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Chapter 10 (5)
 

Chapter 10 (5)

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    Chapter 10 (5) Chapter 10 (5) Presentation Transcript

    • Chapter 10 notes Photosynthesis
    • Photosynthesis In Nature
      • All life acquires organic compounds for energy and carbon skeletons by one of two ways
      • - Autotrophs : ( autos = self, trophos = feed)
      • - they sustain themselves w/out eating other organisms
    • Photosynthesis In Nature
      • - plants are photoautotrophs because they use light as a source of energy
      • - Heterotrophs : ( hetero = other, different)
      • - live on compounds produced by other organisms
      • Heterotrophs are dependent on photoautotrophs for food and oxygen
    • Photosynthesis In Nature
      • Chloroplasts are the site of photosynthesis in plants
      • All green parts of plants have chloroplasts
      • - color is from chlorophyll , the green pigment in the chloroplasts
      • - chloroplasts are mainly found in the mesophyll , interior tissue of the leaf
    •  
    • Photosynthesis In Nature
      • - CO 2 enters/O 2 leaves the leaf through pores called stomata
      • - water is absorbed through the roots
      • 6CO 2 +6H 2 O+light  C 6 H 12 O 6 +6O 2
    • Pathways of Photosynthesis
      • The oxygen produced from photosynthesis comes from the spliting of water, not CO 2
      • - use of oxygen-18 to trace pathway
      • Hydrogen is extracted from water to make sugar
      • - O 2 is a waste product
    • Pathways of Photosynthesis
    • Pathways of Photosynthesis
      • Photosynthesis is made of two processes, each containing several steps
      • 1) Light reaction (AKA light harvesting reaction, light dependent reaction)
      • 2) Calvin cycle (AKA dark reaction, carbon fixation reaction)
    • Pathways of Photosynthesis
      • The light rxn. converts solar energy to chemical energy; occurs in the thylokoid membrane
      • - light absorbed drives a transfer of e- and hydrogen to an acceptor, NADP +
      • - NADP + is reduced to NADPH
      • - ATP is generated from ADP through photophosphorylation
    • Pathways of Photosynthesis
      • The Calvin cycle stores the chemical energy in the form of sugar; occurs in the stroma
      • - CO 2 is incorporated w/ other molecules in the chloroplast through carbon fixation
      • - fixed carbon is reduced to carbohydrates
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    • Pathways of Photosynthesis
      • Light is a form of energy known as electromagnetic energy; travels in waves
      • - wavelength is the distance between crests of electromagnetic waves
      • - electromagnetic spectrum : the entire range of radiation
    • Pathways of Photosynthesis
      • Visible light is the band that ranges from 380 to 750 nm in wavelength
      • - detected as colors by the human eye
      • The amount of energy is inversely related to the wavelength
      • - shorter the wavelength, greater the energy
    •  
    • Pathways of Photosynthesis
      • In the chloroplasts light is absorbed mainly by chlorophyll a .
      • - blue and red light is primarily absorbed
      • - green is the least absorbent color
      • Chlorophyll b absorbs light at slightly different wavelengths
    • Pathways of Photosynthesis
    • Pathways of Photosynthesis
      • Chloroplasts also contain accessory pigments, carotenoids
      • - may broaden the spectrum of colors that can drive photosynthesis
      • - act in photoprotection : they absorb excessive light that might damage chlorophyll
    • Pathways of Photosynthesis
      • Light Dependent Reaction
      • Inside the thylakoid, chlorophyll is organized w/ proteins into photosystems
      • - light gathering “antenna complex”
      • Two types of photosystems
      • - PS II, PS I
    • Pathways of Photosynthesis
      • PS II = P680
      • - best at absorbing light w/ a wavelength of 680 nm
      • PS I = P700
      • - best at absorbing light w/ a wavelength of 700 nm
    • Pathways of Photosynthesis
      • Light drives the synthesis of ATP and NADPH by energizing e- in the photosystems
      • Two possible routes for e- flow
      • - cyclic
      • - noncyclic
    • Pathways of Photosynthesis
      • Noncyclic electron flow :
      • - predominant route
      • 1) P680 absorbs light, and splits a water molecule
      • 2) e- absorb the energy and then cascade down an ETC from PS II to PS I
      • 3) ATP is formed by noncyclic photophosphorylaton
    • Pathways of Photosynthesis
      • 4) P700 absorbs more light to reenergize the e- so it can pass down another ETC
      • 5) NADP + is the final e- accepter as it is reduced to NADPH (through redox rxns.)
    • Pathways of Photosynthesis
    • Pathways of Photosynthesis
    • Pathways of Photosynthesis
    • Pathways of Photosynthesis
    • Pathways of Photosynthesis
    • Pathways of Photosynthesis
      • Cyclic electron flow:
      • - uses PS I, but not PS II
      • - makes ATP, but not NADPH or oxygen
      • - cyclic photophosphorylation
      • - because the Calvin cycle uses more ATP than NADPH, cyclic e- flow makes up the difference
    • Pathways of Photosynthesis
    • Pathways of Photosynthesis
      • Chloroplasts and mitochondria both generate ATP through chemiosmosis
      • - both ETC’s pump protons across the membrane during the redox rxns. (transforms redox energy into proton motive force)
      • - both use ATP synthase to couple diffusion to phosphorylation
    • Pathways of Photosynthesis
      • Differences between oxidative phosphorylation and photophosphorylaton
      • - in mitochondria, high energy e- are from food
      • - in chlorplasts, photosystems capture light energy to drive e- transfer
    • Pathways of Photosynthesis
      • Difference in the spatial organization
      • - mitochondria: the inner membrane pumps protons from the matrix to the innermembrane space
      • - chloroplasts: thylakoid pumps protons to the thylakoid space from the stroma
    • Pathways of Photosynthesis
    • Pathways of Photosynthesis
    • Pathways of Photosynthesis
      • Calvin Cycle
      • - uses ATP and NADPH to incorporate CO 2 into sugar (does not make glucose but a 3 carbon sugar called G3P )
      • - 3 steps to the Calvin cycle
    • Pathways of Photosynthesis
      • Step 1: Carbon fixation
      • - CO 2 is attached to RuBP (rxn. is catalyzed by rubisco )
      • - a 6-carbon intermediate is created  splits into 2 3-carbon molecules
      • Step 2: Reduction
      • - ATP and NADPH are used to transform the molecule into G3P
    • Pathways of Photosynthesis
      • - for every three molecules of CO 2 , there are 6 molecules of G3P; only 1 is a net gain
      • Step 3: Regeneration of RuBP
      • - the remaining 5 molecule of G3P are reconverted back into RuBP to continue the Calvin cycle
    • Pathways of Photosynthesis
      • In hot, dry environments, plants have adapted to maximize photosynthesis, while limiting water loss (transpiration)
      • Most plants will close the stomata to prevent water loss, but this limits CO 2 intake
    • Pathways of Photosynthesis
    • Pathways of Photosynthesis
      • In most plants, carbon fixation leads to a 3-carbon compound; these plants are called C 3 plants
      • - ex. rice, wheat, soy
      • - in hot weather, the stomata close which deprives the plant of CO 2 ; rubisco can accept O 2 instead of CO 2
    • Pathways of Photosynthesis
      • - when oxygen binds to rubisco, photorespiration occurs, not photosynthesis
      • - process break the resulting compound down into CO 2
      • - photorespiration does not make ATP (like cellular respiration) nor food (like photosynthesis)
    • Pathways of Photosynthesis
      • Plants have adapted by developing C 4 photosynthesis and CAM
      • C 4 plants preface the Calvin cycle w/ an alternate mode of carbon fixation
      • - ex. Sugarcane, corn, grasses
      • - form a 4-carbon compound as its first product
    • Pathways of Photosynthesis
      • In C 4 plants there are 2 types of photosynthetic cells
      • - Bundle-sheath cells are arranged into tightly packed sheaths around the veins; mesophyll cells are more loosely arranged
    • Pathways of Photosynthesis
      • Step 1: In the mesophyll cells, PEP carboxylase adds CO 2 to PEP (phosphoenolpyruvate); has a high affinity for CO 2 ; forms the 4-carbon product
      • Step 2: 4-carbon compounds move from mesophyll cells to the bundle-sheath
    • Pathways of Photosynthesis
      • Step 3: Within the bundle-sheath, the 4-carbon compound releases CO 2 which then is combined via rubisco
      • The mesophyll cells pump CO 2 into the bundle-sheath so the [CO 2 ] is high enough for rubisco to accept CO 2 and not oxygen
    • Pathways of Photosynthesis
    • Pathways of Photosynthesis
      • CAM plants open their stomata at night, but keep them closed during the day
      • - found in succulent plants
      • - at night the CO 2 is incorporated into other organic acids; this mode of carbon fixation is called crassulacean acid metabolism ( CAM )
    • Pathways of Photosynthesis
      • The mesophyll cells of CAM plants store the acids in their vacuoles until they are needed the following day
      • C 4 and cam are similar in that CO 2 is first incorporated into an intermediate before entering the Calvin cycle
      • However, C 4 plants have a spatial separation of steps, while CAM is temporal
    • Pathways of Photosynthesis