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Chapter 10 Photosynthesis. Photosynthesis nourishes almost all of the living world directly or indirectly. –All organisms require organic compounds.

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Presentation on theme: "Chapter 10 Photosynthesis. Photosynthesis nourishes almost all of the living world directly or indirectly. –All organisms require organic compounds."— Presentation transcript:

1 Chapter 10 Photosynthesis

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3 Photosynthesis nourishes almost all of the living world directly or indirectly. –All organisms require organic compounds for energy and for carbon skeletons. Autotrophs produce their organic molecules from CO 2 and other inorganic raw materials obtained from the environment. –Autotrophs are the ultimate sure of organic compounds for all nonautotrophic organisms. –Autotrophs are the producers of the biosphere. 1. Plants and other autotrophs are the producers of the biosphere Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

4 Autotrophs can be separated by the source of energy that drives their metabolism. –Photoautotrophs use light as the energy source. –Photosynthesis occurs in plants, algae, some other protists, and some prokaryotes. –Chemoautotrophs harvest energy from oxidizing inorganic substances, including sulfur and ammonia. –Chemoautotrophy is unique to bacteria. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Fig. 9.1

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12 6CO 2 + 6H 2 O > C 6 H 12 O 6 + 6O 2

13 Photosynthesis is two processes, each with multiple stages. The light reactions convert solar energy to chemical energy. The Calvin cycle incorporates CO 2 from the atmosphere into an organic molecule and uses energy from the light reaction to reduce the new carbon piece to sugar. 2. The light reactions and the Calvin cycle cooperate in converting light energy to chemical energy of food: an overview Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

14 In the light reaction light energy absorbed by chlorophyll in the thylakoids drives the transfer of electrons and hydrogen from water to NADP + (nicotinamide adenine dinucleotide phosphate), forming NADPH. –NADPH, an electron acceptor, provides energized electrons, reducing power, to the Calvin cycle. The light reaction also generates ATP by photophosphorylation for the Calvin cycle. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

15 Light Dependent Reactions Carbon Fixation Dark Reaction Light Independent Reactions

16 NADPH NADP+

17 The Calvin cycle is named for Melvin Calvin who worked out many of its steps in the 1940s with his colleagues. It begins with the incorporation of CO 2 into an organic molecule via carbon fixation. This new piece of carbon backbone is reduced with electrons provided by NADPH. ATP from the light reaction also powers parts of the Calvin cycle. While the light reactions occur at the thylakoids, the Calvin cycle occurs in the stroma. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

18 The entire range of electromagnetic radiation is the electromagnetic spectrum. The most important segment for life is a narrow band between 380 to 750 nm, visible light. Fig. 10.5

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21 A spectrophotometer measures the ability of a pigment to absorb various wavelengths of light. –It beams narrow wavelengths of light through a solution containing a pigment and measures the fraction of light transmitted at each wavelength. –An absorption spectrum plots a pigment’s light absorption versus wavelength. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Fig. 10.7

22 The light reaction can perform work with those wavelengths of light that are absorbed. In the thylakoid are several pigments that differ in their absorption spectrum. –Chlorophyll a, the dominant pigment, absorbs best in the red and blue wavelengths, and least in the green. –Other pigments with different structures have different absorption spectra. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Fig. 10.8a

23 Collectively, these photosynthetic pigments determine an overall action spectrum for photosynthesis. –An action spectrum measures changes in some measure of photosynthetic activity (for example, O 2 release) as the wavelength is varied. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Fig. 10.8b

24 420 nm = BLUE

25 The action spectrum of photosynthesis was first demonstrated in 1883 through an elegant experiment by Thomas Engelmann. –In this experiment, different segments of a filamentous alga were exposed to different wavelengths of light. –Areas receiving wavelengths favorable to photosynthesis should produce excess O 2. –Engelmann used the abundance of aerobic bacteria clustered along the alga as a measure of O 2 production. Fig. 10.8c

26 Below is an absorption spectrum for an unknown pigment molecule. What color would this pigment appear to you? –violet –blue –green –yellow –red

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28 photo activation

29 Excited electrons are unstable. Generally, they drop to their ground state in a billionth of a second, releasing heat energy. Some pigments, including chlorophyll, release a photon of light, in a process called fluorescence, as well as heat. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Fig

30 In the thylakoid membrane, chlorophyll is organized along with proteins and smaller organic molecules into photosystems. A photosystem acts like a light-gathering “antenna complex” consisting of a few hundred chlorophyll a, chlorophyll b, and carotenoid molecules. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Fig

31 e–e– Figure How a photosystem harvests light Primary election acceptor Photon Thylakoid Light-harvesting complexes Reaction center Photosystem STROMA Thylakoid membrane Transfer of energy Special chlorophyll a molecules Pigment molecules THYLAKOID SPACE (INTERIOR OF THYLAKOID)

32 Light-dependent reactions create energy molecules (ATP and NADPH) that are used to drive the Light-independent reactions (Calvin Cycle).

33 Light-dependent Reactions Composed of two parts: 1. cyclic photophosphorylation and 2. non-cyclic photophosphorylation Occurs in the grana

34 Cyclic photophosphorylation- the electron is cycled back to P700

35 Cyclic Photophosphorylation uses the energy from the electron flow to make ATP Refer to p178 P700

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37 1. Electrons flowing through the ETC provide energy to pump H+ into the thylakoid space 2. The build up of H+ in the interior thylakoid space causes them to flow out through an ATP synthesizing enzyme. Electron transport chain

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40 Non-cyclic Photophosphorylation- the electrons are carried away on NADPH Non-cyclic Photophosphorylation- the electrons are carried away on NADPH

41 Hydrogen Ion Movement Photosystem II Inner Thylakoid Space Thylakoid Membrane Stroma ATP synthase Electron Transport Chain Photosystem IATP Formation Chloroplast Section 8-3 Figure 8-10 Light-Dependent Reactions e- H+ H ATP e- Light React p1 Light React p2

42 e–e– Figure How a photosystem harvests light Primary election acceptor Photon Thylakoid Light-harvesting complexes Reaction center Photosystem STROMA Thylakoid membrane Transfer of energy Special chlorophyll a molecules Pigment molecules THYLAKOID SPACE (INTERIOR OF THYLAKOID)

43 Figure How noncyclic electron flow during the light reactions generates ATP and NADPH H2OH2OCO 2 Light LIGHT REACTIONS CALVIN CYCLE O2O2 NADP + ADP ATP NADPH [CH 2 O] (sugar) Light Photosystem II (PS II) ee Primary acceptor P Energy of electrons

44 Figure How noncyclic electron flow during the light reactions generates ATP and NADPH H2OH2OCO 2 Light LIGHT REACTIONS CALVIN CYCLE O2O2 NADP + NADPH [CH 2 O] (sugar) Light Photosystem II (PS II) ee Primary acceptor ADP ATP 2 H + + O2O2 1⁄21⁄2 H2OH2O ee ee Energy of electrons P680

45 Figure How noncyclic electron flow during the light reactions generates ATP and NADPH 1 3 O2O2 + H2OH2OCO 2 Light LIGHT REACTIONS CALVIN CYCLE O2O2 NADP + NADPH [CH 2 O] (sugar) Light Photosystem II (PS II) ee Primary acceptor ATP 2 H + 1⁄21⁄2 H2OH2O 2 Energy of electrons ADP Pq Cytochrome complex Pc ATP Electron transport chain 5 4 P680 ee ee

46 Figure How noncyclic electron flow during the light reactions generates ATP and NADPH O2O2 H2OH2O CO 2 Light LIGHT REACTIONS CALVIN CYCLE O2O2 NADPH [CH 2 O] (sugar) Light Photosystem II (PS II) ee Primary acceptor 2 H + 1⁄21⁄2 H2OH2O 2 Energy of electrons ADP Pq Cytochrome complex Pc ATP Electron transport chain 5 NADP + ATP Primary acceptor ee Photosystem I (PS I) Light P680 P700 + ee ee

47 Figure How noncyclic electron flow during the light reactions generates ATP and NADPH P700 + CO 2 Photosystem II (PS II) H2OH2O Light LIGHT REACTIONS CALVIN CYCLE O2O2 NADPH [CH 2 O] (sugar) ee Primary acceptor 2 H + 1⁄21⁄2 H2OH2O ee ee 1 Energy of electrons Pq Cytochrome complex Pc ATP Electron transport chain NADP + Primary acceptor ee Photosystem I (PS I) Light ADP ATP 5 Fd Electron Transport chain 7 NADP + reductase NADPH NADP H H P680 O2O2 ee ee

48 Mill makes ATP e–e– e–e– e–e– e–e– e–e– Photon Photosystem II Photosystem I e–e– e–e– NADPH Photon Z Scheme Figure A mechanical analogy for the light reactions

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52 NADPH NADP+

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55 PGAL

56 NADPH NADP+ Rubisco

57 NADPH NADP+

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59 Problems for Photosynthesis Click to go to site for photosynthesis problems

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66 Calvin Hatch- Slack

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68 Diagram on Page 184

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70 Problems for Photosynthesis Click to go to site for photosynthesis problems set 2

71 Chapter 10 Photosynthesis

72 –violet –blue –green –yellow –red Below is an absorption spectrum for an unknown pigment molecule. What color would this pigment appear to you?

73 In green plants, most of the ATP for synthesis of proteins, cytoplasmic streaming, and other cellular activities comes directly from –photosystem I. –the Calvin cycle. –oxidative phosphorylation. –noncyclic photophosphorylation. –cyclic photophosphorylation.

74 What portion of an illuminated plant cell would you expect to have the lowest pH? –nucleus –vacuole –chloroplast –stroma of chloroplast –thylakoid space

75 A new flower species has a unique photosynthetic pigment. The leaves of this plant appear to be reddish yellow. What wavelengths of visible light are not being absorbed by this pigment? –red and yellow –blue and violet –green and yellow –blue, green, and red –green, blue, and violet

76 Some photosynthetic organisms contain chloroplasts that lack photosystem II, yet are able to survive. The best way to detect the lack of photosystem II in these organisms would be –to determine if they have thylakoids in the chloroplasts. –to test for liberation of O 2 in the light. –to test for CO 2 fixation in the dark. –to do experiments to generate an action spectrum. –to test for production of either sucrose or starch.

77 Assume a thylakoid is somehow punctured so that the interior of the thylakoid is no longer separated from the stroma. This damage will have the most direct effect on which of the following processes? –the splitting of water –the absorption of light energy by chlorophyll –the flow of electrons from photosystem II to photosystem I –the synthesis of ATP –the reduction of NADP +

78 In an experiment studying photosynthesis performed during the day, you provide a plant with radioactive carbon ( 14 C) dioxide as a metabolic tracer. The 14 C is incorporated first into oxaloacetic acid. The plant is best characterized as a –C 4 plant. –C 3 plant. –CAM plant. –heterotroph. –chemoautotroph.

79 Which of the following conclusions does not follow from studying the absorption spectrum for chlorophyll a and the action spectrum for photosynthesis? –Not all wavelengths are equally effective for photosynthesis. –There must be accessory pigments that broaden the spectrum of light that contributes energy for photosynthesis. –The red and blue areas of the spectrum are most effective in driving photosynthesis. –Chlorophyll owes its color to the absorption of green light. –Chlorophyll a has two absorption peaks.

80 Which of the following processes could still occur in a chloroplast in the presence of an inhibitor that prevents H + from passing through ATP synthase complexes? –sugar synthesis –generation of a proton-motive force –photophosphorylation –the Calvin cycle –oxidation of NADPH

81 –ATP –NADPH + H + –G3P –ATP and NADPH + H + –ATP, NADPH + H +, and G3P The diagram below represents an experiment with isolated chloroplasts. The chloroplasts were first made acidic by soaking them in a solution at pH 4. After the thylakoid space reached pH 4, the chloroplasts were transferred to a basic solution at pH 8. The chloroplasts are then placed in the dark. Which of these compounds would you expect to be produced? *


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