1. Chapter 9 Photosynthesis and Cellular Respiration

2. Section 1: Energy in Living Systems
Preview
Chemical Energy
Metabolism and the Carbon Cycle
Transferring Energy
Summary

3. Chemical Energy
Organisms require a constant source of energy. Energy is needed for organisms to maintain their homeostasis.
Homeostasis is the process of maintaining internal order and balance even when the environment changes.
Organisms use and store energy in the chemical bonds of organic compounds. Almost all of the energy in organic compounds comes from the sun.

4. Chemical Energy
Photosynthesis is the process by which plants, algae, and some bacteria use sunlight, carbon dioxide, and water to produce carbohydrates and oxygen.
Organisms that are able to perform photosynthesis, such as plants, are autotrophs.
Autotrophs make organic compounds that serve as food for them and for almost all of the other organisms on Earth,

5. Visual Concept: Photosynthesis

6. Chemical Energy, continued
Organisms that cannot make their own food must absorb food molecules made by autotrophs, eat autotrophs, or eat organisms that consume autotrophs.
Food molecules that are made or consumed by an organism are the fuel for its cells.
Cells use these molecules to release the energy stored in the molecules’ bonds. The energy is used to carry out life processes.

7. Visual Concept: Cellular Respiration
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8. Metabolism and the Carbon Cycle
Metabolism involves either using energy to build organic molecules or breaking down organic molecules in which energy is stored.
Organic molecules contain carbon. Therefore, an organism’s metabolism is part of Earth’s carbon cycle.
Energy from the sun is converted to chemical energy in chloroplasts.

9. Metabolism and the Carbon Cycle, continued
Organisms extract energy in glucose molecules.
Through the process of cellular respiration, cells make the carbon in glucose into stable carbon dioxide molecules and produce energy.
Energy is also released and used to make ATP (adenosine triphospate), an organic molecule that is the main energy source for cell processes.

10. Visual Concept: Linking Photosynthesis and Respiration

11. Transferring Energy
In chemical reactions, energy can be absorbed and released during the breaking and forming of bonds.
In cells, chemical energy is gradually released in a series of chemical reactions that are assisted by enzymes.
Enzymes are proteins that act as catalysts in biochemical reactions.

12. Transferring Energy, continued
ATP
When cells break down food molecules, some of the molecules is released as heat. Much of the remaining energy to make ATP.
ATP is a portable form of energy “currency” inside cells.
ATP is a nucleotide made up of a chain of three phosphate groups. When the bond of the third phosphate group is broken, energy is released, producing ADP.

13. ATP Releases Energy

14. Visual Concept: Comparing ATP and ADP
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15. Transferring Energy, continued
In many cells, ATP synthase recycles ADP by bonding a third phosphate group to the molecule to form ATP.
ATP synthase acts as both an enzyme and a carrier protein for hydrogen ions.

16. Transferring Energy, continued
The flow of H+ ions through ATP synthase powers the production of ATP.
In chloroplasts and mitochondria, a series of molecules, called an electron transport chain, pump H+ ions across the membrane to create a concentration gradient.
The electron transport chain uses energy from released from electron carriers, such as NADH and NADPH, to pump hydrogen ions.

17. Electron carriers

18. Summary
Organisms use and store energy in the chemical bonds of organic molecules.
Metabolism involves either using energy to build organic molecules or breaking down organic molecules in which energy is stored. Organic molecules contain carbon. Therefore, an organism’s metabolism is part of Earth’s carbon cycle.
In cells, chemical energy is gradually released in a series of chemical reactions that are assisted by enzymes.

19. Concept Check
What type of energy is used in cells, and what is the ultimate source of this energy?
How is an organism’s metabolism related to the carbon cycle?
How is energy released in a cell?

20. Test Prep

21. 1. What pigment causes a plant to look green?
A. NADH
B. NAPH
C. carotenoid
D. chlorophyll

22. 2. What is the product of the electron transport chain of photosynthesis?
A. water
B. glucose
C. pyruvate
D. ATP and NADPH

23. Section 2: Photosynthesis
Preview
Harvesting Light Energy
Two Electron Transport Chains
Producing Sugar
Factors that Affect Photosynthesis
Summary

24. Harvesting Light Energy
Photosynthesis is the process that provides energy for almost all life. Chloroplasts are the organelles that convert light energy into chemical energy.
Within the inner membrane of the chloroplast, is the stroma which contains the thylakoid membrane.
This membrane produces flat, disc-like sacs called thylakoids that are arranged in stacks and contain molecules that absorb light energy for photosynthesis.

25. Thylakoids

26. Harvesting Light Energy, continued
Light is a form of electromagnetic radiation, energy that can travel through empty space in the form of waves.
Sunlight contains all of the wavelengths of visible light which we see as different colors.
A pigment is a substance that absorbs certain wavelengths (colors) of light and reflects all of the others.
In plants, light energy is harvested by pigments that are located in the thylakoid membrane of chloroplasts.

27. Harvesting Light Energy,
Chlorophyll is a green pigment in chloroplasts that absorbs light energy to start photosynthesis. It absorbs mostly blue and red light and reflects green and yellow light, which makes plants appear green.

28. Harvesting Light Energy, continued
Plants also have pigments called carotenoids which help plants absorb additional light energy.
When light hits a thylakoid, energy is absorbed by many pigment molecules and eventually transferred to electron carriers.

29. Visual Concept: Spectrum of Light and Plant Pigments

30. Two Electron Transport Chains
Electrons from the electron carrier are used to produce new molecules, including ATP, that temporarily store chemical energy.
During photosynthesis, one electron transport chain provides energy to make ATP, while the other provides energy to make NADPH.
Both chains use energy from electrons excited by light.

31. Two Electron Transport Chains, continued
Producing ATP
Step 1: Electrons excited by light leave the chlorophyll molecules. An enzyme splits water molecules to replace these electrons. Oxygen gas is formed and released into the atmosphere.

32. Two Electron Transport Chains, continued
Producing ATP
Step 2: Excited electrons transfer some of their energy to pump H+ ions into the thylakoid. This process creates a concentration gradient across the thylakoid membrane.

33. Two Electron Transport Chains, continued
Producing ATP
Step 3: The energy from diffusion of H+ ions through the channel portion of ATP synthase is used to catalyze a reaction in which a phosphate group is added to a molecule of ADP, producing ATP.

34. Two Electron Transport Chains, continued
Producing NADPH
Step 4: Light excites electrons in another chlorophyll molecule. The electrons are passed on to the second chain and replaced by the de- energized electrons from the first chain.

35. Two Electron Transport Chains, continued
Producing NADPH
Step 5: Excited electrons combine with H+ ions and NADP+ to form NADPH.
NADPH is an electron carrier that provides high-energy electrons needed to store energy in organic molecules.

36. Electron Transport Chains of Photosynthesis
Click to animate the image.

37. Producing Sugar
The first two stages of photosynthesis depend directly on light because light energy is used to make ATP and NADPH. (a.k.a. Light Reactions)‏
In the final stage of photosynthesis, ATP and NADPH are used to produce energy-storing sugar molecules from the carbon in carbon dioxide.
The use of carbon dioxide to make organic compounds is called carbon dioxide fixation, or carbon fixation.

38. Producing Sugar, continued
The reactions that fix carbon dioxide are light- independent reactions, sometimes called dark reactions.
The most common method of carbon fixation is the Calvin cycle.
Atmospheric carbon dioxide is combined with other carbon compounds to produce organic compounds. ATP and NADPH supply some of the energy required in these reactions.

39. Visual Concept: Calvin Cycle
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41. Factors that Affect Photosynthesis
Light intensity, carbon dioxide concentration, and temperature are three environmental factors that affect photosynthesis.
Although different plants are adapted to different levels of light, the photosynthesis rate increases with increases in light intensity until all of the pigments in a chloroplast are being used.
Photosynthesis is most efficient in a certain range of temperatures.

42. Visual Concept: Environmental Influences on Photosynthesis

43. Summary
In plants, light energy is harvested by pigments located in the thylakoid membrane of chloroplasts.
During photosynthesis, one electron transport chain provides energy used to make ATP, while the other provides energy to make NADPH.

44. Summary, continued
In the final stage of photosynthesis, chemical energy is stored by being used to produce sugar molecules from the carbon in the gas carbon dioxide.
Light intensity, carbon dioxide concentration, and temperature are three environmental factors that affect photosynthesis.

45. Concept Check What is the role of pigments in photosynthesis?
What are the roles of the electron transport chains?
How do plants make sugars and store extra unused energy?
What are the three environmental factors that affect photosynthesis?

46. Test Prep

47. 3. The oxygen that is produced during photosynthesis comes directly from the
A. absorption of light.
B. mitochondrial membranes.
C. splitting of water molecules.
D. splitting of carbon dioxide molecules.

48. B. thylakoid-Calvin cycle C. stroma-light reactions
Use the diagram of a chloroplast to answer the following question. 4. Which of the following correctly identifies the structure marked X and the activities that take place there?
A. stroma-Calvin cycle
B. thylakoid-Calvin cycle
C. stroma-light reactions
D. thylakoid-light reactions

49. Section 3: Cellular Respiration
Preview
Glycolysis
Aerobic Respiration
Fermentation
Summary

50. Glycolysis
The cells of most organisms transfer energy found in organic compounds, such as those in foods, to ATP.
The primary fuel for cellular respiration is glucose. Fats can be broken down to make ATP.
Proteins and nucleic acids can also be used to make ATP, but they are usually used for building important cell parts.

51. Glycolysis, continued
In glycolysis, enzymes break down one six- carbon molecule of glucose into two three- carbon pyruvate molecules.
The breaking of a sugar molecule by glycolysis results in a net gain of two ATP molecules.
This process of glycolysis is anaerobic, or takes place without oxygen.

52. Visual Concept: Glycolysis
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53. Glycolysis, continued
Glycolysis is the only source of energy for some prokaryotes.
Other organisms use oxygen to release even more energy from a glucose molecule. Metabolic processes that require oxygen are aerobic.
In aerobic respiration, the pyruvate product of glycolysis undergoes another series of reactions to produce more ATP molecules.

54. Glycolysis

55. Aerobic Respiration
Organisms such as humans can use oxygen to produce ATP efficiently through aerobic respiration.
The first stage of aerobic respiration is the Krebs cycle, a series of reactions that produce electron carriers.
The electron carriers enter an electron transport chain, which powers ATP synthase.
Up to 34 ATP molecules can be produced from one glucose molecule in aerobic respiration.

56. Aerobic Respiration, continued
Krebs Cycle
Pyruvate (from glycolysis) is broken down and combined with other carbon compounds.
Each time the carbon-carbon bonds are rearranged during the Krebs cycle, energy is released.
The total yield of energy-storing products from one time through the Krebs cycle is one ATP, three NADH, and one FADH2.

57. Visual Concept: Krebs Cycle
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58. Aerobic Respiration, continued
Electron Transport Chain
The second stage of aerobic respiration takes place in the inner membranes of mitochondria, where ATP synthase enzymes are located.
Electron carriers, produced during the Krebs cycle, transfer energy through the electron transport chain.
Energy from the electrons is used to actively transport hydrogen ions out of the inner mitochondrial compartment.

59. Visual Concept: Electron Transport Chain
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60. Aerobic Respiration, continued
Electron Transport Chain
Hydrogen ions diffuse through ATP synthase, providing energy to produce several ATP molecules from ADP.
At the end of the electron transport chain, the electrons combine with an oxygen atom and two hydrogen ions to form two water molecules.
If oxygen is not present, the electron transport chain stops. The electron carriers are not recycled, so the Krebs cycle also stops.

61. Fermentation
To make ATP during glycolysis, NAD+ is converted to NADH. Organisms must recycle NAD+ to continue making ATP through glycolysis.
The process in which carbohydrates are broken down in the absence of oxygen is called fermentation.
Fermentation enables glycolysis to continue supplying a cell with ATP in anaerobic conditions.

62. Fermentation, continued
In lactic acid fermentation, pyruvate is converted to lactic acid.
During vigorous exercise, lactic acid fermentation also occurs in the muscles of animals, including humans.
During alcoholic fermentation, one enzyme removes carbon dioxide from pyruvate. A second enzyme converts the remaining compound to ethanol, recycling NAD+ in the process.

63. Two Types of Fermentation

64. Fermentation, continued
Efficiency of Cellular Respiration
In the first stage of cellular respiration, glucose is broken down to pyruvate during glycolysis, an anaerobic process.
Glycolysis results in a net gain of two ATP molecules for each glucose molecule that is broken down.
In the second stage, pyruvate either passes through the Krebs cycle or undergoes fermentation. Fermentation recycles NAD+ but does not produce ATP.

65. Fermentation, continued
Efficiency of Cellular Respiration
Cells release energy most efficiently when oxygen is present because they make most of their ATP during aerobic respiration.
For each glucose molecule that is broken down, as many as two ATP molecules are made during the Krebs cycle.
The Krebs cycle feeds NADH and FADH2 to the electron transport chain, which can produce up to 34 ATP molecules.

66. Visual Concept: Comparing Aerobic and Anaerobic Respiration

67. Summary
The breaking of a sugar molecule by glycolysis results in a net gain of two ATP molecules.
The total yield of energy-storing products from one time through the Krebs cycle is one ATP, three NADH, and one FADH2.

68. Summary, continued
Electron carriers transfer energy through the electron transport chain, which ultimately powers ATP synthase.
Fermentation enables glycolysis to continue supplying a cell with ATP in anaerobic conditions.

69. Concept Check How does glycolysis produce ATP?
How is ATP produced in aerobic respiration?
Why is fermentation important?

70. Test Prep

71. 5. Which of the following is not involved in the aerobic part of cellular respiration?
A. ATP
B. glycolysis
C. mitochondria
D. the Krebs cycle

72. The graph shows data on photosynthesis in one type of plant
The graph shows data on photosynthesis in one type of plant. Use the graph and your knowledge of science to answer the following question. 6. Which statement is supported by the data?
A. Photosynthesis does not occur at 0 °C.
B. The rate of photosynthesis at 40 °C is greater than the rate at 20 °C.
C. The optimum temperature for photosynthesis is approximately 46 °C.
D. The rate of photosynthesis increases as temperature increases from 25 °C to 30 °C.

73. 7. The inner membrane of a mitochondrion is folded
7. The inner membrane of a mitochondrion is folded. These folds are called christae. How might cellular respiration be different if the inner mitochondrial membrane were not folded?