PHOTOSYNTHESIPHOTOSYNTHESISS

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Autotrouphs

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PhotosynthesisPhotosynthesis• AnabolicAnabolic (small molecules combined) (small molecules combined)• EndergonicEndergonic (stores energy) (stores energy)• Carbon dioxide (COCarbon dioxide (CO22)) requiring requiring

process that uses process that uses light energy light energy (photons)(photons) and and water (Hwater (H22O)O) to produce to produce organic macromolecules (glucose).organic macromolecules (glucose).

6CO2 + 6H2O C6H12O6 + 6O2

glucoseglucose

SUNphotonsphotons

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Question:Question:

Where does Where does photosynthesiphotosynthesis take place?s take place?

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PlantsPlants• Autotrophs Autotrophs – produce their own – produce their own

food food (glucose)(glucose)• Process called Process called photosynthesisphotosynthesis• Mainly occurs in the Mainly occurs in the leaves:leaves:

a.a.stoma - poresstoma - pores

b.b.mesophyll cellsmesophyll cells

StomaMesophyllCell

Chloroplast

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Stomata (stoma)Stomata (stoma)PoresPores in a plant’s cuticle in a plant’s cuticle

through which through which water vaporwater vapor and and gasesgases (CO(CO22 & O & O22)) are are exchanged between the plant exchanged between the plant and the atmosphere.and the atmosphere.

Guard CellGuard CellCarbon Dioxide (CO2)

Oxygen (O2)

Found on the underside of Found on the underside of leavesleaves

StomStomaa

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Question:Question:

Why are Why are plants plants green?green?

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Chlorophyll MoleculesChlorophyll Molecules

• Located in the Located in the thylakoid membranesthylakoid membranes• Chlorophyll have Chlorophyll have MgMg++ in the center in the center• Chlorophyll pigments Chlorophyll pigments harvest energy harvest energy

(photons)(photons) by absorbing certain by absorbing certain wavelengths wavelengths (blue-420 nm and red-(blue-420 nm and red-660 nm660 nm are most important) are most important)

• Plants are Plants are greengreen because the because the green green wavelength is reflectedwavelength is reflected, not absorbed, not absorbed.

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Wavelength of Light (nm)Wavelength of Light (nm)

400 500 600 700

Short wave Long wave(more energy) (less energy)

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Absorption of Light by Absorption of Light by ChlorophyllChlorophyll

wavelengthwavelength

Absorption

violet blue green yellow orange red

Chlorophyll absorbs blue-violet & red Chlorophyll absorbs blue-violet & red light bestlight best

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Question:Question:

During the fall, During the fall, what causes what causes the leaves to the leaves to

change colors?change colors?

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Fall ColorsFall Colors• In addition to the chlorophyll In addition to the chlorophyll

pigments, there are pigments, there are other other pigmentspigments present present

• During the fall, the During the fall, the green green chlorophyll pigments are chlorophyll pigments are greatly reducedgreatly reduced revealing the revealing the other pigmentsother pigments

• CarotenoidsCarotenoids are pigments that are pigments that are either are either redred, , orangeorange, or , or yellowyellow

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Redox ReactionRedox Reaction

The The transfertransfer of one or more of one or more electronselectrons from one reactant from one reactant to anotherto another

Two types:Two types:

1.1. Oxidation is the Oxidation is the lossloss of e of e--

2.2. Reduction is the Reduction is the gaingain of of ee--

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Question:Question:

Why do Why do cells use cells use

for for energy?energy?

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Energy for Life on EarthEnergy for Life on Earth

•Sunlight is the ULTIMATE energy for all life on Earth

•Plants store energy in the chemical bonds of sugars

•Chemical energy is released as ATP during cellular respiration

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Structure of ATPStructure of ATP

• ATP stands for adenosine triphosphate

• It is composed of the nitrogen base ADENINE, the pentose (5C) sugar RIBOSE, and three PHOSPHATE groups

• The LAST phosphate group is bonded with a HIGH ENERGY chemical bond

• This bond can be BROKEN to release ENERGY for CELLS to use

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Removing a Phosphate from Removing a Phosphate from ATPATP

Breaking the LAST PHOSPHATE bond from ATP, will ---– Release ENERGY for cells to use– Form ADP– Produce a FREE PHOSPHATE

GROUP

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High Energy Phosphate High Energy Phosphate BondBond

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FREE PHOSPHATE can be re-FREE PHOSPHATE can be re-attached to ADP reforming ATPattached to ADP reforming ATP

Process called Process called PhosphorylationPhosphorylation

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PhosphorylationPhosphorylation

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Parts of Parts of PhotosynthesisPhotosynthesis

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Two Parts of Two Parts of PhotosynthesisPhotosynthesis

Two reactions make up Two reactions make up photosynthesis:photosynthesis:

1.1.Light Reaction or Light Light Reaction or Light Dependent ReactionDependent Reaction - -

Produces energy from solar Produces energy from solar power (photons) in the form power (photons) in the form of ATP and NADPH.of ATP and NADPH.

SUNSUN

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Two Parts of Two Parts of PhotosynthesisPhotosynthesis

2. 2. Calvin Cycle or Light Calvin Cycle or Light Independent Independent ReactionReaction

• Also called Also called Carbon Carbon FixationFixation or or CC33 Fixation Fixation

• Uses energy (Uses energy (ATP and ATP and NADPHNADPH) from light ) from light reaction to make sugar reaction to make sugar (glucose).(glucose).

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Photosynthesis Overview

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Light Reaction (Electron Light Reaction (Electron Flow)Flow)

• Occurs in the Occurs in the Thylakoid Thylakoid membranesmembranes

• During the During the light reactionlight reaction, , there are there are twotwo possible routes possible routes for electron flow:for electron flow:

A.A. Cyclic Electron FlowCyclic Electron Flow

B.B. Noncyclic Electron FlowNoncyclic Electron Flow

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Energy CarriersEnergy Carriers

• Nicotinamide Adenine Dinucleotide Nicotinamide Adenine Dinucleotide Phosphate Phosphate (NADP(NADP++))

• NADPNADP+ = + = OxidizedOxidized Form (Empty, Form (Empty, needs e-)needs e-)

• Picks Up Picks Up 2 high-energy electrons 2 high-energy electrons and Hand H++ from the Light Reaction to from the Light Reaction to form NADPH (Full)form NADPH (Full)

• NADPHNADPH carries energy to be carries energy to be passed on to another moleculepassed on to another molecule

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NADPHNADPH

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• Occurs across the Occurs across the thylakoid thylakoid membranesmembranes

• Uses light energyUses light energy• Produce Produce OxygenOxygen from water from water• Convert Convert ADP to ATP (ATP ADP to ATP (ATP

Synthease)Synthease)

Also convert NADPAlso convert NADP++ into the into the

energyenergy carrier carrier NADPH (NADP+ NADPH (NADP+ Reductase)Reductase)

Light Dependent Light Dependent ReactionsReactions

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Light Reactions

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ChemiosmosisChemiosmosis

• Powers Powers ATP synthesisATP synthesis• Takes place across the Takes place across the

thylakoid membranethylakoid membrane• Uses Uses ETCETC and and ATP synthase ATP synthase

(enzyme)(enzyme)• H+H+ move down their move down their

concentration gradient through concentration gradient through channels of ATP synthasechannels of ATP synthase forming forming ATP from ADPATP from ADP

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ChemiosmosisChemiosmosis

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Calvin CycleCalvin Cycle• Carbon Fixation Carbon Fixation (light independent (light independent

reaction)reaction)• CC33 plants (80% of plants on earth) plants (80% of plants on earth)• Occurs in the Occurs in the stromastroma• Uses Uses ATP and NADPHATP and NADPH from light from light

reaction as energyreaction as energy• Uses Uses COCO22

• To produce To produce glucoseglucose: it takes : it takes 6 6 turns and uses 18 ATP and 12 turns and uses 18 ATP and 12 NADPH. NADPH.

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Calvin Cycle (CCalvin Cycle (C33 fixation) fixation)

6CO2

6C-C-C-C-C-C

6C-C-C 6C-C-C

6C-C-C-C-C

12PGA

RuBP

12G3P

(unstable)

6NADPH 6NADPH

6ATP 6ATP

6ATP

C-C-C-C-C-CGlucose

(6C)(36C)

(36C)

(36C)

(30C)

(30C)

(6C)

6C-C-C 6C-C-C

C3

glucose

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PhotorespirationPhotorespiration

• Occurs on hot, dry, bright daysOccurs on hot, dry, bright days• Stomates closeStomates close

• Fixation of OFixation of O22 instead of CO instead of CO22

• Produces Produces 2-C molecules 2-C molecules instead of 3-C sugar moleculesinstead of 3-C sugar molecules

• Produces Produces no sugarno sugar molecules molecules or or no ATPno ATP

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PhotorespirationPhotorespiration

Because of photorespiration, Because of photorespiration, plants have special plants have special adaptations to limit the effect adaptations to limit the effect of photorespiration:of photorespiration:

1.1. CC44 plants plants

2.2. CAM plantsCAM plants

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CC44 Plants Plants• Hot, moist Hot, moist

environmentsenvironments• 15% of plants 15% of plants

((grasses, corn, grasses, corn, sugarcane)sugarcane)

• Photosynthesis Photosynthesis occurs in 2 placesoccurs in 2 places

• Light reactionLight reaction - - mesophyll cellsmesophyll cells

• Calvin cycleCalvin cycle - - bundle sheath bundle sheath cellscells

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CAM PlantsCAM Plants• Hot, dry environmentsHot, dry environments• 5%5% of plants (cactus and ice of plants (cactus and ice

plants)plants)• Stomates closed during dayStomates closed during day• Stomates open during the nightStomates open during the night• Light reaction - occurs during Light reaction - occurs during

the daythe day• Calvin Cycle - occurs when COCalvin Cycle - occurs when CO22

is presentis present

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Question:Question:

Why do CAM Why do CAM plants close plants close

their stomata their stomata during the day?during the day?

Cam plants Cam plants close their close their

stomata in the stomata in the hottest part hottest part of the day to of the day to

conserve conserve waterwater