Photosynthesis

Lightenergy

PHOTOSYNTHESIS

6 CO2 6+ H2O

Carbon dioxide Water

C6H12O6 6+ O2

Glucose Oxygen gas

Photosynthesis

– Human demand for energy • Fossil fuel supplies?

– Energy plantations• Biomass energy

• Photoautotrophs

– C source?

– Energy source?

• Heterotrophs

– C source?

– Energy source?

Carbon and Energy

Photoautotrophs

Figure 7.1A–D

•Green parts…– Chloroplasts (stroma and thylakoids)

– Stomata

Leaf Cross Section

Leaf

Mesophyll Cell

Mesophyll

VeinStoma

CO2O2

Chloroplast

Chloroplast

Grana Stroma

TE

M 9

,750

Stroma

Granum Thylakoid Thylakoidspace

OutermembraneInnermembrane

Intermembranespace

LM 2

,600

Where does PS happen?

• By splitting water

Where does O2 come from?

•Redox processes

Reduction

Oxidation

6 O2 6 H2O

Reduction

Oxidation

6 O26 CO2 6 H2O C6H12O6

C6H12O6 6 CO2

Just like respiration?

Linked Processes

Photosynthesis

• Energy-storing

• Releases O2

• Requires CO2

Aerobic Respiration

• Energy-releasing

• Requires O2

• Releases CO2

2 stages•The light reactions…– Energy capture

– produce O2

•The Calvin cycle– Uses CO2

– Makes sugar

•The Coenzymes– ATP

– NADPH

Overview

Light

CO2H2OChloroplast

LIGHTREACTIONS(in thylakoids)

CALVINCYCLE

(in stroma)

NADP+

ADP+ P

ATP

NADPH

O Sugar

Electrons

Visible LightIncreasing energy

10–5 nm 10–3 nm 1 nm 103 nm 106 nm 1 m 103 m

Gammarays

X-rays UV Infrared Micro-waves

Radiowaves

Visible light

400 500 600 700 750

650nm

Wavelength (nm)

Transmittedlight

Absorbedlight

Reflectedlight

Light

Chloroplast

380

Pigments

Colors?

• Wavelengths not absorbed

• Chlorophylls a and b

• Carotenoids

ChlorophyllsW

avel

eng

th a

bso

rpti

on

(%

)

Wavelength (nanometers)

chlorophyll b

chlorophyll a

T.E. Englemann’s Experiment

Photons

• Packets of light energy

• Shortest wavelength (blue-violet light) = highest energy

Strike chlorophyll in photosystemExcite an electron

Figure 7.7B, C

Ene

rgy

of e

lect

ron

Photon

Excited state

Heat

Photon(fluorescence)

Ground state

Chlorophyllmolecule

e–

Photosystem

Light-harvestingcomplexes

Reactioncenter

Primary electronacceptor

e–

To electrontransport chain

Pigment molecules

Chlorophyll a moleculeTransfer of energy

Photon

Thy

lako

id m

embr

ane

Photons and Photosystems

• Photon energy transfer to reaction-center

• Excites electron• Which is taken by the primary

electron acceptor• Which leads to the ETC

Ene

rgy

of e

lect

ron

Photon

Excited state

Heat

Photon(fluorescence)

Ground state

Chlorophyllmolecule

e–

Photosystem

Light-harvestingcomplexes

Reactioncenter

Primary electronacceptor

e–

To electrontransport chain

Pigment molecules

Chlorophyll a moleculeTransfer of energy

PhotonT

hyla

koid

mem

bran

e

Photosystem: Harvester Pigments

• When excited by light energy:

Electron Transfer Chain• Uses electrons from reaction

center• Powers H+ pump to produce ATP • Produces NADPH

Thylakoidspace

Photon

Stroma

Th

yla

koid

me

mb

ran

e

1

Photosystem II

e–

P680

2

H2O 12

+ 2O2 H+

3

ATPElectron transport chainProvides energy for synthesis of

by chemiosmosis

4

Photosystem I

Photon

P700

e–

5

+NADP+ H+ NADPH

6

– Electrons move from photosystem II to I• Make ATP

– Electrons from photosystem I• Reduce NADP+ to NADPH

Figure 7.8B

e–

ATP

MillmakesATP

Pho

ton

Pho

ton

Photosystem II Photosystem I

NADPHe–

e–e–

e–

e–

e–

Electron Transfer Chain

ATP ProductionChloroplast

Stroma (low H+ concentration)

Light Light

NADP+ + H+ NADPH

H+

H+

H+

H+

ATPPADP +

Thylakoidmembrane

H2O 1

2O2 2 H+ H+

H+

H+ H+

H+

H+

H+ H+

H+

H+

Photosystem II Electrontransport chain

Photosystem I ATP synthase

Thylakoid space(high H+ concentration)

+

• They put the “synthesis” in

photosynthesis

• Calvin-Benson cycle

• In stroma

Light-Independent Reactions

Calvin-Benson Cycle

Overall reactants

• CO2

• ATP

• NADPH

Overall products

• Glucose

• ADP

• NADP+

Cyclic! RuBP is regenerated

Figure 7.14_4

• 1st stable molecule is 3C PGA• C3 plants: tomatoes, petunias,

roses, daisies, avocados

C3 Plants

C3 Plants

• Hot, dry days what happens?• Inside leaf?

– O2 increases

– CO2 drops

• PS rate?

C4 Pathway

• CO2 miner

• 4C oxaloacetate forms in bundle sheath cells

• Grasses

CAM Plants

• Opens stomata at night

• Forms 4C compound

• Release CO2

• Succulents and cacti

• Slow growing

C4 and CAM

Greenhouse Effect?

•What is the role of PS in global warming?

– Excess CO2 in the atmosphere

Sunlight

ATMOSPHERE

Some heatenergy escapesinto space

Radiant heattrapped by CO2

and other gases

Greenhouse Effect

Question of the Day

Scientists at Stanford University conducted a study on California grasslands. They looked at the effects of increased levels of CO2 , soil nitrogen, and temperature (modeling our future) on plant growth. What did they find?