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Name _________________________________________ Date _________________ Class _________________ Unit 4: Cellular Energy Study Guide Brief Overview of Unit ATP ATP stands for adenosine triphosphate. ATP is a high energy molecule composed of a ribose sugar, an adenine base, and three high energy phosphate groups. The energy in ATP is found in the bonds that connect each phosphate. Energy is released when a phosphate is broken off. ATP – 1 phosphate = ADP (adenosine diphosphate) ADP – 1 phosphate = AMP (adenosine monophosphate) (Most Energy) ATP …………ADP…………AMP (Least Energy) ATP is the energy currency of the cell. Cell’s use ATP to carry out all biological process, such as breathing, movement, talking, etc… Photosynthesis Introduction Photosynthesis is a process by which plants, green algae, cyanobacteria, and some protists use to convert sunlight into chemical energy. For this biology class we will focus on plant photosynthesis only. 6CO2 + 6H2O + sunlight C6H12O6 + O2 (memorize this formula) carbon dioxide + water + sunlight sugar + oxygen Cross –Section of a Leaf Photosynthesis mainly occurs in the leaves of plants inside the mesophyll cells inside of a leaf, in an organelle called the chloroplast. Inside the chloroplast is a special pigment called chlorophyll. Pigments absorb light. Chlorophyll is capable of absorbing red, violet, and blue. Chlorophyll, however, cannot absorb green! Whatever is not absorbed will be reflected. This is why plants are mainly green because green is reflected onto your eyes. There are two reactions that occur during photosynthesis: light-dependent reaction and light-independent reaction. Name _________________________________________ Date _________________ Class _________________ The light-dependent reaction of photosynthesis occurs within the chloroplast in disk-like structures called thylakoids. The light-independent reaction of photosynthesis (sometimes called the dark reaction) occurs within the chloroplast’s jelly-like substance called the stroma. The general concept of photosynthesis begins in the thylakoids. Light-dependent Light-independent (Light-dependent reaction) *Water and light enter the thylakoids. The light splits the water into oxygen gas, which is released as a byproduct, and ATP & NADPH are formed. The second part of photosynthesis will now continue in the stroma (Light-independent reaction) *The ATP and NADPH made in the light-dependent reaction are used in conjunction with carbon dioxide to power the Calvin cycle. * Once the Calvin cycle is powered, sugars are made. Since the energy in ATP and NADPH has been used, these molecules are recycled as ADP and NADP+. Do not confuse the words stroma and stoma The Light-dependent Reaction: Photoysystem II and Photosystem I The light-dependent reaction occurs in the thylakoids of the chloroplast and is made possible by a machinery of pigments and proteins called photosystem II and photosystem I. Notice that photosystem II occurs first. The products of the light-dependent reaction are oxygen, ATP, and NADPH. PS II Light and water enter the thylakoids within the photosystem II machinery. The light is absorbed by a special chlorophyll pigment which absorbs light at 680 nanometers. We call this pigment P680. The light splits the water, which causes the release of oxygen. This process also produces hydrogen ions (H+ ions) and high energy electrons. The high energy electrons are then passed down an electron transport chain to produce energy in the form of ATP. As electrons pass down the electron transport chain, hydrogen ions are pulled into the thylakoids space. The high concentration of H+ ions are then forced out of an enzyme called ATP synthase. When H+ ions pass through the ATP synthase, energy is formed by combining a phosphate group to ADP to produce ATP. This process of going from ADP to ATP with the help of light is called photophosphorylation. PS I By the time the electrons from photosystem II reach photosystem I, they have very little energy. A second light source must re-charge these electrons when they reach photosystem I. The pigment that absorbs light in photosystem I is called P700 because it absorbs light at 700 nanometers. The electrons are now energized and ready to pass a second and shorter electron transport chain. The electrons are picked up by NADP+ in the stroma, along with H+. This produces the final product of the light-dependent reaction, NADPH. Please LOOK at the picture below and try to see what is happening as you read the information above Name _________________________________________ Date _________________ Class _________________ The Light-independent Reaction: The Calvin cycle The light-independent reaction is sometimes called the dark reaction or the Calvin cycle. We do not call it the dark reaction anymore because it is misleading. It does not need to be dark for it to happen. During the light-independent reaction, ATP, NADPH, and carbon dioxide are used to make high-energy sugars. The Calvin cycle: C3 Pathway Carbon dioxide enters the Calvin cycle and mixes with a sugar called Ribulose Bisphosphate (RuBP). This occurs because of the enzyme Bisphosphate Carboxylase). The first organic compound to be formed in the Calvin cycle is 3 carbon molecule. PGA is then energized by ATP and NADPH to produce a higherenergy molecular state called PGAL or G3P. Since G3P is the first product made, and it contains 3 carbons, this form of photosynthesis is called the C3 pathway. Many plants undergo the C3 pathway. Notice that glucose is NOT the first sugar made. The first sugar made is G3P, which is later turned into a variety of as glucose, sucrose, etc. Photorespiration Plants close their stomata when it is too hot in order to conserve water. Therefore, is not able to enter the plant, and the oxygen made is stuck in the plant. This is not good news. RuBisCo (Ribulose PGA, a sugars, such carbon dioxide Name _________________________________________ Date _________________ Class _________________ At this point, the plant’s enzyme, RuBisCo, will bind to the oxygen. This method does not produce any energy at all (it actually wastes energy). No sugars are produced either. In summary, photorespiration is bad for plants. It takes their energy and does not really do anything good for plants. Evolutionarily speaking, some plants have adapted ways to deal with intense light, high temperatures, and low carbon dioxide levels. C4 Pathway The C4 pathway occurs in plants that are under intense light, high temperatures, and low carbon dioxide. The C4 pathway requires extra energy in the form of ATP, and it is common in corn, sugarcane, and sorghum. The C4 pathway uses two cells to perform photosynthesis: Mesophyll cell and Bundle-sheath cell. Carbon dioxide and PEP combine thanks to the enzyme PEP carboxylase to form a 4 carbon molecule called Oxaloacetate. The Oxaloacetate is later converted to another 4 carbon molecule called Malate. This all happens in the Mesophyll cell. Because Malate is a 4 carbon molecule, we call this the C4 pathway. The Malate is then transferred to the bundle-sheath cell where it is broken down into carbon dioxide and pyruvate. The carbon dioxide is used to power the Calvin cycle while pyruvate is recycled back to the Mesophyll cell to later be turned back into PEP. Crassulacean Acid Metabolism (CAM) Photosynthesis CAM plants are similar to C4 plants because they are adapted to very hot and dry environments. Examples of CAM plants include pineapple trees and many desert cacti. CAM plants allow air to go in only at night when they open their stomata. At night, carbon dioxide is combined with organic acids and stored in the plant. During the day when the stomata are closed, these acids release the carbon dioxide into the Calvin cycle to produce carbohydrates. Name _________________________________________ Date _________________ Class _________________ Cellular Respiration Introduction All organisms get energy from food. The energy in food is expressed in a unit called the calorie. Cellular respiration is the process by which energy is released from food in the presence of oxygen. C6H12O6 + O2 6CO2 + 6H2O + ATP (memorize this formula) sugar + oxygen carbon dioxide + water + energy Notice that the formula for cellular respiration is the same as photosynthesis but backwards. Also notice that the energy in photosynthesis is solar while in cellular respiration it is chemical energy. Cellular respiration can occur aerobically (with oxygen) or anaerobically (without oxygen). The process of glycolysis is always first and is present in aerobic and anaerobic respiration. Glycolysis No OXYGEN OXYGEN Fermentation Krebs cycle (citric acid cycle) Lactic Acid Fermentation Alcoholic Fermentation Electron Transport chain & Oxidative phosphorylation Aerobic Respiration (with oxygen) If oxygen is present, cellular respiration will begin with glycolysis, form an intermediate called acetyl CoA, enter the Krebs cycle, and finish with the electron transport chain and oxidative phosphorylation. Technically speaking, glycolysis does not need oxygen to function, so it is anaerobic. Memorize this. It is usually asked on all tests. Glycolysis occurs in the cytoplasm of cells where 1 molecule of glucose is broken down into pyruvic acid (aka pyruvate), ATP, and NADH. Name _________________________________________ Date _________________ Class _________________ Notice that in photosynthesis we dealt with NADPH and NADP+, but in cellular respiration we deal with NADH and NAD+. After glycolysis, the pyruvic acid is converted into acetyl CoA, which then enters the Krebs cycle. The Krebs cycle takes place in the matrix of the mitochondria of eukaryotic cells. Acetyl CoA mixes with Oxaloacetate to produce citric acid (aka citrate). Since citric acid is the first product, we also call the Krebs cycle the citric acid cycle. The Krebs cycle produces very little energy, some carbon dioxide (which you breathe out), and a lot of electron carriers (NADH, FADH2) which will later be used to make a lot of energy. The electron carries NADH and FADH2 are ready to dump their electrons onto the inner membrane of the mitochondria called the cristae. This is where the electron transport chain is found. The electrons that are dumped on the electron transport chain are passed on from protein to protein. As this is happening, the intermembrane space of the mitochondria becomes filled with hydrogen ions. These hydrogen ions are then forced to go back into the matrix through the enzyme ATP synthase. Energy (ATP) is produced in the process when ADP is attached to a phosphate. This is called phosphorylation. Since oxygen is the final electron acceptor in the chain, we specifically call this step oxidative phosphorylation. The electron transport chain and oxidative phosphorylation together produce the most amount of energy (about 36 molecules of ATP from 1 sugar in eukaryotes). Notice how the electrons force the H+ to go to the intermembrane space. Then notice how the H+ is forced back into the matrix of the mitochondria by the “red” enzyme ATP synthase. This produces ATP. Name _________________________________________ Date _________________ Class _________________ Keep in mind that while not all organisms perform photosynthesis, ALL organisms perform cellular respiration, including plants (ALL ORGANISMS) One last thing to note is that while eukaryotes perform cellular respiration in their mitochondria, bacterial cells do not contain mitochondria! So how do they do cellular respiration? They perform the same functions in their cell membrane. Anaerobic Respiration (without oxygen) What happens where there is no oxygen? Glycolysis will continue to run, since it is an anerobic process. It will produce the same products, pyruvic acid, energy, and NADH. Unfortunately, we cannot have all this high energy NADH running around, so we need something to bring it back to its lower energy state, NAD+. In alcoholic fermentation, the products of glycolysis are turned into an alcohol called ethanol, carbon dioxide, and NAD+ (look we managed to bring that high energy NADH back down to NAD+). Unfortunately, no ATP is produced =( ….but at least we get alcohol and bread =) By the way, humans cannot do alcoholic fermentation. This is done by the fungus yeast. In lactic acid fermentation, the products of glycolysis are turned into lactic acid and NAD+ (look we managed to bring that high energy NADH back down to NAD+). The lactic acid may cause muscle soreness after you exercise. More fascinating though, bacteria use lactic acid fermentation to produce cheese, yogurt, buttermilk, and sour-cream. COOL! Comparing photosynthesis and cellular respiration Photosynthesis Equation: 6CO2 + 6H2O + sunlight C6H12O6 + O2 Cellular Respiration Equation: C6H12O6 + O2 6CO2 + 6H2O + ATP Notice that these are the same equations but in reverse to each other. In photosynthesis we have solar energy while in respiration we have chemical energy (ATP) Photosynthesis removes carbon dioxide from the environment while cellular respiration puts it back in the environment. Keep in mind that animals cannot do photosynthesis. Only plants, some bacteria, and some protists can perform photosynthesis. *Also, keep in mind that ALL organisms can perform cellular respiration. Plants are fortunate because they can do both photosynthesis and respiration. Very Important – Remember This!!!! Name _________________________________________ Date _________________ Class _________________ Some factors affect the rate of photosynthesis. These factors include light intensity, temperature, and water. If photosynthesis is affected, so will cellular respiration. For the most part, high light intensity and temperature increases photosynthesis (and thus respiration). The reverse is also true. Low light and low temperatures stop photosynthesis (and thus respiration). One last thing, fungi cannot perform photosynthesis! I know these little guys look like plants but they are not plants. Fungi are decomposers; they are Heterotrophs (consumers not producers). Name _________________________________________ Date _________________ Class _________________ Cellular Respiration Questions 1.Label the following 2. Identify the location in the structure to the left where the following processes occur: glycolysis: fermentation: Krebs Cycle: ETC: 3. What is the purpose of cellular respiration? 4. What is ATP and what does it stand for? ____________________________________________________ 5. What does ADP stand for? ________________________________________________________________ 6. What are the 3 steps of cellular respiration? _________________________________________________________________________________ 7. What molecule does glycolysis start with? ______________________________________ 8. What molecules does glycolysis end with? )________________________________ 9. Is glycolysis aerobic or anaerobic? _________________________________________ 10. What is the final electron acceptor of the ETC of Cellular Respiration? ________________________________ 11. Is the ETC of Cellular Respiration aerobic or anaerobic? _____________________________________________ 12. Under what circumstances does fermentation occur? 13. Is fermentation aerobic or anaerobic? _____________________________________________________________ 14. What are two types of fermentation? _____________________________________________________________ 15. Which organism performs alcoholic fermentation? ______________________________________________ 16. What is produced by alcoholic fermentation? ___________________________________________________ 17. Which types of cells perform lactic acid fermentation? _______________________________________________ 18. What is produced by lactic acid fermentation? ____________________________________________________ 19. What is the physical result of lactic acid fermentation in humans? _____________________________________ Name _________________________________________ Date _________________ Class _________________ 20. What is the chemical equation for cellular respiration? Use your notes and/or to read about cellular respiration and glycolysis. Use each of the terms below only once to complete the passage. aerobic anaerobic ATP cellular respiration cytoplasm glucose glycolysis mitochondria NADH oxygen energy Organisms obtain energy in a process called (21) ___________________________ . This process harvests electrons from carbon compounds, such as (22) _________________________ , and uses that energy to make (23) ___________________________ . ATP is used to provide (24) ___________________________ for cells to do work. In (25) __________________________ , glucose is broken down into pyruvate. Glycolysis is a(n) (26) __________________________ process because it does not require oxygen. Glycolysis takes place in the (27) _________________________ . Two molecules of ATP and two molecules of (28) _________________________ are formed for every glucose molecule that is broken down. (29) _________________________ respiration takes place in the (30) _________________________ . It is aerobic because the process requires (31) _________________________ . Refer to the diagram of glycolysis. Label the steps in the description to match the diagram. 32.Step _______ . Each three-carbon compound is converted into a three-carbon pyruvate. 33.Step _______ . A six-carbon compound is broken down into two three-carbon compounds. 34.Step _______ . Phosphate groups from two ATP molecules are transferred to a glucose molecule. 35.Step _______ . Two NADH molecules and four ATP molecules are produced. Respond to each question. 36.Interpret How many total ATP molecules are produced from the glycolysis of one six-carbon glucose? 37.Explain Why is there a net gain of only two ATP molecules in the glycolysis of one six-carbon glucose? 38. What proteins make sure that the release of the energy in glucose happens in a controlled manner? Glycolysis Name _________________________________________ Date _________________ Use your notes and/or textbook to read about the Krebs cycle, electron transport, and anaerobic respiration. Refer to the diagram of cellular respiration. Respond to each question and statement. Class _________________ Cellular Respiration Glucose without oxygen 39.Recall What is the net yield of ATP produced by each of the circled processes in the diagram? Glycolysis 2 ATP Glycolysis = ___________ ATP Krebs cycle = ___________ ATP Pyruvate Electron transport chain = ___________ ATP with oxygen 40.Find the total net yield of ATP from one molecule of glucose. Acetyl-CoA 41.Specify Based on the diagram and your calculations, which process produces more energy—the anaerobic pathway or the aerobic pathway? For each statement below, write true or false. Krebs cycle 2 ATP Electron transport chain 32 ATP ________________ 42. The anaerobic pathway that follows glycolysis in the absence of oxygen is fermentation. ________________ 43. The hydrogen necessary in the electron transport chain comes from the splitting of carbon dioxide molecules. ________________ 44. Cellular respiration in eukaryotes is slightly more efficient than in prokaryotes. ________________ 45. The Krebs cycle is sometimes called the TCA cycle or the citric acid cycle. ________________ 46. Fermentation occurs in the mitochondria. ________________ 47. Skeletal muscle produces lactic acid when the body cannot supply enough oxygen. ________________ 48. Alcohol fermentation is found in some bacteria and in humans. ________________ 49. The two pyruvate molecules formed during glycolysis result in two Krebs cycles. ________________ 50. Electron transport is the first step in the breakdown of glucose. Name _________________________________________ Date _________________ Class _________________ Photosynthesis Practice Questions 51. Label the following cross section of a leaf 52. Label the following chloroplast. 53. What is the purpose of chlorophyll? 54. Where is chlorophyll found? ___________________________________ 55. In what organisms is chlorophyll found? ______________________________________ Use your notes and/or textbook to read about the light reactions. Number the following steps of light reactions in the order in which they occur. __________ 56. The energy lost by electrons as they pass through the electron transport chain is used to make ATP. Name _________________________________________ Date _________________ Class _________________ __________ 57. The electrons pass from the chlorophyll to an electron transport chain. __________ 58. Sunlight strikes the chlorophyll molecules in the thylakoid membranes. __________ 59. NADP+ molecules change to NADPH as they carry the electrons to the stroma of the chloroplast. __________ 60. Light energy is transferred to the chlorophyll’s electrons. __________ 61. The electrons are passed down a second electron transport chain. Refer to the graph. Respond to each statement. 62. Explain why there are usually several types of pigments present in chloroplasts. 63. State the name of the pigment that absorbs the most light at about 450 nm__________ Use your notes and/or to read about the Calvin cycle and alternative photosynthesis pathways. Complete the table by checking the correct column(s) for each description. Description Calvin C4 CAM 64. The second phase of photosynthesis, in which energy is stored in glucose 65. Pathway(s) that help(s) plants photosynthesize while minimizing water loss 66. Pathway that allows carbon dioxide to enter leaves only at night 67. Light-independent reactions 68. Uses the enzyme rubisco to convert carbon dioxide into molecules that can be used by the cell 69. Type of plant found in hot, dry environments Comparing Cellular Respiration and Photosynthesis 70. What is the relationship between the equation for the overall photosynthesis reaction and the equation for the cellular respiration reaction? 71. Do plants carry out cellular respiration? Why or why not? Name _________________________________________ Date _________________ Class _________________ 72. Two hundred years ago, a very old Native American became ill. To help keep his strength up, his family encouraged him to eat the corn tortillas and buffalo meat that formed such an important part of their diet. The wise chief ate a little, then said: “It is my time to go and when I die, I want to be buried beneath the large cottonwood at the bend in the creek. In this way, I will continue to live in the generations of my great grandchildren.” Using ideas from the unit, explain what the chief meant by his final instructions. In particular, how could one of his carbon atoms end up in a great grandchild that he never sees? Trace this atom through decomposers (worms, bacteria, etc.), through corn and buffalo to a great grandchild. 73. What kind of energy is stored in glucose and ATP? _________________________________________________ 74. What are 2 ways in which humans depend on plants in order to stay alive? 75. Why do cells bother to make ATP instead of just using a lot of glucose? 76. How do cells get energy out of ATP? What molecules are left? 77. Fill in the chart comparing and contrasting cell respiration and photosynthesis. Photosynthesis Cell Respiration Organelle for process Inputs (Reactants) Cycle of chemical reactions Outputs (Products) 78. How do the reactants and products of cellular respiration and photosynthesis (other than glucose) get into and out of cells?