1

PhotosynthesiPhotosynthesiss

Energy & Life

2

Overview of Overview of PhotosynthesiPhotosynthesi

ss

3

Autotrophs (Producers)Autotrophs (Producers)Plants and Plants and some other some other types of types of organisms that organisms that contain contain chlorophyllchlorophyll are are able to use able to use light energy light energy from the sunfrom the sun to to produce food.produce food.

4

AutotrophsAutotrophs• Autotrophs Autotrophs

include include organismsorganisms that make that make their own foodtheir own food

• Autotrophs Autotrophs can use the can use the sun’s energy sun’s energy directlydirectly

EuglenaEuglena

5

HeterotrophsHeterotrophs• Heterotrophs Heterotrophs

are are organisms organisms that can NOT that can NOT make their make their own foodown food

• Heterotrophs Heterotrophs can NOT can NOT directly use directly use the sun’s the sun’s energyenergy

6

EnergyEnergy• Energy Takes Many Energy Takes Many

Forms such as Forms such as light, light, heat, electrical, heat, electrical, chemical, mechanicalchemical, mechanical

• Energy can be Energy can be changed from changed from one one form to anotherform to another

• Energy can be stored Energy can be stored in chemical bonds & in chemical bonds & then released laterthen released later

Candles release energy as HEAT & LIGHTCandles release energy as HEAT & LIGHT

7

ATP – Cellular EnergyATP – Cellular Energy• Adenosine TriphosphateAdenosine Triphosphate• Contains two, high-energy Contains two, high-energy

phosphate bondsphosphate bonds• Also contains the nitrogen base Also contains the nitrogen base

adenine & a ribose sugaradenine & a ribose sugar

8

ADPADP• Adenosine DiphosphateAdenosine Diphosphate• ATP releases ATP releases energyenergy, a , a free free

phosphate,phosphate, & & ADPADP when cells when cells take energy from ATPtake energy from ATP

One phosphate bond has been removed

9

Importance of ATPImportance of ATP

Principal Compound Used To Store Energy In Living Organisms

10

Releasing Energy From Releasing Energy From ATPATP

• ATP is constantly being ATP is constantly being used and used and remade by cellsremade by cells

• ATP provides all of the energy ATP provides all of the energy for for cell activitiescell activities

• The high energy phosphate The high energy phosphate bonds can be bonds can be BROKENBROKEN to to release release energyenergy

• The process of releasing ATP’s The process of releasing ATP’s energy & reforming the molecule energy & reforming the molecule is called is called phosphorylationphosphorylation

11

Releasing Energy From Releasing Energy From ATPATP

• AddingAdding A A Phosphate Phosphate Group To ADP Group To ADP stores Energy in stores Energy in ATPATP

• RemovingRemoving A A Phosphate Phosphate Group From ATP Group From ATP Releases Energy Releases Energy & forms ADP& forms ADP

Loose

Gain

12

Cells Using Biochemical Cells Using Biochemical EnergyEnergy

Cells Use ATP For:• Active transport• Movement• Photosynthesis• Protein Synthesis• Cellular

respiration• All other cellular

reactions

13

More on ATPMore on ATP• Cells Have Enough ATP To Cells Have Enough ATP To

Last For A Last For A Few SecondsFew Seconds• ATP must ATP must constantlyconstantly be be

mademade• ATP ATP Transfers Energy Transfers Energy

Very WellVery Well• ATP Is ATP Is NOTNOT Good At Good At

Energy StorageEnergy Storage

14

GlucoseGlucose•Glucose is a Glucose is a

monosaccharidemonosaccharide•CC66HH1212OO66

•One Molecule of glucose One Molecule of glucose Stores Stores 90 Times90 Times More More Chemical Energy Than Chemical Energy Than One Molecule of ATPOne Molecule of ATP

15

History of History of Photosynthesis & Photosynthesis & Plant PigmentsPlant Pigments

16

PhotosynthesisPhotosynthesis• Involves the Use Of light Involves the Use Of light

Energy to convert Energy to convert Water Water (H(H220)0) and and Carbon Dioxide Carbon Dioxide (CO(CO22)) into into Oxygen (OOxygen (O22)) and and High Energy CarbohydratesHigh Energy Carbohydrates (sugars, e.g. Glucose) & (sugars, e.g. Glucose) & StarchesStarches

17

Early Questions on Early Questions on PlantsPlants

Several Centuries Ago, Several Centuries Ago, The Question Was:The Question Was:

Does the increase in Does the increase in mass of a plant come mass of a plant come from the air? The soil? from the air? The soil?

The Water?The Water?

18

Van Helmont’s Van Helmont’s Experiment 1643Experiment 1643

• Planted a Planted a seedseed into into A pre-measured A pre-measured amount of soil and amount of soil and wateredwatered for 5 years for 5 years

• Weighed Plant & Weighed Plant & Soil.Soil. Plant Was 75 Plant Was 75 kg, Soil The Same.kg, Soil The Same.

• Concluded Mass Concluded Mass Came From WaterCame From Water

19

Priestley’s Experiment Priestley’s Experiment 17711771

• Burned Candle In Bell Jar Until It Went Out.

• Placed Sprig Of Mint In Bell Jar For A Few Days.

• Candle Could Be Relit And Burn.

• Concluded Plants Released Substance (O2) Necessary For burning.

20

Ingenhousz’s Ingenhousz’s Experiment 1779Experiment 1779

Repeated Priestly experiment with & without Repeated Priestly experiment with & without sunlightsunlight

21

Results of Ingenhousz’s Results of Ingenhousz’s ExperimentExperiment

• Showed That Priestley’s Showed That Priestley’s Results Only Occurred In Results Only Occurred In The Presence Of The Presence Of SunlightSunlight..

• Light Was Necessary For Light Was Necessary For Plants To Produce The Plants To Produce The “Burning Gas” or “Burning Gas” or oxygenoxygen

22

Julius Robert Mayer Julius Robert Mayer 18451845

Proposed That Proposed That Plants can Plants can Convert Convert Light Light Energy Into Energy Into ChemicalChemical EnergyEnergy

23

Samuel Ruben & Martin Samuel Ruben & Martin KamenKamen19411941

Used Isotopes Used Isotopes To Determine To Determine That The That The OxygenOxygen Liberated In Liberated In PhotosynthePhotosynthesis sis Comes Comes From WaterFrom Water

KAMENKAMEN

RUBINRUBIN

24

Melvin Calvin 1948Melvin Calvin 1948•First to trace the path First to trace the path that that carbon (COcarbon (CO22)) takes takes in forming in forming GlucoseGlucose•Does Does NOTNOT require require sunlightsunlight•Called the Called the Calvin CycleCalvin Cycle or or Light Independent Light Independent ReactionReaction•Also knownAlso known as the as the Dark Dark ReactionReaction

25

The Photosynthesis The Photosynthesis EquationEquation

26

PigmentsPigments•In addition to water,

carbon dioxide, and light energy, photosynthesis requires Pigments

•Chlorophyll is the primary light-absorbing pigment in autotrophs

•Chlorophyll is found inside chloroplasts

27

Photosynthesis• Where does it take place?

– Inside the CHLOROPLAST• Thylakoid membrane

– Stacks of these are called granum

– Light Reactions happen here

– Contains: Chlorophyll (light absorbing/reflecting pigment)

» Electrons get excited and start chemical rxns

• Stroma– Dark Reactions happen here

                                                                                               

28

Light and Light and PigmentsPigments

• Energy From The Sun Enters Earth’s Biosphere As Photons

•Photon = Light Energy Unit

• Light Contains A Mixture Of Wavelengths

•Different Wavelengths Have Different Colors

29

Light & PigmentsLight & Pigments• Different pigmentsDifferent pigments absorb absorb

different different wavelengthswavelengths of light of light• Photons of light Photons of light “excite”“excite”

electrons in the plant’s electrons in the plant’s pigmentspigments

• Excited electrons carry the Excited electrons carry the absorbed energyabsorbed energy

• Excited electrons move to Excited electrons move to HIGHERHIGHER energy levels energy levels

30

Chlorophyll a and bChlorophyll a and b

31

Chlorophyll aChlorophyll a•Found in all Found in all plants, plants, algae, & cyanobacteriaalgae, & cyanobacteria•Makes photosynthesis Makes photosynthesis possiblepossible•Participates Participates directlydirectly in in the Light Reactionsthe Light Reactions•Can Can accept energyaccept energy from from chlorophyll bchlorophyll b

32

Chlorophyll bChlorophyll b• Chlorophyll b is an Chlorophyll b is an

accessory pigmentaccessory pigment• Chlorophyll b acts Chlorophyll b acts

indirectlyindirectly in in photosynthesis by photosynthesis by transferring the light it transferring the light it absorbs to chlorophyll absorbs to chlorophyll aa

• Like chlorophyll a, it Like chlorophyll a, it absorbs red & blue light absorbs red & blue light and and REFLECTS GREENREFLECTS GREEN

33

The The Biochemical Biochemical ReactionsReactions

34

It Begins with Sunlight!It Begins with Sunlight!

35

Photoautotrophs Absorb Photoautotrophs Absorb Light EnergyLight Energy

36

Inside A ChloroplastInside A Chloroplast

37

Structure of the Structure of the ChloroplastChloroplast

• Double membraneDouble membrane organelle organelle• Outer membrane Outer membrane smoothsmooth• Inner membraneInner membrane forms forms

stacks of connected sacs stacks of connected sacs called called thylakoidsthylakoids

• Thylakoid stack is called the Thylakoid stack is called the granungranun (grana-plural) (grana-plural)

• Gel-like material around Gel-like material around grana called grana called stromastroma

38

Function of the StromaFunction of the Stroma•Light IndependentLight Independent

reactions occur herereactions occur here•ATP usedATP used to make to make

carbohydrates like carbohydrates like glucoseglucose

•Location of the Location of the Calvin Calvin CycleCycle

39

40

Thylakoid membranesThylakoid membranes• Light DependentLight Dependent reactions reactions

occur hereoccur here• Photosystems are made up Photosystems are made up

of of clusters of chlorophyll clusters of chlorophyll moleculesmolecules

• Photosystems are Photosystems are embedded embedded in the thylakoid membranesin the thylakoid membranes

• The two photosystems are:The two photosystems are: Photosytem IPhotosytem I Photosystem IIPhotosystem II

41

Photosynthesis Photosynthesis OverviewOverview

42

• 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 ATPADP to ATP• Also convert Also convert NADPNADP++ into into

the energy carrier the energy carrier NADPHNADPH

Light Dependent Light Dependent ReactionsReactions

43

Light Dependent Light Dependent ReactionReaction

44

Light Dependent Light Dependent ReactionReaction

45

Photosynthesis BeginsPhotosynthesis BeginsPhotosystem Photosystem II absorbs light II absorbs light

energyenergyElectrons are energizedElectrons are energized and passed and passed

to the to the Electron Transport ChainElectron Transport ChainLost electrons are replaced from Lost electrons are replaced from

the splitting of waterthe splitting of water into 2H into 2H+, +,

free electrons, and Oxygenfree electrons, and Oxygen2H2H+ + pumped across thylakoid pumped across thylakoid

membranemembrane

46

Photosystem IPhotosystem IHigh-energy electronsHigh-energy electrons are are

moved to Photosystem I moved to Photosystem I through the Electron through the Electron Transport ChainTransport Chain

Energy is used to Energy is used to transport transport HH++ from stroma to inner from stroma to inner thylakoid membranethylakoid membrane

NADP+ converted to NADP+ converted to NADPHNADPH when it picks up 2 when it picks up 2 electrons & H+electrons & H+

47

One more pause for the visual learners...

48

Chemiosmosis powers ATP synthesis

• Energy released during electron flow through the photosystems drives the transport of Hydrogen ions across the thylakoid membrane.

• Energy from those electrons is used to make ATP by chemiosmosis– Using the same H+ concentration gradient through the

ATP Synthase• During photosynthesis it is known as:

Photophosphorylation because it all stated with light from the sun

49

Chemiosmosis

50

Let’s Look at That

51

PhosphorylationPhosphorylationEnzyme in thylakoid Enzyme in thylakoid

membrane called membrane called ATP ATP SynthaseSynthase

As H+ ions passed As H+ ions passed through thylakoid through thylakoid membrane, membrane, enzyme enzyme binds them to ADPbinds them to ADP

Forms Forms ATPATP for cellular for cellular processes.processes.

52

53

Light Reaction SummaryLight Reaction SummaryReactants:Reactants:• HH22OO• Light EnergyLight Energy

Energy Products:Energy Products:• ATPATP• NADPHNADPH

54

Light Independent Light Independent ReactionReaction

• ATP & NADPHATP & NADPH from light from light reactions used as energyreactions used as energy

• Atmospheric Atmospheric C0C022 is used is used to to make sugarsmake sugars like like glucose and fructoseglucose and fructose

• Six-carbon Sugars made Six-carbon Sugars made during the during the Calvin CycleCalvin Cycle

• Occurs in theOccurs in the stroma stroma

55

The Calvin CycleThe Calvin Cycle

56

The Calvin CycleThe Calvin Cycle• Two turnsTwo turns of the Calvin Cycle of the Calvin Cycle

are required to make one are required to make one molecule of glucosemolecule of glucose

• 3-CO3-CO22 molecules enter the molecules enter the cycle to form several cycle to form several intermediate compounds intermediate compounds (PGA)(PGA)

• A 3-carbon molecule called A 3-carbon molecule called Ribulose BiphosphateRibulose Biphosphate (RuBP) (RuBP) is used to regenerate the is used to regenerate the Calvin cycleCalvin cycle

57

58

Factors Affecting the Factors Affecting the Rate of PhotosynthesisRate of Photosynthesis

• Amount of Amount of available available waterwater

• TemperatureTemperature• Amount of Amount of

available available light energylight energy

A General summary• 1. Light- Dependent Reactions (Non Cyclic)• Inputs are light and water • Light strikes photosystem II (P680) • Electrons pass along until they reach the primary electron acceptor • Photolysis occurs - water is split into hydrogen ions and oxygen atoms • Electrons pass down the ETC to photosystem I (P700), forming ATP

by chemiosmosis • Three products of the light reaction are NADPH, ATP, and O2 • Oxygen produced comes from water • NADPH & ATP are then used in the Calvin Cycle

• 2. Light - Dependent Reactions (Cyclic)• Only involves photosystem I • ATP is the only product of these reactions • No NADPH or oxygen is produced • These reactions exist because the Calvin cycle uses

more ATP then NADPH, this is how the difference is made up

• 3. Light Independent Reactions (Calvin Cycle)• Occurs in stroma of the chloroplast • Inputs are NADPH, ATP, and CO2 • First step is carbon fixation, which is catalyzed by an

enzyme named rubisco • A series of reactions lead to the production of

NADP+ and ADP, and sugar • More ATP is used the NADPH, which creates the

need for the cyclic light reaction • The carbon of the sugar product comes from CO2

• The Light Dependent Reaction• Occurs in the thylakoid of the chloroplast• Pigments that aid in photosynthsis - Chlorophyll a (major pigment) and

Chlorophyll b (accessory pigment)Pigments vary in the types of light they can absorb (wavelengths) .

• When chlorophyll a is hit by light, the electrons inside it is elevated to a higher energy level (it is "excited"),the excited electron is then passed to a PRIMARY ELECTRON ACCEPTOR

• The pigments in the thylakoid space organize themselves into PHOTOSYSTEMSPhotosystems contain combinations of chlorophyll a and b and also other pigments called phycobilins, and carotenoids (they help pick up other wavelenthgs of light)

• Now, PHOTOSYSTEM I and II are involved in the light dependent reactions, but not in the order. It always starts with PHOTOSYSTEM II.