PHOTOSYNTHESISPHOTOSYNTHESIS

6.16.1

The main form of energy from the sun is in the form of electromagnetic radiation

Visible radiation (white light) used for photosynthesis

Remember : Remember : ROY G. BIV?ROY G. BIV?

The electromagnetic spectrum

A Red Object absorbs the blue and green wavelengths and reflects the red wavelengthsA Red Object absorbs the blue and green wavelengths and reflects the red wavelengths

Why are Why are plants plants green?green?

pigment a compound that absorbs light different pigments absorb different wavelengths of white

light.

chlorophyll is a pigment that absorbs red & blue light (photons) so green is reflected or transmitted.

Chlorophyll is located in the Chlorophyll is located in the thylakoid thylakoid membranesmembranes

So, So, Plants are green because the green wavelength Plants are green because the green wavelength is reflected, not absorbed.is reflected, not absorbed.

2 types of chlorophyll2 types of chlorophyll Chlorophyll Chlorophyll aa – involved in – involved in light reactionslight reactions

Chlorophyll Chlorophyll bb – assists in capturing light – assists in capturing light energy – energy – accessory pigmentaccessory pigment

CarotenoidsCarotenoids – accessory pigments – – accessory pigments – captures more light energy captures more light energy RedRed,, orange orange & & yellowyellow

The electromagnetic wavelengths and the The electromagnetic wavelengths and the wavelengths that are absorbed by the wavelengths that are absorbed by the chlorophyllchlorophyll

During the fall, what During the fall, what causes the leaves causes the leaves to change colors?to change colors?

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 greatly chlorophyll pigments are greatly reducedreduced revealing the other revealing the other pigmentspigments

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

Photosynthesis is - Photosynthesis is -

conversion of light energy into chemical conversion of light energy into chemical energy that is stored in organic compounds energy that is stored in organic compounds (carbohydrates > glucose)(carbohydrates > glucose)

Used by autotrophs such as:Used by autotrophs such as: PlantsPlants AlgaeAlgae Some bacteria (prokaryotes) Some bacteria (prokaryotes)

glucose - energy-rich chemical produced through photosynthesis C6H12O6

Biochemical pathwayBiochemical pathway – series of reactions – series of reactions where the product of one reaction is where the product of one reaction is consumed in the nextconsumed in the next

E.g. photosynthesis product is glucose which is E.g. photosynthesis product is glucose which is used in cellular respiration to make ATPused in cellular respiration to make ATP

(carbohydrate)

Photosynthesis equation

Light energy

6CO2 + 6H2O C6H12O6 + 6O2

Chlorophyll

Reactants: Carbon dioxide and water

Products: : glucose and oxygen which is a glucose and oxygen which is a byproductbyproduct

Where does Where does photosynthesis photosynthesis

take place?take place?

PlantsPlants Mainly occurs in the Mainly occurs in the leaves:leaves:

a.a.stoma - poresstoma - pores

b.b.mesophyll cellsmesophyll cells

StomaMesophyllCell

Chloroplast

Mesophyll Cell of LeafMesophyll Cell of Leaf

Cell WallNucleusNucleus

Chloroplast

Central Vacuole

Photosynthesis occurs in these Photosynthesis occurs in these cells!cells!

Stomata (stoma)Stomata (stoma)Pores in a plant’s cuticle through Pores in a plant’s cuticle through

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

Guard CellGuard CellCarbon Dioxide (CO2)

Oxygen (O2)

Found on the underside of Found on the underside of leavesleaves

StomStomaa

ChloroplastChloroplast

OrganelleOrganelle where where photosynthesisphotosynthesis takes takes place.place.

GranumThylakoid

Stroma

Outer Membrane

Inner Membrane

Thylakoid stacks are connected Thylakoid stacks are connected togethertogether

PartsPartschloroplastschloroplasts – dbl membrane organelle that – dbl membrane organelle that

absorbs light energyabsorbs light energyThylakoidsThylakoids – flattened sacs contain pigment - – flattened sacs contain pigment -

chlorophyllchlorophyllGranaGrana ( (pl: pl: granum) – layered thylakoids (like granum) – layered thylakoids (like

pancakes)pancakes)StromaStroma – solution around thylakoids – solution around thylakoidsStomataStomata – pore on underside of leaf where O – pore on underside of leaf where O22 is is

released and COreleased and CO22 enters enters

Stroma : chloroplast :: cytosol : cytoplasm

ThylakoidThylakoid

Thylakoid Membrane

Thylakoid SpaceGranum

Grana make up the inner Grana make up the inner membranemembrane

What do What do cells use cells use

for energy?for energy?

Energy for Life on EarthEnergy for Life on Earth

Sunlight Sunlight is the ULTIMATE is the ULTIMATE energy for all life on Earthenergy for all life on Earth

Plants store energy in the Plants store energy in the chemical bonds of sugarschemical bonds of sugars

Chemical energy is released Chemical energy is released as as ATPATP during during cellular cellular respirationrespiration

Structure of ATPStructure of ATP ATPATP stands for stands for adenosine adenosine

triphosphatetriphosphate It is composed of the nitrogen It is composed of the nitrogen

base base ADENINEADENINE, the pentose (5C) , the pentose (5C) sugar sugar RIBOSERIBOSE, and three , and three PHOSPHATEPHOSPHATE groups groups

The The LAST phosphate groupLAST phosphate group is is bonded with a bonded with a HIGH ENERGYHIGH ENERGY chemical bondchemical bond

This bond can be This bond can be BROKENBROKEN to to release ENERGY for CELLS to userelease ENERGY for CELLS to use

Removing a Phosphate from Removing a Phosphate from ATPATP

Breaking the LAST PHOSPHATE Breaking the LAST PHOSPHATE bond from ATP, will ---bond from ATP, will --- Release Release ENERGYENERGY for cells to use for cells to use Form Form ADP (adenosine diphosphate)ADP (adenosine diphosphate) Produce a Produce a FREE PHOSPHATE FREE PHOSPHATE

GROUPGROUP

High Energy Phosphate High Energy Phosphate BondBond

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

Process called Process called PhosphorylationPhosphorylation

PhosphorylationPhosphorylation

PhotosynthesisPhotosynthesis

1. 1. Light Reaction -Light Reaction -

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

2. 2. Calvin CycleCalvin Cycle Also called Also called Carbon FixationCarbon Fixation or or

Carbon CycleCarbon Cycle, Uses energy (, Uses energy (ATP ATP and NADPHand NADPH) from light reaction ) from light reaction to make sugar to make sugar (glucose).(glucose).

SUNSUN

3 stages of photosynthesis-3 stages of photosynthesis-

Stages:Stages:

STAGE 1STAGE 1 - - LIGHT REACTIONS LIGHT REACTIONS - energy from - energy from sun is used to split water into H+ an O2sun is used to split water into H+ an O2

  STAGE 2STAGE 2 – energy is converted to chemical – energy is converted to chemical energy & stored in ATP & NADPH in stromaenergy & stored in ATP & NADPH in stroma

STAGE 3STAGE 3 - - CALVIN CYCLECALVIN CYCLE where carbon is where carbon is fixed into glucosefixed into glucose

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

Occurs in the Thylakoid Occurs in the Thylakoid membranesmembranes

2 possible routes for electron flow:2 possible routes for electron flow:

Use Use Photosystem I and Photosystem I and Electron Electron Transport Chain Transport Chain (ETC) and g(ETC) and generate enerate ATP onlyATP only

OROR use use Photosystem II Photosystem II and and Photosystem I with ETC and Photosystem I with ETC and generate Ogenerate O22, ATP and NADPH, ATP and NADPH

Photosynthesis animationPhotosynthesis animation

http://www.mhhe.com/biosci/genbio/biolink/j_explorations/ch09expl.htm

ELECTRON TRANSPORT - LIGHT ELECTRON TRANSPORT - LIGHT REACTIONS in 5 stepsREACTIONS in 5 steps

Photosystem I and IIPhotosystem I and II Step 1Step 1 – light excites – light excites e-e- in photosystem II in photosystem II Step 2Step 2 – – e-e- move to primary e- acceptor move to primary e- acceptor

Step 3Step 3 – – e-e- move along electron transport move along electron transport chain (etc)chain (etc)

Step 4Step 4 – light excites – light excites e-e- in photosystem I in photosystem I Step 5Step 5 – – e-e- move along 2 move along 2ndnd (etc) (etc) End – NADP+ combine H+ to make NADPHEnd – NADP+ combine H+ to make NADPH

Light reaction animationLight reaction animation

http://www.science.smith.edu/departments/Biology/Bio231/ltrxn.html

Electron transport chain Electron transport chain songsong

Play the "Play the "Come On Down (The Electron Transport Chain)" song performed by Sam Reid. " song performed by Sam Reid. 

PhotolysisPhotolysis – –photo-chemical splitting of water photo-chemical splitting of water ((restoring photosystem II)restoring photosystem II)

ChemiosmosisChemiosmosis – synthesis of ATP – synthesis of ATP

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 H+H+ move down their move down their

concentration gradient forming concentration gradient forming ATP from ADPATP from ADP

Concentration of protons is greater in Concentration of protons is greater in thylakoid than stromathylakoid than stroma

ChemiosmosisChemiosmosisH+ H+

ATP Synthase

H+ H+ H+ H+

H+ H+ high Hhigh H++

concentrationconcentration

H+ADP + P ATP

PS II PS IE

TC

low Hlow H++

concentrationconcentration

H+ThylakoidThylakoidSpaceSpace

ThylakoidThylakoid

SUN (Proton Pumping)

The Calvin CycleThe Calvin Cycle

6.26.2

Calvin Cycle - Calvin Cycle - Biochemical pathway in photosynthesis that Biochemical pathway in photosynthesis that

produces organic compounds using ATP & produces organic compounds using ATP & NADPHNADPH

Carbon fixationCarbon fixation – carbon atoms from CO – carbon atoms from CO2 2 are are

bonded or ‘fixed’ into carbohydratesbonded or ‘fixed’ into carbohydrates

occurs in stromaoccurs in stroma

Calvin CycleCalvin Cycle Carbon Fixation Carbon Fixation 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.

ChloroplastChloroplast

GranumThylakoid

STROMA– where Calvin Cycle occursOuter Membrane

Inner Membrane

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

Calvin CycleCalvin Cycle

Remember: CRemember: C33 = Calvin Cycle = Calvin Cycle

C3

Glucose

Step 1 - Step 1 -

COCO2 2 diffuses fr cytosol & combines with diffuses fr cytosol & combines with

RuBP which splits into pair of PGARuBP which splits into pair of PGA

Step 2 - Step 2 -

PGA gets phosphate gr fr ATP gets PGA gets phosphate gr fr ATP gets proton fr NADPH to become PGALproton fr NADPH to become PGAL

Reaction produces: ADP, NADP+ & Reaction produces: ADP, NADP+ & phosphate to be used again phosphate to be used again

Step 3 - Step 3 -

PGAL converts back to RuBPPGAL converts back to RuBP

Allows Calvin cycle to continueAllows Calvin cycle to continue

Alternates:Alternates:

CC33 plants plants – use Calvin cycle exclusively – use Calvin cycle exclusively Form 3-carbon compoundsForm 3-carbon compounds

CC44 pathway pathway – evolved in hot, dry climate – evolved in hot, dry climate Form 4-carbon compoundsForm 4-carbon compounds Partially close stomataPartially close stomata E.g. Corn, sugar cane, crabgrassE.g. Corn, sugar cane, crabgrass

CAMCAM – open stomata at night, close in day – open stomata at night, close in day Grow slow, lose less waterGrow slow, lose less water E.g. cactus, pineappleE.g. cactus, pineapple

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 places:occurs in 2 places: Light reactionLight reaction - -

mesophyll cellsmesophyll cells Calvin cycleCalvin cycle - -

bundle sheath cellsbundle sheath cells

CC44 Plants Plants

Mesophyll CellMesophyll Cell

CO2

C-C-C

PEP

C-C-C-CMalate-4C sugar

ATP

Bundle Sheath CellBundle Sheath Cell

C-C-C

Pyruvic Acid

C-C-C-C

CO2

C3

Malate

Transported

glucoseVascular Tissue

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

CAM PlantsCAM PlantsNight (Stomates Open) Day (Stomates Closed)

Vacuole

C-C-C-CMalate

C-C-C-CMalate Malate

C-C-C-CCO2

CO2

C3

C-C-CPyruvic acid

ATPC-C-CPEP glucose

Rate of photosynthesis is Rate of photosynthesis is effected by - effected by - light intensity, COlight intensity, CO22 or temperature or temperature

High intensity or high COHigh intensity or high CO22 = high rate = high rate Growth graph levels off (plateau)Growth graph levels off (plateau)

High temp = initial high rate but peaksHigh temp = initial high rate but peaks Rate drops when stomata closesRate drops when stomata closes

RecapRecap Photosynthesis converts light energy into chemical Photosynthesis converts light energy into chemical

energy thru series of biochemical pathwaysenergy thru series of biochemical pathways Electrons excite in photosystem II – move along Electrons excite in photosystem II – move along

ETC to photosystem I ETC to photosystem I electrons are replaced when water is split electrons are replaced when water is split oxygen is byproductoxygen is byproduct ATP synthesized across thylakoidATP synthesized across thylakoid Calvin cycle – carbon is fixed & sugar producedCalvin cycle – carbon is fixed & sugar produced 3 turns produce PGAL (PGAL keeps cycle going3 turns produce PGAL (PGAL keeps cycle going Other pathways – COther pathways – C33, C, C44, CAM, CAM

ReferencesReferences

www.biologyjunction.comwww.biologyjunction.com