AP BioAP Bio

PhotosynthesisPhotosynthesis

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PhotosynthesisPhotosynthesis

• Uses light energy as energy sourceUses light energy as energy source• Uses COUses CO22 as a carbon source as a carbon source• Synthesizes energy rich organic molecules Synthesizes energy rich organic molecules

(sugar and others)(sugar and others)• Supplies energy, stored in sugars, to most Supplies energy, stored in sugars, to most

living organismsliving organisms• Occurs in the chloroplasts of autotrophs Occurs in the chloroplasts of autotrophs

(green plants)(green plants)

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Photosynthesis PhactsPhotosynthesis Phacts• On a global scale, photosynthesis makes On a global scale, photosynthesis makes

about 160 billion metric tons of about 160 billion metric tons of carbohydrates a year.carbohydrates a year.

• Sucrose is the transport form of Sucrose is the transport form of carbohydrates in most plants.carbohydrates in most plants.

• Plants consume about 50% of the Plants consume about 50% of the photosynthate as fuel for cellular photosynthate as fuel for cellular respiration.respiration.

• Extra sugars are synthesized into starch Extra sugars are synthesized into starch and stored in cells of roots, tubers, seeds, and stored in cells of roots, tubers, seeds, and fruits.and fruits.

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Summary EquationSummary EquationOne Overall Equation:One Overall Equation:

6 CO6 CO22 + 12 H + 12 H22O + light energy O + light energy

CC66HH1212OO66 + 6 O + 6 O22 + 6 H + 6 H22OOIn Two Stages:In Two Stages:a) Light Dependent Reactionsa) Light Dependent Reactionsb) Light Independent Reactionsb) Light Independent Reactions

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Chloroplast StructureChloroplast Structure

Inner & OuterInner & OuterMembranesMembranes

ThylakoidsThylakoids

GranumGranum

StromaStroma

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Organization of PhotosynthesisOrganization of Photosynthesis

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Leaf StructureLeaf Structure

MesophyllMesophyllCellsCells

MesophyllMesophyllCellsCells

Upper EpidermisUpper EpidermisUpper EpidermisUpper Epidermis

LowerLowerEpidermisEpidermis

LowerLowerEpidermisEpidermisVeinVeinVeinVein StomaStomaStomaStoma

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The Light-Dependent ReactionsThe Light-Dependent Reactions

1.1. Occur in thylakoid membranesOccur in thylakoid membranes

2.2. OO22 released by splitting water released by splitting water3.3. Light energy boosts P.E. of electronsLight energy boosts P.E. of electrons

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Photosynthetic PigmentsPhotosynthetic Pigments

• Chlorophyll aChlorophyll a - main photosynthetic - main photosynthetic pigment in all organisms except bacteria pigment in all organisms except bacteria

• Accessory pigmentsAccessory pigments absorb slightly absorb slightly different wavelengths of light different wavelengths of light • Chlorophyll b Chlorophyll b • CarotenoidsCarotenoids

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Absorption SpectraAbsorption Spectra

The The combination combination of all of the of all of the pigments pigments increases increases the range of the range of colors that colors that plants can plants can use in use in photosynthephotosynthesis.sis.

11 The PhotosystemsThe Photosystems

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13 Photosystem II

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The Light-Dependent ReactionsThe Light-Dependent Reactions

1.1. Occur in thylakoid membranesOccur in thylakoid membranes• PhotosystemsPhotosystems

2.2. OO22 released by splitting water released by splitting water• PhotolysisPhotolysis

3.3. Light energy boosts P.E. of electronsLight energy boosts P.E. of electrons• PhotoexcitationPhotoexcitation

4.4. ATP is generatedATP is generated• PhotophosphorylationPhotophosphorylation

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Chemiosmosis 1Chemiosmosis 1

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Chemiosmosis 2Chemiosmosis 2

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http://www.cst.cmich.edu/users/baile1re/bio101fall/enzphoto/photoanima.htm#

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http://www.stolaf.edu/people/giannini/flashanimat/metabolism/photosynthesis.swf

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Light-Dependent ReactionsLight-Dependent Reactions

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GlucoseGlucose

OO22

Overview of PhotosynthesisOverview of Photosynthesis

Light-DependentLight-DependentReactionsReactions

(in thylakoids)(in thylakoids)

Light-IndependentLight-IndependentReactionsReactions

(in stroma)(in stroma)

DepletedDepletedCarriersCarriers

(ADP, NADP(ADP, NADP++))

DepletedDepletedCarriersCarriers

(ADP, NADP(ADP, NADP++))

EnergizedEnergizedCarriersCarriers

(ATP, NADPH)(ATP, NADPH)

HH22OO

COCO22+H+H22OO

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Rubisco (RuBP carboxylase)Rubisco (RuBP carboxylase)

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The Light-Independent ReactionsThe Light-Independent Reactions

1.1. Occur in the stromaOccur in the stroma2.2. Does not require light, but does require Does not require light, but does require

the products of the light reactions (ATP the products of the light reactions (ATP and NADPH)and NADPH)

3.3. Calvin Cycle (Melvin Calvin)Calvin Cycle (Melvin Calvin)• 3 Phases3 Phases

Assimilation of atmospheric carbon dioxide into Assimilation of atmospheric carbon dioxide into carbohydrates.carbohydrates.

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The CThe C33 Cycle Cycle of Carbon of Carbon FixationFixation

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A Summary of PhotosynthesisA Summary of Photosynthesis

Light-dependent Light-dependent reactions occur reactions occur

in thylakoidsin thylakoids Light-Light-independent independent reactions (creactions (c33

cycle) occur in cycle) occur in stromastroma

25 CC33 Plants & the Pathway Plants & the Pathway

CC33 plants use the C plants use the C33 pathwaypathway

In a CIn a C33 plant, most plant, most chloroplasts are in chloroplasts are in

mesophyll cells.mesophyll cells.

26 CC33 Plants Plants

Much photorespiration Much photorespiration occurs under hot, dry occurs under hot, dry

conditionsconditions

27 CC44 Plants & the C Plants & the C4 4 PathwayPathway

CC44 plants use the C plants use the C44 pathwaypathway

In a CIn a C44 plant, both plant, both mesophyll & bundle-mesophyll & bundle-sheath cells contain sheath cells contain

chloroplasts.chloroplasts.

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CC44 Plants & the Plants & the CC4 4 PathwayPathway

Almost no Almost no photorespiration photorespiration occurs under hot, occurs under hot,

dry conditions.dry conditions.

COCO22 is captured is captured with a highly with a highly

specific enzyme.specific enzyme.

Much glucose Much glucose synthesis occurs.synthesis occurs.

Mesophyll cell in a CMesophyll cell in a C44 plant plant

Bundle-sheath cell in a CBundle-sheath cell in a C44 plant plant

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Relationship ofRelationship ofPhotosynthesis & RespirationPhotosynthesis & Respiration

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The endThe end