Cellular Respiration and Fermentation PDF

Cellular Respiration and Fermentation Cellular Basis of Life Q: How do organisms obtain energy? Chapter 9 Flash Cards 210 inSiDe: Diving Without a Breath 9.1 Cellular respiration: You...

Cellular Respiration and Fermentation Cellular Basis of Life Q: How do organisms obtain energy? Chapter 9 Flash Cards 210 inSiDe: Diving Without a Breath 9.1 Cellular respiration: You know what it is like to feel out of breath. Just a few an overview minutes of hard exercise can have some people huffing and puffing for air. But what if you couldn’t get air? What 9.2 the Process of Cellular if you were asked to hold your breath and exercise? Before respiration too long, you’d run out of oxygen and pass out. You would 9.3 Fermentation not be able to get enough oxygen. It may seem like a bad idea to hold your breath while exercising, but there are animals that do it all the time—whales. Because whales Mitochondria (red) and are air-breathing mammals, they still need to come to smooth endoplasmic the surface for air. But after a breath, some whales can reticulum (yellow) in an ovarian cell dive underwater for as long as 45 minutes! How is that (SEM 75,0003). possible? Diving takes a lot of energy. How do whales stay active for so long on only one breath? read for Mystery Clues As you read this chapter, look for clues to help you discover how whales can stay underwater so long. Then, solve the mystery at the end of the chapter. Cells need chemical energy to stay alive. Special parts of the cell help them get this energy. Before you read the chapter, label six index cards with the words water, pyruvic acid, carbon dioxide, oxygen, energy, and glucose. Label one sheet of paper with the words cytoplasm and mitochondrion. At the end of the chapter are two activities that use the cards and sheet of paper. They will help you answer the question: How do organisms obtain energy? CYTOPLASM Carbon dioxide MITOCHONDRION Untamed Science Video Chapter Mystery Cellular Respiration and Fermentation 211  Cellular Respiration: An Overview Key Questions Chemical Energy and Food Where do organisms get energy? How do you feel when you are hungry? Do you feel sluggish, dizzy, or a little weak? That weakness comes from a lack of the food you need What is cellular respiration? for energy. But what does food have to do with energy? What is the relationship between photosynthesis and Food gives living things the energy they need to grow. Some living cellular respiration? things, such as plants, are autotrophs (aw toh trohfs). They make their own food through photosynthesis. Other living things are heterotrophs (het ur oh trohfs). They have to eat other living things for food. For all living things, food molecules store chemical energy. Living things release that energy when they break those food molecules down. Preview Visuals Before you Energy in food can be measured in units called calories. A calorie is read, study The Stages of Cellular the amount of energy needed to raise the temperature of 1 gram of Respiration figure. Make a list of water 1 degree Celsius. The Calorie you see on food labels is actually questions that you have about the figure. As you read, write down the a kilocalorie, or 1000 calories. The amount of energy in different kinds answers to the questions. of food varies. This is because of differences in the way the atoms in In Your Workbook Go to food molecules are bonded together. For example, 1 gram of the your workbook to learn more about sugar glucose gives off 3811 calories of energy when it is burned. But, Previewing Visuals. Complete the 1 gram of the fat found in beef gives off 8893 calories of energy when Previewing Visuals activity for it is burned. Lesson 9.1. Cells break down food molecules over time, getting a little bit of chemical energy at key steps. This chemical energy helps cells use the energy in foods to make compounds such as ATP. ATP and other useful energy compounds directly power the activities of the cell. Key Question Where do organisms get energy? Organisms get the energy they need from food. A Controlled Release The energy stored in food is released slowly. If the energy were given off all at once, most of it would be lost as light and heat. That is what happens when a marshmallow catches fire. 212 Chapter 9 Lesson 1  Composition of Some Common Foods You Are What You Eat Food Protein (g) Carbohydrate (g) Fat (g) Different types of food can store Apple, 1 medium 0 22 0 very different amounts of energy. Bacon, 2 slices 5 0 6 Most foods have a mix of proteins, Chocolate, 1 bar 3 23 13 carbohydrates, and fats. One gram Eggs, 2 whole 12 0 9 of protein or a carbohydrate such 2% milk, 1 cup 8 12 5 as glucose has about 4 Calories. Potato chips, 15 chips 2 14 10 One gram of fat, though, has about Skinless roasted turkey, 11 3 1 3 slices 9 Calories. The table to the right shows what is found in one serving 3. Calculate Walking uses around 5 Calories of some common foods. per minute. At that rate, how many minutes 1. Interpret Data The food from the table that would you have to walk to burn the Calories in has the most protein is ______. The food that one chocolate bar? Use the equations below to has the most carbohydrates is ______. The help you with your calculations. food that has the most fat is ______. ____ Calories from protein 2. Calculate + ____ Calories from carbohydrates a. How many Calories total are there in + ____ Calories from fat ______ 2 slices of bacon? = ____ Total Calories in a chocolate bar b. How many Calories total are there in ____ Total Calories _________________ = ____ minutes 3 slices of roasted turkey? 5 Calories/minute c. What is the difference in total Calories between these two foods? Why is there In Your Workbook Get more help for this activity in your workbook. a difference? Overview of Cellular Respiration Living things can get energy from food through cellular respiration. Cellular respiration is the process that releases energy from food, such as the simple sugar glucose, when there is oxygen present. Cellular respiration gives off carbon dioxide, water, and energy. The process can cellular respiration be summarized like this: the process that releases energy by breaking down glucose and other 6O2 + C6H12O6 6CO2 + 6H2O + Energy food molecules in the presence of oxygen But cellular respiration does not take place in just one step. If it did, all of the energy from sugar would be given off at once. Most of it would MULTIPLE MEANINGS be lost in the form of light and heat. A living cell has to release the Respiration is another word for chemical energy in food molecules a little bit at a time. The cell uses breathing, the exchange of oxygen that energy to make ATP. and carbon dioxide within the lungs. Cellular respiration requires Key Question What is cellular respiration? the same exchange of gases, only within the living cell. Cellular respiration is the process that releases energy from food when oxygen is present. Cellular Respiration and Fermentation 213  Glucose Glycolysis The Stages of Cellular Respiration Energy There are three stages to cellular respiration: glycolysis, the Krebs cycle, and the electron transport chain. Krebs Cycle Energy CO2 Electron Transport Energy O2 H2O Three Main Stages Cellular respiration gets energy from food in three stages. These stages are glycolysis, the Krebs cycle, and the electron transport chain. When looking at these stages, it is helpful to use an example. We will use the sugar glucose. Glucose enters the first stage, known as glycolysis (gly kahl ih sis). Only a small amount of energy is used to make ATP during this stage. The rest is still locked in the bonds of a molecule called pyruvic (py roo vik) acid. Pyruvic acid enters the second stage, the Krebs cycle, where a little more energy aerobic is given off. Most of the energy from cellular respiration comes from a process that requires oxygen the last stage, the electron transport chain. This stage uses oxygen and anaerobic reactants from the other two stages to finish the job. a process that does not require oxygen Oxygen and Energy You get oxygen from the air you breathe. Oxygen is used at the end of the electron transport chain. Any time PREFIXES a cell needs more energy, it needs more oxygen, too. That is why you The prefix an- means “without” and the prefix aero- means “air.” breathe hard when you exercise. You use up energy and need more Aerobic means “with air” and oxygen, which means taking more breaths. anaerobic means “without air.” Chemical pathways that need oxygen are called aerobic, which means “in air.” The Krebs cycle and electron transport chain are both aerobic. Even though the Krebs cycle does not directly need oxygen, it cannot run without the electron transport chain, which does need oxygen. Glycolysis, however, does not need oxygen. It does not depend on an aerobic process, either. Glycolysis is anaerobic, which means “without air.” Mitochondria (myt oh kahn dree uh) are the organelles most important in cellular respiration. Glycolysis actually takes place in the cytoplasm of a cell, but the Krebs cycle and electron transport chain take place inside the mitochondria. If oxygen is not present, another anaerobic path, known as fermentation, keeps glycolysis running. You will learn more about fermentation later in this chapter. 214 Chapter 9 Lesson 1 Comparing Photosynthesis Light energy and Cellular Respiration If nearly all living things break down food through cellular respiration, why doesn’t Earth run out of PHOTOSYNTHESIS oxygen? Where does all of the carbon dioxide go? Where do the cells get food molecules from? Cellular respiration is balanced by photosynthesis. The energy from each process flows in opposite directions. The equations for photosynthesis and cellular respiration are the reverse of each other. Photosynthesis removes carbon dioxide from the air. Cellular respiration puts it back. Photosynthesis gives off oxygen and makes sugars. Cellular respiration uses that oxygen to get C6H12O6 + 6O2 6H2O + 6CO2 energy from sugars. Cellular respiration takes place ATP, Heat energy in nearly all life: plants, animals, fungi, protists, and most bacteria. Photosynthesis, on the other hand, takes place only in plants, algae, and some bacteria. Key Question What is the relationship between photosynthesis and cellular respiration? Photosynthesis produces food molecules and removes carbon dioxide from the air, and cellular respiration puts it back. Photosynthesis gives off CELLULAR RESPIRATION oxygen, and cellular respiration uses that oxygen to Opposite Processes Photosynthesis and cellular release energy from food. respiration can be thought of as opposite processes. Apply Vocabulary 5. Apply Concepts Aerobics is a kind of exercise Use the highlighted words from the lesson to that involves rhythmic movement and stretching, complete each sentence correctly. usually to music. What does the name aerobics 1. A process that needs oxygen to take place is tell you about this kind of exercise? called _____. 6. Write to Learn Answer the first clue of the 2. Glycolysis is _____ because it can happen when mystery. Think about the difference between there is no oxygen. aerobic and anaerobic processes. Critical Thinking 3. Infer Do plant cells carry out cellular respiration? What organelle do they have that If whales stay underwater for 45 helps you know the answer? minutes or more, do you think they 4. Compare and Contrast How are the mostly use aerobic or anaerobic processes? (Hint: See p. 214.) equations for cellular respiration and photosynthesis similar? How are they different? Lesson 9.1 Lesson Assessment Art in Motion 215  The Process of Cellular Respiration Key Questions Glycolysis What happens during the Food burns. In fact, flour is so flammable that is has caused many process of glycolysis? explosions. Because of this, you should never store flour above a What happens during the stove. But how do living things get the energy they need from food Krebs cycle? without starting a fire? How does the electron transport chain use high-energy Living things use a series of reactions and steps to get energy from food electrons from glycolysis and the molecules. The first set of reactions in cellular respiration is known as Krebs cycle? glycolysis. In one of the reactions of glycolysis, a 6-carbon sugar made How much ATP does from glucose is split into two. The final step produces two molecules cellular respiration generate? of pyruvic acid. Pyruvic acid has 3 carbons. Energy is given off as the bonds in glucose are broken and formed again between different atoms. Making ATP Glycolysis gives off energy. But the cell needs to put in a little energy to get things going. At the beginning, 2 ATP molecules are used up. Glycolysis makes 4 ATP molecules. This gives the cell a net gain Compare/Contrast Table As you of 2 ATP molecules for each molecule of glucose that enters glycolysis. read, make a compare/contrast table for glycolysis, the Krebs cycle, Making NADH One of the steps of glycolysis passes 4 electrons and the electron transport chain. In to an electron carrier. This carrier is called NAD+, or nicotinamide your table, show where each step adenine dinucleotide. Like NADP+ in photosynthesis, each NAD+ takes place, what reactants it uses, molecule can pick up a hydrogen ion and carry a pair of high-energy what products it makes, and how electrons. The new molecule is known as NADH. It holds the many molecules of ATP are made. electrons until they can be moved to other molecules. Later on, when In Your Workbook Go to your workbook to learn more about there is oxygen present, these high-energy electrons can be used to making a compare/contrast table. make even more ATP. Complete the compare/contrast table for Lesson 9.2. Breaking Down Sugars Animals get sugars from food. Sugars such as glucose are then broken down by cells through the process of glycolysis. 216 Chapter 9 Lesson 2  Glucose Glycolysis Energy Glucose Krebs Cycle Energy 2 ATP Splitting glucose to CO2 make 2 smaller CYTOPLASM molecules takes 2 Electron Transport molecules of ATP. 2 ADP Energy O2 H2O 2 NAD + 4 ADP NAD+ picks up 4 high- The last steps make energy electrons from a 4 molecules of ATP, glycolysis reaction. This which means a net step makes 2 NADH. 2 NADH 4 ATP gain of 2 ATP. 2 Pyruvic Acid To Electron Transport Chain To Krebs Cycle Glycolysis Glycolysis is the first stage of cellular respiration. During glycolysis, glucose is broken down into 2 molecules of pyruvic acid. ATP and NADH are also made. Why Glycolysis Is Useful During glycolysis, 4 ATP molecules are made from 4 ADP molecules. Given that 2 ATP molecules are used to start the process, there is a net gain of just 2 ATP molecules. Even though the energy given off by glycolysis is small, the process is so fast that cells can make thousands of ATP molecules in just a few milliseconds. The speed of glycolysis can be a big plus when the cell suddenly needs a lot of energy. glycolysis Besides speed, another useful thing about glycolysis is that it does not The first set of reactions in cellular need oxygen. This means that glycolysis can quickly get chemical energy respiration in which a molecule to cells when there is not any oxygen present. When oxygen is present, of glucose is broken into two however, the pyruvic acid and NADH made during glycolysis become molecules of pyruvic acid the materials needed for the other stages of cellular respiration. NAD+ nicotinamide adenine dinucleotide: Key Question What happens during the process of glycolysis? an electron carrier involved in During glycolysis, 1 molecule of glucose, which has 6 carbon glycolysis atoms, is changed into 2 molecules of pyruvic acid, which each have WORD ORIGINS 3 carbon atoms. The Greek word glukus means “sweet.” The Latin word lysis means to “loosen.” The term glycolysis thus means “loosening” or “breaking glucose.” Lesson 9.2 InterActive Art 217  The Krebs Cycle When there is oxygen present, pyruvic acid made in glycolysis passes Krebs cycle to the second stage of cellular respiration. This stage is called the The second stage of cellular Krebs cycle. During the Krebs cycle, pyruvic acid is broken down respiration in which pyruvic acid is over many steps. broken down into carbon dioxide in a series of energy-extracting Making Citric Acid The Krebs cycle begins when pyruvic acid goes reactions. into the mitochondrion. It passes two membranes and goes into the matrix matrix. The matrix is the innermost part of the mitochondrion. the innermost compartment of the mitochondrion The Krebs cycle takes place here. Once inside the matrix, 1 carbon is split off from pyruvic acid, releasing a molecule of carbon dioxide. WORD ORIGINS The other 2 carbon atoms join a 4-carbon molecule already present The Krebs cycle was named after in the cycle. They form citric acid, which has 6 carbons. As the cycle the British biologist Hans Krebs, keeps going, citric acid is broken down. More carbon dioxide is given who won the Nobel Prize in 1953 off, and high-energy electrons are moved to energy carriers, such for its discovery. as NAD+. As each molecule of carbon dioxide leaves, the citric acid molecule loses a carbon atom. In the end a 4-carbon molecule is formed. Then the cycle begins all over again. Electron Carriers as Energy For each turn of the cycle, a phosphate is added to ADP to make ATP. Each glucose molecule causes two complete turns of the Krebs cycle. So, for each molecule of glucose, the cycle makes two more ATP molecules. When we add these to the two made in glycolysis, so far we have gained just 4 ATP molecules. That doesn’t sound like much. However, most of the chemical energy released in the cycle goes to produce high-energy electrons. These are passed to the electron carriers NAD+ and FAD. This changes them into NADH and FADH2. What happens to the carbon dioxide, ATP, and electron carriers produced in the Krebs cycle? Carbon dioxide is not useful to the cell. It is expelled every time you breathe out. The ATP molecules are very useful. They are immediately available as energy for cellular activities. When oxygen is present, the electron carrier molecules are used make huge amounts of ATP. Intermembrane Outer space membrane Key Question What happens during the Krebs cycle? Inner During the Krebs cycle, pyruvic acid is broken down into carbon membrane dioxide in a series of steps that releases chemical energy. Matrix Mitochondrion The Krebs cycle takes place within the matrix, or the innermost space, of the mitochondrion. Mitochondrion 218 Chapter 9 Lesson 2  Glucose Glycolysis Energy The Krebs Cycle During the Krebs cycle, pyruvic acid from glycolysis is used to make carbon dioxide, NADH, Krebs Cycle CYT O PLASM ATP, and FADH2. Because glycolysis makes 2 molecules of pyruvic acid Energy from each glucose molecule, the Krebs CO2 cycle “turns” twice for each glucose molecule that enters glycolysis. Electron Transport Energy Pyruvic Acid Outer O2 H2O mitochondrial membrane 1 Pyruvic acid from glycolysis enters the mitochondrion’s matrix. Inner mitochondrial 2 Enzymes split CO2 membrane off from pyruvic acid, leaving a 2-carbon molecule. NADH is NAD + produced from NAD+. MAT RIX NADH CO2 6 The 4-carbon- atom molecule can go through the 3 The 2-carbon-atom cycle again. Citric molecule joins a Acid 4-carbon-atom molecule NADH to become citric acid. NAD + 5 More CO2 reactions make high-energy NAD + molecules of ATP, FADH2, NADH and NADH. CO2 4 More CO2 and FADH 2 NAD + NADH are made as citric acid becomes FAD a 4-carbon-atom NADH molecule. ATP ADP To Electron Transport Chain To Electron Transport Chain Cellular Respiration and Fermentation 219  Electron Transport and ATP Synthesis Carriers from glycolysis and the Krebs cycle go into the last stage of cellular respiration. This last stage is the electron transport chain. The NADH made during glycolysis can enter the mitochondrion. There, they join the NADH and FADH2 made by the Krebs cycle. Electrons are then passed from all of those carriers to the electron transport chain. The electron transport chain uses them to change ADP into ATP. Electron Transport High-energy electrons are passed from one carrier to the next. At the end of the electron transport chain, an enzyme adds these electrons to hydrogen ions and oxygen to form water. Every time 2 electrons pass down the chain, their energy is used to move hydrogen ions (H+) across the inner mitochondrial membrane. As this happens, H+ ions build up in the intermembrane space. That space becomes more positively charged than the matrix. Making ATP The cell uses this charge difference between the two spaces to make ATP. As in photosynthesis, the cell uses enzymes known as ATP synthases. The charge difference makes the H+ ions move through channels in these enzymes. Each time a H+ ion moves through it, the ATP synthase turns. With each turn, the enzyme attaches a phosphate to ADP to produce ATP. On average, each pair of high-energy electrons that moves down the full length of the electron transport chain gives off enough energy to make 3 molecules of ATP. Key Question How does the electron transport chain use high-energy electrons from glycolysis and the Krebs cycle? The electron transport chain uses the high-energy electrons from glycolysis and the Krebs cycle to change ADP into ATP. Electron Transport The electron transport chain provides most of the energy that athletes use during cellular respiration. 220 Lesson 9.2 Art Review Tutor Tube  The Electron Transport Chain and Glucose Glycolysis ATP Synthesis The electron transport Energy chain uses high-energy electrons carried by NADH and FADH2 to change ADP into ATP. Krebs Cycle Energy CO2 Electron Transport Energy O2 H2O H+ From Krebs Cycle MATRIX NADH FADH 2 ATP Production H+ ions pass back across the From mitochondrial membrane through Glycolysis Electron Transport ATP synthase causing the base of High-energy electrons from NADH the synthase molecule to rotate. NADH and FADH2 are passed from With each rotation, driven by the carrier to carrier, down the movement of an H+ ion, ATP electron transport chain. Water is synthase attaches a phosphate to formed when oxygen accepts the ADP to make ATP. electrons in combination with hydrogen ions. Energy generated by the electron transport chain is H+ ATP ATP used to move H+ ions across the inner mitochondrial membrane and into the intermembrane space. ADP + + NAD + NADH 4H+ O2 4e- 2 H2O Inner mitochondrial H+ membrane FAD FADH 2 H+ H+ Electron carriers H+ H+ H+ INTERMEMBRANE SPACE Outer mitochondrial membrane CYTOPLASM Cellular Respiration and Fermentation 221 Energy Totals Breaking down glucose through cellular respiration The Totals makes 36 molecules of ATP. Together, glycolysis, the Krebs cycle, and the electron transport chain make about 36 molecules of ATP per molecule of glucose. Glucose Glycolysis We eat more than just glucose, of course, but that’s no problem for the cell. Complex sugars are broken down to simple sugars such as glucose. Lipids and proteins can be broken down into molecules 2 ATP that enter the Krebs cycle or glycolysis. Like a furnace, a cell can use more than one type of reactant, not just glucose, to produce energy. Both the cell and the furnace release heat. Krebs Cycle How good is cellular respiration at capturing chemical energy? Those 36 ATP molecules represent about 36 percent of the total 2 ATP energy of glucose. That might not seem like much, but it means that the cell is actually better at using food than a car’s engine CO2 is at burning gasoline! Just as the fuel in a car, the rest of the energy of glucose is given off as heat. This extra heat is one of Electron Transport the reasons your body feels warmer after exercise, and why your body temperature stays the same day and night. 32 ATP Key Question How much ATP does cellular respiration generate? O2 H2O Together, glycolysis, the Krebs cycle, and the electron transport chain make about 36 molecules of ATP per molecule of glucose. Apply Vocabulary 7. Use Analogies How is the cell like a furnace? Use the highlighted words from the lesson to 8. Write to Learn Answer the second clue of the complete each sentence correctly. mystery. In your answer, describe how whales and humans differ in their ability to stand 1. Glucose is first split during ______. CO2 buildup in blood. 2. ______ is an electron carrier that is used during glycolysis and the Krebs cycle. 3. During the ______ , pyruvic acid is broken down into carbon dioxide. 4. The Krebs cycle takes place in the ______. When we are underwater, our bodies react to a buildup of CO2 in the blood. This buildup makes Critical Thinking us want to go to the surface and gasp for 5. Compare and Contrast How is the function of breath. The average human can hold his or NAD+ similar to that of NADP+? her breath for only about a minute. Whales stay underwater for much longer. What does 6. Infer Why do you often breathe faster during this suggest about a whale’s ability to stand heavy exercise? How is this related to oxygen CO2? (Hint: See p. 218.) and cellular respiration? Lesson 9.2 Lesson Assessment 222  Fermentation Fermentation Key Questions How do organisms How do your cells get energy when you use up oxygen so quickly generate energy when oxygen that you cannot get more oxygen fast enough? And what about is not available? organisms that live in places where there isn’t oxygen? How do their How does the body cells get energy from food? produce ATP during different stages of exercise? Glycolysis can make ATP quickly and it does not need oxygen. However, in just a few seconds, glycolysis fills all of the cell’s NAD+ molecules with electrons. Without oxygen, the electron transport chain does not run, so there is nowhere for the NADH molecules to leave their electrons. So, NADH doesn’t get converted back to NAD+. Without NAD+, the cell cannot keep glycolysis going. That’s where fermentation comes in. When oxygen is not present, glycolysis is followed by fermentation. During fermentation, cells change Venn Diagram As you read, NADH to NAD+ by passing the electrons back to pyruvic acid. The create a Venn diagram that NAD+ can then fuel glycolysis again. The cells can make ATP again. compares alcoholic fermentation Fermentation is an aerobic process and takes place in the cytoplasm. and lactic acid fermentation. Sometimes glycolysis and fermentation are called anaerobic In Your Workbook Go to respiration. There are two different kinds—alcoholic fermentation your workbook to learn more about making a Venn diagram. Complete and lactic acid fermentation. the Venn diagram for Lesson 9.3. Alcoholic Fermentation Yeasts and a few other microorganisms use alcoholic fermentation. A summary of alcoholic fermentation after glycolysis is as follows: Pyruvic acid + NADH Alcohol + CO2 + NAD+ Humans use alcoholic fermentation to make alcoholic beverages. It is also what causes bread dough to rise. When yeast cells in the dough run out of oxygen, the dough begins to give off tiny bubbles of carbon dioxide. These bubbles form the air spaces you see in a slice of bread. The small amount of alcohol made in the dough evaporates when the bread is baked. Cellular Respiration and Fermentation 223  Lactic Acid Fermentation Most living things carry out fermentation by changing pyruvic acid into lactic acid. Unlike alcoholic fermentation, lactic acid fermentation does not give off carbon fermentation dioxide. Like alcoholic fermentation, lactic acid fermentation makes the process by which cells release NAD so that glycolysis can continue. Lactic acid fermentation after energy in the absence of oxygen glycolysis can be written as: RELATED WORD Pyruvic acid + NADH Lactic acid + NAD+ FORMS The noun fermentation and the verb Bacteria that use lactic acid fermentation are used to make many ferment are related word forms. kinds of foods. Examples are cheese, yogurt, buttermilk, and sour Dough that is beginning to ferment is just starting to undergo the cream. The acid is part of why these foods have a sour taste. Many process of fermentation. kinds of pickles, sauerkraut, and kimchi are also made using lactic acid fermentation. People also use lactic acid fermentation. Many of the cells in our body are able to make ATP by lactic acid fermentation when they are without oxygen for a few seconds. Muscle cells use this kind of fermentation when they need a lot of ATP for quick bursts of activity. Lactic acid builds up in muscles after a burst of activity. The only way to get rid of lactic acid is in a chemical pathway that uses extra oxygen. This is why exercise can leave you huffing and puffing. Key Question How do organisms generate energy when oxygen is not available? Fermentation In alcoholic In the absence of oxygen, fermentation releases energy from food fermentation, pyruvic acid from glycolysis is changed into alcohol molecules by making ATP. and carbon dioxide. In lactic acid fermentation, pyruvic acid from glycolysis is changed into lactic acid. Glycolysis Glucose CYTO PLASM 2 NAD + 2 ADP NAD+ NAD+ cycles cycles back 2 NADH 2 ATP back 2 Pyruvic Acid 2 NADH 2 NADH 2 NAD + 2 NAD + 2 CO2 Alcoholic Lactic Acid Fermentation Fermentation 2 Ethyl Alcohol 2 Lactic Acid 224 Chapter 9 Lesson 3 Energy and Exercise Think about the last time you ran a race. At each stage of the race your body used different paths to get energy. You have three main sources of ATP: ATP already in muscles, ATP made by lactic acid fermentation, and ATP made by cellular respiration. At the beginning of a race, the body uses all three sources. However, stored ATP and lactic acid fermentation can give energy only for a short time. Quick Energy Cells usually have only a little ATP stored up from cellular respiration. At the very beginning of a race, the muscles have only enough for a few seconds of activity. Usually by the 50-meter mark, that store of ATP is nearly gone. Then, the muscle cells make their ATP by lactic acid fermentation, which gives enough ATP to last about 90 seconds, or about 200 or 300 meters. Energy and Exercise During a race, Long-Term Energy For exercise longer than about 90 seconds, runners rely on the energy supplied cellular respiration is the only way to keep making ATP. Your body by ATP to make it to the finish line. stores energy in muscle in the form of the carbohydrate glycogen. These stores are usually enough to last for 15 or 20 minutes of activity. After that, your body begins to break down other stored molecules, including fats, for energy. Key Question How does the body produce ATP during different stages of exercise? For quick bursts of energy, the body uses ATP already in muscles and ATP from lactic acid fermentation. For exercise longer than 90 seconds, the body uses cellular respiration. Apply Vocabulary 5. Infer Why might aerobic exercise help Use the highlighted words from the lesson to someone lose weight? complete the following sentence correctly. 6. Write to Learn Answer the third clue of the mystery. In your answer explain what whales 1. When there is no oxygen present, the cell uses do with lactic acid from fermentation. _____ to make ATP. Critical Thinking 2. Compare and Contrast What reactants and products do the two types of fermentation have Whales use lactic acid fermentation in common? to get much of their energy during a 3. Apply Why do runners breathe heavily after a deep dive. If they can’t breathe in sprint race? to get oxygen, what do they do with all of the lactic acid made by 4. Sequence List the body’s sources of energy in fermentation? (Hint: See p. 224.) the order in which they are used during a long-distance race. Lesson 9.3 Lesson Assessment Cellular Respiration and Fermentation 225  guiDED iNQuiRY Pre-Lab: Comparing Fermentation Rates of Sugars Problem How does the type of sugar affect the rate Pre-Lab Questions of fermentation? Preview the procedure in the lab manual. Materials computer, probe interface, gas pressure 1. Infer Why do you think you will add a layer of probe, hot plate, 400-mL beaker, thermometer, ring vegetable oil above the sugar and yeast mixture? stand, test-tube clamp, medium test tube, test-tube 2. Relate Cause and Effect Explain why it is possible rack, sugar solution, yeast suspension, pipettes, to compare the rates of fermentation by measuring vegetable oil, 1-hole rubber stopper, plastic tubing gas pressure in the test tubes. with lock fitting 3. Predict Which of the sugars do you think will have the highest rate of fermentation, and why? Lab Manual Chapter 9 Lab Chapter 9 Skills Focus Predict, Measure, Analyze Data, Infer Visit Chapter 9 online to test yourself on chapter Connect to the In most cells, the content as well as find activities to help you learn. pathways that release energy from food start with the conversion of glucose to pyruvic acid. This process does Untamed Science Video go underwater with the untamed Science crew to discover why marine not require oxygen. When oxygen is present, however, mammals can stay submerged for such a long time. pyruvic acid can react to form acetyl-CoA, which is used in the second stage of cellular respiration. When Tutor Tube improve your understanding of respiration oxygen is not present, the pyruvic acid can be used in by working “backward” from a breath of oxygen. an anaerobic pathway. This alternate pathway from Art Review Review the components of electron glucose to ATP is called fermentation. In this lab, you transport and ATP synthesis. will use yeast to ferment sugars and compare the rates of fermentation. InterActive Art See glycolysis and the Krebs cycle in action. Background Questions Art in Motion See how matter and energy cycle a. Review What is the importance of the NAD+ that is between photosynthesis and respiration. produced during the fermentation of pyruvic acid? b. Review What other products are produced besides NAD+ when yeast ferment sugar? c. Compare and Contrast How are simple sugars different from disaccharides? (If needed, review Lesson 2.3 in your textbook.) d. Use Analogies What do fermentation and a detour that drivers must use when roads are closed have in common? 226 Chapter 9 Pre-Lab  9.1 Cellular Respiration: An Overview 9.2 The Process of Cellular Respiration Living things get the energy they need from food. During glycolysis, 1 molecule of glucose, a 6-carbon compound, is changed into 2 molecules Cellular respiration is the process that releases of pyruvic acid, a 3-carbon compound. energy from food when oxygen is present. During the Krebs cycle, pyruvic acid is broken Photosynthesis produces food molecules. down into carbon dioxide. Photosynthesis takes carbon dioxide from the air. Cellular respiration puts it back. Photosynthesis The electron transport chain uses the high-energy puts oxygen into the air. Cellular respiration uses electrons from glycolysis and the Krebs cycle to that oxygen to get energy from food. change ADP into ATP. Together, glycolysis, the Krebs cycle, and the cellular respiration (p. 213) electron transport chain make about 36 molecules aerobic (p. 214) anaerobic (p. 214) of ATP per molecule of glucose. glycolysis (p. 216) Krebs cycle (p. 218) Glucose Glycolysis NAD+ (p. 216) matrix (p. 223) 2 ATP 9.3 Fermentation When there is no oxygen, fermentation releases energy from food molecules by making ATP. Krebs Cycle For short, quick bursts of energy, the body uses ATP already in muscles and ATP made by lactic 2 ATP acid fermentation. For exercise longer than about 90 seconds, cellular CO2 respiration is the only way to continue making ATP. Electron Transport fermentation (p. 223) 32 ATP O2 H2O Chapter 9 Match It Chapter Assessment 227  Hint Enzymes in cellular process often work Cellular Basis of Life faster at higher temperatures. Write an answer to the question below. Hint The air bubbles in bread are caused by Q: How do organisms obtain energy? fermentation. Constructed Response Foundations for Learning Wrap-Up Write an answer to each of the questions below. Use the index cards and notebook pages you The answer to each question should be one or two prepared when you started the chapter as a tool paragraphs. To help you begin, read the Hints below to help you organize your thoughts about cellular the questions. respiration. 1. Carbon dioxide is a waste product of Activity 1 Working with a partner, use the index cellular respiration. Plants carry out both cards and notebook page to create a diagram to show photosynthesis and cellular respiration. Why the three stages of cellular respiration. is it wrong to say that carbon dioxide is a waste product in plants? Hint Photosynthesis and cellular respiration are Glucose opposite processes. Hint The reactants for photosynthesis are CYTOPLASM Pyruvic carbon dioxide and water. acid 2. When you run a race, you usually have a burst of energy at the beginning. But, that burst of MITOCHONDRION energy soon fades, and you eventually settle Water down to a steady pace. How do the different pathways that the body takes to get energy explain how different parts of a race feel? Hint Muscle cells get energy from three Activity 2 Working with a partner, label six more different sources during a race. index cards with the chemical symbols for each Hint Stored ATP and lactic acid fermentation word on the index cards from Activity 1. Then label can give energy only for a short time. three more index cards with +, +, and →. Now use 3. Some kinds of bread are lighter and more airy the index cards to create a chemical equation that than others. How might rising and baking summarizes cellular respiration. temperature affect how dense bread is? 228 Check Understanding  9.1 Cellular Respiration: An Overview 7. The Krebs cycle takes place within the a. chloroplast. c. mitochondrion. b. cytoplasm. d. nucleus. Understand Key Concepts 8. The electron transport chain uses the 1. Cells use the energy stored in food to make high-energy electrons from the Krebs cycle to a. ADP. c. glucose. a. make glucose. b. ATP. d. water. b. convert glucose to pyruvic acid. 2. The process that gets energy from food when c. convert pyruvic acid to citric acid. oxygen is present is d. move H+ ions across the inner mitochondrial a. ATP synthase. c. photosynthesis. membrane. b. cellular respiration. d. synthesis. 9. What powers the making of ATP by ATP 3. The first step in getting energy in the cell by synthase? breaking down glucose is known as a. the splitting of glycogen a. the Krebs cycle. c. fermentation. b. the spinning of the mitochondrion b. electron transport. d. glycolysis. c. the movement of ions across the membrane Test-Taking Tip d. the movement of electrons through membrane channels Watch For Key Words Read questions carefully for key words such as first, most, or last. Question 3 10. What happens to high-energy electrons made asks for the “first step in getting energy in the cell by during the Krebs cycle? breaking down glucose.” Answers a, b, and c are all steps in getting energy. But, d is the first step. So d Think Critically glycolysis, is the correct answer. 11. Compare and Contrast How is the function of NAD+ in cellular respiration similar to that of 4. What does it mean if a process is anaerobic? NADP+ in photosynthesis? Which part of cellular respiration is anaerobic? 12. Use Models Draw and label a mitochondrion surrounded by cytoplasm. Show where glycolysis, Think Critically the Krebs cycle, and the electron transport chain 5. Compare and Contrast Why are cellular take place in a eukaryotic cell. respiration and photosynthesis considered opposite reactions? 9.3 Fermentation 9.2 The Process of Cellular Respiration Understand Key Concepts 13. Because fermentation takes place without Understand Key Concepts oxygen, it is said to be 6. The net gain of energy from glycolysis is a. aerobic. c. cyclic. a. 8 ADP molecules. b. anaerobic. d. oxygen-rich. b. 4 ATP molecules. c. 3 pyruvic acid molecules. d. 2 ATP molecules. Check Understanding 229 14. The process carried out by yeast that causes DIVING WITHOUT A BREATH bread dough to rise is To be able to stay underwater for a. alcoholic fermentation. 45-minutes at a time, whales b. cellular respiration. use many different tricks. For c. lactic acid fermentation. example, whale blood can d. mitosis. handle the large amount of CO2 that is made during the 15. Which of the following is a product of alcoholic Krebs cycle. This lets whales stay fermentation? underwater for a long time without a. carbon dioxide c. oxygen making them feel a need to go to the b. lactic acid d. pyruvic acid surface. The Krebs cycle and electron transport need oxygen. And once the oxygen is used—and Think Critically it’s used quickly!—whale muscles use lactic acid 16. Predict Often, regular exercise causes the fermentation to get energy. In humans, lactic acid number of mitochondria in muscle cells to go causes the pH of the blood to drop. If the blood up. How might that situation help someone do gets too acidic, a dangerous state called acidosis better at activities that use up a lot of energy? can take place. Whale muscles can handle a lot of lactic acid. The lactic acid stays in the muscles without causing acidosis. When whales come up Connecting the Concepts after a long dive, they breathe in oxygen, which clears away the lactic acid buildup. Use Science Graphics Use the nutritional information to answer questions 17 1. Relate Cause and Effect Why must whales and 18. have blood that can hold a lot of CO2? 2. Predict Myoglobin is a molecule that stores oxygen in muscles. Would you expect to find more or less myoglobin than average in the muscle cells of whales if you were to look at them under the microscope? 3. Infer How might being able to dive into very deep water be an advantage for whales? Never Stop Exploring Your World. Finding the solution to the mystery is only the 17. Apply Concepts On average, how many Calories beginning. Take a video field trip with the are there in 1 gram of a lipid, carbohydrate, and ecogeeks of Untamed Science to see where protein? Why the differences? the mystery leads. 18. Calculate One gram of protein or a carbohydrate contains about 4 Calories. How many grams of protein must there be in this food in order to account for the number of Calories per serving shown in the label? 230 Check Understanding Standardized Test Prep Multiple Choice 8. Which of the following is an aerobic process? 1. What raw materials are needed for cellular A the Krebs cycle C alcoholic fermentation respiration? B glycolysis D lactic acid fermentation A glucose and carbon dioxide Questions 9 and 10 B glucose and oxygen The graph below shows the rate of alcoholic C carbon dioxide and oxygen fermentation for yeast at different temperatures. D oxygen and lactic acid Rate of Fermentation Versus Temperature 2. During the Krebs cycle A hydrogen ions and oxygen form water. 100 B the cell gives off a small amount of energy Fermentation 75 through fermentation. Rate of 50 C each glucose molecule is broken down into 2 molecules of pyruvic acid. 25 D pyruvic acid is broken down into carbon 0 0 10 20 30 40 dioxide over many steps. Temperature (˚C) 3. Which substance is needed to begin glycolysis? 9. According to the graph, what is the A ATP C pyruvic acid relationship between the rate of fermentation B NADP D carbon dioxide and temperature? 4. In eukaryotic cells, MOST of cellular respiration A The rate of fermentation continually increases takes place in the as temperature increases. A nuclei. C mitochondria. B The rate of fermentation continually decreases B cytoplasm. D cell walls. as temperature increases. C The rate of fermentation increases with 5. Which substance is broken down during temperature at first, then it rapidly decreases. glycolysis? D The rate of fermentation decreases with A carbon C glucose temperature at first, then it rapidly increases. B NAD+ D pyruvic acid 10. Which statement could explain the data shown in 6. The human body can use all of the following as the graph? energy sources EXCEPT A The molecules that carry out fermentation A ATP in muscles. perform best at temperatures above 30°C. B glycolysis. B The yeast begins releasing carbon dioxide at C lactic acid fermentation. 30°C. D alcoholic fermentation. C The yeast cannot survive above 30°C. 7. During cellular respiration, which of the D The molecules that carry out fermentation following are given off? perform best at temperatures below 10°C. A CO2 and O2 C O2 and H2O Open-Ended Response B H2O and O2 D CO2 and H2O 11. Explain how a sprinter gets energy during a 30-second race. Is the process aerobic or anaerobic? Compare it to a long-distance runner getting energy during a 5-kilometer race. If You Have Trouble With... Question 1 2 3 4 5 6 7 8 9 10 11 See Lesson 9.1 9.2 9.2 9.1 9.2 9.3 9.1 9.1 9.3 9.3 9.3 Cellular Respiration and Fermentation 231