5. Photosynthesis (Chap. 10)

8/14/2019 5. Photosynthesis (Chap. 10)

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C

hapter

10

-

P

hot

osyn

thes

is

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How can sunlight,

seen here as a spectrum of colors in a rainbow,

power the synthesis of organic substances?

*rainbow


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lf-feeding/make own food-producers (organicsfr. CO2 & inorganics)hotoautotrophic/chemo-

autotrophic-plants, algae, someprotists &bacteria

- feed on others-consumers (includingdecomposers)

- animals, fungi & many bacter

-dependent of photoautotrophs

food

Autotrophic vs.

Heterotrophic

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The major site ofphotosynthesis

, and specifically occur in

osynthesis occurs in all green parts of a

Chloroplasts,

Chlorophyll

- green pigment in chloropl

- absorbs light energy for

- found primarily in mesoph

leaves

O2 + 6H2O + light energy C6H12O6 + 6O2

Figure 10.3 Tracking atoms through photosynthesis

6CO2 + 12H2O + light energy C6H12O6 +

6O2 + 6H20


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- CO2 enters O2 exit

throughstomata.

These closewhen the

Transports waterand food

*leaf cross section


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Photosynthetic pigments

are found in the

thylakoid membrane.

Stacks of thylakoidmembranes are grana.

Stroma is the dense fluid

in the chloroplast.

*chloroplast

AKA

thylakoid

lumen

Leaf cross section

Vein

Mesophyll

StomataCO2 O2

ChloroplastMesophyll cell

Outer

membrane

Intermembrane

space5 m

Inner

membrane

Thylakoid

space

Thylakoid

GranumStroma

1 m

Leaf

Mesophyll

Chloroplast

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How does photosynthetic prokaryotes (bacteria), which lack

chloroplasts, go through photosynthesis?

Have chlorophyll built into plasma membrane or vesicles

Respiration Photosynthesise- from H (in glucose) trans-

ported to oxygen to make

H2O

water split & e- w/ H+ trans-

ferred to CO2 to make sugar

is redox processwhere energy is

from the oxidation of sugar to

form ATP.

exothermicreleased

is redox processwhere energy is to

reduce carbon dioxide to form

sugar.

endothermic required

Respiration vs.

Photosynthesis


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Photosynthesis can be summarized as the

following equation:6 CO2 + 12 H2O + Light energyC6H12 O6 + 6 O2 + 6 H2O

Chloroplasts split H2O into hydrogen and oxygen,

incorporating the electrons of hydrogen into sugar molecules

Reactants: 6 CO2

Products:

12 H2O

6 O26 H2OC6H12 O6

*Photosynthesis equation


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Light Reactions Calvin Cycle

-convertslight energy tochem

energy inATP & NADPH

- occur inthylakoid membranes

-reduce NADP+(adding 2 e- &

1p+)to NADPH + H+

(nicotinamide adeninedinucleotide phosphate)

- splits H2O, giving off O2

-make ATP throughphotophos-

phorylation

-carbon fixationconvert

CO2 to sugar G3P

- occurs instroma

-AKAdark orlight-independent

rxns

-NADPHprovides reducingpower (adds e- to CO2)

- ATPprovides chemical

energy

2 stages of photosynthesis are:

- returns ADP, Pi, &

NADP+ to light rxns


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Light

H2O

Chloroplast

LightReactions

NADP+

P

ADP

i+

*photosynthesis - light reactions 1


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Light

H2O

Chloroplast

LightReactions

NADP+

P

ADP

i+

ATP

NADPH

O2



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Light

H2O

Chloroplast

LightReactions

NADP+

P

ADP

i+

ATP

NADPH

O2

Calvin

Cycle

CO2*photosynthesis - light reactions 3


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Light

H2O

Chloroplast

LightReactions

NADP+

P

ADP

i+

ATP

NADPH

O2

Calvin

Cycle

CO2

[CH2O]

(sugar)



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*electromagnetic

spectrum





Shorter wavelength Longer wavelength

Higher energy Lower energy

Wavelength is distance between crests.

Photons have a fixed quantity of E, even

though not discrete particles.


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*determining an

absorption spectrum

Chl h ll


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Chlorophyll a

Chlorophyll b

Carotenoids

When photon is absorbed,color disappears

e- is elevated to orbital w/

more potential E

(fr. ground to

excited state, higherorbital)

E is = to diff betw ground

& excited state,

thus each pigmentabsorbs only

photons w/ specific

wavelengths

When e- drops back toground state, HEAT.For chlorophyll a


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(a) Excitation of isolated chlorophyll molecule

Heat

Excited

state

(b) Fluorescence

PhotonGroundstate

Photon(fluorescence)

Energy

ofelec

tron

e

Chlorophyll

molecule

*fluorescence


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Englemannselegant

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Englemanns elegant

experiment:

He established thatonly certain

wavelengths of light

stimulate

photosynthesis.

Used prism to break

up light.

In areas withsuccessful

photosynthesis, O2

production increased

and bacteria grew.


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Photosystem - Light gathering unit of photosynthesis

(thylakoid membrane & proteins)

Light Reaction

t hl h llt hl h ll


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photon

transfer of

energy

rxn

center

Primary e- acceptor:Primary e- acceptor: this molecule traps excited

e- so doesnt go

back to ground state

& release E energy stored in trapped e-

makes ATP &

NADPH

rxn center chlorophyll a:rxn center chlorophyll a:special molecule that can transfer

excited e- to start light rxnsp700 for Phosys I, p680 for

Phosys II - identical but

each w/ diff protein

A photosystemA photosystem

e- transfer

antennaantenna

(accessory)(accessory)

moleculesmoleculesfew hundred pigments

(a, b, carotenoids)absorb photons & pass E

to rxn center

chlorophyll


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THYLAKOID SPACE(INTERIOR OF THYLAKOID)

STROMA

e

Pigmentmolecules

Photon

Transferof energy

Special pair ofchlorophyll amolecules

Thylako

idmembrane

Photosystem

Primaryelectronacceptor

Reaction-centercomplex

Light-harvesting

complexes

*photosystem


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ow noncyc c


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ow noncyc celectron flow during

the light rxnsgenerates ATP & NADPH




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1. Photosystem II absorbs light e- excited in P680 captured

by primary electron acceptor (need to fill e- hole)

2. Missing e- from chlorophyll a replaced by splitting of water -this is how O2 is formed

3. Excited e- pass from Photosys II to Photosys I by ETC

4. As e- go down chain, ATP is produced by phosphorylation

(just like in cellular respiration)P680P700123456Photosystem IIPhotosystemI2 H++ H2O

1/2 O2

2e-2e-primary-acceptorprimary-acceptor

PqcytochromcomplexPcATPNADP+Reductas

Fd2e-2e-NADP++

2 H+

NADPH

+ H+

2e-

PhotosystemII


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P680P700123456Photosystem IIPhotosystemI2 H++ H2O

1/2 O2

2e-2e-primary-acceptorprimary-acceptorPqcytochromcomplexPcATPNADP+ReductasFd2e-2e-NADP+

+

2 H+

NADPH

+ H+

2e-

5. At bottom of ETC, the e- fills hole in P700 replacing

excited e- of Photosys I

6. Excited e- passed to ferrodoxin (Fd) then to NADP+

forming NADPH

Photosyste

m I

Linear vs Cyclic Electron


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- conc. of NADPH may regulate which pathway is active

More NADPH than ATP

Less NADPH than ATP

Linear vs. Cyclic ElectronFlow

Pushes e- from water

(low potential E) toNADPH (high potential E)

Thylakoid membrane

converts light E to

chemical E stored inNADPH and ATP in =

quantities

Uses photosystem I but not

photosytem IIGenerates ATP, Does NOT

produce NADPH or O2

Evolved before linear flow to

protect from light induced

damage

Makes up the difference from

Calvin cycle since CC

consumes more ATP than

NADPH



cyclic

linear


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Chemiosmosis

mitochondria

chloroplast

similarities differences

e- are passed thruseries of carriers that

are progressively

more electronegative

establishes H+

gradient to increase

potential E

ATP synthase

couples H+ diffusion

to phosphorylate

ADP

Oxidative phosphorylation

e- are extracted fr. food

fr. intermembrane spaceto matrix

Photophosphorylation

e- driven to top of chain fr.

captured light energy

fr. thylakoid space (pH 5)

to stroma (pH 8)

Mit h d i Chl l


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*ATP synthase

Key

Mitochondrion Chloroplast

CHLOROPLAST

STRUCTURE

MITOCHONDRION

STRUCTURE

Intermembrane

space

Inner

membrane

Electrontransport

chain

H+

Diffusion

Matrix

Higher [H+]

Lower [H+

]

Stroma

ATPsynthase

ADP + P iH+

ATP

Thylakoid

space

Thylakoid

membrane


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*graphic of photosystem II & I


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ATP & NADPH produced in light reaction are used in CC

- ATP is energy source- NADPH is reducing agent that adds high energy e- to

form sugar

carbon enters as CO2 and leaves as sugar (G3P)

-G3P is raw material used to make glucose & other

carbos

to make one molecule of G3P, 3 CO2 must enter CC,

and 9 ATP & 6 NADPH used

to make 1 molecule of C6H12 O6, 18 ATP & 12 NADPH are

used

Calvin Cycle Notes

*graphic of CalvinCycle


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Rubisco

Enzyme - one of

the most abundant

proteins on Earth

Occurs in

stroma

Forms unstable

6C molecule -

immediately splitsinto 2 3C molecules

3-Phosphoglycerate6 ATP

6 ADP

1,3-Biphosphoglycerate

6 NADPH

6 NADP+

6 Pi

Glyceraldehyde 3-phosphate(G3P)

more potential

energy

G3P

(to sugar)Glucose & other

organic compounds

5 G3P

series of rxns

rearranges carbon

skeleton

3 ATP

3 ADP

Ribulose Biphosphate

(RuBP)

18 ATP & 12 NADPH used

to make glucose!

y


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- opposite of photosynthesis

fostered by hot, dry, bright days when stomata closes to

prevent dehydration by reducing water loss so O2

accumulates

occurs b/c active site of rubisco can accept both O2 & CO2

photo b/c occurs in light when PS reduces CO2 & raises

O2 in leaf space, respiration b/c consumes O2,

releases CO2

produces no ATP, decreases PS output by as much as 50%

limits damaging products of light reactions that build up in the

absence of the Calvin cycle

Photorespiration


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C3 Plants

Named because first organic product of carbon

fixation is a 3C molecule (3-phosphoglycerate)

include rice, wheat, soybeans

Produce less food when their stomata close onhot, dry days.

As O2 exceeds CO2, rubisco adds O2 instead

of CO2, forming a 2C molecule that getsbroken down by peroxisomes into CO2.

If less CO2, then cant feed Calvin

Cycle.



C4


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Named because first organic product of carbon

fixation is a 4C moleculeAre members of grass family incl. sugarcane &

cornCO2 is fixed to PEP (phosphoenolpyruvate) by

PEP carboxylase (has a highaffinity to CO2 therefore fixes CO2 more

efficiently than rubisco) in the mesophyllcells

Bundle-sheath cell performs Calvin cycleadaptive b/c enhances carbon fixing under

C4Plant

s


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CAM Plants

Named because crassulaceae

is plant family thatperforms crassulaceanacid metabolism (CAM)

In succulent (H2O-storing)

plants like cacti &pineapples.

Performs same 2 steps as in C4 plants,but occurs in same part of plant atdifferent times of day

d ti i id diti



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5. Photosynthesis (Chap. 10)

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