The Energy The Energy Conversion ProcessConversion Processof Photosynthesisof Photosynthesis

Chloroplasts: The Sites of Chloroplasts: The Sites of Photosynthesis in PlantsPhotosynthesis in Plants

Leaves are the major locations of Leaves are the major locations of photosynthesisphotosynthesis

Their green color is from Their green color is from chlorophyllchlorophyll, the , the green pigment within chloroplastsgreen pigment within chloroplasts

Light energy absorbed by chlorophyll drives Light energy absorbed by chlorophyll drives the synthesis of organic molecules in the the synthesis of organic molecules in the chloroplastchloroplast

COCO22 enters and O enters and O22 exits the leaf through exits the leaf through

microscopic pores called microscopic pores called stomatastomata

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Chloroplasts are found mainly in cells of the Chloroplasts are found mainly in cells of the mesophyllmesophyll, the interior tissue of the leaf, the interior tissue of the leaf

A typical mesophyll cell has 30–40 A typical mesophyll cell has 30–40 chloroplastschloroplasts

The chlorophyll is in the membranes of The chlorophyll is in the membranes of thylakoids thylakoids (connected sacs in the (connected sacs in the chloroplast); thylakoids may be stacked in chloroplast); thylakoids may be stacked in columns called columns called granagrana

Chloroplasts also contain Chloroplasts also contain stromastroma, a dense , a dense fluid fluid

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Fig. 10-3Fig. 10-3Leaf cross section

Vein

Mesophyll

StomataCO2 O2

ChloroplastMesophyll cell

Outermembrane

Intermembranespace

5 µm

Innermembrane

Thylakoidspace

Thylakoid

GranumStroma

1 µm

Fig. 10-3aFig. 10-3a

5 µm

Mesophyll cell

StomataCO2 O2

Chloroplast

Mesophyll

Vein

Leaf cross section

Fig. 10-3bFig. 10-3b

1 µm

Thylakoidspace

Chloroplast

GranumIntermembranespace

Innermembrane

Outermembrane

Stroma

Thylakoid

Photosynthesis Photosynthesis

PhotosynthesisPhotosynthesis- - Converting solar energy into the usable Converting solar energy into the usable

energy of carbohydrates.energy of carbohydrates. Photosynthesis requiresPhotosynthesis requires: :

Light EnergyLight Energy Carbon DioxideCarbon Dioxide Water Water ChlorophyllChlorophyll

Putting together with light

Chloroplasts split HChloroplasts split H22O into hydrogen and oxygen, incorporating the electrons of hydrogen into sugar molecules. O into hydrogen and oxygen, incorporating the electrons of hydrogen into sugar molecules.

Photosynthesis consists of the Photosynthesis consists of the light reactions light reactions (the (the photophoto part) and part) and Calvin cycle Calvin cycle (the (the synthesissynthesis part) part) The light reactions (in the thylakoids):The light reactions (in the thylakoids):

Split HSplit H22OO

Release ORelease O22

Reduce Reduce NADPNADP++ to NADPH to NADPH Generate ATP from ADP by Generate ATP from ADP by photophosphorylationphotophosphorylation

Light EnergyLight Energy

PhotonPhoton- packets of Energy- packets of Energy Light travels in waves and is a type of Light travels in waves and is a type of

radiationradiation Short wave length radiation has high Short wave length radiation has high

energy photonsenergy photons Long wave length radiation has lower Long wave length radiation has lower

energy photons energy photons

Light EnergyLight Energy

Photons of visible light have enough Photons of visible light have enough energy to raise electrons to higher levels energy to raise electrons to higher levels of energy which is needed for of energy which is needed for photosynthesis.photosynthesis.

Visible light energy is absorbed by plants Visible light energy is absorbed by plants to produce sugar. (Cto produce sugar. (C66HH1212OO66) )

Chlorophyll is the substance that absorbs Chlorophyll is the substance that absorbs light energy.light energy.

Pop QuizPop Quiz 1. In your own words, define photosynthesis1. In your own words, define photosynthesis 2. In your own words, define cellular 2. In your own words, define cellular

respiration.respiration. 3. What is ATP3. What is ATP 4. How is ATP generated or made?4. How is ATP generated or made? 5. Which bond in ATP is loaded with energy?5. Which bond in ATP is loaded with energy?

Chlorophyll (borophyll)Chlorophyll (borophyll)

Two Types of ChlorophyllTwo Types of Chlorophyll Chlorophyll AChlorophyll A Chlorophyll BChlorophyll B

CarotenoidsCarotenoids Other pigments that are yellow-orange in plants Other pigments that are yellow-orange in plants

which absorb violets, blues, and greens.which absorb violets, blues, and greens.

As chlorophyll A and B breakdown they become more As chlorophyll A and B breakdown they become more noticeable, especially during the fall.noticeable, especially during the fall.

Both absorb violet, blue, and red light. Because green is only minimally absorbed, the leaf appears green. The green light is reflected off of the leaf.

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Photosynthesis- Photosynthesis- the formulathe formula

6 CO6 CO22 + 6 H + 6 H22O O C C66HH1212OO66 + 6 O + 6 O22

LIGHT

CHLOROPHYLL

Light

Fig. 10-5-1Fig. 10-5-1

H2O

Chloroplast

LightReactions

NADP+

P

ADP

i+

Light

Fig. 10-5-2Fig. 10-5-2

H2O

Chloroplast

LightReactions

NADP+

P

ADP

i+

ATP

NADPH

O2

Light

Fig. 10-5-3Fig. 10-5-3

H2O

Chloroplast

LightReactions

NADP+

P

ADP

i+

ATP

NADPH

O2

CalvinCycle

CO2

Chloroplasts Chloroplasts –– contain contain chlorophyllchlorophyll

Chloroplasts are double membrane Chloroplasts are double membrane organelles. (See figure in book)organelles. (See figure in book) Note the granum, stroma, thylakoid, and Note the granum, stroma, thylakoid, and

thylakoid spacethylakoid space

Chlorophyll is found within the Chlorophyll is found within the membranes of the thylakoidsmembranes of the thylakoids

Photosynthesis has two Photosynthesis has two reactionsreactions

Light dependent Reactions (light RXN)Light dependent Reactions (light RXN) Light capturing reaction Light capturing reaction absorbs solar energyabsorbs solar energy Occurs in the thylakoid membraneOccurs in the thylakoid membrane

Light independent Reactions (dark RXN) Light independent Reactions (dark RXN) Now called the Calvin CycleNow called the Calvin Cycle Synthesis reactionSynthesis reaction Produces glucoseProduces glucose Occurs in the stromaOccurs in the stroma

Light Dependent ReactionsLight Dependent Reactions

Takes place in the thylakoid membraneTakes place in the thylakoid membrane Requires two light gathering systemsRequires two light gathering systems

PhotosystemsPhotosystems- systems used to gather solar energy - systems used to gather solar energy which contain chlorophyll A,B, and carotenoids.which contain chlorophyll A,B, and carotenoids.

The photosystems were named in the order that The photosystems were named in the order that they were discovered, not the order in which they they were discovered, not the order in which they occur.occur. Photosystem IPhotosystem I (PSI) (PSI) The molecules of The molecules of

Chlorophyll a & b Chlorophyll a & b which which make up make up the photosystems the photosystems Photosystem IIPhotosystem II (PSII) (PSII) act like act like antennas gathering antennas gathering solar solar energy and focus it to energy and focus it to a a particular spot. particular spot.

}

Light

Fig. 10-5-4Fig. 10-5-4

H2O

Chloroplast

LightReactions

NADP+

P

ADP

i+

ATP

NADPH

O2

CalvinCycle

CO2

[CH2O]

(sugar)

PSI and PSIIPSI and PSII

Basically, the function of the photosystems is Basically, the function of the photosystems is to convert energy so that glucose can be to convert energy so that glucose can be produced. This is accomplished by generating produced. This is accomplished by generating electron flow.electron flow.

Sometimes PSI occurs exclusively called the Sometimes PSI occurs exclusively called the cyclic electron pathwaycyclic electron pathway..

When both PSI and PSII occur PSII occurs first When both PSI and PSII occur PSII occurs first and then PSI. This process is the and then PSI. This process is the non-cyclic non-cyclic electron pathwayelectron pathway. .

Generating electron flowGenerating electron flow

Energy is directed onto a particular Energy is directed onto a particular molecule of chlorophyll A . The electrons molecule of chlorophyll A . The electrons of this molecule are so excited that they of this molecule are so excited that they escape their orbitals and move through a escape their orbitals and move through a series of electron acceptors.series of electron acceptors.

Reaction centerReaction center- The molecule of - The molecule of chlorophyll A that loses an electron. chlorophyll A that loses an electron.

Fig. 10-12Fig. 10-12

THYLAKOID SPACE(INTERIOR OF THYLAKOID)

STROMA

e–

Pigmentmolecules

Photon

Transferof energy

Special pair ofchlorophyll amolecules

Th

yla

koid

me

mb

ran

e

Photosystem

Primaryelectronacceptor

Reaction-centercomplex

Light-harvestingcomplexes

Cyclic Electron Pathway Cyclic Electron Pathway (PS1) ((PS1) (not play station 1not play station 1))

An electron leaves the RXN center but An electron leaves the RXN center but eventually returns to it.eventually returns to it.

As the electron is passed from acceptor As the electron is passed from acceptor to acceptor Energy for ATP is released.to acceptor Energy for ATP is released.

Occurs when:Occurs when: COCO22 levels are extremely low levels are extremely low

by photosynthetic bacteriaby photosynthetic bacteria

Cyclic pathway – PS1 Cyclic pathway – PS1 ((cont.cont.))

Does not produce NADPH Does not produce NADPH Produces ONLY ATPProduces ONLY ATP Probably first to evolve, Probably first to evolve, Because COBecause CO22 levels are low no glucose levels are low no glucose

is produced and the organism must is produced and the organism must survive on the small amount of ATP that survive on the small amount of ATP that is generatedis generated

Non-cyclic Pathway (PS Non-cyclic Pathway (PS 2) 2) (not play station 2)(not play station 2)

Water is split and an electron enters PSIIWater is split and an electron enters PSII Causes the reaction center to lose an electron Causes the reaction center to lose an electron

and travel through a series of electron and travel through a series of electron acceptors.acceptors.

As the electron is passed along ATP is As the electron is passed along ATP is generated. This ATP will be used in the Light generated. This ATP will be used in the Light independent reactionsindependent reactions

The electron then enters PSI which during the The electron then enters PSI which during the non-cyclic pathway produces the molecule non-cyclic pathway produces the molecule NADPH instead of ATP.NADPH instead of ATP.

Non-cyclic (cont.)Non-cyclic (cont.)

The products of the non-cyclic pathway, The products of the non-cyclic pathway, NADPH and ATP, enter the StromaNADPH and ATP, enter the Stroma NADP is one of several biological molecules that act NADP is one of several biological molecules that act

as an electron carrier. as an electron carrier.

In the stroma, the light independent reactions In the stroma, the light independent reactions occur.occur.

The splitting of water results in a H ion (which The splitting of water results in a H ion (which is basically an electron) and O which is is basically an electron) and O which is released from the leaf as a waste product.released from the leaf as a waste product.

Pigmentmolecules

Light

P680

e–

Primaryacceptor

2

1

e–

e–

2 H+

O2

+3

H2O

1/2

4

Pq

Pc

Cytochromecomplex

Electron transport chain

5

ATP

Photosystem I(PS I)

Light

Primaryacceptor

e–

P700

6

Fd

Electron transport chain

NADP+

reductase

NADP+

+ H+

NADPH

8

7

e–

e–

6

Fig. 10-13-5Fig. 10-13-5

Photosystem II(PS II)

Fig. 10-21Fig. 10-21

LightReactions:

Photosystem II Electron transport chain

Photosystem I Electron transport chain

CO2

NADP+

ADP

P i+

RuBP 3-Phosphoglycerate

CalvinCycle

G3PATP

NADPHStarch(storage)

Sucrose (export)

Chloroplast

Light

H2O

O2

PhotophosphorylationPhotophosphorylation

Occurs when ATP is generated using Occurs when ATP is generated using photosynthesis. photosynthesis.

Photophosphorylation occurs because of Photophosphorylation occurs because of severe differences in the concentration of severe differences in the concentration of H+ ions inside the thylakoid space H+ ions inside the thylakoid space compared to the stroma.compared to the stroma.

The movement of ions allows for a The movement of ions allows for a phosphate to be added to ADP. phosphate to be added to ADP.

Diagram of the Light Dependent Reactions and ATP Synthase

QuizQuiz

1. How is the cyclic pathway different than the 1. How is the cyclic pathway different than the non-cyclic pathway?non-cyclic pathway?

2. In the non-cyclic pathway, what produces 2. In the non-cyclic pathway, what produces ATP?ATP?

3. In the non-cyclic pathway, what produces 3. In the non-cyclic pathway, what produces NADPH?NADPH?

4. What is the role of NADPH?4. What is the role of NADPH?

Light Independent Light Independent Reactions AKA- Calvin Cycle Reactions AKA- Calvin Cycle (The Dark RXN)(The Dark RXN)

The products of the light dependent The products of the light dependent reactions are NADPH and ATP.reactions are NADPH and ATP.

Both are used in the light independent Both are used in the light independent reactions.reactions.

The actual process of producing glucose The actual process of producing glucose during the light independent RXN is during the light independent RXN is called the called the Calvin Cycle.Calvin Cycle.

A Comparison of Chemiosmosis in A Comparison of Chemiosmosis in Chloroplasts and MitochondriaChloroplasts and Mitochondria

Chloroplasts and mitochondria generate ATP by Chloroplasts and mitochondria generate ATP by chemiosmosis, but use different sources of energychemiosmosis, but use different sources of energy

Mitochondria transfer chemical energy from food Mitochondria transfer chemical energy from food to ATP; chloroplasts transform light energy into the to ATP; chloroplasts transform light energy into the chemical energy of ATPchemical energy of ATP

Spatial organization of chemiosmosis differs Spatial organization of chemiosmosis differs between chloroplasts and mitochondria but also between chloroplasts and mitochondria but also shows similaritiesshows similarities

In mitochondria, protons are pumped to the In mitochondria, protons are pumped to the intermembrane space and drive ATP intermembrane space and drive ATP synthesis as they diffuse back into the synthesis as they diffuse back into the mitochondrial matrixmitochondrial matrix

In chloroplasts, protons are pumped into the In chloroplasts, protons are pumped into the thylakoid space and drive ATP synthesis as thylakoid space and drive ATP synthesis as they diffuse back into the stromathey diffuse back into the stroma

Fig. 10-16Fig. 10-16

Key

Mitochondrion Chloroplast

CHLOROPLASTSTRUCTURE

MITOCHONDRIONSTRUCTURE

Intermembranespace

Innermembrane

Electrontransport

chain

H+ Diffusion

Matrix

Higher [H+]Lower [H+]

Stroma

ATPsynthase

ADP + P i

H+ATP

Thylakoidspace

Thylakoidmembrane

In summary, light reactions generate ATP In summary, light reactions generate ATP and increase the potential energy of and increase the potential energy of electrons by moving them from Helectrons by moving them from H22O to O to

NADPHNADPH

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The Calvin CycleThe Calvin Cycle (light independent reactions)(light independent reactions)

Has three steps/parts (see fig)Has three steps/parts (see fig)

1. CO1. CO22 fixation fixation

2. CO2. CO2 2 reduction reduction

3. Regeneration of RuBP3. Regeneration of RuBP RuBP is a 5 carbon compound that will RuBP is a 5 carbon compound that will

combine with COcombine with CO2 2 to form a 6 Carbon to form a 6 Carbon

Compound. Compound. Remember, glucose is a 6 C compound Remember, glucose is a 6 C compound

Step 1- COStep 1- CO22 Fixation Fixation

Refers to the attachment of CORefers to the attachment of CO22 to an organic to an organic

compound. compound. 3 CO3 CO2 2 bind with 3 RuBP molecules. bind with 3 RuBP molecules.

Results in 3 six Carbon compoundsResults in 3 six Carbon compounds which change to 6 three carbon compoundswhich change to 6 three carbon compounds

The three Carbon compound is called PGAThe three Carbon compound is called PGA The Calvin Cycle is sometimes called the C-3 The Calvin Cycle is sometimes called the C-3

cycle because of PGA.cycle because of PGA.

Fig. 10-18-1Fig. 10-18-1

Ribulose bisphosphate(RuBP)

3-Phosphoglycerate

Short-livedintermediate

Phase 1: Carbon fixation

(Entering oneat a time)

Rubisco

Input

CO2

P

3 6

3

3

P

PPP

Step 2 - COStep 2 - CO22 Reduction Reduction Requires ATP and NADPH (from light RXN)Requires ATP and NADPH (from light RXN) PGA gets converted to G3P (PGAL) using ATP PGA gets converted to G3P (PGAL) using ATP

and NADPH.and NADPH. ATP ATP ADP + P ADP + P NADPH NADPH NADP NADP PGA PGA G3P (PGAL) G3P (PGAL)

The reduction of COThe reduction of CO22 to CH to CH22O results in 6 total O results in 6 total PGAL molecules.PGAL molecules.

5 molecules of G3P (PGAL) will be used to 5 molecules of G3P (PGAL) will be used to regenerate RuBP.regenerate RuBP.

It takes 3 turns of the Calvin Cycle to have a It takes 3 turns of the Calvin Cycle to have a net gain of 1 G3P (PGAL)net gain of 1 G3P (PGAL)

Fig. 10-18-2Fig. 10-18-2

Ribulose bisphosphate(RuBP)

3-Phosphoglycerate

Short-livedintermediate

Phase 1: Carbon fixation

(Entering oneat a time)

Rubisco

Input

CO2

P

3 6

3

3

P

PPP

ATP6

6 ADP

P P6

1,3-Bisphosphoglycerate

6

P

P6

66 NADP+

NADPH

i

Phase 2:Reduction

Glyceraldehyde-3-phosphate(G3P)

1 POutput G3P

(a sugar)

Glucose andother organiccompounds

CalvinCycle

G3P G3P (PGAL)(PGAL) Glucose Glucose

Glucose is used to produce ATPGlucose is used to produce ATP Plants need several other organic Plants need several other organic

compounds.compounds. G3P (PGAL) can be converted to many G3P (PGAL) can be converted to many

other compounds such as: fatty acids, other compounds such as: fatty acids, Amino Acids, and of course Glucose.Amino Acids, and of course Glucose.

Technically, the Calvin cycle ends with Technically, the Calvin cycle ends with the production of G3P (PGAL)the production of G3P (PGAL)

Step 3 - RuBP Step 3 - RuBP RegenerationRegeneration

5 (PGAL) G3P5 (PGAL) G3P 3 RuBP 3 RuBP 3 ATP 3 ATP 3 ADP + P 3 ADP + P ATP comes from the light dependent ATP comes from the light dependent

reactions reactions

Fig. 10-18-3Fig. 10-18-3

Ribulose bisphosphate(RuBP)

3-Phosphoglycerate

Short-livedintermediate

Phase 1: Carbon fixation

(Entering oneat a time)

Rubisco

Input

CO2

P

3 6

3

3

P

PPP

ATP6

6 ADP

P P6

1,3-Bisphosphoglycerate

6

P

P6

66 NADP+

NADPH

i

Phase 2:Reduction

Glyceraldehyde-3-phosphate(G3P)

1 POutput G3P

(a sugar)

Glucose andother organiccompounds

CalvinCycle

3

3 ADP

ATP

5 P

Phase 3:Regeneration ofthe CO2 acceptor(RuBP)

G3P

Fig. 10-21Fig. 10-21

LightReactions:

Photosystem II Electron transport chain

Photosystem I Electron transport chain

CO2

NADP+

ADP

P i+

RuBP 3-Phosphoglycerate

CalvinCycle

G3PATP

NADPHStarch(storage)

Sucrose (export)

Chloroplast

Light

H2O

O2

Variations in Variations in PhotosynthesisPhotosynthesis

The C-3 Pathway – The C-3 Pathway – COCO22 is fixed during the Calvin cycle, and the first is fixed during the Calvin cycle, and the first

detectable molecule is a 3 Carbon compound detectable molecule is a 3 Carbon compound (PGA).(PGA).

The C-4 Pathway – The C-4 Pathway – COCO2 2 is fixed to a 3 C compound (forming a 4 C is fixed to a 3 C compound (forming a 4 C

compound) prior to the Calvin Cycle.compound) prior to the Calvin Cycle. CAM Plant Pathway – CAM Plant Pathway –

Similar to the C- 4 Pathway, but at a slightly Similar to the C- 4 Pathway, but at a slightly different time.different time.

C-3 PathwayC-3 Pathway

Occurs in the mesophyll of the leafOccurs in the mesophyll of the leaf RuBP RuBP PGA PGA P3G (PGAL) P3G (PGAL) See Figure 10-18. See Figure 10-18.

C-4 PathwayC-4 Pathway

COCO22 is attached to a 3 C compound called PEP is attached to a 3 C compound called PEP with an enzyme called PEP-carboxylase.with an enzyme called PEP-carboxylase.

This process forms oxaloacetate and occurs in This process forms oxaloacetate and occurs in the mesophyll.the mesophyll.

Oxaloacetate enters the bundle sheath cells Oxaloacetate enters the bundle sheath cells where the Calvin Cycle takes placewhere the Calvin Cycle takes place

Occurs in warm dry climatesOccurs in warm dry climates Partition PSS in spacePartition PSS in space See Figure 10.14See Figure 10.14

Fig. 10-19bFig. 10-19b

Sugar

CO2

Bundle-sheathcell

ATP

ADP

Oxaloacetate (4C) PEP (3C)

PEP carboxylase

Malate (4C)

Mesophyllcell

CO2

CalvinCycle

Pyruvate (3C)

Vasculartissue

The C4

pathway

CAM plant PathwayCAM plant Pathway

A C4 compound is produced similar to the C-4 A C4 compound is produced similar to the C-4 pathway.pathway.

That compound is produced during the night, That compound is produced during the night, and stored in the vacuole until day.and stored in the vacuole until day.

Occurs in the mesophyllOccurs in the mesophyll Occurs in hot, dry and stressful environmentsOccurs in hot, dry and stressful environments Allows Stomates to open at night when it is Allows Stomates to open at night when it is

cooler and less water is lost to evaporation.cooler and less water is lost to evaporation.

Fig. 10-20Fig. 10-20

CO2

Sugarcane

Mesophyllcell

CO2

C4

Bundle-sheathcell

Organic acidsrelease CO2 to Calvin cycle

CO2 incorporatedinto four-carbonorganic acids(carbon fixation)

Pineapple

Night

Day

CAM

SugarSugar

CalvinCycle

CalvinCycle

Organic acid Organic acid

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

CO2 CO2

1

2

The Importance of Photosynthesis: The Importance of Photosynthesis: A ReviewA Review

The energy entering chloroplasts as sunlight gets The energy entering chloroplasts as sunlight gets stored as chemical energy in organic compoundsstored as chemical energy in organic compounds

Sugar made in the chloroplasts supplies chemical Sugar made in the chloroplasts supplies chemical energy and carbon skeletons to synthesize the energy and carbon skeletons to synthesize the organic molecules of cellsorganic molecules of cells

Plants store excess sugar as starch in structures Plants store excess sugar as starch in structures such as roots, tubers, seeds, and fruitssuch as roots, tubers, seeds, and fruits

In addition to food production, photosynthesis In addition to food production, photosynthesis produces the Oproduces the O22 in our atmosphere in our atmosphere