Chapter 10: Photosynthesis

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Chapter 10:Chapter 10:

PhotosynthesisPhotosynthesis

Figure 10.2

(a) Plants(b) Multicellular

(c) Unicellularprotists

(d) Cyanobacteria

(e) Purple sulfurbacteria

What we What we (should) already (should) already

know!know!

Sunlight energy

ECOSYSTEM

Photosynthesisin chloroplasts

GlucoseCO2

Cellular respirationin mitochondria

(for cellular work)

Heat energy

Plants are producersPlants are producers

• Autotrophs – make their own organic Autotrophs – make their own organic molecules from inorganic carbon (COmolecules from inorganic carbon (CO22))

• Photoautotrophs – use light to Photoautotrophs – use light to make organic moleculesmake organic molecules

• Heterotrophs - obtain organic molecules Heterotrophs - obtain organic molecules from another organismfrom another organism

• ConsumersConsumers

• DecomposersDecomposers

Figure 10.4a

Mesophyll

Leaf cross section

Chloroplasts Vein

Stomata

Chloroplast Mesophyllcell

CO2 O2

Leaf Leaf StructurStructur

Figure 10.4b

Outermembrane

IntermembranespaceInnermembrane

Thylakoidspace

ThylakoidGranumStroma

Chloroplast

ChloroplasChloroplaststs

Figure 10.5

Reactants:

Products:

6 H2O 6 O2

12 H2O

C6H12O6

PhotosynthesisPhotosynthesis

Tracer ExperimentTracer Experiment

• Used radiolabeled oxygen atoms in the reactants Used radiolabeled oxygen atoms in the reactants to determine which contributed the O2 that is to determine which contributed the O2 that is released by plantsreleased by plants

• Could be from COCould be from CO22 or H or H22OO

Oxidation-Reduction Reactions Oxidation-Reduction Reactions (Redox)(Redox)• Occurs when electrons are moved from one Occurs when electrons are moved from one

molecule to anothermolecule to another

• The molecule that loses the The molecule that loses the electron(s) is OXIDIZED (called electron(s) is OXIDIZED (called oxidation)oxidation)

• The molecule that gains the The molecule that gains the electron(s) is REDUCED (called electron(s) is REDUCED (called reductions)reductions)

• They will always go togetherThey will always go together

• As electrons move, they gain potential As electrons move, they gain potential energy (in photosynthesis)energy (in photosynthesis)

• In photosynthesis, electrons move from In photosynthesis, electrons move from water to CO2, forming sugarswater to CO2, forming sugars

Figure 10.UN01

Energy 6 CO2 6 H2OC6 H12 O6 6 O2

becomes reduced

becomes oxidized

Photosynthesis is a Redox Photosynthesis is a Redox ReactionReaction

Figure 10.6-1

LightReactions

Chloroplast

Figure 10.6-2

LightReactions

Chloroplast

Figure 10.6-3

LightReactions

CalvinCycle

Chloroplast

H2O CO2

Figure 10.6-4

LightReactions

CalvinCycle

Chloroplast

[CH2O](sugar)

H2O CO2

Figure 10.7

Gammarays X-rays UV Infrared

Micro-waves

Radiowaves

Visible light

Shorter wavelength Longer wavelength

Lower energyHigher energy

380 450 500 550 600 650 700 750 nm

105 nm 103 nm 1 nm 103 nm 106 nm (109 nm) 103 m1 m

magneti

c Spect

Figure 10.8

Chloroplast

LightReflectedlight

Absorbedlight

Transmittedlight

Granum

Chloroplasts absorb only certain Chloroplasts absorb only certain colorscolors

Figure 10.9

Whitelight

Refractingprism

Chlorophyllsolution

Photoelectrictube

Galvanometer

Slit moves topass lightof selectedwavelength.

Greenlight

High transmittance(low absorption):Chlorophyll absorbsvery little green light.

Bluelight

Low transmittance(high absorption):Chlorophyll absorbsmost blue light.

TECHNIQUE

Figure 10.10

(b) Action spectrum

(a) Absorptionspectra

Engelmann’sexperiment

Chloro-phyll a Chlorophyll b

Carotenoids

Wavelength of light (nm)

Aerobic bacteria

Filamentof alga

400 500 600 700

RESULTS

Pigments in chloroplastsPigments in chloroplasts

1.1. Chlorophyll Chlorophyll aa: absorbs blue-violet and : absorbs blue-violet and redred

2.2. Chlorophyll Chlorophyll bb: absorbs blue and : absorbs blue and orangeorange

3.3. Carotenoids: absorbs other Carotenoids: absorbs other wavelengthswavelengths

4.4. Other pigments: found in various Other pigments: found in various plantsplants

Figure 10.11

Hydrocarbon tail(H atoms not shown)

Porphyrin ring

CH3 in chlorophyll aCHO in chlorophyll b

rophyll

““Excited” electronsExcited” electrons

• Ground state – where the electron is normallyGround state – where the electron is normally

• Excited state – where the electron is when it Excited state – where the electron is when it becomes excited (usually an energy level farther becomes excited (usually an energy level farther from the nucleus)from the nucleus)

• More unstableMore unstable

• More potential energyMore potential energy

Figure 10.12

Excitedstate

Photon(fluorescence)

Groundstate

PhotonChlorophyll

molecule

(a) Excitation of isolated chlorophyll molecule (b) Fluorescence

““Falling” electrons release energyFalling” electrons release energy

Figure 10.13a

(a) How a photosystem harvests light

PhotonPhotosystem STROMA

Light-harvestingcomplexes

Reaction-centercomplex

Primaryelectronacceptor

Transferof energy

Special pair ofchlorophyll amolecules

Pigmentmolecules

THYLAKOID SPACE(INTERIOR OF THYLAKOID)

PhotosystemsPhotosystems

There are two photsystems in plants:There are two photsystems in plants:

• Photosystem II (P680): reaction center Photosystem II (P680): reaction center chlorophyll a absorbs light at 680 nmchlorophyll a absorbs light at 680 nm

• Photosystem I (P700): reaction center Photosystem I (P700): reaction center chlorophyll a absorbs light at 700 nmchlorophyll a absorbs light at 700 nm

The Light ReactionsThe Light Reactions

• Sunlight used to make ATP and NADPH for the Sunlight used to make ATP and NADPH for the Calvin CycleCalvin Cycle

• Works by exciting electrons so that when they Works by exciting electrons so that when they “fall”:“fall”:

1. The energy can be captured to make ATP1. The energy can be captured to make ATP

2. The electrons can be placed on NADPH 2. The electrons can be placed on NADPH

Figure 10.14-1

Primaryacceptor

Pigmentmolecules

Photosystem II(PS II)

Linear Electron FlowLinear Electron Flow

Figure 10.14-2

Primaryacceptor

Pigmentmolecules

Linear Electron Flow (cont.)Linear Electron Flow (cont.)

Figure 10.14-3

Cytochromecomplex

Primaryacceptor

Pigmentmolecules

Electron transport chaine

Figure 10.14-4

Cytochromecomplex

Primaryacceptor

Pigmentmolecules

Photosystem I(PS I)

Electron transport chain

Figure 10.14-5

Cytochromecomplex

Primaryacceptor

Pigmentmolecules

Photosystem I(PS I)

Electron transport chain

Electron

transport

+ HNADP

reductase

Figure 10.15

Photosystem II Photosystem I

Millmakes

Figure 10.16

Photosystem I

Primaryacceptor

Cytochromecomplex

Primaryacceptor

reductase

Photosystem II

Cyclic Electron FlowCyclic Electron Flow

Figure 10.17Mitochondrion Chloroplast

MITOCHONDRIONSTRUCTURE

CHLOROPLASTSTRUCTURE

Intermembranespace

Innermembrane

Matrix

Thylakoidspace

Thylakoidmembrane

Stroma

Electrontransport

H Diffusion

ATPsynthase

ADP P iKey Higher [H ]

Lower [H ]

Figure 10.18

STROMA(low H concentration)

THYLAKOID SPACE(high H concentration)

Photosystem II

Cytochromecomplex Photosystem I

reductase

NADP + H

ToCalvinCycle

ATPsynthase

Thylakoidmembrane

4 H++2 H+

ADP+P i

Chemiosmosis (…again)Chemiosmosis (…again)

PhotophosphorylatiPhotophosphorylation vs. Oxidative on vs. Oxidative PhosphorylationPhosphorylation

How are they different?:How are they different?:

1.1. Source of the Source of the electronselectrons

Photo ________Photo ________

Oxi __________Oxi __________

2.2. Source of the energySource of the energy

Photo Photo ________________

Oxi Oxi ____________________

3.3. Fate of the electronsFate of the electrons

Photo ________Photo ________

Oxi __________Oxi __________

CALVINCYCLE

Output: G3P

The The Calvin Calvin CycleCycle

Figure 10.19-1Input

3 (Entering oneat a time)

Phase 1: Carbon fixation

Rubisco

Short-livedintermediate

3-Phosphoglycerate3 P P

Ribulose bisphosphate(RuBP)

Figure 10.19-2Input

Rubisco

3-Phosphoglycerate6

6 P P1,3-Bisphosphoglycerate

CalvinCycle

6 NADPH

6 NADP

Phase 2: Reduction

Glyceraldehyde 3-phosphate(G3P)

3 P PRibulose bisphosphate

(RuBP)

1 PG3P

(a sugar)Output

Glucose andother organiccompounds

Figure 10.19-3Input

Rubisco

3-Phosphoglycerate6

6 P P1,3-Bisphosphoglycerate

CalvinCycle

6 NADPH

6 NADP

Phase 2: Reduction

Glyceraldehyde 3-phosphate(G3P)

Phase 3:Regeneration ofthe CO2 acceptor(RuBP)

3 P PRibulose bisphosphate

(RuBP)

1 PG3P

(a sugar)Output

Glucose andother organiccompounds

Fig. 10-21

LightReactions:

Photosystem II Electron transport chain

Photosystem I Electron transport chain

RuBP 3-Phosphoglycerate

CalvinCycle

G3PATP

NADPHStarch(storage)

Sucrose (export)

Chloroplast

Figure 10.21

Sugarcane

Mesophyllcell

Bundle-sheathcell

C4 CO2

Organic acid

CalvinCycle

(a) Spatial separation of steps (b) Temporal separation of steps

Organic acid

CalvinCycle

Pineapple

CO2 incorporated(carbon fixation)

CO2 releasedto the Calvincycle

r Savin

Greenhouse EffectGreenhouse Effect

Sunlight

Radiant heattrapped by CO2

and other gases

Atmosphere

Some heatenergy escapesinto space

So what?So what?

Chapter 10: Photosynthesis

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