8-3 the reactions of photosynthesis

1. Unit 3: Cells
Chapter 8:
Photosynthesis
8-3: The Reactions
of Photosynthesis
Ms. Petrucci
Biology

2. PhotosynthesiPhotosynthesi
ss
8-3 The Reactions of Photosynthesis

3. 3
The BiochemicalThe Biochemical
ReactionsReactions

4. 4
It Begins with Sunlight!It Begins with Sunlight!

5. 5
Photoautotrophs Absorb LightPhotoautotrophs Absorb Light
EnergyEnergy

6. 6
Inside A ChloroplastInside A Chloroplast

7. 7
Structure of the ChloroplastStructure of the Chloroplast
• Double membraneDouble membrane organelleorganelle
• Outer membraneOuter membrane smoothsmooth
• Inner membraneInner membrane forms stacks offorms stacks of
connected sacs calledconnected sacs called thylakoidsthylakoids
• Thylakoid stack is called theThylakoid stack is called the
granumgranum (grana-plural)(grana-plural)
• Gel-like material around granaGel-like material around grana
calledcalled stromastroma

8. 8

9. 9
Thylakoid membranesThylakoid membranes
• Light DependentLight Dependent reactions occurreactions occur
herehere
• Photosystems are made up ofPhotosystems are made up of
clusters of chlorophyll moleculesclusters of chlorophyll molecules
• Photosystems arePhotosystems are embedded inembedded in
the thylakoid membranesthe thylakoid membranes
• The two photosystems are:The two photosystems are:
– Photosytem IPhotosytem I
– Photosystem IIPhotosystem II

10. 10
Function of the StromaFunction of the Stroma
• Light IndependentLight Independent reactionsreactions
occur hereoccur here
• ATP usedATP used to maketo make
carbohydrates likecarbohydrates like glucoseglucose
• Location of theLocation of the Calvin CycleCalvin Cycle

11. 11
Photosynthesis OverviewPhotosynthesis Overview

12. 12
Energy CarriersEnergy Carriers
• Nicotinamide Adenine DinucleotideNicotinamide Adenine Dinucleotide
PhosphatePhosphate (NADP(NADP++
))
• Picks UpPicks Up 2 high-energy2 high-energy
electrons and Helectrons and H++
from the Lightfrom the Light
Reaction to form NADPHReaction to form NADPH
• NADPHNADPH carries energy to becarries energy to be
passed on to another moleculepassed on to another molecule

13. 13
NADPHNADPH

14. 14
• Occurs across theOccurs across the thylakoidthylakoid
membranesmembranes
• Uses light energyUses light energy
• ProduceProduce OxygenOxygen from waterfrom water
• ConvertConvert ADP to ATPADP to ATP
• Also convertAlso convert NADPNADP++
intointo
the energy carrierthe energy carrier
NADPHNADPH
Light Dependent ReactionsLight Dependent Reactions

15. 15
Light Dependent ReactionLight Dependent Reaction

16. 16
Light Dependent ReactionLight Dependent Reaction

17. 17
Photosystem IPhotosystem I
•DiscoveredDiscovered FirstFirst
•Active in the final stage of theActive in the final stage of the
Light Dependent ReactionLight Dependent Reaction
•Made of 300 molecules ofMade of 300 molecules of
ChlorophyllChlorophyll
•Almost completely chlorophyll aAlmost completely chlorophyll a

18. 18
Photosystem IIPhotosystem II
•DiscoveredDiscovered SecondSecond
•Active in the beginning stage OfActive in the beginning stage Of
the Light Dependent Reactionthe Light Dependent Reaction
•Contains aboutContains about equal amounts ofequal amounts of
chlorophyll a and chlorophyll bchlorophyll a and chlorophyll b

19. 19
Photosynthesis BeginsPhotosynthesis Begins
PhotosystemPhotosystem II absorbs lightII absorbs light
energyenergy
Electrons are energizedElectrons are energized and passedand passed
to theto the Electron Transport ChainElectron Transport Chain
Lost electrons are replaced fromLost electrons are replaced from
the splitting of waterthe splitting of water into 2Hinto 2H+,+,
free electrons, and Oxygenfree electrons, and Oxygen
2H2H++
pumped across thylakoidpumped across thylakoid
membranemembrane

20. 20
Photosystem IPhotosystem I
High-energy electronsHigh-energy electrons areare
moved to Photosystem Imoved to Photosystem I
through the Electronthrough the Electron
Transport ChainTransport Chain
Energy is used toEnergy is used to transport Htransport H++
from stroma to innerfrom stroma to inner
thylakoid membranethylakoid membrane
NADP+ converted to NADPHNADP+ converted to NADPH
when it picks up 2 electrons &when it picks up 2 electrons &
H+H+

21. 21
PhosphorylationPhosphorylation
Enzyme in thylakoidEnzyme in thylakoid
membrane calledmembrane called ATPATP
SynthetaseSynthetase
As H+ ions passed throughAs H+ ions passed through
thylakoid membrane,thylakoid membrane,
enzyme binds them to ADPenzyme binds them to ADP
FormsForms ATPATP for cellularfor cellular

22. 22

23. 23
Light Reaction SummaryLight Reaction Summary
Reactants:Reactants:
• HH22OO
• Light EnergyLight Energy
Energy Products:Energy Products:
• ATPATP
• NADPHNADPH
Other Product:Other Product:
• OxygenOxygen

24. 24
Light Independent ReactionLight Independent Reaction
• ATP & NADPHATP & NADPH from lightfrom light
reactions used as energyreactions used as energy
• AtmosphericAtmospheric C0C022 is usedis used toto makemake
sugarssugars like glucose and fructoselike glucose and fructose
• Six-carbon Sugars made duringSix-carbon Sugars made during
thethe Calvin CycleCalvin Cycle
• Occurs in theOccurs in the stromastroma

25. 25
The Calvin CycleThe Calvin Cycle

26. 26
The Calvin CycleThe Calvin Cycle
• Two turnsTwo turns of the Calvin Cycle areof the Calvin Cycle are
required to make one molecule ofrequired to make one molecule of
glucoseglucose
• 3-CO3-CO22 molecules enter the cycle tomolecules enter the cycle to
form severalform several intermediate compoundsintermediate compounds
(PGA)(PGA)
• A 3-carbon molecule calledA 3-carbon molecule called RibuloseRibulose
BiphosphateBiphosphate (RuBP) is used to(RuBP) is used to
regenerate the Calvin cycleregenerate the Calvin cycle

27. 27

28. 28
Factors Affecting the RateFactors Affecting the Rate
of Photosynthesisof Photosynthesis
• Amount ofAmount of
available wateravailable water
• TemperatureTemperature
• Amount ofAmount of
available lightavailable light
energyenergy