Unit 1: What is Biology? Unit 2: Ecology Unit 3: The Life of a Cell Unit 4: Genetics Unit 5: Change Through Time Unit 6: Viruses, Bacteria, Protists, and Fungi Unit 7: Plants Unit 8: Invertebrates Unit 9: Vertebrates Unit 10: The Human Body Unit 1: What is Biology? Chapter 1: Biology: The Study of Life Unit 2: Ecology Chapter 2: Principles of Ecology Chapter 3: Communities and Biomes Chapter 4: Population Biology Chapter 5: Biological Diversity and Conservation Unit 3: The Life of a Cell Chapter 6: The Chemistry of Life Chapter 7: A View of the Cell Chapter 8: Cellular Transport and the Cell Cycle Chapter 9: Energy in a Cell Unit 4: Genetics Chapter 10: Mendel and Meiosis Chapter 11: DNA and Genes Chapter 12: Patterns of Heredity and Human Genetics Chapter 13: Genetic Technology Unit 5: Change Through Time Chapter 14: The History of Life Chapter 15: The Theory of Evolution Chapter 16: Primate Evolution Chapter 17: Organizing Life’s Diversity Unit 6: Viruses, Bacteria, Protists, and Fungi Chapter 18: Viruses and Bacteria Chapter 19: Protists Chapter 20: Fungi Unit 7: Plants Chapter 21: Chapter 22: Chapter 23: Chapter 24: What Is a Plant? The Diversity of Plants Plant Structure and Function Reproduction in Plants Unit 8: Invertebrates Chapter 25: What Is an Animal? Chapter 26: Sponges, Cnidarians, Flatworms, and Roundworms Chapter 27: Mollusks and Segmented Worms Chapter 28: Arthropods Chapter 29: Echinoderms and Invertebrate Chordates Unit 9: Vertebrates Chapter 30: Fishes and Amphibians Chapter 31: Reptiles and Birds Chapter 32: Mammals Chapter 33: Animal Behavior Unit 10: The Human Body Chapter 34: Protection, Support, and Locomotion Chapter 35: The Digestive and Endocrine Systems Chapter 36: The Nervous System Chapter 37: Respiration, Circulation, and Excretion Chapter 38: Reproduction and Development Chapter 39: Immunity from Disease The Life of a Cell The Chemistry of Life A View of the Cell Cellular Transport and the Cell Cycle Energy in a Cell Chapter 9 Energy in a Cell 9.1: The Need for Energy 9.1: Section Check 9.2: Photosynthesis: Trapping the Sun’s Energy 9.2: Section Check 9.3: Getting Energy to Make ATP 9.3: Section Check Chapter 9 Summary Chapter 9 Assessment What You’ll Learn You will recognize why organisms need a constant supply of energy and where that energy comes from. You will identify how cells store and release energy as ATP. You will describe the pathways by which cells obtain energy. What You’ll Learn You will compare ATP production in mitochondria and in chloroplasts. Section Objectives: • Explain why organisms need a supply of energy. • Describe how energy is stored and released by ATP. Cell Energy • All living organisms must be able to obtain energy from the environment in which they live. • Plants and other green organisms are able to trap the light energy in sunlight and store it in the bonds of certain molecules for later use. Cell Energy • Other organisms cannot use sunlight directly. • They eat green plants. In that way, they obtain the energy stored in plants. Work and the need for energy • Active transport, cell division, movement of flagella or cilia, and the production, transport, and storage of proteins are some examples of cell processes that require energy. • There is a molecule in your cells that is a quick source of energy for any organelle in the cell that needs it. Work and the need for energy • The name of this energy molecule is adenosine triphosphate or ATP for short. • ATP is composed of an adenosine molecule with three phosphate groups attached. Forming and Breaking Down ATP • The charged phosphate groups act like the positive poles of two magnets. • Bonding three phosphate groups to form adenosine triphosphate requires considerable energy. Forming and Breaking Down ATP • When only one phosphate group bonds, a small amount of energy is required and the chemical bond does not store much energy. This molecule is called adenosine monophosphate (AMP). • When a second phosphate group is added, more energy is required to force the two groups together. This molecule is called adenosine diphosphate, or ADP. Forming and Breaking Down ATP • An even greater amount of energy is required to force a third charged phosphate group close enough to the other two to form a bond. When this bond is broken, energy is released. Forming and Breaking Down ATP • The energy of ATP becomes available to a cell when the molecule is broken down. Adenosine P P P Adenosine triphosphate (ATP) P P Adenosine diphosphate (ADP) Adenosine P P How cells tap into the energy stored in ATP • When ATP is broken down and the energy is released, the energy must be captured and used efficiently by cells. • Many proteins have a specific site where ATP can bind. How cells tap into the energy stored in ATP • Then, when the phosphate bond is broken and the energy released, the cell can use the energy for activities such as making a protein or transporting molecules through the plasma membrane. ATP Protein P ADP ADP Energy How cells tap into the energy stored in ATP • When ATP has been broken down to ADP, the ADP is released from the binding site in the protein and the binding site may then be filled by another ATP molecule. Question 1 What is the primary difference in the ways that plants and animals obtain energy? (TX Obj 2; 8C, TX Obj 3; 13A) Answer All living organisms need energy. Plants can trap light energy in sunlight and store it for later use. Animals cannot trap energy from sunlight and must eat plants that contain stored energy. Question 2 Why does the formation of ATP require energy? (TX Obj 2; 4B) One molecule of ATP contains three phosphate groups, which are charged particles. Energy is required to bond the phosphate groups onto the same molecule because they behave the same way that the poles of magnets do and repel groups with like charges. When the ATP molecule is broken down, the chemical energy stored in it becomes available to the cell for life processes. Question 3 A molecule of adenosine that has one phosphate group bonded to it is ______. (TX Obj 2; 4B) A. AMP B. ADP C. ATP D. ACP The answer is A. AMP is adenosine monophosphate. Adenosine P P P Adenosine triphosphate (ATP) P P Adenosine diphosphate (ADP) Adenosine P P The addition and release of a phosphate group on adenosine diphosphate creates a cycle of ATP formation and breakdown. Question 4 What is the function of the protein molecule shown in this diagram? (TX Obj 2; 4B) ATP Protein P ADP ADP Energy This protein molecule has a specific binding site for ATP. In order to access the energy stored ATP, the protein molecule binds the ATP and uncouples one phosphate group. This action releases energy that is then available to the cell. ATP Protein P ADP ADP Energy Section Objectives: • Relate the structure of chloroplasts to the events in photosynthesis. • Describe light-dependent reactions. • Explain the reactions and products of the light-independent Calvin cycle. Trapping Energy from Sunlight • The process that uses the sun’s energy to make simple sugars is called photosynthesis. Trapping Energy from Sunlight • Photosynthesis happens in two phases. 1. The light-dependent reactions convert light energy into chemical energy. 2. The molecules of ATP produced in the lightdependent reactions are then used to fuel the light-independent reactions that produce simple sugars. • The general equation for photosynthesis is written as 6CO2 + 6H2O→C6H12O6 + 6O2 Trapping Energy from Sunlight Click image to view movie. The chloroplast and pigments • To trap the energy in the sun’s light, the thylakoid membranes contain pigments, molecules that absorb specific wavelengths of sunlight. • Although a photosystem contains several kinds of pigments, the most common is chlorophyll. • Chlorophyll absorbs most wavelengths of light except green. Light-Dependent Reactions • As sunlight strikes the chlorophyll molecules in a photosystem of the thylakoid membrane, the energy in the light is transferred to electrons. • These highly energized, or excited, electrons are passed from chlorophyll to an electron transport chain, a series of proteins embedded in the thylakoid membrane. Sun Light-Dependent Reactions • At each step along the transport chain, the electrons lose energy. Light energy transfers to chlorophyll. Chlorophyll passes energy down through the electron transport chain. Energized electrons provide energy that splits H2 O H+ NADP+ bonds P to ADP forming oxygen ATP released NADPH for the use in light-independent reactions Light-Dependent Reactions • This “lost” energy can be used to form ATP from ADP, or to pump hydrogen ions into the center of the thylakoid disc. • Electrons are re-energized in a second photosystem and passed down a second electron transport chain. Light-Dependent Reactions • The electrons are transferred to the stroma of the chloroplast. To do this, an electron carrier molecule called NADP is used. • NADP can combine with two excited electrons and a hydrogen ion (H+) to become NADPH. • NADPH will play an important role in the light-independent reactions. Restoring electrons • To replace the lost electrons, molecules of water are split in the first photosystem. This reaction is called photolysis. Sun Chlorophyll H2O + + _12 O2 + 2e- 2e- _1 O + 2H+ 2 2 H2O Restoring electrons • The oxygen produced by photolysis is released into the air and supplies the oxygen we breathe. • The electrons are returned to chlorophyll. • The hydrogen ions are pumped into the thylakoid, where they accumulate in high concentration. (CO2) The Calvin Cycle (Unstable intermediate) (RuPB) ADP + ATP ATP ADP + NADPH NADP+ (PGAL) (PGAL) (Sugars and other carbohydrates) (PGAL) The Calvin Cycle • Carbon fixation The carbon atom from CO2 bonds with a five-carbon sugar called ribulose biphosphate (RuBP) to form an unstable six(CO ) carbon sugar. 2 • The stroma in chloroplasts hosts the Calvin cycle. (RuBP) The Calvin Cycle • Formation of 3carbon molecules The six-carbon sugar formed in Step A immediately splits to form two three-carbon molecules. (Unstable intermediate) The Calvin Cycle • Use of ATP and NADPH A series of reactions involving ATP and NADPH from the lightdependent reactions converts the three-carbon molecules into phosphoglyceraldehyde (PGAL), three-carbon sugars with higher energy bonds. ATP ADP + NADPH NADP+ (PGAL) The Calvin Cycle • Sugar production One out of every six molecules of PGAL is transferred to the cytoplasm and used in the synthesis of sugars and other carbohydrates. After three rounds of the cycle, six molecules of PGAL are produced. (PGAL) (Sugars and other carbohydrates) The Calvin Cycle • RuBP is replenished Five molecules of PGAL, each with three carbon atoms, produce three molecules of the five-carbon RuBP. This replenishes the RuBP that was used up, and the cycle can continue. ADP+ P ATP (PGAL) Question 1 The process that uses the sun’s energy to make simple sugars is ________. (TX Obj 2; 4B, 8C TX Obj 3; 9D) A. cellular respiration B. glycolysis C. photosynthesis D. photolysis The answer is C. Photosynthesis happens in two phases to make simple sugars and convert the sugars into complex carbohydrates for energy storage. Question 2 The function accomplished by the lightdependent reactions is ________. (TX Obj 2; 4B, 8C, TX Obj 3; 9D) A. energy storage B. sugar production C. carbon fixation D. conversion of sugar to PGAL The answer is A. The light-dependent reactions transfer energy from the sun to chlorophyll, and pass energized electrons to proteins embedded in the thylakoid membrane for storage in ATP and NADPH molecules. Sun Light energy transfers to chlorophyll. Chlorophyll passes energy down through the electron transport chain. Energized electrons provide energy that splits H2 O H+ NADP+ bonds P to ADP forming oxygen ATP released NADPH for the use in light-independent reactions Question 3 The first step in the Calvin cycle is the ________. (TX Obj 2; 4B, 8C, TX Obj 3; 9D) A. replenishing of ribulose biphosphate B. production of phosphoglyceraldehyde C. Splitting of six-carbon sugar into two three-carbon molecules D. Bonding of carbon to ribulose biphosphate The answer is D. The carbon atom from CO2 bonds with a five-carbon sugar to form an unstable six-carbon sugar. This molecule then splits to form two three-carbon molecules. Question 4 How many rounds of the Calvin cycle must occur in order for one molecule of PGAL to be transferred to the cell’s cytoplasm? (TX Obj 2; 4B, 8C, TX Obj 3; 9D) A. 1 B. 2 C. 3 D. 4 The answer is C. Each round of the Calvin cycle produces two molecules of PGAL. Section Objectives: • Compare and contrast cellular respiration and fermentation. • Explain how cells obtain energy from cellular respiration. Cellular Respiration • The process by which mitochondria break down food molecules to produce ATP is called cellular respiration. • There are three stages of cellular respiration: glycolysis, the citric acid cycle, and the electron transport chain. Cellular Respiration • The first stage, glycolysis, is anaerobic—no oxygen is required. • The last two stages are aerobic and require oxygen to be completed. Glycolysis • Glycolysis is a series of chemical reactions in the cytoplasm of a cell that break down glucose, a six-carbon compound, into two molecules of pyruvic acid, a three-carbon compound. 4ATP 2ATP Glucose 2ADP 4ADP + 4P 2PGAL 2 Pyruvic acid 2NAD+ 2NADH + 2H+ Glycolysis • Glycolysis is not very effective, producing only two ATP molecules for each glucose molecule broken down. 4ATP 2ATP Glucose 2ADP 4ADP + 4P 2PGAL 2 Pyruvic acid 2NAD+ 2NADH + 2H+ Glycolysis • Before citric acid cycle and electron transport chain can begin, pyruvic acid undergoes a series of reactions in which it gives off a molecule of CO2 and combines with a molecule called coenzyme A to form acetyl-CoA. Mitochondrial membrane Outside the mitochondrion Pyruvic acid CO2 Inside the mitochondrion Pyruvic acid Coenzyme A Intermediate by-product NAD+ - CoA Acetyl-CoA NADH + H+ The citric acid cycle • The citric acid cycle, also called the Krebs cycle, is a series of chemical reactions similar to the Calvin cycle in that the molecule used in the first reaction is also one of the end products. • For every turn of the cycle, one molecule of ATP and two molecules of carbon dioxide are produced. The Citric Acid Cycle (Acetyl-CoA) NADH + H+ NAD+ The mitochondria host the citric acid cycle. Oxaloacetic acid Citric acid NAD+ NADH + H+ O= =O (CO2) Citric Acid Cycle NAD+ NADH + H+ O= =O ADP + ATP FADH2 FAD (CO2) • Citric acid The two-carbon compound acetylCoA reacts with a four-carbon compound called oxaloacetic acid to form citric acid, a six-carbon molecule. The citric acid cycle Acetyl-CoA Oxaloacetic acid Citric acid • Formation of CO2 The citric acid cycle A molecule of CO2 NAD is formed, NADH + H reducing the O= =O eventual product (CO ) to a five-carbon compound. In the process, a molecule of NADH and H+ is produced. + + 2 • Formation of the second CO2 Another molecule of CO2 is released, forming a fourcarbon compound. One molecule of ATP and a molecule of NADH are also produced. The citric acid cycle NAD+ NADH + H+ O= =O ADP + (CO2) ATP • Recycling of The citric acid cycle oxaloacetic acid The four-carbon molecule goes through a series of reactions in which NADH + H FADH2, NADH, and NAD + H are formed. The carbon chain is FADH FAD rearranged, and oxaloacetic acid is again made available for the cycle. + + 2 The electron transport chain • In the electron transport chain, the carrier molecules NADH and FADH2 gives up electrons that pass through a series of reactions. Oxygen is the final electron acceptor. Electron carrier proteins Space between inner and outer membranes Enzyme Inner membrane e- Electron pathway NADH NAD+ FADH2 FAD 4H+ + O2 + 4 electrons H2O ADP + H2O ATP Center of mitochondrion The electron transport chain • Overall, the electron transport chain adds 32 ATP molecules to the four already produced. Fermentation • During heavy exercise, when your cells are without oxygen for a short period of time, an anaerobic process called fermentation follows glycolysis and provides a means to continue producing ATP until oxygen is available again. Lactic acid fermentation • Lactic acid fermentation is one of the processes that supplies energy when oxygen is scarce. • In this process, the reactions that produced pyruvic acid are reversed. • Two molecules of pyruvic acid use NADH to form two molecules of lactic acid. Lactic acid fermentation • This releases NAD+ to be used in glycolysis, allowing two ATP molecules to be formed for each glucose molecule. • The lactic acid is transferred from muscle cells, to the liver that converts it back to pyruvic acid. Alcoholic fermentation • Another type of fermentation, alcoholic fermentation, is used by yeast cells and some bacteria to produce CO2 and ethyl alcohol. Comparing Photosynthesis and Cellular Respiration Table 9.1 Comparison of Photosynthesis and Cellular Respiration Photosynthesis Cellular Respiration Food synthesized Energy from sun stored in glucose Food broken down Energy of glucose released Carbon dioxide taken in Carbon dioxide given off Oxygen given off Oxygen taken in Produces sugars from PGAL Produces CO2 and H2O Requires light Does not require light Occurs only in presence of chlorophyll Occurs in all living cells Question 1 What do the Calvin cycle and the Citric acid cycle have in common? (TX Obj 2; 4B, 8C, TX Obj 3; 9D) A. The molecule used in the first reaction is also one of the end products. B. Both require input of ATP molecules. C. Both generate ADP. D. From every turn of the cycle, two molecules of carbon dioxide are produced. The answer is A. In the Calvin cycle, RuBP bonds to carbon in the first step and is produced in the last step. In the citric acid cycle, oxaloacetic acid reacts in the first step and is recycled in the last step. Question 2 The process by which mitochondria break down food molecules to produce ATP is called ________. (TX Obj 2; 4B, 8C TX Obj 3; 9D) A. photosynthesis B. cellular respiration C. the light-independent reaction D. the Calvin cycle The answer is B. Photosynthesis, lightindependent reactions, and the Calvin cycle all occur in plants. Question 3 The three stages of cellular respiration are ________. (TX Obj 2; 4B, 8C, TX Obj 3; 9D) A. glycolysis, the Calvin cycle, and the electron transport chain B. carbon fixation, the citric acid cycle, and the electron transport chain Question 3 The three stages of cellular respiration are ________. (TX Obj 2; 4B, 8C, TX Obj 3; 9D) C. glycolysis, the citric acid cycle, and the electron transport chain D. the light-dependent reactions, the citric acid cycle and the electron transport chain The answer is C. The first stage is anaerobic, but the last two stages require oxygen to be completed. Question 4 Which of the following yields the greatest net ATP? TX Obj 2; 4B, 8C, TX Obj 3; 9D) A. Lactic acid fermentation B. Alcoholic fermentation C. Calvin cycle D. Cellular respiration The answer is D. Cellular respiration is far more efficient in ATP production than the fermentation reactions. Comparison of Fermentation to Cellular Respiration Lactic Acid glucose glycolysis (pyruvic acid) Alcoholic Cellular respiration glucose glucose glycolysis (pyruvic acid) glycolysis (pyruvic acid) carbon dioxide carbon dioxide lactic acid alcohol water 2 ATP 2 ATP 38 ATP The Need for Energy • ATP is the molecule that stores energy for easy use within the cell. • ATP is formed when a phosphate group is added to ADP. When ATP is broken down, ADP and phosphate are formed and energy is released. • Green organisms trap the energy in sunlight and store it in the bonds of certain molecules for later use. The Need for Energy • Organisms that cannot use sunlight directly obtain energy by consuming plants or other organisms that have consumed plants. Photosynthesis: Trapping the Sun’s Energy • Photosynthesis is the process by which cells use light energy to make simple sugars. • Chlorophyll in the chloroplasts of plant cells traps light energy needed for photosynthesis. • The light reactions of photosynthesis produce ATP and result in the splitting of water molecules. Photosynthesis: Trapping the Sun’s Energy • The reactions of the Calvin Cycle make carbohydrates using CO2 along with ATP and NADPH from the light reactions. Getting Energy to Make ATP • In cellular respiration, cells break down carbohydrates to release energy. • The first stage of cellular respiration, glycolysis, takes place in the cytoplasm and does not require oxygen. • The citric acid cycle takes place in mitochondria and requires oxygen. Question 1 Name two differences between photosynthesis and cellular respiration. (TX Obj 2; 4B, 8C, TX Obj 3; 9D) Although both processes use electron carriers and form ATP, they accomplish quite different tasks as shown in the table. Table 9.1 Comparison of Photosynthesis and Cellular Respiration Photosynthesis Cellular Respiration Food synthesized Energy from sun stored in glucose Food broken down Energy of glucose released Carbon dioxide taken in Carbon dioxide given off Oxygen given off Oxygen taken in Produces sugars from PGAL Produces CO2 and H2O Requires light Does not require light Occurs only in presence of chlorophyll Occurs in all living cells Question 2 Choose the word from this list that does NOT belong with the others. (TX Obj 2; 4B, 8C TX Obj 3; 9D) A. B. C. D. oxaloacetic acid FADH2 Acetyl-CoA ribulose biphosphate The answer is D. RuBP is utilized in the Calvin cycle; the others are part of the citric acid cycle. Question 3 Six molecules of glucose would give a net yield of _____ ATP following glycolysis. (TX Obj 2; 4B, 8C, TX Obj 3; 9D) A. 8 B. 16 C. 6 D. 12 The answer is D. Glycolysis produces two ATP molecules for each glucose molecule broken down. Question 4 In which of the following structures do the light-dependent reactions of photosynthesis take place? (TX Obj 2; 4B, 8C, TX Obj 3; 9D) A. C. B. D. The answer is D. The light-dependent reactions of photosynthesis take place in the thylakoid membranes of chloroplasts. Question 5 In which stage of photosynthesis is carbon from CO2 used to form a six-carbon sugar? (TX Obj 2; 4B, 8C, TX Obj 3; 9D ) A. Calvin cycle B. glycolysis C. citric acid cycle D. electron transport chain The answer is A. (CO2) (Unstable intermediate) (RuPB) ADP + ATP ATP ADP + NADPH NADP+ (PGAL) (PGAL) (Sugars and other carbohydrates) (PGAL) Question 6 What component of thylakoid membranes absorbs specific wavelengths of sunlight? (TX Obj 2; 4B, 8C, TX Obj 3; 9D) A. B. C. D. electrons pigments chloroplasts mitochondria The answer is B. Pigments are arranged within the thylakoid membranes in photosystems; the most common pigment is chlorophyll. Question 7 Which of the following is a product of cellular respiration? TX Obj 2; 4B, 8C TX Obj 3; 9D) A. lactic acid B. alcohol C. glucose D. carbon dioxide The answer is D. Carbon dioxide, water, and ATP are the products of cellular respiration. Question 8 Complete the concept map using the following terms: RuBP replenishing, formation of 3-carbon molecules, Calvin cycle, carbon fixation. 1 2 3 are steps in (TX Obj 2; 4B, 8C, TX Obj 3; 9D) 4 which takes place in stroma Completed concept map should reflect carbon fixation, RuBP replenishing, and formation of 3-carbon molecules as steps in the Calvin cycle which takes place in stroma. To advance to the next item or next page click on any of the following keys: mouse, space bar, enter, down or forward arrow. Click on this icon to return to the table of contents Click on this icon to return to the previous slide Click on this icon to move to the next slide Click on this icon to open the resources file. End of Chapter 9 Show