Chapter 8: Photosynthesis, Section 8-1 Energy and Life Photo Credit: ©Stone Copyright Pearson Prentice Hall

Autotrophs and Heterotrophs Living things need energy to survive. This energy comes from food. The energy in most food comes from the sun. Where do plants get the energy they need to produce food? Copyright Pearson Prentice Hall

Autotrophs and Heterotrophs Plants and some other types of organisms are able to use light energy from the sun to produce food. Copyright Pearson Prentice Hall

Chemical Energy and ATP Energy comes in many forms including light, heat, and electricity. Energy can be stored in chemical compounds, too. Copyright Pearson Prentice Hall

Chemical Energy and ATP An important chemical compound that cells use to store and release energy is adenosine triphosphate, abbreviated ATP. ATP is used by all types of cells as their basic energy source. Copyright Pearson Prentice Hall

Chemical Energy and ATP ATP consists of: adenine ribose (a 5-carbon sugar) 3 phosphate groups Adenine Ribose 3 Phosphate groups ATP is used by all types of cells as their basic energy source. ATP Copyright Pearson Prentice Hall

Chemical Energy and ATP Storing Energy ADP has two phosphate groups instead of three. A cell can store small amounts of energy by adding a phosphate group to ADP. ATP ADP Energy + Energy Adenosine Triphosphate (ATP) Adenosine Diphosphate (ADP) + Phosphate Partially charged battery Fully charged battery Copyright Pearson Prentice Hall

Chemical Energy and ATP Releasing Energy Energy stored in ATP is released by breaking the chemical bond between the second and third phosphates. 2 Phosphate groups P ADP Copyright Pearson Prentice Hall

Chemical Energy and ATP What is the role of ATP in cellular activities? Copyright Pearson Prentice Hall

Chemical Energy and ATP The energy from ATP is needed for many cellular activities, including active transport across cell membranes, protein synthesis and muscle contraction. ATP’s characteristics make it exceptionally useful as the basic energy source of all cells. Copyright Pearson Prentice Hall

Using Biochemical Energy Most cells have only a small amount of ATP, because it is not a good way to store large amounts of energy. Cells can regenerate ATP from ADP as needed by using the energy in foods like glucose. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall 8-1 Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall 8-1 Organisms that make their own food are called autotrophs. heterotrophs. decomposers. consumers. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall 8-1 Most autotrophs obtain their energy from chemicals in the environment. sunlight. carbon dioxide in the air. other producers. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall 8-1 How is energy released from ATP? A phosphate is added. An adenine is added. A phosphate is removed. A ribose is removed. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall 8-1 How is it possible for most cells to function with only a small amount of ATP? Cells do not require ATP for energy. ATP can be quickly regenerated from ADP and P. Cells use very small amounts of energy. ATP stores large amounts of energy. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall 8-1 Compared to the energy stored in a molecule of glucose, ATP stores much more energy. much less energy. about the same amount of energy. more energy sometimes and less at others. Copyright Pearson Prentice Hall

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Chapter 8: Photosynthesis, Section 8-2: An Overview Photo Credit: ©Stone Copyright Pearson Prentice Hall 19

8-2 Photosynthesis: An Overview The key cellular process identified with energy production is photosynthesis. Photosynthesis: The process in which green plants use the energy of sunlight to convert water and carbon dioxide into high-energy carbohydrates and oxygen. Copyright Pearson Prentice Hall 20

Investigating Photosynthesis What did the experiments of van Helmont, Priestley, and Ingenhousz reveal about how plants grow? Copyright Pearson Prentice Hall 21

Investigating Photosynthesis Research into photosynthesis began centuries ago. Copyright Pearson Prentice Hall 22

Investigating Photosynthesis Van Helmont’s Experiment In the 1600s, Jan van Helmont wanted to find out if plants grew by taking material out of the soil. He determined the mass of a pot of dry soil and a small seedling, planted the seedling in the pot, and watered it regularly. Copyright Pearson Prentice Hall 23

Investigating Photosynthesis After five years, the seedling was a small tree and had gained 75 kg, but the soil’s mass was almost unchanged. Copyright Pearson Prentice Hall

Investigating Photosynthesis Van Helmont’s Conclusion: The gain in mass came from water because water was the only thing he had added. This experiment accounts for the “hydrate,” or water, portion of the carbohydrate produced by photosynthesis. But where does the carbon of the “carbo-” portion come from??? Copyright Pearson Prentice Hall 25

Investigating Photosynthesis Although van Helmont did not realize it, carbon dioxide in the air made a major contribution to the mass of his tree. In photosynthesis, the carbon in carbon dioxide is used to make sugars and other carbohydrates. Van Helmont had only part of the story, but he had made a major contribution to science. Copyright Pearson Prentice Hall 26

Investigating Photosynthesis Priestley’s Experiment More than 100 years later… Joseph Priestley provided another insight into the process of photosynthesis. Priestley took a candle, placed a glass jar over it, and watched as the flame gradually died out. Copyright Pearson Prentice Hall 27

Investigating Photosynthesis Priestley’s Experiment He reasoned that the flame needed something in the air to keep burning and when it was used up, the flame went out. That substance was oxygen. Priestley then placed a live sprig of mint under the jar and allowed a few days to pass. He found that the candle could be re-lighted and would remain lighted for awhile. Copyright Pearson Prentice Hall 28

Investigating Photosynthesis The mint plant had produced the substance required for burning. In other words, it had released oxygen. Copyright Pearson Prentice Hall 29

Investigating Photosynthesis Jan Ingenhousz Later showed that the effect observed by Priestley occurred only when the plant was exposed to light. The results of both Priestley’s and Ingenhousz’s experiments showed that light is necessary for plants to produce oxygen. Copyright Pearson Prentice Hall 30

Investigating Photosynthesis The experiments performed by van Helmont, Priestley, and Ingenhousz led to work by other scientists who finally discovered that, in the presence of light, plants transform carbon dioxide and water into carbohydrates, and they also release oxygen. MORE TO FOLLOW…. Copyright Pearson Prentice Hall 31

Julius Robert Mayer German physician and physicist 1845: Photosynthesis converts light energy into chemical energy

Samuel Ruben and Martin Kamen 1941 Experiment: Used radioactive isotope tracers (Carbon-14) in water to carry out photosynthetic reaction Proved that oxygen produced during photosynthesis comes from water.

Melvin Calvin 1948 Experiment: Used radioactively labeled isotope (C) to follow pathway of carbon in photosynthesis to form carbohydrates. Aka Calvin Cycle – light independent reactions Aka called Calvin/Benson/Bassham Cycle (CBB) referring to the other scientists involved in the experiment.

Rudolph Marcus 1992 Experiment: Electrons are transferred from one molecule to another in the ELECTRON TRANSPORT CHAIN

So Iwata & Jim Barber 2004 Experiment: Identified the process of water molecules splitting during photosynthesis

The Photosynthesis Equation What is the overall equation for photosynthesis? Copyright Pearson Prentice Hall 37

The Photosynthesis Equation The equation for photosynthesis is: 6CO2 + 6H2O C6H12O6 + 6O2 carbon dioxide + water sugars + oxygen Light Light Copyright Pearson Prentice Hall 38

The Photosynthesis Equation Photosynthesis uses the energy of sunlight to convert water and carbon dioxide into high-energy sugars and oxygen. Copyright Pearson Prentice Hall 39

The Photosynthesis Equation Light energy H2O Light-Dependent Reactions (thylakoids) O2 ADP NADP+ ATP NADPH Photosynthesis is a series of reactions that uses light energy from the sun to convert water and carbon dioxide into sugars and oxygen. CO2 + H20 Sugar Calvin Cycle (stroma) Copyright Pearson Prentice Hall 40

Copyright Pearson Prentice Hall Light and Pigments What is the role of light and chlorophyll in photosynthesis? Copyright Pearson Prentice Hall 41

Copyright Pearson Prentice Hall Light and Pigments Light and Pigments How do plants capture the energy of sunlight? In addition to water and carbon dioxide, photosynthesis requires light and chlorophyll. Copyright Pearson Prentice Hall 42

Copyright Pearson Prentice Hall ROYGBIV Copyright Pearson Prentice Hall

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Copyright Pearson Prentice Hall Light and Pigments Plants gather the sun's energy with light-absorbing molecules called pigments. The main pigment in plants is chlorophyll. There are two main types of chlorophyll: chlorophyll a chlorophyll b Copyright Pearson Prentice Hall 45

Copyright Pearson Prentice Hall Light and Pigments Chlorophyll absorbs light well in the blue-violet and red regions of the visible spectrum. 100 80 60 40 20 Chlorophyll b Estimated Absorption (%) Chlorophyll a Photosynthesis requires light and chlorophyll. In the graph above, notice how chlorophyll a absorbs light mostly in the blue-violet and red regions of the visible spectrum, whereas chlorophyll b absorbs light in the blue and red regions of the visible spectrum. Wavelength (nm) 400 450 500 550 600 650 700 750 Wavelength (nm) Copyright Pearson Prentice Hall 46

Copyright Pearson Prentice Hall Light and Pigments Chlorophyll does not absorb light well in the green region of the spectrum. Green light is reflected by leaves, which is why plants look green. 100 80 60 40 20 Chlorophyll b Estimated Absorption (%) Chlorophyll a Photosynthesis requires light and chlorophyll. In the graph above, notice how chlorophyll a absorbs light mostly in the blue-violet and red regions of the visible spectrum, whereas chlorophyll b absorbs light in the blue and red regions of the visible spectrum. 400 450 500 550 600 650 700 750 Wavelength (nm) Copyright Pearson Prentice Hall 47

Copyright Pearson Prentice Hall Light and Pigments Light is a form of energy, so any compound that absorbs light also absorbs energy from that light. When chlorophyll absorbs light, much of the energy is transferred directly to electrons in the chlorophyll molecule, raising the energy levels of these electrons. These high-energy electrons are what make photosynthesis work. Copyright Pearson Prentice Hall 48

Copyright Pearson Prentice Hall Cross-section of a leaf Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Inside a Chloroplast Inside a Chloroplast In plants, photosynthesis takes place inside chloroplasts. Plant Chloroplast Plant cells Copyright Pearson Prentice Hall 50

Copyright Pearson Prentice Hall Inside a Chloroplast Chloroplasts contain thylakoids—saclike photosynthetic membranes. Single thylakoid Chloroplast Copyright Pearson Prentice Hall 51

Copyright Pearson Prentice Hall Inside a Chloroplast Thylakoids are arranged in stacks known as grana. A singular stack is called a granum. Stroma: liquid-filled space around thylakoids. Granum Stroma Chloroplast Copyright Pearson Prentice Hall 52

Copyright Pearson Prentice Hall Inside a Chloroplast Proteins in the thylakoid membrane organize chlorophyll and other pigments into clusters called photosystems, which are the light-collecting units of the chloroplast. Photosystems Chloroplast Copyright Pearson Prentice Hall 53

Light- dependent reactions Inside a Chloroplast H2O CO2 Light NADP+ ADP + P Light- dependent reactions Calvin Cycle Calvin cycle The process of photosynthesis includes the light-dependent reactions as well as the Calvin cycle. Chloroplast O2 Sugars Copyright Pearson Prentice Hall 54

Copyright Pearson Prentice Hall 8-2 Copyright Pearson Prentice Hall 55

Copyright Pearson Prentice Hall 8-2 In van Helmont's experiment, most of the added mass of the tree came from soil and carbon dioxide. water and carbon dioxide. oxygen and carbon dioxide. soil and oxygen. Copyright Pearson Prentice Hall 56

Copyright Pearson Prentice Hall 8-2 Plants use the sugars produced in photosynthesis to make polysaccharides such as oxygen. starch. carbon dioxide. protein. Copyright Pearson Prentice Hall 57

Copyright Pearson Prentice Hall 8-2 The raw materials required for plants to carry out photosynthesis are carbon dioxide and oxygen. oxygen and sugars. carbon dioxide and water. oxygen and water. Copyright Pearson Prentice Hall 58

Copyright Pearson Prentice Hall 8-2 The principal pigment in plants is chloroplast. chlorophyll. carotene. carbohydrate. Copyright Pearson Prentice Hall 59

Copyright Pearson Prentice Hall 8-2 The colors of light that are absorbed by chlorophylls are green and yellow. green, blue, and violet. blue, violet, and red. red and yellow. Copyright Pearson Prentice Hall 60

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Chapter 8: Photosynthesis, Section 8-3 The Reactions of Photosynthesis Photo Credit: ©Stone Copyright Pearson Prentice Hall 62

Light- dependent reactions Inside a Chloroplast H2O CO2 Light NADP+ ADP + P Light- dependent reactions Calvin Cycle Calvin cycle The process of photosynthesis includes the light-dependent reactions as well as the Calvin cycle. Chloroplast O2 Sugars Copyright Pearson Prentice Hall 63

Copyright Pearson Prentice Hall Electron Carriers Electron Carriers When electrons in chlorophyll absorb sunlight, the electrons gain a great deal of energy. Cells use electron carriers to transport these high-energy electrons from chlorophyll to other molecules. Copyright Pearson Prentice Hall 64

Copyright Pearson Prentice Hall Electron Carriers One carrier molecule is NADP+. Electron carriers, such as NADP+, transport electrons. NADP+ accepts and holds 2 high-energy electrons along with a hydrogen ion (H+). This converts the NADP+ into NADPH. Copyright Pearson Prentice Hall 65

Light-Dependent Reactions The light-dependent reactions require light. The light-dependent reactions produce oxygen gas and convert ADP and NADP+ into the energy carriers ATP and NADPH. Copyright Pearson Prentice Hall 66

Light-Dependent Reactions The light-dependent reactions use energy from sunlight to produce ATP, NADPH, and oxygen. The light-dependent reactions take place within the thylakoid membranes of chloroplasts. Copyright Pearson Prentice Hall 67

Light-Dependent Reactions Photosynthesis begins when pigments in photosystem II absorb light, increasing their energy level. Photosystem II The light-dependent reactions use energy from sunlight to produce ATP, NADPH, and oxygen. The light-dependent reactions take place within the thylakoid membranes of chloroplasts. Copyright Pearson Prentice Hall 68

Light-Dependent Reactions These high-energy electrons are passed on to the electron transport chain. Photosystem II Electron carriers High-energy electron Copyright Pearson Prentice Hall 69

Light-Dependent Reactions Enzymes on the thylakoid membrane break water molecules into: Photosystem II 2H2O The light-dependent reactions use energy from sunlight to produce ATP, NADPH, and oxygen. Electron carriers High-energy electron Copyright Pearson Prentice Hall 70

Light-Dependent Reactions hydrogen ions oxygen atoms energized electrons Photosystem II + O2 2H2O The light-dependent reactions use energy from sunlight to produce ATP, NADPH, and oxygen. Electron carriers High-energy electron Copyright Pearson Prentice Hall 71

Light-Dependent Reactions The energized electrons from water replace the high-energy electrons that chlorophyll lost to the electron transport chain. Photosystem II + O2 2H2O The light-dependent reactions use energy from sunlight to produce ATP, NADPH, and oxygen. High-energy electron Copyright Pearson Prentice Hall 72

Light-Dependent Reactions As plants remove electrons from water, oxygen is left behind and is released into the air. Photosystem II + O2 2H2O The light-dependent reactions use energy from sunlight to produce ATP, NADPH, and oxygen. The light-dependent reactions take place within the thylakoid membranes of chloroplasts. High-energy electron Copyright Pearson Prentice Hall 73

Light-Dependent Reactions The hydrogen ions left behind when water is broken apart are released inside the thylakoid membrane. Photosystem II + O2 2H2O The light-dependent reactions use energy from sunlight to produce ATP, NADPH, and oxygen. High-energy electron Copyright Pearson Prentice Hall 74

Light-Dependent Reactions Energy from the electrons is used to transport H+ ions from the stroma into the inner thylakoid space. Photosystem II + O2 2H2O The light-dependent reactions use energy from sunlight to produce ATP, NADPH, and oxygen. Copyright Pearson Prentice Hall 75

Light-Dependent Reactions High-energy electrons move through the electron transport chain from photosystem II to photosystem I. Photosystem II + O2 2H2O The light-dependent reactions use energy from sunlight to produce ATP, NADPH, and oxygen. Photosystem I Copyright Pearson Prentice Hall 76

Light-Dependent Reactions Pigments in photosystem I use energy from light to re-energize the electrons. + O2 2H2O The light-dependent reactions use energy from sunlight to produce ATP, NADPH, and oxygen. Photosystem I Copyright Pearson Prentice Hall 77

Light-Dependent Reactions NADP+ then picks up these high-energy electrons, along with H+ ions, and becomes NADPH. + O2 2H2O The light-dependent reactions use energy from sunlight to produce ATP, NADPH, and oxygen. 2 NADP+ 2 2 NADPH Copyright Pearson Prentice Hall 78

Light-Dependent Reactions As electrons are passed from chlorophyll to NADP+, more H+ ions are pumped across the membrane. + O2 2H2O The light-dependent reactions use energy from sunlight to produce ATP, NADPH, and oxygen. 2 NADP+ 2 2 NADPH Copyright Pearson Prentice Hall 79

Light-Dependent Reactions Soon, the inside of the membrane fills up with positively charged hydrogen ions, which makes the outside of the membrane negatively charged. + O2 2H2O The light-dependent reactions use energy from sunlight to produce ATP, NADPH, and oxygen. 2 NADP+ 2 2 NADPH Copyright Pearson Prentice Hall 80

Light-Dependent Reactions The difference in charges across the membrane provides the energy to make ATP + O2 2H2O The light-dependent reactions use energy from sunlight to produce ATP, NADPH, and oxygen. 2 NADP+ 2 2 NADPH Copyright Pearson Prentice Hall 81

Light-Dependent Reactions H+ ions cannot cross the membrane directly. ATP synthase + O2 2H2O The light-dependent reactions use energy from sunlight to produce ATP, NADPH, and oxygen. 2 NADP+ 2 2 NADPH Copyright Pearson Prentice Hall 82

Light-Dependent Reactions The cell membrane contains a protein called ATP synthase that allows H+ ions to pass through it ATP synthase + O2 2H2O The light-dependent reactions use energy from sunlight to produce ATP, NADPH, and oxygen. 2 NADP+ 2 2 NADPH Copyright Pearson Prentice Hall 83

Light-Dependent Reactions As H+ ions pass through ATP synthase, the protein rotates. ATP synthase + O2 2H2O The light-dependent reactions use energy from sunlight to produce ATP, NADPH, and oxygen. 2 NADP+ 2 2 NADPH Copyright Pearson Prentice Hall 84

Light-Dependent Reactions As it rotates, ATP synthase binds ADP and a phosphate group together to produce ATP. ATP synthase + O2 2H2O The light-dependent reactions use energy from sunlight to produce ATP, NADPH, and oxygen. ADP 2 NADP+ 2 2 NADPH Copyright Pearson Prentice Hall 85

Light-Dependent Reactions Because of this system, light-dependent electron transport produces not only high-energy electrons but ATP as well. ATP synthase + O2 2H2O The light-dependent reactions use energy from sunlight to produce ATP, NADPH, and oxygen. ADP 2 NADP+ 2 2 NADPH Copyright Pearson Prentice Hall 86

Copyright Pearson Prentice Hall The Calvin Cycle What is the Calvin cycle? Copyright Pearson Prentice Hall 87

Copyright Pearson Prentice Hall The Calvin Cycle The Calvin cycle uses ATP and NADPH from the light-dependent reactions to produce high-energy sugars. Because the Calvin cycle does not require light, these reactions are also called the light-independent reactions. Copyright Pearson Prentice Hall 88

Copyright Pearson Prentice Hall The Calvin Cycle Six carbon dioxide molecules enter the cycle from the atmosphere and combine with six 5-carbon molecules. CO2 Enters the Cycle The Calvin cycle uses ATP and NADPH to produce high-energy sugars. Copyright Pearson Prentice Hall 89

Copyright Pearson Prentice Hall The Calvin Cycle The result is twelve 3-carbon molecules, which are then converted into higher-energy forms. The Calvin cycle uses ATP and NADPH to produce high-energy sugars. Copyright Pearson Prentice Hall 90

Copyright Pearson Prentice Hall The Calvin Cycle The energy for this conversion comes from ATP and high-energy electrons from NADPH. Energy Input 12 12 ADP 12 NADPH 12 NADP+ The Calvin cycle uses ATP and NADPH to produce high-energy sugars. Copyright Pearson Prentice Hall 91

Copyright Pearson Prentice Hall The Calvin Cycle Two of twelve 3-carbon molecules are removed from the cycle. Energy Input 12 12 ADP 12 NADPH 12 NADP+ The Calvin cycle uses ATP and NADPH to produce high-energy sugars. Copyright Pearson Prentice Hall 92

6-Carbon sugar produced Sugars and other compounds The Calvin Cycle The molecules are used to produce sugars, lipids, amino acids and other compounds. 12 12 ADP 12 NADPH 12 NADP+ The Calvin cycle uses ATP and NADPH to produce high-energy sugars. 6-Carbon sugar produced Sugars and other compounds Copyright Pearson Prentice Hall 93

5-Carbon Molecules Regenerated Sugars and other compounds The Calvin Cycle The 10 remaining 3-carbon molecules are converted back into six 5-carbon molecules, which are used to begin the next cycle. 12 12 ADP 6 ADP 12 NADPH 6 12 NADP+ The Calvin cycle uses ATP and NADPH to produce high-energy sugars. 5-Carbon Molecules Regenerated Sugars and other compounds Copyright Pearson Prentice Hall 94

Copyright Pearson Prentice Hall The Calvin Cycle The two sets of photosynthetic reactions work together. The light-dependent reactions trap sunlight energy in chemical form. The light-independent reactions use that chemical energy to produce stable, high-energy sugars from carbon dioxide and water. Copyright Pearson Prentice Hall 95

Factors Affecting Photosynthesis Temperature Light Water Copyright Pearson Prentice Hall

Factors Affecting Photosynthesis Lower CO2, hot dry conditions Plants use different chemical pathways C4 plants: Low CO2 - corn, sugar cane CAM plants: Preserve water by taking in air at night – cacti, pineapple Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall 8-3 Copyright Pearson Prentice Hall 98

Copyright Pearson Prentice Hall 8-3 In plants, photosynthesis takes place inside the thylakoids. chloroplasts. photosystems. chlorophyll. Copyright Pearson Prentice Hall 99

Copyright Pearson Prentice Hall 8-3 Energy to make ATP in the chloroplast comes most directly from hydrogen ions flowing through an enzyme in the thylakoid membrane. transfer of a phosphate from ADP. electrons moving through the electron transport chain. electrons transferred directly from NADPH. Copyright Pearson Prentice Hall 100

Copyright Pearson Prentice Hall 8-3 NADPH is produced in light-dependent reactions and carries energy in the form of ATP. high-energy electrons. low-energy electrons. ADP. Copyright Pearson Prentice Hall 101

Copyright Pearson Prentice Hall 8-3 What is another name for the Calvin cycle? light-dependent reactions light-independent reactions electron transport chain photosynthesis Copyright Pearson Prentice Hall 102

Copyright Pearson Prentice Hall 8-3 Which of the following factors does NOT directly affect photosynthesis? wind water supply temperature light intensity Copyright Pearson Prentice Hall 103

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