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Plants and Photosynthesis. Photosynthesis Organisms –Autotrophs: Self Feeders Photo-: Light Chemo-: Oxidize inorganics (Ex: Sulfur, Ammonia), unique.

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Presentation on theme: "Plants and Photosynthesis. Photosynthesis Organisms –Autotrophs: Self Feeders Photo-: Light Chemo-: Oxidize inorganics (Ex: Sulfur, Ammonia), unique."— Presentation transcript:

1 Plants and Photosynthesis

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5 Photosynthesis Organisms –Autotrophs: Self Feeders Photo-: Light Chemo-: Oxidize inorganics (Ex: Sulfur, Ammonia), unique to bacteria –Heterotrophs: Other Feeders

6 History Jean-Baptiste van Helmont (1600s) –grew willow tree Weighed soil before and after Added only water –Tree gained 75 kg –No change in mass of soil –Concluded: mass in plants comes from water

7 Site of Photosynthesis Mesophyll Cells Upper Epidermis Lower Epidermis VeinVein StomaStoma

8 Site of Photosynthesis Inner & Outer Membranes Thylakoids Granum Stroma

9 Photosynthesis Conversion of Light E into Chem E Light E –Travels in waves (photons) –Wavelength ( ) : crest to crest (measured in nm) inversely related to frequency Higher frequency = more E –Different = different properties

10 Nature of Light Gamma Rays X-RaysUVInfrared Micro- waves Radio Waves Visible Light 400450500550600650700 750 Wavelength (nanometers) Visible spectrum is ~380–750 nm

11 Nature of Light Pigments absorb certain and reflect or transmit others

12 Nature of Light Spectrophotometers measure amount of Light pigments absorb or reflect

13 Nature of Light Pigments –Absorb and reflect light –Specific pigment = specific light –Chlorophylls a and b – both absorb blues and reds a is 1 pigment for photosynthesis – focuses solar E onto a pair of e - s

14 Nature of Light Accessory pigments – funnel the E they collect to a central Chlorophyll A –Carotenoids Carotenes – reflect oranges Xanthophylls – reflect yellows –Phycocyanins – reflect blues Some accessory pigments provide photoprotection against excess light –Carotenoids in human eyes serve same function

15 Absorption/Action Spectra0 20 40 60 80100 % Light Absorption 400450500550600650700 750 Wavelength (nanometers) 400450500550600650700 750 Chlorophyll Collectively Visible Light Phycocyanin Carotenoids

16 Engelmanns Experiment Simple experiment in 1883 Compare to action spectrum

17 Photosynthesis Can be divided into –Light-dependent rxn Makes E storing compounds NADPH and ATP to fuel L-i rxn Occurs in thylakoids –Light-independent rxn Uses NADPH and ATP to produce glucose, a more stable form of E Occurs in stroma

18 Photosynthesis

19 Light-dependent rxn

20 Light is absorbed in photosystem II, an antenna complex of hundreds of pigments that funnel E to a reaction center Rxn Center: central chlorophyll a molecule next to a protein, the 1° e - acceptor

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22 Light-dependent rxn Chemi- osmosis

23 Photosynthesis

24 Light-dependent rxn

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27 The e - s from the broken bonds slide down the ETC, slowly losing E The e - s are recharged by sunlight in photosystem I and are passed along more carrier proteins to NADP +, reducing it to NADPH

28 H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H20H20 O2O2 sun Light-dependent

29 H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ sun Light-dependent ADPATP H+H+ H20H20 O2O2 sun

30 Light-dependent rxn summary H 2 O is broken up by sunlight O 2 is released as waste e - s flow down ETC, pump H + ions, and finally make NADPH H + ions diffuse across thylakoid membrane and help form ATP ATP and NADPH move on to the light- independent rxn

31 Photosynthesis

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33 L-i rxn – C fixation

34 L-i rxn – Reduction 12 ATPs phosphorylate the 12 3PGs to form 12 1,3 bisphosphoglycerates A pair of e - s from NADPH reduces each 1,3 bisphosphoglycerate to glyceraldehyde-3-phosphate (G3P) –The electrons reduce a carboxyl group to a carbonyl group

35 L-i rxn – Reduction

36 Two G3Ps can now be removed from the cycle to make glucose or be used for as any other carb the plant cell needs

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38 Light-independent rxn summary Carbon Fixation –CO 2 needed to begin the process Synthesis of G3P (Glyceraldehyde 3 phosphate) –ATP and NADPH are used Regeneration of 5C compound –Need more ATP to reset the cylce

39 Photorespiration Stomata not only allow gas exchange, but transpiration also Hot, dry day – stomata close –Problem: CO 2, O 2 Rubisco can bind either CO 2 OR O 2 to RuBP When O 2 binds, no useful cellular E is produced

40 Photorespiration When rubisco adds O 2 to RuBP, RuBP splits into a 3-C piece and a 2-C piece –The 2-C fragment is exported from the chloroplast and degraded to CO 2 by mitochondria and peroxisomes Photorespiration decreases photosynthetic output by siphoning organic material from the Calvin cycle Up to 50% of the C fixed by Calvin cycle can be drained away on a hot, dry day

41 C 4 Plants Mesophyll cells use PEP carboxylase to fix CO 2 to phosphoenolpyruvate, forming oxaloacetate (4C) –PEP carboxylase has a very high affinity for CO 2 and can fix CO 2 efficiently when rubisco cannot - on hot, dry days with the stomata closed

42 C 4 Plants Oxaloacetate then dumps the extra CO 2 into the Calvin cycle in bundle- sheath cells Rubisco can then work with a high concentration of CO 2, thus minimizing photorespiration C 4 plants thrive in hot regions with intense sunlight –Examples: sugar, corn

43 C 4 Plants

44 CAM Plants Crassulacean Acid Metabolism CO 2 is fixed at night, but NO photosynthesis takes place at night During the day, the light reactions supply ATP and NADPH to the Calvin cycle and CO 2 is released from the organic acids

45 CAM Plants Allows plants to keep their stomata closed during the hot, dry hours of day and open in the cooler hours of night –Less water is lost in the process –Less photorespiration occurs –Ex: succulent plants, cacti, pineapples, and several other plant families

46 CAM Plants

47 Both C 4 and CAM plants add CO 2 into organic intermediates before it enters the Calvin cycle –In C4 plants, carbon fixation and the Calvin cycle are spatially separated –In CAM plants, carbon fixation and the Calvin cycle are temporally separated Both eventually use the Calvin cycle to incorporate light energy into the production of sugar


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