Fig. 10-2

(a) Plants

(c) Unicellular protist10 µm

1.5 µm

40 µm(d) Cyanobacteria

(e) Purple sulfur bacteria

(b) Multicellular alga

Fig. 10-3a

5 µm

Mesophyll cell

StomataCO2 O2

Chloroplast

Mesophyll

Vein

Leaf cross section

Fig. 10-3b

1 µm

Thylakoidspace

Chloroplast

GranumIntermembranespace

Innermembrane

Outermembrane

Stroma

Thylakoid

Reactants:

Fig. 10-4

6 CO2

Products:

12 H2O

6 O26 H2OC6H12O6

Fig. 10-7

Reflectedlight

Absorbedlight

Light

Chloroplast

Transmittedlight

Granum

UV

Fig. 10-6

Visible light

InfraredMicro-waves

RadiowavesX-raysGamma

rays

103 m1 m

(109 nm)106 nm103 nm1 nm10–3 nm10–5 nm

380 450 500 550 600 650 700 750 nm

Longer wavelength

Lower energyHigher energy

Shorter wavelength

Fig. 10-9

Wavelength of light (nm)

(b) Action spectrum

(a) Absorption spectra

(c) Engelmann’s experiment

Aerobic bacteria

RESULTS

Ra

te o

f p

ho

tos

yn

the

sis

(me

as

ure

d b

y O

2 re

lea

se

)A

bs

orp

tio

n o

f li

gh

t b

yc

hlo

rop

las

t p

igm

en

ts

Filamentof alga

Chloro- phyll a Chlorophyll b

Carotenoids

500400 600 700

700600500400

Light

Fig. 10-5-4

H2O

Chloroplast

LightReactions

NADP+

P

ADP

i+

ATP

NADPH

O2

CalvinCycle

CO2

[CH2O]

(sugar)

Fig. 10-11

(a) Excitation of isolated chlorophyll molecule

Heat

Excitedstate

(b) Fluorescence

Photon Groundstate

Photon(fluorescence)

En

erg

y o

f el

ectr

on

e–

Chlorophyllmolecule

Fig. 10-12

THYLAKOID SPACE(INTERIOR OF THYLAKOID)

STROMA

e–

Pigmentmolecules

Photon

Transferof energy

Special pair ofchlorophyll amolecules

Th

yla

koid

me

mb

ran

e

Photosystem

Primaryelectronacceptor

Reaction-centercomplex

Light-harvestingcomplexes

Pigmentmolecules

Light

P680

e–

Primaryacceptor

2

1

e–

e–

2 H+

O2

+3

H2O

1/2

4

Pq

Pc

Cytochromecomplex

Electron transport chain

5

ATP

Photosystem I(PS I)

Light

Primaryacceptor

e–

P700

6

Fig. 10-13-4

Photosystem II(PS II)

Pigmentmolecules

Light

P680

e–

Primaryacceptor

2

1

e–

e–

2 H+

O2

+3

H2O

1/2

4

Pq

Pc

Cytochromecomplex

Electron transport chain

5

ATP

Photosystem I(PS I)

Light

Primaryacceptor

e–

P700

6

Fd

Electron transport chain

NADP+

reductase

NADP+

+ H+

NADPH

8

7

e–

e–

6

Fig. 10-13-5

Photosystem II(PS II)

Fig. 10-14

MillmakesATP

e–

NADPH

Ph

oto

n

e–

e–

e–

e–

e–

Ph

oto

n

ATP

Photosystem II Photosystem I

e–

Fig. 10-16

Key

Mitochondrion Chloroplast

CHLOROPLASTSTRUCTURE

MITOCHONDRIONSTRUCTURE

Intermembranespace

Innermembrane

Electrontransport

chain

H+ Diffusion

Matrix

Higher [H+]Lower [H+]

Stroma

ATPsynthase

ADP + P i

H+ATP

Thylakoidspace

Thylakoidmembrane

Fig. 10-17

Light

Fd

Cytochromecomplex

ADP +

i H+

ATPP

ATPsynthase

ToCalvinCycle

STROMA(low H+ concentration)

Thylakoidmembrane

THYLAKOID SPACE(high H+ concentration)

STROMA(low H+ concentration)

Photosystem II Photosystem I

4 H+

4 H+

Pq

Pc

LightNADP+

reductase

NADP+ + H+

NADPH

+2 H+

H2OO2

e–

e–

1/21

2

3

Fig. 10-18-3

Ribulose bisphosphate(RuBP)

3-Phosphoglycerate

Short-livedintermediate

Phase 1: Carbon fixation

(Entering oneat a time)

Rubisco

Input

CO2

P

3 6

3

3

P

PPP

ATP6

6 ADP

P P6

1,3-Bisphosphoglycerate

6

P

P6

66 NADP+

NADPH

i

Phase 2:Reduction

Glyceraldehyde-3-phosphate(G3P)

1 POutput G3P

(a sugar)

Glucose andother organiccompounds

CalvinCycle

3

3 ADP

ATP

5 P

Phase 3:Regeneration ofthe CO2 acceptor(RuBP)

G3P

Photorespiration: An Evolutionary Relic?

• In most plants (C3 plants), initial fixation of CO2, via rubisco, forms a three-carbon compound

• In photorespiration, rubisco adds O2 instead of CO2 in the Calvin cycle

• Photorespiration consumes O2 and organic fuel and releases CO2 without producing ATP or sugar

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

• Photorespiration may be an evolutionary relic because rubisco first evolved at a time when the atmosphere had far less O2 and more CO2

• Photorespiration limits damaging products of light reactions that build up in the absence of the Calvin cycle

• In many plants, photorespiration is a problem because on a hot, dry day it can drain as much as 50% of the carbon fixed by the Calvin cycle

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

C4 Plants

• C4 plants minimize the cost of photorespiration by incorporating CO2 into four-carbon compounds in mesophyll cells

• This step requires the enzyme PEP carboxylase

• PEP carboxylase has a higher affinity for CO2 than rubisco does; it can fix CO2 even when CO2 concentrations are low

• These four-carbon compounds are exported to bundle-sheath cells, where they release CO2 that is then used in the Calvin cycle

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Fig. 10-19

C4 leaf anatomy

Mesophyll cellPhotosyntheticcells of C4

plant leafBundle-sheathcell

Vein(vascular tissue)

Stoma

The C4 pathway

Mesophyllcell CO2PEP carboxylase

Oxaloacetate (4C)

Malate (4C)

PEP (3C)ADP

ATP

Pyruvate (3C)

CO2

Bundle-sheathcell

CalvinCycle

Sugar

Vasculartissue

CAM Plants

• Some plants, including succulents, use crassulacean acid metabolism (CAM) to fix carbon

• CAM plants open their stomata at night, incorporating CO2 into organic acids

• Stomata close during the day, and CO2 is released from organic acids and used in the Calvin cycle

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Fig. 10-20

CO2

Sugarcane

Mesophyllcell

CO2

C4

Bundle-sheathcell

Organic acidsrelease CO2 to Calvin cycle

CO2 incorporatedinto four-carbonorganic acids(carbon fixation)

Pineapple

Night

Day

CAM

SugarSugar

CalvinCycle

CalvinCycle

Organic acid Organic acid

(a) Spatial separation of steps (b) Temporal separation of steps

CO2 CO2

1

2

The Importance of Photosynthesis: A Review

• The energy entering chloroplasts as sunlight gets stored as chemical energy in organic compounds

• Sugar made in the chloroplasts supplies chemical energy and carbon skeletons to synthesize the organic molecules of cells

• Plants store excess sugar as starch in structures such as roots, tubers, seeds, and fruits

• In addition to food production, photosynthesis produces the O2 in our atmosphere

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Fig. 10-21

LightReactions:

Photosystem II Electron transport chain

Photosystem I Electron transport chain

CO2

NADP+

ADP

P i+

RuBP 3-Phosphoglycerate

CalvinCycle

G3PATP

NADPHStarch(storage)

Sucrose (export)

Chloroplast

Light

H2O

O2

Fig. 10-UN1

CO2

NADP+

reductase

Photosystem II

H2O

O2

ATP

Pc

Cytochromecomplex

Primaryacceptor

Primaryacceptor

Photosystem I

NADP+

+ H+

Fd

NADPH

Electron transport

chain

Electron transport

chain

O2

H2O Pq

Drought? …. Abscisic acid Drought? …. Abscisic acid

•In preparation for winter, ABA is In preparation for winter, ABA is produced in produced in terminal buds, this slows , this slows plant growth. plant growth.

•ABA also inhibits the division of cells ABA also inhibits the division of cells adjusting to cold conditions in the adjusting to cold conditions in the winter by suspending primary and winter by suspending primary and secondary growth.secondary growth.

•ABA then translocates to the leaves, ABA then translocates to the leaves, where it rapidly alters the osmotic where it rapidly alters the osmotic potential of stomatal guard cells, potential of stomatal guard cells, causing them to shrink and causing them to shrink and stomata to to close. close.

•Reduces Reduces transpiration

Indian PipeIndian Pipe