Cellular Respiration and Fermentation (Biology 10, PDF)

CHAPTER 9 Connect to the Big Idea Use the micrograph of the mitochondria to Cellular Respiration help students start thinking about the...

CHAPTER 9 Connect to the Big Idea Use the micrograph of the mitochondria to Cellular Respiration help students start thinking about the con- cepts of cellular respiration and fermenta- tion. First, activate prior knowledge by asking them if and Fermentation they know what mitochondria are and what their function is. (cellular organelles that convert the Cellular Basis of Life chemical energy stored in food into chemical com- Q: How do organisms obtain energy? pounds that cells can use) Now ask students what links the cereal they had for breakfast with the mitochondria in the micrograph. (energy) Point out that food, like this morning’s cereal, contains molecules that the mitochondria can use to make energy available to cells. Then, ask why cells need energy. (to carry out cell activities) Ask stu- dents to anticipate the answer to the question, How do organisms obtain energy? Have students read over the Chapter Mystery and predict how sperm whales can stay active for so long on only one breath. To make their predic- tions, suggest students think about how cells obtain and release the energy whales need to dive. Use their predictions to help them start connecting the Chapter Mystery to the Big Idea of the Cellular Basis of Life. Have students preview the chapter vocabulary terms using the Flash Cards. NATIONAL SCIENCE EDUCATION STANDARDS Chapter 9 Flash Cards 248 UNIFYING CONCEPTS AND PROCESSES I, III, V 0001_Bio10_se_Ch09_CO.indd 1 6/2/09 6:44:14 PM CONTENT Understanding by Design B.3, C.1.a, C.1.b, C.5.a, C.5.b, C.5.c, C.5.d, F.1, G.1 A cell is the basic unit of life; the processes that occur at the cellular level provide the energy and basic structure organisms need to survive. Students explore this Enduring INQUIRY Understanding in Chapter 9 by examining the processes of cellular respiration and A.1.b, A.1.c, A.1.f, A.2.a, A.2.d fermentation. As shown in the graphic organizer at the right, the Big Idea, Essential Question, and lesson-level Guiding Questions help frame their exploration. PERFORMANCE GOALS In Chapter 9, students will learn how cellular respiration and fermentation provide organisms with the energy they need to survive. Students will show this understand- ing by interpreting multiple, detailed figures. They will also practice their data analysis skills by collecting and interpreting data on the byproducts of cellular respiration. At the end of the chapter, students will transfer their knowledge by keeping an exercise journal and relating the entries to cellular respiration and fermentation. 248 Chapter 9  CHAPTER 9 What’s Online INSIDE: DIVING WITHOUT A BREATH Extend your reach by using 9.1 Cellular Respiration: An Overview Everyone is familiar with the sensation these and other digital assets offered at 9.2 The Process of Cellular Respiration of being “out of breath.” Just a few Biology.com. 9.3 Fermentation minutes of vigorous exercise can have humans huffing and puffing for air. But CHAPTER MYSTERY what if you couldn’t get air? What if Discover how the processes of cellular respiration you were asked to hold your breath and and fermentation can affect the behavior and func- exercise? Before too long, you’d pass tion of an entire organism—in this case, how often out due to a lack of oxygen. This may whales need to breathe. seem like a silly thought experiment, but there are animals that exercise UNTAMED SCIENCE Mitochondria (red) and smooth endoplasmic reticulum (yellow) without breathing and without passing Dive below the ocean surface to explore how marine in an ovarian cell (SEM 75,000×). out all the time—whales. Unlike most mammals can survive on a single breath for as long animals that live their entire lives in as they do. water, whales still rely on oxygen obtained from air when they surface. Amazingly, sperm whales routinely stay underwater for 45 minutes or more when diving. Some scientists suspect that they can stay underwater for 90 minutes! How is that possible? Diving takes a lot of energy. How do whales stay active for so long on only one breath? As you read this chapter, look for clues. Then, solve the mystery. Never Stop Exploring Your World. Learning about whales and their extraordinary ability to hold their ART IN MOTION breaths is just the beginning. Take a An animated diagram highlights the relationship video field trip with the ecogeeks of between photosynthesis and cellular respiration. Untamed Science to see where this mystery leads. INTERACTIVE ART In this short animation, students watch how glucose is broken down and energy is transferred during the process of cellular respiration. ART REVIEW Untamed Science Video Chapter Mystery Students explore the details of electron transport and Cellular Respiration and Fermentation 249 ATP synthesis. TUTOR TUBE This short, online tutorial provides extra help on the 0001_Bio10_se_Ch09_CO.indd 249 6/9/09 1:36:31 PM electron transport chain and ATP production. Chapter 9 Big Idea: DATA ANALYSIS Cellular Basis of Life 9.1 GQ: Why do most organisms undergo the Students analyze data to learn more about lactic acid process of cellular respiration? and exercise. Chapter 9 EQ: 9.2 GQ: How do cells release energy from How do organisms food in the presence of oxygen? obtain energy? 9.3 GQ: How do cells release energy from food without oxygen? Cellular Respiration and Fermentation 249 LESSON 9.1 Getting Started Cellular Respiration: Objectives An Overview 9.1.1 Explain where organisms get the energy they need for life processes. 9.1.2 Define cellular respiration. Key Questions THINK ABOUT IT When you are hungry, how do you feel? If you 9.1.3 Compare photosynthesis and cellular Where do organisms get are like most people, you might feel sluggish, a little dizzy, and—above respiration. energy? all—weak. Weakness is a feeling triggered by a lack of energy. You feel What is cellular respiration? weak when you are hungry because food serves as a source of energy. Weakness is your body’s way of telling you that your energy supplies What is the relationship between photosynthesis and are low. But how does food get converted into a usable form of energy? Student Resources cellular respiration? Car engines have to burn gasoline in order to release its energy. Do our bodies burn food the way a car burns gasoline, or is there something Study Workbooks A and B, 9.1 Worksheets Vocabulary more to it? Spanish Study Workbook, 9.1 Worksheets calorie cellular respiration Lab Manual B, 9.1 Data Analysis Worksheet aerobic anaerobic Chemical Energy and Food Taking Notes Where do organisms get energy? Lesson Overview Lesson Notes Preview Visuals Before you Food provides living things with the chemical building blocks they need read, study Figure 9–2 on Activity: Art in Motion Assessment: Self- page 252. Make a list of ques- to grow and reproduce. Recall that some organisms, such as plants, are Test, Lesson Assessment autotrophs, meaning that they make their own food through photo- tions that you have about the dia- gram. As you read, write down synthesis. Other organisms are heterotrophs, meaning that they rely on the answers to the questions. other organisms for food. For all organisms, food molecules contain For corresponding lesson in the chemical energy that is released when their chemical bonds are broken. Foundation Edition, see pages 212–215. Organisms get the energy they need from food. How much energy is actually present in food? Quite a lot, although it varies with the type of food. Energy stored in food is expressed in units of calories. A calorie is the amount of energy needed to raise the Activate Prior Knowledge BUILD Vocabulary temperature of 1 gram of water 1 degree Celsius. The Calorie (capital PREFIXES The prefix macro- C) that is used on food labels is a kilocalorie, or 1000 calories. Cells can Write the term cellular respiration on the board. means “large” or “elongated.” use all sorts of molecules for food, including fats, proteins, and carbo- Then, make a T-Chart below it. Label one column Macromolecules are made hydrates. The energy stored in each of these macromolecules varies up of many smaller molecular because their chemical structures, and therefore their energy-storing Facts and the other Questions. Have each student subunits. Carbohydrates, come up to the board and write either a fact they proteins, and lipids are bonds, differ. For example, 1 gram of the sugar glucose releases 3811 important macromolecules calories of heat energy when it is burned. By contrast, 1 gram of the tri- know or a question they have about cellular respira- found in living things. glyceride fats found in beef releases 8893 calories of heat energy when tion. Discuss the T-Chart as a class. Answer any ques- its bonds are broken. In general, carbohydrates and proteins contain tions that students will need to know before reading approximately 4000 calories (4 Calories) of energy per gram, while fats the lesson. contain approximately 9000 calories (9 Calories) per gram. Cells, of course, don’t simply burn food and release energy as heat. Study Wkbks A/B, Appendix S30, T-Chart. Instead, they break down food molecules gradually, capturing a little Transparencies, GO15. bit of chemical energy at key steps. This enables cells to use the energy stored in the chemical bonds of foods like glucose to produce com- pounds such as ATP that directly power the activities of the cell. NATIONAL SCIENCE EDUCATION STANDARDS 250 Lesson 9.1 Lesson Overview Lesson Notes UNIFYING CONCEPTS AND PROCESSES I, V 0001_Bio10_se_Ch09_S1.indd 1 6/2/09 6:46:28 PM CONTENT Teach for Understanding B.3, C.1.a, C.1.b, C.5.a, C.5.c, C.5.d ENDURING UNDERSTANDING A cell is the basic unit of life; the processes that occur INQUIRY at the cellular level provide the energy and basic structure organisms need to survive. A.1.c, A.2.a, A.2.d GUIDING QUESTION Why do most organisms undergo the process of cellular respiration? EVIDENCE OF UNDERSTANDING At the end of the lesson, have students complete this assessment to show they understand the importance of cellular respiration for life on Earth. Have students make a case for cellular respiration. Ask them to write a short persuasive argument that explains why cellular respiration is an important process on an individual organism level as well as on a global scale. 250 Chapter 9 Lesson 1  LESSON 9.1 Teach Composition of Some Common Foods You Are What You Eat Food Protein (g) Carbohydrate (g) Fat (g) Organisms get energy from the Apple, 1 medium 0 22 0 Lead a Discussion food they eat, but the energy con- Bacon, 2 slices 5 0 6 tained in foods varies greatly. Most Make sure students understand the overall chemical Chocolate, 1 bar 3 23 13 foods contain a combination of Eggs, 2 whole 12 0 9 summary for cellular respiration. Reinforce that the proteins, carbohydrates, and fats. 2% milk, 1 cup 8 12 5 bolded reactions shown are simplifications, or sum- One gram of protein or a carbo- Potato chips, 15 chips 2 14 10 mations, of many sub-reactions. Have students verify hydrate such as glucose contains Skinless roasted turkey, 11 3 1 that the reaction shown is balanced by counting the roughly 4 Calories. One gram of fat, 3 slices however, contains about 9 Calories. molecules of each element on the right and left sides The accompanying table shows the 2. Calculate Approximately how many more Calories of the reaction. approximate composition of one are there in 2 slices of bacon than there are in 3 slices serving of some common foods. of roasted turkey? Why is there a difference? DIFFERENTIATED INSTRUCTION 1. Interpret Data Per serving, which 3. Calculate Walking at a moderate pace consumes of the foods included in the table around 300 Calories per hour. At that rate, how many L1 Struggling Students Write the word form of has the most protein? Which has minutes would you have to walk to burn the Calories the cellular respiration summary on the board. Then, the most carbohydrates? Which in one chocolate bar? (Hint: Start by calculating the read it aloud, pointing to each word and reaction has the most fat? number of Calories consumed per minute by walking.) symbol as you read. For example, you might say, “oxygen and glucose are converted into carbon diox- ide and water and energy.” As you say oxygen, point Overview of Cellular Respiration to the word; as you say and, point to the plus sign. What is cellular respiration? Then, write the symbol form of the summary below If oxygen is available, organisms can obtain energy from food by a it. Draw lines from each chemical formula to its cor- process called cellular respiration. Cellular respiration is the responding name in the word form of the summary. process that releases energy from food in the presence of oxygen. Although cellular respiration involves dozens of separate reactions, an overall chemical summary of the process is remarkably simple: ELL Focus on ELL: In Symbols: Build Background 6O2 + C6H12O6 6CO2 + 6H2O + Energy BEGINNING AND INTERMEDIATE SPEAKERS In Words: Oxygen + Glucose Carbon dioxide + Water + Energy Distribute copies of a BKWL Chart to your students. Then, show students a short animation, As you can see, cellular respiration requires oxygen and a food molecule video, or several drawings of the process of such as glucose, and it gives off carbon dioxide, water, and energy. Do cellular respiration. Have them take notes on the not be misled, however, by the simplicity of this equation. If cellular respiration took place in just one step, all of the energy from glucose FIGURE 9 –1 A Controlled Release visuals in the build background column. Write Cellular respiration involves a series would be released at once, and most of it would be lost in the form of controlled reactions that slowly the words obtain, release, extract, respiration, of light and heat. Clearly, a living cell has to control that energy. It release the energy stored in food. If and energy on the board. Have them copy the can’t simply start a fire—the cell has to release the explosive chemical the energy were to be released too suddenly, most of it would be lost in words and define each in the build background energy in food molecules a little bit at a time. The cell needs to find a the forms of light and heat—just as it column. Then, have students fill out the K and way to trap those little bits of energy by using them to make ATP. is when a marshmallow catches fire. W columns of the chart. As students read the In Your Notebook Do plants undergo cellular respiration? What lesson, have them fill in the L column. organelle(s) do they have that helps you determine the answer? Study Wkbks A/B, Appendix S27, BKWL Chart. Cellular Respiration and Fermentation 251 Transparencies, GO12. 0001_Bio10_se_Ch09_S1.indd 2 6/2/09 6:46:33 PM PURPOSE Students will examine and ANSWERS interpret data to find how the energy 1. Eggs have the most protein; chocolate content in foods varies. has the most carbohydrates; choco- PLANNING Have a few of the foods late has the most fat. listed in the table on hand, and display 2. There are approximately 9 more them for students before they do the Calories in 2 slices of bacon than in activity. Ask students to predict which 3 slices of roast turkey. The primary of the foods contain the most Calories, difference is that the bacon contains and have them explain their reasoning. so much more fat than the turkey. Answers 3. a little over 44 minutes IN YOUR NOTEBOOK Yes; they contain mitochondria. Cellular Respiration and Fermentation 251 LESSON 9.1 Glucose Glycolysis Stages of Cellular Respiration Cellular respiration captures the energy from food in three main stages—glycolysis, the Krebs cycle, Teach continued Energy and the electron transport chain. Although cells can use just about any food molecule for energy, we will concentrate on just one as an example—the simple sugar glucose. Glucose first enters a chemical Use Visuals pathway known as glycolysis (gly kahl ih sis). Only a small amount Krebs Cycle of energy is captured to produce ATP during this stage. In fact, at Use Figure 9–2 to talk about the overall process of the end of glycolysis, about 90 percent of the chemical energy that cellular respiration. Start by helping students make was available in glucose is still unused, locked in chemical bonds of a Energy the connection between this visual and the chemical molecule called pyruvic (py roo vik) acid. CO2 How does the cell extract the rest of that energy? First, pyruvic summary equations from the previous page. Point acid enters the second stage of cellular respiration, the Krebs cycle, out where and how glucose and oxygen are used Electron Transport where a little more energy is generated. The bulk of the energy, during the process and that water, carbon dioxide, however, comes from the final stage of cellular respiration, the elec- and energy are released. Make sure students under- tron transport chain. This stage requires reactants from the other Energy stand that cellular respiration can be divided into two stages of the process, as shown by dashed lines in Figure 9–2. How does the electron transport chain extract so much energy from three basic stages. Tell them that they will learn more O2 H 2O these reactants? It uses one of the world’s most powerful electron detailed information about each of these stages in acceptors—oxygen. later lessons. FIGURE 9 –2 The Stages of Cellular Respiration There are three stages Oxygen and Energy Oxygen is required at the very end of to cellular respiration: glycolysis, the electron transport chain. Any time a cell’s demand for energy DIFFERENTIATED INSTRUCTION the Krebs cycle, and the electron transport chain. Interpret Visuals increases, its use of oxygen increases, too. As you know, the word Which stage(s) of cellular respiration respiration is often used as a synonym for breathing. This is why we L1 Struggling Students Have students read the occur in the mitochondrion? have used the term cellular respiration to refer to energy-releasing section, Stages of Cellular Respiration, in the text pathways within the cell. The double meaning of respiration points and look carefully at Figure 9–2. As a class, discuss out a crucial connection between cells and organisms: Most of the the first pictured stage, glycolysis. Then, have stu- energy-releasing pathways within cells require oxygen, and that is the dents write a one-sentence summary of the discus- reason we need to breathe, to respire. Pathways of cellular respiration that require oxygen are said to sion. For example, students might write, “During be aerobic (“in air”). The Krebs cycle and electron transport chain glycolysis, glucose is broken down into pyruvic acid are both aerobic processes. Even though the Krebs cycle does not and energy is released.” Then, discuss and summa- directly require oxygen, it is classified as an aerobic process because rize each of the next two stages. it cannot run without the oxygen-requiring electron transport chain. Glycolysis, however, does not directly require oxygen, nor does it rely on an oxygen-requiring process to run. Glycolysis is therefore said to be anaerobic (“without air”). Even though glycoly- To help students answer the question, sis is anaerobic, it is considered part of cellular respiration because remind them that whales need to sur- its final products are key reactants for the aerobic stages. If whales remain Recall that mitochondria are structures in the cell that convert face to breathe air. Make the connec- underwater for chemical energy stored in food to usable energy for the cell. tion between aerobic pathways and the whale’s 45 minutes or more, Glycolysis actually occurs in the cytoplasm of a cell, but the Krebs do you think they breathing. Ask them to speculate on how long the rely primarily on cycle and electron transport chain, which generate the majority of breath might last and how the whale might obtain aerobic or anaerobic ATP during cellular respiration, take place inside the mitochondria. pathways? If oxygen is not present, another anaerobic pathway, known energy once that air runs out. Students can go online as fermentation, makes it possible for the cell to keep glycolysis run- to Biology.com to gather their evidence. ning, generating ATP to power cellular activity. You will learn more about fermentation later in this chapter. In Your Notebook Make a flowchart that shows the different Address Misconceptions steps of cellular respiration. Cellular Respiration v. Respiration Some of your stu- dents may have difficulty distinguishing between 252 Chapter 9 Lesson 1 the concepts of cellular respiration and respiration as breathing. Have students read the first paragraph of the Oxygen and Energy section, research the 0001_Bio10_se_Ch09_S1.indd 3 6/2/09 6:46:38 PM connection between the two processes, and make Check for Understanding a poster for the classroom wall that graphically shows the relationship. INDEX CARD SUMMARIES Give students each an index card, and ask them to write one important idea about cellular respiration that they understand on the front of the card. Then, have them write something about cellular respiration that they don’t understand on the back of the card in the form of a question. Answers ADJUST INSTRUCTION FIGURE 9–2 the Krebs cycle and the electron transport chain Read over students’ cards to get a sense of which concepts they understand and which they are struggling with. If a question will be answered by reading the rest IN YOUR NOTEBOOK Flowcharts should accurately of the chapter, use that card when the time comes to emphasize a concept. If the show the connections between glycolysis, the Krebs answer to a question is necessary to move forward, review the topic as a class to cycle, and the electron transport chain. allow students to hear the concept discussed in different ways. 252 Chapter 9 Lesson 1  LESSON 9.1 Comparing Photosynthesis Light energy and Cellular Respiration To better understand the relationship What is the relationship between photosynthesis and cellular respiration? between photosynthesis and cellular respira- If nearly all organisms break down food by the PHOTOSYNTHESIS tion, students can watch the animation, process of cellular respiration, why doesn’t Earth Art in Motion: Opposite Processes. run out of oxygen? Where does all of the carbon dioxide waste product go? How does the chemical energy stored in food get replaced? As it happens, cellular respiration is balanced by another process: Assess and Remediate photosynthesis. The energy in photosynthesis and cellular respiration flows in opposite directions. EVALUATE UNDERSTANDING Look at Figure 9–3 and think of the chemical energy in carbohydrates as money in the Earth’s Have pairs of students use Figure 9–3 to help them C6H12O6 + 6O2 6H2O + 6CO2 savings account. Photosynthesis is the process ATP, Heat energy summarize the content of the lesson. For example, that “deposits” energy. Cellular respiration is the ask them to explain why both the rabbit and the process that “withdraws” energy. As you might plant are producing ATP and heat. Listen to their expect, the equations for photosynthesis and cellular respiration are the reverse of each other. discussions to help you evaluate their grasp of On a global level, photosynthesis and cellular lesson concepts. Then, have them complete the respiration are also opposites. Photosynthesis 9.1 Assessment. removes carbon dioxide from the atmosphere, and cellular respiration puts it back. Photosynthesis REMEDIATION SUGGESTION releases oxygen into the atmosphere, and cellular CELLULAR RESPIRATION LPR Less Proficient Readers If students have respiration uses that oxygen to release energy from food. The release of energy by cellular respi- FIGURE 9 –3 Opposite Processes Photosynthesis trouble understanding Question 2b, suggest they ration takes place in nearly all life: plants, animals, and cellular respiration can be thought of as use the Glossary at the back of this text to review the fungi, protists, and most bacteria. Energy capture opposite processes. Compare and Contrast Exactly how is the equation for photosynthesis different meaning of the term homeostasis. by photosynthesis, however, occurs only in plants, from the equation for cellular respiration? algae, and some bacteria. Students can check their under- standing of lesson concepts with the Self- Test assessment. They can then take an online Review Key Concepts 3. a. Review In what ways are cellular respiration version of the Lesson Assessment. 1. a. Review Why do all organisms and photosynthesis considered opposite processes? need food? b. Use Analogies How is the chemical energy in b. Relate Cause and Effect Why do glucose similar to money in a savings account? macromolecules differ in the amount of energy they contain? 2. a. Review Write the overall reaction 4. The Greek word glukus means “sweet,” and the Latin word lysis refers to a process of loosening or Answers for cellular respiration. b. Apply Concepts How does the decomposing. Based on this information, write a FIGURE 9–3 The products of photosynthesis are the process of cellular respiration main- definition for the word glycolysis. reactants of cellular respiration, and the reactants of tain homeostasis at the cellular level? cellular respiration are the products of photosynthesis. Lesson 9.1 Lesson Assessment Self-Test Art in Motion Cellular Respiration and Fermentation 253 0001_Bio10_se_Ch09_S1.indd 4 6/2/09 6:46:44 PM Assessment Answers 1a. Food provides organisms with the energy 2b. The process of cellular respiration pro- 3b. Chemical energy is stored in the chemical they need to carry out life processes such vides the energy a cell needs to carry out bonds of glucose, just as money is stored as growth and reproduction. basic cell processes, which, in turn, control in a savings account. 1b. The amount of energy stored in macro- the cell’s internal conditions. molecules varies because their chemical 3a. Photosynthesis “deposits” energy, structures, and therefore the energy con- uses carbon dioxide and water, and pro- 4. Sample answer: a process that involves the tained in their chemical bonds, differ. duces oxygen and glucose. By contrast, breaking down of a sweet substance 2a. 6O2 + C6H12O6 → 6CO2 + 6H2O + Energy cellular respiration “withdraws” energy, uses oxygen and glucose, and produces carbon dioxide and water. Cellular Respiration and Fermentation 253 LESSON 9.2 The Process of Getting Started Objectives Cellular Respiration 9.2.1 Describe what happens during glycolysis. 9.2.2 Describe what happens during the Krebs cycle. Key Questions THINK ABOUT IT 9.2.3 Explain how high-energy electrons are used What happens during the Food burns! It’s true, by the electron transport chain. process of glycolysis? of course, that many What happens during the common foods (think 9.2.4 Identify how much ATP cellular respiration Krebs cycle? of apples, bananas, and generates. How does the electron ground beef) have too transport chain use high-energy much water in them electrons from glycolysis and the to actually light with a Krebs cycle? match. However, foods Student Resources with little water, includ- How much ATP does cellular respiration generate? ing sugar and cooking oil, will indeed burn. In fact, flour, which con- Study Workbooks A and B, 9.2 Worksheets tains both carbohydrates and protein, is so flammable that it has caused Spanish Study Workbook, 9.2 Worksheets Vocabulary several explosions, including the one seen here at London’s City Flour glycolysis NAD+ Mills in 1872 (which is why you’re not supposed to store flour above a Lesson Overview Lesson Notes Krebs cycle matrix stove). So, plenty of energy is available in food, but how does a living cell extract that energy without setting a fire or blowing things up? Activities: InterActive Art, Art Review, Taking Notes Tutor Tube Assessment: Self-Test, Lesson Assessment Compare/Contrast Table As you read, make a compare/contrast Glycolysis table showing the location, start- What happens during the process of glycolysis? ing reactants, and end products of glycolysis, the Krebs cycle, The first set of reactions in cellular respiration is known as glycolysis, For corresponding lesson in the a word that literally means “sugar-breaking.” Glycolysis involves many and the electron transport chain. Foundation Edition, see pages 216–222. Also include how many mol- chemical steps that transform glucose. The end result is 2 molecules ecules of ATP are produced in of a 3-carbon molecule called pyruvic acid. During glycolysis, each step of the process. 1 molecule of glucose, a 6-carbon compound, is transformed into 2 molecules of pyruvic acid, a 3-carbon compound. As the bonds in Activate Prior Knowledge glucose are broken and rearranged, energy is released. The process of Ask students to think about how they get to school glycolysis can be seen in Figure 9–4. every day. Have them break this process into several ATP Production Even though glycolysis is an energy-releasing stages. For example, they might describe getting process, the cell needs to put in a little energy to get things going. ready to leave home, taking the bus, and walking At the pathway’s beginning, 2 ATP molecules are used up. Earlier in into school. Then, have them describe some of the this chapter, photosynthesis and respiration were compared, respec- tively, to a deposit to and a withdrawal from a savings account. smaller steps they make to accomplish these three Similarly, the 2 ATP molecules used at the onset of glycolysis are like stages. Discuss how this analogy relates to the proc- an investment that pays back interest. In order to earn interest from a ess of cellular respiration. bank, first you have to put money into an account. Although the cell puts 2 ATP molecules into its “account” to get glycolysis going, glycoly- sis produces 4 ATP molecules. This gives the cell a net gain of 2 ATP molecules for each molecule of glucose that enters glycolysis. NATIONAL SCIENCE EDUCATION STANDARDS 254 Lesson 9.2 Lesson Overview Lesson Notes InterActive Art UNIFYING CONCEPTS AND PROCESSES I, V 0001_Bio10_se_Ch09_S2.indd 1 6/2/09 6:47:10 PM CONTENT Teach for Understanding B.3, C.1.a, C.1.b, C.5.c, C.5.d ENDURING UNDERSTANDING A cell is the basic unit of life; the processes that occur at the cellular level provide the energy and basic structure organisms need to survive. INQUIRY GUIDING QUESTION How do cells release energy from food in the presence A.1.c, A.2.a of oxygen? EVIDENCE OF UNDERSTANDING At the end of this lesson, give students the following assessment to show they understand how cellular respiration provides organisms with a way to efficiently release energy from food. Have students make a sketch of the overall process of cellular respiration. Ask them to make it as detailed as they can. Then, have them discuss with a partner why it makes sense that cellular respiration is a complex process involving many steps. 254 Chapter 9 Lesson 2  LESSON 9.2 Glucose Glycolysis Energy Teach Glucose Krebs Cycle Energy 2 ATP CO2 CYTOPLASM Suggest students look carefully at Figure 9–4. Then, Elec ectro ectronn Transport o ATP Production use the figure to start a discussion on glycolysis. Call 2 ADP Two ATP molecules are Energy “invested” to get the process on students at random to answer questions about of glycolysis going. Overall, what they observe. O2 H2O 4 ATP molecules are produced, for a net gain of 2 ATP per NADH Production 2 NAD + 4 ADP molecule of glucose. Ask What do the six dark balls at the top of the fig- Four high-energy electrons are ure represent? ( the six carbon atoms in a molecule passed to the carrier NAD+ to produce NADH. NADH of glucose) carries these electrons to the 2 NADH 4 ATP Ask What does it mean to “invest” a molecule of electron transport chain. ATP? ( The energy stored in ATP is released and used to help start the process of glycolysis.) 2 Pyruvic Acid GLYCOLYSIS Ask What are the products of glycolysis? (2 NADH To Electron To Krebs Cycle FIGURE 9–4 Glycolysis is the first molecules, 2 pyruvic acid molecules, and 4 ATP Transport Chain stage of cellular respiration. During glycolysis, glucose is broken down molecules) into 2 molecules of pyruvic acid. ATP Ask Where do these products go? ( The NADH goes and NADH are produced as part of the process. Interpret Visuals How to the electron transport chain, the pyruvic acid goes NADH Production One of the reactions of glycolysis removes many carbon atoms are there in to the Krebs cycle, and the ATP gets used by cells.) glucose? How many carbon atoms 4 electrons, now in a high-energy state, and passes them to an electron are in each molecule of pyruvic acid? carrier called NAD+, or nicotinamide adenine dinucleotide. Like NADP+ in photosynthesis, each NAD+ molecule accepts a pair of DIFFERENTIATED INSTRUCTION high-energy electrons. This molecule, now known as NADH, holds L1 Special Needs Have students work in pairs the electrons until they can be transferred to other molecules. As you will see, in the presence of oxygen, these high-energy electrons can be to make a model of glycolysis. Have them use pop used to produce even more ATP molecules. beads to represent carbon molecules, and different- BUILD Vocabulary size paper clips to model ATP/ADP and NAD+/NADH. The Advantages of Glycolysis In the process of glycolysis, 4 ATP ACADEMIC WORDS The verb Have pairs discuss the process as they model it. molecules are synthesized from 4 ADP molecules. Given that 2 ATP synthesize means “to bring together molecules are used to start the process, there is a net gain of just as a whole.” Therefore, a molecule of ATP is synthesized when a 2 ATP molecules. Although the energy yield from glycolysis is small, phosphate group combines with the process is so fast that cells can produce thousands of ATP mol- the molecule ADP, forming a high- ecules in just a few milliseconds. The speed of glycolysis can be a big energy bond. For an overview of the processes advantage when the energy demands of a cell suddenly increase. covered in this chapter, suggest students Besides speed, another advantage of glycolysis is that the process watch InterActive Art: Cellular Respiration itself does not require oxygen. This means that glycolysis can quickly and Fermentation. supply chemical energy to cells when oxygen is not available. When oxygen is available, however, the pyruvic acid and NADH “outputs” generated during glycolysis become the “inputs” for the other proc- esses of cellular respiration. Address Misconceptions In Your Notebook In your own words, describe the advantages of Energy Some students may think that energy is glycolysis to the cell in terms of energy production. somehow created during glycolysis and the other stages of cellular respiration. Remind students that Cellular Respiration and Fermentation 255 energy cannot be created or destroyed. Reinforce the fact that the energy used in glycolysis to make ATP is stored in the chemical bonds of glucose. Suggest 0001_Bio10_se_Ch09_S2.indd 2 6/2/09 6:47:25 PM students investigate how energy is stored as poten- Quick Facts tial energy in chemical bonds and make a presenta- tion to the class of what they learn. BEGINNING WITH GLUCOSE Why do biologists pay so much attention to glucose? It’s because most other food molecules are broken down to release energy in much the same way. Proteins are broken down into individual amino acids, which are converted to compounds that can enter either glycolysis or the Krebs cycle. Carbohydrates are generally broken into Answers simple sugars and then converted into glucose. Lipids are broken down into fatty FIGURE 9–4 6 carbon atoms in glucose; 3 carbon acids and glycerol. These compounds enter the mitochondria where special enzymes atoms in each molecule of pyruvic acid cut them up, two carbon atoms at a time, to produce acetyl-CoA, which then enters IN YOUR NOTEBOOK Students’ descriptions should the Krebs cycle. This means that literally any food can provide the chemical energy for mention that there is a net gain of 2 ATP molecules, cellular respiration—the body is a furnace that can run on any fuel. that the process is fast, and that it can supply energy to the cell when oxygen is not available. Cellular Respiration and Fermentation 255 LESSON 9.2 The Krebs Cycle Teach continued What happens during the Krebs cycle? In the presence of oxygen, pyruvic acid produced in glycolysis passes to the second stage of cellular respiration, the Krebs cycle. The Krebs cycle Connect to Chemistry The urge to is named after Hans Krebs, the British biochemist who demonstrated its surface and gasp existence in 1937. During the Krebs cycle, pyruvic acid is broken An understanding of the three stages of cellular res- for breath when down into carbon dioxide in a series of energy-extracting reactions. piration depends on some knowledge of basic chem- underwater is a Because citric acid is the first compound formed in this series of reac- response to CO2 tions, the Krebs cycle is also known as the citric acid cycle. istry. Before students study the Krebs cycle, point buildup in the blood. out that the cycle is a series of chemical reactions The average human can hold Citric Acid Production The Krebs cycle begins when pyruvic acid his or her breath for only mainly involving carbon compounds. Explain that about a minute. Whales stay produced by glycolysis passes through the two membranes of the mito- the element carbon has a remarkable ability to easily underwater for much longer. chondrion and into the matrix. The matrix is the innermost compart- What does this suggest about ment of the mitochondrion and the site of the Krebs cycle reactions. combine with both itself and other atoms, and the Once inside the matrix, 1 carbon atom from pyruvic acid becomes part a whale’s tolerance of CO2? result is a tremendous number of carbon compounds of a molecule of carbon dioxide, which is eventually released into the air. in living things. Point out that following the chang- The other 2 carbon atoms from pyruvic acid rearrange and form acetic ing carbon compounds is key to understanding the FPO P0750 acid, which is joined to a compound called coenzyme A. The resulting Krebs cycle. molecule is called acetyl-CoA. (The acetyl part of acetyl-CoA is made up of 2 carbon atoms, 1 oxygen atom, and 3 hydrogen atoms.) As the Krebs cycle begins, acetyl-CoA adds the 2-carbon acetyl group to a 4-carbon DIFFERENTIATED INSTRUCTION molecule already present in the cycle, producing a 6-carbon molecule called citric acid. L1 Struggling Students Some students may have a difficult time understanding how ATP stores Energy Extraction As the cycle continues, citric acid is broken down energy. Tell students that a common analogy used into a 4-carbon molecule, more carbon dioxide is released, and electrons are transferred to energy carriers. Follow the reactions in Figure 9–5 for ATP is that its three phosphates are like a loaded and you will see how this happens. First, look at the 6 carbon atoms in spring. Losing one of the phosphates—the source of citric acid. One is removed, and then another, releasing 2 molecules of energy for a cell—is like relaxing the spring. Adding carbon dioxide and leaving a 4-carbon molecule. Why is the Krebs cycle a phosphate to a molecule of ADP is like loading, or a “cycle”? Because the 4-carbon molecule produced in the last step is the compressing, the spring again. same molecule that accepts the acetyl-CoA in the first step. The molecule needed to start the reactions of the cycle is remade with every “turn.” LPR Less Proficient Readers Struggling readers Next, look for ATP. For each turn of the cycle, a molecule of ADP is may stumble on the names of the compounds pyru- converted to a molecule of ATP. Recall that glycolysis produces 2 mol- ecules of pyruvic acid from 1 molecule of glucose. So, each starting vic acid, acetyl-CoA, and citric acid. Before students molecule of glucose results in two complete turns of the Krebs cycle read, preview these terms by writing the names on and, therefore, 2 ATP molecules. Finally, look at the electron carriers, the board and saying each name aloud. Have stu- NAD+ and FAD (flavine adenine dinucleotide). At five places, electron dents repeat the words so they become comfortable carriers accept a pair of high-energy electrons, changing NAD+ to reading and pronouncing them. NADH and FAD to FADH2. FAD and FADH2 are molecules similar to NAD+ and NADH, respectively. What happens to each of these Krebs cycle products—carbon dioxide, ATP, and electron carriers? Carbon dioxide is not useful to the To help students answer the question, cell and is expelled every time you exhale. The ATP molecules are very useful and become immediately available to power cellular activities. explain that tolerance means “able to As for the carrier molecules like NADH, in the presence of oxygen, the withstand the effects of something electrons they hold are used to generate huge amounts of ATP. without showing the usual unfavorable effects.” Point out that some people, for example, are able to In Your Notebook List the electron carriers involved in the Krebs cycle. Include their names before and after they accept the electrons. tolerate colder temperatures than others. Students can go online to Biology.com to gather their 256 Chapter 9 Lesson 2 evidence. 0001_Bio10_se_Ch09_S2.indd 3 6/2/09 6:47:35 PM Check for Understanding ORAL QUESTIONING Use the following prompts to gauge student understanding of the Krebs cycle: Why does glycolysis have to occur before the Krebs cycle can occur? For each turn of the Krebs cycle, what is produced that can immediately be used to power cell activities? Answers How does the cell use the NADH and FADH2 produced in the Krebs cycle? IN YOUR NOTEBOOK The electron carriers involved ADJUST INSTRUCTION + in the Krebs cycle are NAD and FAD. After they Evaluate students’ answers to get a sense of which concepts they understand and accept electrons, NAD+ becomes NADH and FAD which concepts they are having trouble with. Because understanding the Krebs cycle becomes FADH2. is essential to understanding the whole process of cellular respiration, review difficult concepts as a class so students can hear events described in different ways. 256 Chapter 9 Lesson 2  LESSON 9.2 CYTOPLASM Glucose Glycolysis Energy Outer Pyruvic Acid THE KREBS CYCLE mitochondrial FIGURE 9–5 During the Krebs cycle, pyruvic membrane acid from glycolysis is used to make carbon Krebs Cycle dioxide, NADH, ATP, and FADH2. Because Divide the class into small groups, and ask students glycolysis produces 2 molecules of pyruvic acid to study the illustration of the Krebs cycle. Have each Energy from each glucose molecule, the Krebs cycle CO2 “turns” twice for each glucose molecule that group write five questions about the Krebs cycle, enters glycolysis. Interpret Diagrams What each on a separate note card. Questions should Elec lectro ro on Transport o happens to the NADH and FADH2 molecules Inner generated in the Krebs cycle? focus on information students think is essential to Energy mitochondrial understanding what occurs in the Krebs cycle and membrane O2 H2O why it is important to the cell. Then, have groups NAD + trade cards and write the answers to the questions on the back of each card. Call on each group to read NADH the question that was most difficult to answer and CO2 Citric Acid Production Pyruvic acid from glycolysis discuss it as a class. M AT RIX reacts to form acetyl-CoA, which then enters the Krebs cycle. In Co A the process, a molecule of CO2 DIFFERENTIATED INSTRUCTION is produced and 2 high-energy Acetyl-CoA Co A electrons are passed to NAD+ to L1 Special Needs Have students model the Krebs produce NADH. Acetyl-CoA combines with a 4-carbon cycle using clay balls to represent carbon molecules compound in the Krebs cycle to and toothpicks. Start with a three-carbon chain to produce citric acid. NADH Citric represent pyruvic acid. As they work through the Acid