A⫹B → AB. 5. -!4( IN "IOLOGY For the fol- lowing chemical reaction, label the ◗ Activation energy is the energy 2. Diagram the energy changes that reactants and products, and then required to begin a reaction. can take place in a chemical reaction. balance the chemical equation. ◗ Catalysts are substances that alter 3. Explain why the number of atoms ____H2O2 → ____H2O + ____O2 chemical reactions. of reactants must equal the number of atoms of products formed. 6. "IOLOGY Draw ◗ Enzymes are biological catalysts. 4. Describe the importance of a diagram of a roller coaster and enzymes to living organisms. write a paragraph relating the ride to activation energy and a chemical reaction. 160 Chapter 6 Chemistry in Biology Self-Check Quiz biologygmh.com  Biology/Life Sciences 1.b Students know enzymes are proteins that catalyze biochemical reactions without altering the reaction equilibrium and the activities of enzymes depend on the temperature, ionic conditions, and Section 6. 3 the pH of the surroundings. Also covers: Biology/Life Sciences 6.d Objectives ◗ Evaluate how the structure of Water and Solutions water makes it a good solvent. ◗ Compare and contrast solutions -!). )DEA The properties of water make it well suited to help and suspensions. maintain homeostasis in an organism. ◗ Describe the difference between Real-World Reading Link You probably know that the main color on a globe is acids and bases. usually blue. That’s because water covers about 70 percent of Earth’s surface, giving it Review Vocabulary the blue color you see from a distance. Now zoom in to a single cell of an organism on Earth. Water accounts for approximately 70 percent of that cell’s mass. It is one of physical property: characteristic of matter, such as color or melting the most important molecules for life. point, that can be observed or measured without changing the composition of the substance Water’s Polarity Earlier in this chapter, you discovered that water molecules are formed New Vocabulary by covalent bonds that link two hydrogen (H) atoms to one oxygen (O) polar molecule atom. Because electrons are more strongly attracted to oxygen’s nucleus, hydrogen bond the electrons in the covalent bond with hydrogen are not shared equally. mixture In water, the electrons spend more time near the oxygen nucleus than solution solvent they do near the hydrogen nuclei. Figure 6.19 shows that there is an solute unequal distribution of electrons in a water molecule. This, along with acid the bent shape of water, results in the oxygen end of the molecule having base a slightly negative charge and the hydrogen ends of the molecule a pH slightly positive charge. Molecules that have an unequal distribution of buffer charges are called polar molecules, meaning that they have oppositely charged regions. Polarity is the property of having two opposite poles, or ends. A mag- net has polarity—there is a north pole and a south pole. When the two ends are brought close to each other, they attract each other. Similarly, when a charged region of a polar molecule comes close to the oppositely charged region of another polar molecule, a weak electrostatic attraction Figure 6.19 Because water has a bent shape results. In water, the electrostatic attraction is called a hydrogen bond. A and electrons are not shared equally between hydrogen bond is a weak interaction involving a hydrogen atom and a hydrogen and oxygen, hydrogen bonds form among the molecules. Due to the attraction among the atoms fluorine, oxygen, or nitrogen atom. Hydrogen bonding is a strong type of that make up water, the surface of water supports a van der Waals interaction. Figure 6.20 describes polarity and the other water strider. unique properties of water that make it important to living things. 3LIGHTLY POSITIVE ENDS ( ( / / ( ( / ( ( ( ( / / 7ATER 3LIGHTLY ( (YDROGEN ( MOLECULE BOND NEGATIVE END Water strider Section 3 Water and Solutions 161 Color-Pic/Animals Animals  Visualizing Properties of Water 7ATER -OLECULE (YDROGEN "ONDING 3LIGHTLY POSITIVE HYDROGEN ATOMS (YDROGEN BOND 3LIGHTLY NEGATIVE OXYGEN ATOM 3OLID ,IQUID Interactive Figure To see an animation of water, visit biologygmh.com. 162 Chapter 6 Chemistry in Biology David Whitten/index Stock Imagery Mixtures with water Most students are familiar with powdered drink products that dissolve in water to form a flavored beverage. When you add a powdered sub- stance to water, it does not react with water to form a new product. You create a mixture. A mixture is a combination of two or more sub- stances in which each substance retains its individual characteristics and properties. Homogenous mixtures When a mixture has a uniform composition throughout, it is called a homogeneous (hoh muh JEE nee us) mixture. A solution is another name for a homogeneous mixture. For example, in the powdered tea drink solution shown in Figure 6.21, tea is on top, tea is in the middle, and tea is at the bottom of the container. The water retains its properties and the drink mix retains its properties. In a solution, there are two components: a solvent and a solute. A Figure 6.21 Tea forms a homogeneous solvent is a substance in which another substance is dissolved. A solute mixture in water. The particles of solute (tea) is the substance that is dissolved in the solvent. In the case of the drink are dissolved and spread throughout the mix, water is the solvent and the powdered substance is the solute. A solvent (water). mixture of salt and water is another example of a solution because the solute (salt) dissolves completely in the solvent (water). Saliva moistens your mouth and begins the digestion of some of your food. Saliva is a solution that contains water, proteins, and salts. In addition, the air you breathe is a solution of gases. Heterogenous mixtures Think about the last time you ate a salad. Perhaps it contained lettuce and other vegetables, croutons, and salad dressing. Your salad was a heterogeneous mixture. In a heteroge- neous mixture, the components remain distinct, that is, you can tell what they are individually. Compare the mixture of sand and water to the solution of salt and water next to it in Figure 6.22. Sand and water VOCABULARY form a type of heterogeneous mixture called a suspension. Over time, ACADEMIC VOCABULARY the particles in a suspension settle to the bottom. Suspend: A colloid is a heterogeneous mixture in which the particles do not to keep from falling or sinking. settle out like the sand settled from the water. You are probably famil- A slender thread suspended the spider iar with many colloids, including fog, smoke, butter, mayonnaise, milk, from the web. paint, and ink. Blood is a colloid made up of plasma, cells, and other substances. Reading Check Distinguish between solutions and suspensions. Figure 6.22 Left: Sand and water form a heterogeneous mixture—you can see both the liquid and the solid. The homogeneous mixture of salt and water is a liquid—you cannot see the salt. Right: Blood is a heterogeneous mixture called a colloid. Section 3 Water and Solutions 163 (t)David Young-Wolff/PhotoEdit, (bl)Matt Meadows, (br)Martin Rotker/PhotoTake NYC  Figure 6.23 Substances that release H+ 3UBSTANCE WITH ( ION in water are acids. Substances that release OH– 7ATER ( in water are bases. (