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Photosynthesis in Plants Lecture Powerpoint

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					Photosynthesis


Introduction to Biology
• How does a tree gain mass as it grows?
• Law of Conservation of Mass: Mass cannot be
  created or destroyed, it only changes form.
Van Helmont’s Experiment
• Jan Baptista van Helmont, a scientist from
  Belgium, conducted an experiment to
  determine the source of a tree’s mass.
  o He grew a Willow tree in a pot for 5 years and re-
    measured the mass.
  o The Willow tree grew by 74kg, but the mass of the soil
    changed very little.
  o Van Helmont concluded that the source of the plant’s
    mass is water.
  Woodward’s Experiment
• John Woodward, a professor at Cambridge
  university in the 1600s, decided to test this
  conclusion.
  o He measured the mass of water he added to the plants.
  o He also measured the mass of the plants as they grew.
  o After 77 days of plant growth, the plant increased in
    mass by 1 gram. Over 76,000 grams of water had been
    added.
    Priestley’s Experiment
• Joseph Priestley believed that plants changed
  the air somehow.
• He placed a small mint plant in a jar with a lit
  candle.
  o He closed the jar, the candle used up the oxygen, and
    the flame extinguished.
  o After about a month, he was able to re-light the candle,
    proving that the plant had changed the air by
    producing oxygen.
        Priestley’s Second
           Experiment
• In his second experiment, Joseph Priestley
  kept a mouse in a closed jar of air until it
  collapsed.
• He then repeated the experiment, but
  included a large plant in the jar with the
  mouse.
  o The mouse survived!
               The Answer
• What are plants made of?
  o Primarily carbohydrates such as cellulose, sucrose,
    fructose, etc.
  o Carbohydrates are made of carbon, oxygen, and
    hydrogen.
• What would be the source of each of these
  elements for plants?

  o Hydrogen: Water
  o Oxygen: Water
  o Carbon: ..?
          Photosynthesis
• Photo = “light”, Synthesis “to make”
• Photosynthesis is using light energy to make
  organic compounds such as sugars.
• Autotrophs are able to produce the molecules
  they need for life without eating anything.
  o Photoautotrophs use sunlight as their energy source.
  o Chemoautotrophs use non-living chemicals (like
    Hydrogen sulfide gas) as their energy source
• Almost all plants are photoautotrophs.
  o Also includes algae, some protozoa, and some
    bacteria.
LE 10-2




                      Plants




                               Unicellular protist 10 µm




                                                               Purple sulfur   1.5 µm
                                                               bacteria



Multicellular algae                  Cyanobacteria     40 µm
• Heterotrophs obtain their organic material by
  eating other organisms
• Almost all heterotrophs, including humans,
  depend on photoautotrophs like plants for
  food and oxygen
         Energy in Sunlight
• Energy from the sun travels to Earth in the form
  of light.
• Sunlight is a mixture of many different types of
  energy:
  o Ultraviolet: Invisible to us, causes sunburns
  o Visible Light: Wavelengths of light we can see,
  o Infrared: Energy in the form of heat
                     Energy
• Our eyes see the different wavelengths of the visible
  spectrum as different colors: red, orange, yellow,
  green, blue, indigo, and violet.
                   Pigments
• Plants gather the sun’s energy
  with light-absorbing molecules
  called pigments.
• The plants’ principal pigment is
  chlorophyll.
  o Chlorophyll is a green pigment.
  o Plants are green because chlorophyll
    reflects green light and absorbs every
    other wavelength.
                      Pigments
• There are two types of chlorophyll found in
  plants, chlorophyll a and chlorophyll b.
• Chlorophyll absorbs blue-violet and red light
  very well, but not green.
  o Remember, green light is reflected, and not absorbed.
         Measuring Light
          Absorption
• A spectrophotometer measures a pigment’s
  ability to absorb various wavelengths
• This machine sends light through pigments
  and measures the fraction of light transmitted
  at each wavelength
LE 10-8a




 White     Refracting      Chlorophyll   Photoelectric
 light     prism           solution      tube

                                                     Galvanometer


                                                         0     100




                                               The high transmittance
           Slit moves to   Green
                                               (low absorption)
           pass light      light
                                               reading indicates that
           of selected
                                               chlorophyll absorbs
           wavelength
                                               very little green light.
LE 10-8b




 White     Refracting      Chlorophyll   Photoelectric
 light     prism           solution      tube




                                                         0    100




           Slit moves to                        The low transmittance
           pass light      Blue                 (high absorption)
           of selected     light                reading indicates that
           wavelength                           chlorophyll absorbs
                                                most blue light.
• An absorption spectrum is a graph plotting a
  pigment’s light absorption versus wavelength
• The absorption spectrum of chlorophyll a
  suggests that violet-blue and red light work
  best for photosynthesis
LE 10-9a


                           Chlorophyll a
  Absorption of light by
  chloroplast pigments                Chlorophyll b

                                           Carotenoids




                           400        500            600        700
                                     Wavelength of light (nm)
 Absorption spectra
                   Pigments
• Plant cells contain other pigments besides
  chlorophyll that increase the wavelengths
  absorbed.
  o These are called carotenoids.
• During the summer, so much chlorophyll is
  produced that the green color overwhelms
  the other pigments.
• When temperatures drop, the plants stop
  producing chlorophyll, and the other
  pigments may be seen.
            Chloroplasts
• Photosynthesis takes place inside organelles
  called chloroplasts.
• Chloroplasts contain stacks called grana.
• The grana contained stacked membranes
  called thylakoids, which are interconnected.
              Chloroplasts
• Leaves are the major locations of
  photosynthesis
• Their green color is from chlorophyll, the green
  pigment within chloroplasts
• Light energy absorbed by chlorophyll drives
  the reactions needed to produce sugars from
  carbon dioxide.
• The plant “breathes” through microscopic
  pores called stomata.
  o CO2 enters the leaf and O2 exits
             Chloroplasts
• Pigments are located in the thylakoid
  membranes.
• The fluid portion outside of the thylakoids is
  known as the stroma.
   Photosynthesis Equation
• Photosynthesis can be summarized in the
  following equation:


6 CO2 + 12 H2O + Light energy  C6H12O6 + 6 O2 + 6 H2 O
Carbon    Water    Sunlight      Glucose   Oxygen   Water
dioxide                                             (Less)
LE 10-3
                                                    Leaf cross section
                                                                   Vein



                                 Mesophyll




                                                Stomata        CO2 O2


                                                     Mesophyll cell
                                 Chloroplast




                                                                   5 µm


                                                    Outer
                                                    membrane
                       Thylakoid
                             Thylakoid          Intermembrane
          Stroma Granum                         space
                             space
                                             Inner
                                             membrane




                                             1 µm
LE 10-4




Reactants:             6 CO2           12 H2O




Products:    C6H12O6           6 H2O            6 O2
  Stages of Photosynthesis
• Photosynthesis consists of the light reactions
  (the photo part) and Calvin cycle (the
  synthesis part)
• The light reactions occur in the thylakoids of
  the chloroplast.
  o Splits water, releases O2, produces ATP and NADPH
• The Calvin cycle occurs in the stroma of the
  chloroplast.
  o Forms sugar from CO2 using ATP and NADPH
LE 10-5_1




                        H2O



            Light




                       LIGHT
                     REACTIONS




       Chloroplast
LE 10-5_2




                             H2O


             Light




                            LIGHT
                          REACTIONS
                                       ATP

                                      NADPH



            Chloroplast

                             O2
LE 10-5_3




                             H2O               CO2


             Light

                                      NADP+
                                       ADP
                                       + Pi
                                              CALVIN
                            LIGHT             CYCLE
                          REACTIONS
                                       ATP

                                      NADPH



            Chloroplast
                                              [CH2O]
                             O2
                                              (sugar)
        ATP and NADPH
• Chloroplasts are solar-powered chemical
  factories
• Their thylakoids transform light energy into the
  chemical energy of ATP and NADPH.
  o These are small energy-containing molecules that can
    be used to make glucose later.
LE 10-7



                              Light
                                                    Reflected
                                                    light

          Chloroplast




                   Absorbed                         Granum
                   light



                                      Transmitted
                                      light
   Absorption of Sunlight
• When chlorophyll absorbs light, it goes from a
  low-energy ground state to an high-energy
  excited state, which is unstable.
• When excited electrons fall back to the
  ground state, photons are given off causing
  fluorescence.
LE 10-11




                             Excited
                   e–        state


                                       Heat




                               Photon
                               (fluorescence)
     Photon
                              Ground
              Chlorophyll
               molecule       state



Excitation of isolated chlorophyll molecule     Fluorescence
        The Photosystem
• The basic unit of photosynthesis in the
  thylakoid is called a photosystem.
• A photosystem contains a reaction center
  surrounded by light-harvesting complexes
• The light-harvesting complexes (pigment
  molecules) funnel the energy from photons of
  sunlight to the reaction center.
• The reaction center contains chlorophyll,
  which absorbs the energy from the photon.
  • This splits a water molecule into O2 , 2 H+ ions, and 2
    electrons.
  • These electrons are energized and passed onto another
    molecule called the primary electron acceptor.
 LE 10-12

Thylakoid
                                                      Photosystem                STROMA
                                 Photon
                                            Light-harvesting    Reaction
                                               complexes        center     Primary electron
                                                                           acceptor




            Thylakoid membrane


                                                               e–




                                      Transfer    Special                       Pigment
                                      of energy   chlorophyll a                 molecules
                                                  molecules
                                                                    THYLAKOID SPACE
                                                                (INTERIOR OF THYLAKOID)
• There are two types of photosystems in the
  thylakoid membrane:
  • Photosystem II absorbs wavelengths of sunlight 680nm
    long.
  • Photosystem I then absorbs wavelengths of sunlight
    700nm long.
• The two photosystems work together to use
  light energy to generate ATP and NADPH
LE 10-13_1
                                                  H2O                    CO2
                                       Light

                                                           NADP+
                                                            ADP
                                                                     CALVIN
                                                 LIGHT
                                                                     CYCLE
                                               REACTIONS
                                                            ATP

                                                           NADPH



                                                  O2               [CH2O] (sugar)




                                                        Primary
                                                        acceptor

                                                             e–
             Energy of electrons




                                   Light
                                                                  P680




                                                    Photosystem II
                                                        (PS II)
LE 10-13_2
                                                       H2O                    CO2
                                       Light

                                                                NADP+
                                                                 ADP
                                                                           CALVIN
                                                      LIGHT
                                                                           CYCLE
                                                    REACTIONS
                                                                 ATP

                                                                NADPH



                                                       O2               [CH2O] (sugar)




                                                             Primary
                                                             acceptor

                                                     H2O          e–
                                           2   H+
                                               +
             Energy of electrons




                                       1/ 2    O2
                                                       e–
                                                        e–
                                   Light
                                                                       P680




                                                         Photosystem II
                                                             (PS II)
LE 10-13_3
                                                     H2O                    CO2
                                       Light

                                                              NADP+
                                                               ADP
                                                                         CALVIN
                                                    LIGHT
                                                                         CYCLE
                                                  REACTIONS
                                                               ATP

                                                              NADPH



                                                     O2               [CH2O] (sugar)




                                                           Primary
                                                           acceptor
                                                                                       Pq
                                                   H2O          e–
                                         2 H+                                               Cytochrome
                                                                                             complex
                                           +
             Energy of electrons




                                       1/ 2 O 2

                                                     e–                                                  Pc
                                                      e–
                                   Light
                                                                     P680




                                                                                             ATP




                                                       Photosystem II
                                                           (PS II)
LE 10-13_4
                                           H2O                    CO2
                           Light

                                                    NADP+
                                                     ADP
                                                               CALVIN
                                          LIGHT
                                                               CYCLE
                                        REACTIONS
                                                     ATP

                                                    NADPH



                                           O2               [CH2O] (sugar)

                                                                                                      Primary
                                                 Primary                                              acceptor
                                                 acceptor
                                                                             Pq                          e–
                                         H2O          e–
                               2   H+                                             Cytochrome
                                                                                   complex
                                   +
 Energy of electrons




                           1/ 2    O2
                                           e–                                                  Pc
                                            e–                                                             P700
                       Light
                                                           P680                                                     Light




                                                                                   ATP




                                                                                                    Photosystem I
                                             Photosystem II                                             (PS I)
                                                 (PS II)
                      LE 10-13_5
                                           H2 O                   CO2
                           Light

                                                    NADP+
                                                    ADP
                                                                CALVIN
                                          LIGHT
                                                                CYCLE
                                        REACTIONS
                                                     ATP

                                                    NADPH




                                           O2                [CH2O] (sugar)


                                                                                                       Primary
                                                  Primary                                              acceptor
                                                  acceptor                                                           Fd
                                                                              Pq                          e–
                                                                                                                      e–
                                        H2O           e–                                                                   e–                NADP+
                               2   H+                                              Cytochrome
                                                                                                                                   NADP+     + 2 H+
                                                                                    complex
                               +
Energy of electrons




                                                                                                                                 reductase
                           1/2 O2                                                                                                            NADPH
                                           e–                                                   Pc
                                                                                                                                              + H+
                                            e–                                                              P700
                       Light
                                                           P680                                                                 Light




                                                                                    ATP




                                                                                                     Photosystem I
                                                                                                         (PS I)
                                                Photosystem II
                                                    (PS II)
LE 10-14


                                                         e–
                                        ATP



                       e–                                       e–


                                                               NADPH
                                 e–
                                               e–
                                          e–


                                       Mill
                                      makes
                                       ATP


           e–




                Photosystem II                      Photosystem I
  LE 10-17
                                               H2 O                     CO2

                             Light

                                                           NADP+
                                                           ADP
                                                                      CALVIN
                                              LIGHT
                                                                      CYCLE
                                            REACTIONS
                                                            ATP

                                                           NADPH




                                               O2                  [CH2O] (sugar)
STROMA
(Low H+ concentration)                                     Cytochrome
                             Photosystem II                                              Photosystem I
                                                            complex
                                                                              Light                              NADP+
                Light
                                                2     H+                                                       reductase
                                                                                                         Fd                     NADP+ + 2H+

                                                                                                                           NADPH + H+
                                                      Pq
                                                                                    Pc

                      H 2O
THYLAKOID SPACE                  1/2   O2
(High H+ concentration)              +2 H+                    2 H+


                                                                                                                                         To
                                                                                                                                        Calvin
                                                                                                                                        cycle



                                     Thylakoid
                                     membrane                                     ATP
STROMA                                                                          synthase
                                                                                            ADP
(Low H+ concentration)                                                                       +                ATP
                                                                                             Pi
                                                                                                   H+
         Building Glucose
• The Calvin cycle builds sugar from smaller
  molecules by using ATP and NADPH
• Carbon enters the cycle as CO2 and leaves as
  a sugar named glyceraldehyde-3-phospate
  (G3P)
  o To make one G3P, the cycle must take place three
    times, using up three molecules of CO2
• The Calvin cycle has three phases:
   o Three atoms of carbon from carbon dioxide
     are added to the cycle using an enzyme
     called rubisco.
      • This creates a 6-carbon molecule
   o ATP and NADPH is used to create two
     molecules of G3P
                        Play
      • One leaves the cycle, one stays behind
   o The original molecules in the cycle are then
     regenerated using more ATP
LE 10-18_1




            H2 O                  CO2
                                                                        Input
 Light

                     NADP+
                                                                        3   (Entering one
                      ADP                                                CO2 at a time)
           LIGHT                CALVIN
         REACTIONS              CYCLE

                      ATP

                     NADPH
                                                                                                   Phase 1: Carbon fixation


                                                                        Rubisco
            O2               [CH2O] (sugar)
                                                                                3 P                     P
                                                                                 Short-lived
                                                                                intermediate
                                              3 P                   P                           6           P
                                              Ribulose bisphosphate                            3-Phosphoglycerate
                                                     (RuBP)                                                                   6   ATP

                                                                                                                        6 ADP


                                                                            CALVIN
                                                                            CYCLE
LE 10-18_2
                   H2O                  CO2

        Light
                                                                                 Input

                            NADP+
                                                                                 3  (Entering one
                             ADP                                                 CO2 at a time)
                  LIGHT                CALVIN
                REACTIONS              CYCLE

                             ATP

                            NADPH
                                                                                                             Phase 1: Carbon fixation

                                                                             Rubisco
                   O2               [CH2O] (sugar)
                                                                                         3 P                       P
                                                                                          Short-lived
                                                                                         intermediate
                                                     3 P                 P                               6              P
                                                 Ribulose bisphosphate                                  3-Phosphoglycerate
                                                        (RuBP)                                                                       6    ATP

                                                                                                                                  6 ADP


                                                                                     CALVIN
                                                                                     CYCLE
                                                                                                             6 P             P
                                                                                                        1,3-Bisphosphoglycerate
                                                                                                                                     6 NADPH

                                                                                                                                  6 NADP+
                                                                                                                                 6 Pi


                                                                                                   6          P
                                                                                         Glyceraldehyde-3-phosphate              Phase 2:
                                                                                                    (G3P)                        Reduction




                                                                             1                 P
                                                                                     G3P                Glucose and
                                                                                  (a sugar)             other organic
                                                                                   Output               compounds
LE 10-18_3
                   H2O                   CO2

        Light
                                                                                  Input

                             NADP+
                                                                                  3  (Entering one
                              ADP                                                 CO2 at a time)
                  LIGHT                 CALVIN
                REACTIONS               CYCLE

                              ATP

                             NADPH
                                                                                                              Phase 1: Carbon fixation

                                                                              Rubisco
                   O2                [CH2O] (sugar)
                                                                                          3 P                       P
                                                                                           Short-lived
                                                                                          intermediate
                                                      3 P                 P                               6              P
                                                  Ribulose bisphosphate                                  3-Phosphoglycerate
                                                         (RuBP)                                                                       6    ATP

                                                                                                                                   6 ADP


                                     3 ADP                                            CALVIN
                                                                                      CYCLE
                                                                                                              6 P             P
                         3    ATP
                                                                                                         1,3-Bisphosphoglycerate
                                                                                                                                      6 NADPH
                                    Phase 3:
                                    Regeneration of                                                                                6 NADP+
                                    the CO2 acceptor                                                                              6 Pi
                                    (RuBP)
                                                            5         P
                                                                G3P                                            P
                                                                                                    6
                                                                                          Glyceraldehyde-3-phosphate              Phase 2:
                                                                                                     (G3P)                        Reduction




                                                                              1                 P
                                                                                      G3P                Glucose and
                                                                                   (a sugar)             other organic
                                                                                    Output               compounds
      Adaptations in Arid
        Environments
• Dehydration is a problem for plants, especially
  in hot, arid ecosystems.
• On hot, dry days, plants close their stomata,
  which conserves water but also limits
  photosynthesis.
  o Plants are unable to take in CO2 and remove O2.
• These conditions favor a seemingly wasteful
  process called photorespiration.
     Photorespiration: An
     Evolutionary Relic?
• In photorespiration, O2 is added to the Calvin
  cycle instead of CO2
• This produces a molecule that must be sent to
  the mitochondria before it can be sent back
  and the Calvin cycle finished.
  o This uses more energy to produce G3P, and is much less
    efficient for the plant.
• Photorespiration may be an evolutionary relic
  because rubisco first evolved at a time when
  the atmosphere had far less O2 and more CO2
• In many plants, photorespiration is a problem
  because on a hot, dry day it can drain much
  of the plant’s ATP and NADPH.
                 C4 Plants
• Some plants have an adaptation to manage
  life in arid climates. These are called C4
  plants.
  o Example: Sugar cane, corn
• These plants minimize the cost of
  photorespiration by incorporating CO2 into
  four-carbon compounds and storing them in
  areas of the leaf less exposed to the dry air.
• These four-carbon compounds can be used
  to release carbon dioxide when the stomata
  are closed, allowing the Calvin cycle to
  continue like normal.
            CAM Plants
• CAM plants open their stomata at night,
  incorporating CO2 into organic acids
• Stomata close during the day, and CO2 is
  released from organic acids and used in the
  Calvin cycle
LE 10-20




       Sugarcane                                    Pineapple



                             C4                                    CAM
                                    CO2                                    CO2
           Mesophyll                        CO2 incorporated                     Night
           cell      Organic acid           into four-carbon Organic acid
                                            organic acids
                                            (carbon fixation)
           Bundle-          CO2                                     CO2          Day
           sheath
           cell                             Organic acids
                          CALVIN                                  CALVIN
                                            release CO2 to
                          CYCLE                                   CYCLE
                                            Calvin cycle

                           Sugar                                   Sugar

              Spatial separation of steps                       Temporal separation of steps

				
DOCUMENT INFO
Description: Lecture Powerpoint covering the topic of photosynthesis in plants, written for an introduction to biology class.