PHOTOSYNTHESISPHOTOSYNTHESIS

PhotosynthesisPhotosynthesis

• An anabolic, endergonic, carbon dioxide anabolic, endergonic, carbon dioxide (CO(CO22)) requiring process that uses light energy light energy

(photons)(photons) and water (Hwater (H22O)O) to produce organic organic

macromolecules (glucose).macromolecules (glucose).

6CO2 + 6H2O C6H12O6 + 6O2glucoseglucose

SUN

photonsphotons

Question:Question:

• Where does photosynthesis take place?Where does photosynthesis take place?

PlantsPlants

• Autotrophs:Autotrophs: self-producers.• Location:

1. Leaves

a. stoma

b. mesophyll cells

StomaMesophyllCell

Chloroplast

Stomata (stoma)Stomata (stoma)

• PoresPores in a plant’s cuticle through which waterwater and gasesgases are exchanged between the plant and the atmosphere.

Guard Cell

Guard Cell

Carbon Dioxide (CO2)

Oxygen (O2)

Mesophyll CellMesophyll Cell

Cell Wall

Nucleus

Chloroplast

Central Vacuole

ChloroplastChloroplast• OrganelleOrganelle where photosynthesisphotosynthesis takes place.

GranumThylakoid

Stroma

Outer Membrane

Inner Membrane

ThylakoidThylakoid

Thylakoid Membrane

Thylakoid SpaceGranum

Question:Question:

• Why are plants green?Why are plants green?

Chlorophyll MoleculesChlorophyll Molecules

• Located in the thylakoid membranesthylakoid membranes.

• Chlorophyll have MgMg++ in the center.

• Chlorophyll pigmentsChlorophyll pigments harvest energy (photons) by absorbingabsorbing certain wavelengthswavelengths (blue-420 blue-420 nmnm and red-660 nm are most important).

• PlantsPlants are greengreen because the green wavelengthwavelength is reflectedreflected, not absorbednot absorbed.

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

400 500 600 700

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

Absorption of ChlorophyllAbsorption of Chlorophyll

wavelengthwavelength

Absorption

violet blue green yellow orange red

Question:Question:

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

Fall ColorsFall Colors

• In addition to the chlorophyll pigments, there are other pigmentspigments present.

• During the fall, the green chlorophyllgreen chlorophyll pigments are greatly reducedgreatly reduced revealing the other pigmentspigments.

• CarotenoidsCarotenoids are pigments that are either redred or yellowyellow.

Redox ReactionRedox Reaction

• The transfertransfer of oneone or more electronsmore electrons from one reactantone reactant to anotheranother.

• Two types:Two types:

1.1. OxidationOxidation

2.2. ReductionReduction

Oxidation ReactionOxidation Reaction

• The lossloss of electronselectrons from a substance.• Or the gaingain of oxygenoxygen.

glucoseglucose

6CO2 + 6H2O C6H12O6 + 6O2

OxidationOxidation

Reduction ReactionReduction Reaction

• The gaingain of electrons to a substance.• Or the lossloss of oxygenoxygen.

glucoseglucose

6CO2 + 6H2O C6H12O6 + 6O2

ReductionReduction

Breakdown of PhotosynthesisBreakdown of Photosynthesis

• Two main parts (reactions).Two main parts (reactions).

1. Light Reaction or1. Light Reaction or

Light Dependent ReactionLight Dependent Reaction

Produces energyenergy from solar powersolar power (photons)(photons) in the form of ATPATP and NADPHNADPH.

Breakdown of PhotosynthesisBreakdown of Photosynthesis

2.2. Calvin Cycle orCalvin Cycle or

Light Independent Reaction orLight Independent Reaction or

Carbon Fixation orCarbon Fixation or

CC33 Fixation Fixation

Uses energyenergy (ATP and NADPH)(ATP and NADPH) from light light rxnrxn to make sugar (glucose).sugar (glucose).

1. Light Reaction (Electron Flow)1. Light Reaction (Electron Flow)

• Occurs in the Thylakoid membranesThylakoid membranes

• During the light reactionlight reaction, there are two two possiblepossible routes for electron flowelectron flow.

A.A. Cyclic Electron FlowCyclic Electron Flow

B.B. Noncyclic Electron FlowNoncyclic Electron Flow

A. Cyclic Electron FlowA. Cyclic Electron Flow

• Occurs in the thylakoid membranethylakoid membrane.• Uses Photosystem I onlyPhotosystem I only• P700 reaction center- chlorophyll a • Uses Electron Transport Chain (ETC)Electron Transport Chain (ETC)• Generates ATP only

ADP + ATPATPP

A. Cyclic Electron FlowA. Cyclic Electron Flow

P700

PrimaryElectronAcceptor

e-

e-

e-

e-

ATPATPproducedby ETC

Photosystem I

AccessoryPigments

SUN

Photons

B. Noncyclic Electron FlowB. Noncyclic Electron Flow

• Occurs in the thylakoid membranethylakoid membrane

• Uses PS IIPS II and PS IPS I

• P680 rxn center (PSII) - chlorophyll a

• P700 rxn center (PS I) - chlorophyll a

• Uses Electron Transport Chain (ETC)Electron Transport Chain (ETC)

• Generates OGenerates O22, ATP and NADPH, ATP and NADPH

B. Noncyclic Electron FlowB. Noncyclic Electron Flow

P700

Photosystem IP680

Photosystem II

PrimaryElectronAcceptor

PrimaryElectronAcceptor

ETC

EnzymeReaction

H2O

1/2O1/2O22 + 2H+

ATPATP

NADPHNADPHPhoton

2e-

2e-

2e-

2e-

2e-

SUN

Photon

B. Noncyclic Electron FlowB. Noncyclic Electron Flow

• ADP + ATPATP

• NADP+ + H NADPHNADPH

• Oxygen comes from the splitting of Oxygen comes from the splitting of HH22OO, not , not COCO22

HH22O O 1/2 O2 + 2H+

(Reduced)

P(Reduced)

(Oxidized)

ChemiosmosisChemiosmosis

• Powers ATP synthesisATP synthesis.

• Located in the thylakoid membranesthylakoid membranes.

• Uses ETC and ATP synthase (enzyme)(enzyme) to make ATP.

• Photophosphorylation:Photophosphorylation: addition of phosphatephosphate to ADPADP to make ATPATP.

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)

Calvin Cycle• Carbon Fixation (light independent rxn).Carbon Fixation (light independent rxn).

• C3 plants (80% of plants on earth).

• Occurs in the stroma.

• Uses ATP and NADPH from light rxn.

• Uses CO2.

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

ChloroplastChloroplast

GranumThylakoid

Stroma

Outer 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:Remember: C3 = Calvin CycleC3 = Calvin Cycle

C3

Glucose

PhotorespirationPhotorespiration

• Occurs on hot, dry, bright dayshot, dry, bright days.

• Stomates close.

• Fixation of O2 instead of CO2.

• Produces 2-C molecules2-C molecules instead of 3-C sugar 3-C sugar moleculesmolecules.

• Produces no sugar molecules or no ATP.

PhotorespirationPhotorespiration

• Because of photorespirationBecause of photorespiration: PlantsPlants have special adaptationsspecial adaptations to limit the effect of photorespirationphotorespiration.

1.1. C4 plantsC4 plants

2.2. CAM plantsCAM plants

C4 PlantsC4 Plants

• Hot, moist environmentsHot, moist environments.

• 15% of plants (grasses, corn, sugarcane).15% of plants (grasses, corn, sugarcane).

• Divides photosynthesis spatially.Divides photosynthesis spatially.

• Light rxn - mesophyll cells.

• Calvin cycle - bundle sheath cells.

C4 PlantsC4 Plants

Mesophyll CellMesophyll Cell

CO2

C-C-C

PEP

C-C-C-CMalate

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% of plants (cactus and ice plants).5% of plants (cactus and ice plants).

• Stomates Stomates closed during dayclosed during day..

• Stomates Stomates open during the nightopen during the night.

• Light rxn - occurs during the day.

• Calvin Cycle - occurs when CO2 is 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

Question:Question:

• Why would CAM plants close their Why would CAM plants close their stomates during the day?stomates during the day?

Photosynthesis

Photosynthesis is a process which light energy is used in the

synthesis of organic molecules.

What is the equation for photosynthesis?

Water + carbon dioxide +light energy

=

Oxygen + glucose

The role of chloroplasts in Photosynthesis.

• Chloroplast is an organelle in the leaf of a plant that contain the thylakoid cells and the stroma. These are shown on the following diagram.

• Here 2 important reactions take place. The light dependant reactions take place in the thylakoid cells and the light independent in the stroma.

Chloroplasts

What happens in the light dependent reactions.

• Electrons in the chloroplast gain energy from sunlight , this energy is used to add a phosphate group to ADP making ATP.

• The energy is used also used in the photolysis of water to split it into oxygen and hydrogen molecules

• The electrons, protons and energy for the light dependent reactions are used to make NaDPH2.

• The ATP/NADPH2 from the Light Dependent reactions enter the light independent reactions.

What happens in the light independent reactions.

The light independent reactions occur at night for only a few

seconds due to limited amounts of ATP and supply of NADPH2.

Role of NADPH2 and ATP

Energy from ATP and electrons from NADPH2 are used to reduce

carbon dioxide and build it to sugars

The following cycle is called the Calvin cycle.

• This is called Fixing the carbon dioxide. The carbohydrates(sugars) are in a form of RuBP.

• The following cycle is called the Calvin cycle.

• What happens in the Calvin cycle?

• RuBP with the addition of carbon dioxide splits into 2 moles of GP. For GP to be turned to Carbohydrates it requires ATP and NADPH2. The NADPH2 give up its electrons which enter the GP molecules making GALP.

GALP

GALP is converted to a whole series of mostly sugars, some

lipids and some Proteins.

• Also some GALP is regenerated back to RUBP if sufficient amounts of NADPH2 and ATP are provided.

PhotosynthesisPhotosynthesis

HH22OO COCO22

OO22 CC66HH1212OO66

Light Light ReactionReaction

Dark ReactionDark Reaction

Light is AdsorbedLight is AdsorbedBy By

ChlorophyllChlorophyll

Which splitsWhich splitswaterwater

ChloroplastChloroplast

ATP andATP andNADPHNADPH22

ADPADPNADPNADP

Calvin CycleCalvin Cycle

EnergyEnergy

Used Energy and is Used Energy and is recycled.recycled.

++

++

C3