1. Chapter 6_Section (1Revised) -2 Mr. Camm Biology Review text pages: 112-129 1

2. Sites of Photosynthesis Stoma Mesophyll 2

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6. Overview of Photosynthesis 6

7. Light Energy and Pigments 7

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9. Light Reactions 9 11 12 13 14 15 16 17 18

10. Light Reactions 10

11. Calvin Cycle_DARK REACTIONS (Carbon Fixation) Enzymatic reactions; temperature sensitive Occur in STROMA of chloroplast ATP and NADPH produced in light reactions drive the second stage of photosynthesis, the Calvin cycle by reducing CO 2 Occurs via cyclical reaction = CALVIN CYCLE In the Calvin cycle, CO 2 is incorporated into organic compounds, a process called carbon fixation. also known as C 3 photosynthesis Chapter 6_Section 2 p. 120-124 11

12. The Calvin cycle, which occurs in the stroma of the chloroplast, is a series of enzyme-assisted chemical reactions that produces a three- carbon sugar. Most of the three-carbon sugars (G3P) generated in the Calvin cycle are converted to a five-carbon sugar (RuBP) to keep the Calvin cycle operating. But some of the three-carbon sugars leave the Calvin cycle and are used to make organic compounds, in which energy is stored for later use. 12

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14. Alternative Pathways The C 4 Pathway –Some plants that evolved in hot, dry climates fix carbon through the C 4 pathway. These plants have their stomata partially closed during the hottest part of the day. –Certain cells in these plants have an enzyme that can fix CO 2 into four-carbon compounds even when the CO 2 level is low and the O 2 level is high. These compounds are then transported to other cells, where the Calvin cycle ensues. 14

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16. Factors that Affect Photosynthesis Light Intensity –The rate of photosynthesis increases as light intensity increases, because more electrons are excited in both photosystems. –However, at some point all of the available electrons are excited, and the maximum rate of photosynthesis is reached. The rate then stays level regardless of further increases in light intensity. Carbon Dioxide Levels –As with increasing light intensity, increasing levels of carbon dioxide also stimulate photosynthesis until the rate levels off. 16

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18. NADPH 18

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22. Photosynthesis in Dry Climates 22

23. Photosynthesis in Dry Climates 23

24. I.The primary difference between C 3 photosynthesis and the C 4 and CAM photosynthetic pathways is in the process of carbon dioxide fixation. As you will recall in C 3 photosynthesis, carbon dioxide is captured by the Rubisco enzyme and added to RuBP inside the chloroplast. This produces 3– PGA, a three–carbon compound that gives the C 3 process its name. II.In C 4 and CAM photosynthesis, carbon dioxide is fixed in the cytoplasm of the mesophyll cells, not inside the chloroplasts. Carbon dioxide enters these cells by diffusion from the stoma. C 4 plants have a special carbon acceptor molecule, phosphoenolpyruvate (PEP). PEP carboxylase, a highly efficient enzyme, reacts with carbon dioxide and PEP to produce oxaloacetate, a four–carbon compound that gives C 4 photosynthesis its name. The oxaloacetate quickly is converted into aspartic or malic acid (both of which are also 4–carbon molecules). You will notice that C 4 photosynthesis uses an ATP molecule to fix the carbon dioxide. This energy expense is compensated by the reduction of photorespiration in conditions limiting the availability of carbon dioxide. This use of ATP in the C 4 process makes the C 4 pathway more efficient in conditions with little photorespiration. 24

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29. Root Words & Chapter Vocab Word Roots: – auto- = self; -troph =Nutrition “ food” – htero-= other; -troph= Nutrition “food” – chloro- = green; -phyll = leaf – electro- = electricity; magnet- = magnetic – photo- = light (photosystem: cluster of pigment molecules) Key Terms: Photosynthesis-The conversion of light energy to chemical energy that is stored in glucose or other organic compounds; occurs in plants, algae, and certain prokaryotes. light reactions -The steps in photosynthesis that occur on the thylakoid membranes of the chloroplast and that convert solar energy to the chemical energy of ATP and NADPH, evolving oxygen in the process. Calvin cycle-The second of two major stages in photosynthesis (following the light reactions), involving atmospheric CO 2 fixation and reduction of the fixed carbon into carbohydrate. 29

30. Carotenoid-An accessory pigment, either yellow or orange, in the chloroplasts of plants. By absorbing wavelengths of light that chlorophyll cannot, carotenoids broaden the spectrum of colors that can drive photosynthesis. Chlorophyll-A green pigment located within the chloroplasts of plants. Chlorophyll a can participate directly in the light reactions, which convert solar energy to chemical energy. 30

31. 31 photosystem -Light-capturing unit located in the thylakoid membrane of the chloroplast, consisting of a reaction center surrounded by numerous light-harvesting complexes. There are two types of photosystems, I and II; they absorb light best at different wavelengths. photosystem I -One of two light-capturing units in a chloroplast’s thylakoid membrane; it has two molecules of P700 chlorophyll a at its reaction center. photosystem II -One of two light-capturing units in a chloroplast’s thylakoid membrane; it has two molecules of P680 chlorophyll a at its reaction center.

32. C 3 plant -A plant that uses the Calvin cycle for the initial steps that incorporate CO 2 into organic material, forming a three-carbon compound as the first stable intermediate. C 4 plant -A plant that prefaces the Calvin cycle with reactions that incorporate CO 2 into a four-carbon compound, the end product of which supplies CO 2 for the Calvin cycle. CAM plant -A plant that uses crassulacean acid metabolism, an adaptation for photosynthesis in arid conditions, first discovered in the family Crassulaceae. Carbon dioxide entering open stomata during the night is converted into organic acids, which release CO 2 for the Calvin cycle during the day, when stomata are closed. 32

33. electromagnetic spectrum- The entire spectrum of radiation ranging in wavelength from less than a nanometer to more than a kilometer. NADP + -Nicotinamide adenine dinucleotide phosphate, an acceptor that temporarily stores energized electrons produced during the light reactions. photophosphorylation -The process of generating ATP from ADP and phosphate by means of a proton-motive force generated by the thylakoid membrane of the chloroplast during the light reactions of photosynthesis. 33

34. 34 Photorespiration- A metabolic pathway that consumes oxygen, releases carbon dioxide, generates no ATP, and decreases photosynthetic output; generally occurs on hot, dry, bright days, when stomata close and the oxygen concentration in the leaf exceeds that of carbon dioxide. primary electron acceptor- A specialized molecule sharing the reaction center with the pair of reaction-center chlorophyll a molecules; it accepts an electron from one of these two chlorophylls. reaction center- Complex of proteins associated with two special chlorophyll a molecules and a primary electron acceptor. Located centrally in a photosystem, this complex triggers the light reactions of photosynthesis. Excited by light energy, one of the chlorophylls donates an electron to the primary electron acceptor, which passes an electron to an electron transport chain. rubisco -Ribulose carboxylase, the enzyme that catalyzes the first step of the Calvin cycle (the addition of CO 2 to RuBP, or ribulose bisphosphate).

35. Stoma -A microscopic pore surrounded by guard cells in the epidermis of leaves and stems that allows gas exchange between the environment and the interior of the plant. stroma -The fluid of the chloroplast surrounding the thylakoid membrane; involved in the synthesis of organic molecules from carbon dioxide and water. thylakoid -A flattened membrane sac inside the chloroplast, used to convert light energy to chemical energy. visible light -That portion of the electromagnetic spectrum detected as various colors by the human eye, ranging in wavelength from about 380 nm to about 750 nm. Wavelength- The distance between crests of waves, such as those of the electromagnetic spectrum. 35