Chapter 6Chapter 6PhotosynthesisPhotosynthesis

6.1 The Light Reactions6.1 The Light Reactions

Part 2Part 2

Light Light Chemical Energy Chemical Energy

• Review...Review...

• What absorbs light in the plant?What absorbs light in the plant?

• Organelle?Organelle?

• Pigment?Pigment?

• Now we need to convert that LIGHT Now we need to convert that LIGHT energy into CHEMICAL energy the plant energy into CHEMICAL energy the plant (and Heterotrophs) can USE!!(and Heterotrophs) can USE!!

1. Light-Dependent Reactions:1. Light-Dependent Reactions:PhotosystemsPhotosystems

PhotosystemsPhotosystems==

• Where?Where?

• __________-_____________ Rxns!__________-_____________ Rxns!

Step 1Step 1•Light absorbed by Light absorbed by

•Absorb itsAbsorb its

•To PS2To PS2

•Chl’s e- “excited”:Chl’s e- “excited”:

•e- leave chl (e- leave chl (

rxn)...something must rxn)...something must

be GER!be GER!

PigmentsPigments• Where?

• Function:

Examples: Examples: Chloroplast PigmentsChloroplast Pigments

Chlorophylls

Where?

Reflect:

• Chl a• Chl b

Chloroplast Pigments

Carotenoids

Where?

Reflect:

“Accessory” Pigments:

Help photosyn b/c

Autumn! Autumn! • Chlorophyll in

leaves decays

• Green color fades

• Replaced by oranges & reds of carotenoids!!

Replacing ElectronsReplacing Electrons• Photolysis:Photolysis:

enzymes split water enzymes split water

• 2H2H220 4H0 4H++ + 4 + 4e- e- + O+ O22

Step 2Step 2•Next ptn in Next ptn in

membrane = membrane =

•GERGER

Step 3Step 3 donates the e- donates the e-

againagain

•____________ ____________

_____________ Chain_____________ Chain

•Slowly passing e-Slowly passing e-

•Why?Why?

Step 3Step 3The electron energy is The electron energy is

used to move Protons used to move Protons

(H+) (H+) intointo the thylakoid the thylakoid

Step 4Step 4•PS___PS___

•Light absorbedLight absorbed

•Same thing!Same thing!

•ETCETC

•H+ back outH+ back out

Step 5Step 5•Stroma Stroma

•e- , H+, NADP+ e- , H+, NADP+

•To To

•ATP too...ATP too...

ChemiosmosisChemiosmosis

• Using diffusion to make ATPUsing diffusion to make ATP– Conc gradient across thylakoid membraneConc gradient across thylakoid membrane

• H+ higher inside thylakoid than stromaH+ higher inside thylakoid than stroma

– ATP synthase @ end of ETCATP synthase @ end of ETC• H+ thru it (out to stroma)H+ thru it (out to stroma)• form ATPform ATP

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Label this!

6.2 Calvin cycle6.2 Calvin cycle

• Oh, Melvin!Oh, Melvin!

When’sWhen’s the Calvin Cycle? the Calvin Cycle?

• AFTER the Light Reactions!AFTER the Light Reactions!

• What What TWO productsTWO products of Light Rxns of Light Rxns are sent to Calvin Cycle?are sent to Calvin Cycle?

• NADPH & ATP!NADPH & ATP!

2. Light-Independent Reactions2. Light-Independent Reactions

• Series of rxns w/enzymesSeries of rxns w/enzymes

• Product: a 3-Carbon sugar Product: a 3-Carbon sugar – (like ½ of a glucose)(like ½ of a glucose)

• 4 basic steps4 basic steps

1. CO1. CO22 into stroma (c’plast) into stroma (c’plast)

• RuBP (5C) + CORuBP (5C) + CO22 6C 6C

immediately splits in ½ immediately splits in ½

3-PGA (3C)3-PGA (3C)

2. 3-PGA 2. 3-PGA G3P G3P

• ATP & NADPH usedATP & NADPH used

• ADP, NADP return to the...(lt reactions)ADP, NADP return to the...(lt reactions)

3. 1 G3P exits C Cycle3. 1 G3P exits C Cycle

• Used to make carbs...Used to make carbs...– After 2 turns of the C. Cycle, you can make After 2 turns of the C. Cycle, you can make

a glucosea glucose

4. Other G3Ps4. Other G3Ps

• Continue cycle, Continue cycle, RuBP made again RuBP made again

• Use more ATPUse more ATP

What are these???What are these???

• StomatesStomates

• Space b/w two cells Space b/w two cells

• On leavesOn leaves

• Out:Out:

• Water and oxygenWater and oxygen

• In:In:

• Carbon dioxideCarbon dioxide

Two Alternative Pathways:Two Alternative Pathways: C4C4• Close stomata @ Close stomata @

hottest part of dayhottest part of day• Make 4C to keep phot Make 4C to keep phot

goinggoing• Sugar caneSugar cane

CAMCAM• Open stomata @ night Open stomata @ night

(close @ day)(close @ day)• Make Crassulacean Make Crassulacean

acid to keep phot acid to keep phot goinggoing

• Cactus, pineappleCactus, pineapple

Factors Affecting PhotosynthesisFactors Affecting Photosynthesis

1.1. LightLight

Carbon Dioxide Level

2. CO2. CO22 3. Temp3. Temp

REVIEW: When’s this REVIEW: When’s this usedused??• Light?Light?• Water?Water?• Electron Transport Chain?Electron Transport Chain?• ATP?ATP?• Chemiosmosis?Chemiosmosis?• NADPH?NADPH?• COCO22??

• So, what are the products So, what are the products of the Light Rxns?of the Light Rxns?

• Of the Calvin Cycle?Of the Calvin Cycle?

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Quiz Tomorrow!!...Ch ReviewQuiz Tomorrow!!...Ch Review

Review

Review

p.126 #3,9,10,11,12,14,15,17,21

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