PHOTOSYNTHESISCHAPTER 7

Where It Starts - Photosynthesis

IMPACTS, ISSUES: SUNLIGHT AND SURVIVAL Plants are autotrophs, or self-nourishing organisms

The first autotrophs filled Earth’s atmosphere with oxygen, creating an ozone (O3) layer

The ozone layer became a shield against deadly UV rays from the sun, allowing life to move out of the ocean

ELECTROMAGNETIC SPECTRUM Shortest Gamma rayswavelength X-rays

UV radiationVisible lightInfrared

radiationMicrowaves

Longest Radio waveswavelength

PHOTONS Packets of light energy

Each type of photon has fixed amount of energy

Photons having most energy travel as shortest wavelength (blue-violet light)

VISIBLE LIGHT Wavelengths humans perceive as different

colors Violet (380 nm) to red (750 nm) Longer wavelengths, lower energy

Figure 7-2Page 108

shortest wavelengths

(most energetic)

range of most radiation

reaching Earth’s surfacegamm

a rays

range of heat escaping

from Earth’s surface

longest wavelengths

(lowest energy)x

raysultraviol

etradiation

near-infraredradiation

infraredradiation microwave

sradiowaves

VISIBLE LIGHT

Wavelengths of light (nanometers)

Fig. 7-2, p.108

VISIBLE LIGHT

400 450 500 550 600 650 700

PIGMENTS

Color you see is the wavelengths not absorbed Light-catching part of molecule often has

alternating single and double bonds These bonds contain electrons that are capable

of being moved to higher energy levels by absorbing light

VARIETY OF PIGMENTS

Chlorophylls a and bCarotenoids

AnthocyaninsPhycobilins

CHLOROPHYLLSMain pigments in most photoautotrophs

Wav

elen

gth

abso

rpti

on (

%)

Wavelength (nanometers)

chlorophyll b

chlorophyll a

ACCESSORY PIGMENTSpe

rcen

t of

wav

elen

gths

abs

orbe

d

wavelengths (nanometers)

beta-carotenephycoeryth

rin (a phycobilin)

Carotenoids, Phycobilins, Anthocyanins

PIGMENTS IN PHOTOSYNTHESIS Bacteria

Pigments in plasma membranes Plants

Pigments and proteins organized into photosystems that are embedded in thylakoid membrane system

T.E. ENGLEMANN’S EXPERIMENT

Background Certain bacterial cells will move

toward places where oxygen concentration is high

Photosynthesis produces oxygen

T.E. ENGLEMANN’S EXPERIMENT

Fig. 7-4c, p.110

T.E. Englemann’s Experiment

LINKED PROCESSESPhotosynthesis

Energy-storing pathway

Releases oxygen

Requires carbon dioxide

Aerobic Respiration

Energy-releasing pathway

Requires oxygen

Releases carbon dioxide

CHLOROPLAST STRUCTURE

two outer membranes

inner membrane system(thylakoids connected by channels)

stroma

Fig. 7-6, p.111

PHOTOSYNTHESIS EQUATION

12H2O + 6CO2 6O2 + C2H12O6 + 6H2OWater Carbon

Dioxide

Oxygen Glucose Water

LIGHT ENERGY

In-text figurePage 111

Fig. 7-6a, p.111

Photosynthesis

CO2H2O

SUNLIGHT

Fig. 7-6c, p.111

O2

light-dependa

nt reaction

s

light-independa

nt reactions

sugars

CHLOROPLAST

NADPH, ATP

NADP+, ADP

Photosynthesis

WHERE ATOMS END UP

Products 6O2 C6H12O6

6H2O

Reactants 12H2O

6CO2

TWO STAGES OF PHOTOSYNTHESISsunlight water uptake carbon dioxide uptake

ATP

ADP + Pi

NADPH

NADP+

glucoseP

oxygen release

LIGHT-INDEPENDENT

REACTIONS

LIGHT-DEPENDENT REACTIONS

new water

ARRANGEMENT OF PHOTOSYSTEMS

water-splitting complex thylakoidcompartment

H2O 2H + 1/2O2

P680acceptor

P700acceptor

pool of electron carriers stromaPHOTOSYSTEM II

PHOTOSYSTEM I

LIGHT-DEPENDENT REACTIONS

Pigments absorb light energy, give up e-, which enter electron transfer chains

Water molecules split, ATP and NADH form, and oxygen is released

Pigments that gave up electrons get replacements

Fig. 7-7, p.112

photon

Light-Harvesting Complex

Photosystem

LIGHT-DEPENDENT REACTIONS

NADPH

NADP + + H+

thylakoidcompartment

thylakoidmembrane

stromaATPADP + Pi

H+

H+

H+ H+

H+

H+H+

H+ H+H+

H+

PHOTOSYSTEM IsunlightPHOTOSYSTEM II

LIGHT-HARVESTIN

GCOMPLEX

Fig. 7-8, p.113

H+

e- e-e- e-e- e-

H+

e-

O2

H2O

cross-section through a disk-

shaped fold in the thylakoid

membrane

PIGMENTS IN A PHOTOSYSTEM

reaction center

PHOTOSYSTEM FUNCTION: REACTION CENTER Energy is reduced to level that can be

captured by molecule of chlorophyll a

This molecule (P700 or P680) is the reaction center of a photosystem

Reaction center accepts energy and donates electron to acceptor molecule

ELECTRON TRANSFER CHAIN Adjacent to photosystem Acceptor molecule donates electrons from

reaction center

As electrons pass along chain, energy they release is used to produce ATP

CYCLIC ELECTRON FLOW Electrons

are donated by P700 in photosystem I to acceptor molecule

flow through electron transfer chain and back to P700

Electron flow drives ATP formation No NADPH is formed

CYCLIC ELECTRON FLOW

electron acceptor

electron transfer chain

e–

e–

e–

e–

ATP

Electron flow through transfer

chain sets up conditions for ATP formation at other membrane sites.

NONCYCLIC ELECTRON FLOW Two-step pathway for light absorption and

electron excitation Uses two photosystems: type I and

type II Produces ATP and NADPH Involves photolysis - splitting of water

MACHINERY OF NONCYCLIC ELECTRON FLOW

photolysis

H2O

NADP+ NADPH

e–

ATP

ATP SYNTHASE

PHOTOSYSTEM IPHOTOSYSTEM II ADP + Pi

e–

first electron transfer chain

second electron

transfer chain

ENERGY CHANGESPo

tent

ial t

o tr

ansf

er e

nerg

y (v

olts

)

H2O 1/2O2 + 2H+

(Photosystem II)

(Photosystem I)

e– e–

e–e–

secondtransfer

chainNADPHfirst

transfer chain

PHOTOSYSTEM I

p700*

photon e-H+

Cyclic Pathway of ATP Formation

Hig

her

ener

gy p700

Fig. 7-9a, p.114

PHOTOSYSTEM I

e-

Noncyclic Pathway of ATP and NADPH Formation

2H2O

NADPH

NADH+

p700*

p700photon

PHOTOSYSTEM II

p680*

p680

4H+ + O2

Fig. 7-9b, p.114

CHEMIOSMOTIC MODEL OF ATP FORMATION Electrical and H+ concentration gradients are

created between thylakoid compartment and stroma

H+ flows down gradients into stroma through ATP synthesis

Flow of ions drives formation of ATP

CHEMIOSMOTIC MODEL FOR ATP FORMATION

ADP + Pi

ATP SYNTHASE

Gradients propel H+ through ATP synthases;ATP forms by phosphate-group transfer

ATP

H+ is shunted across membrane by some components of the first electron transfer chain

PHOTOSYSTEM II

H2Oe– acceptor

Photolysis in the thylakoid compartment splits water

PHOTOSYNTHESIS QUIZ 1 1. Give the equation for photosynthesis. 2. Give the 2 major reactions occurring in photosynthesis. 3. What reactant goes into the light reactions? What product? 4. What reactant goes into the Calvin cycle? What product? 5. Within the chloroplast, where do the light reactions occur? 6. Within the chloroplast, where does the Calvin cycle occur? 7. What does noncyclic electron flow produce (besides ATP) that

that cyclic electron flow does not produce? 8. Why doesn’t the overall action spectrum of photosynthesis

exactly match the absorption spectrum for chlorophyll? 9. Which photosystem acts first in noncyclic electron flow? ****BONUS**** 1. What are Pq, Pc, and Fd?

2. EXPLAIN WHAT CHEMIOSMOSIS IS.

LIGHT-INDEPENDENT REACTIONS Synthesis part of photosynthesis Can proceed in the dark Take place in the stroma Calvin-Benson cycle

CALVIN-BENSON CYCLE Overall reactants

Carbon dioxideATPNADPH

Overall productsGlucoseADPNADP+

Reaction pathway is cyclic and RuBP (ribulose bisphosphate) is regenerated

CALVIN- BENSON CYCLE

CARBON FIXATION

6 CO2 (from the air)

6 6RuBP

PGA

unstable intermediate

6 ADP

612

12ATP

ATP

NADPH

1012

PGAL

glucoseP

PGAL2

Pi

12 ADP12 Pi12 NADP+

12

4 Pi

PGAL

Fig. 7-10a, p.115

THESE REACTIONS PROCEED IN THE CHLOROPLAST’S

STROMA

Calvin- Benson Cycle

ATP

6 RuBP

phosphorylated glucose

10 PGAL

1 Pi

12 PGA

Calvin-Benson cycle

Fig. 7-10b, p.115

6 ADP

ATP

12 ADP +12 Pi

6CO2

NADPH

12 NADP+

12 PGAL

4 Pi

1

12

12

Calvin- Benson

Cycle

THE C3 PATHWAY In Calvin-Benson cycle, the first stable

intermediate is a three-carbon PGA

Because the first intermediate has three carbons, the pathway is called the C3 pathway

PHOTORESPIRATION IN C3 PLANTS On hot, dry days stomata close Inside leaf

Oxygen levels rise Carbon dioxide levels drop

Rubisco attaches RuBP to oxygen instead of carbon dioxide

Only one PGAL forms instead of two

Fig. 7-11a1, p.116

C3 Plants

upperepidermis

palisademesophyll

spongymesophyll

lowerepidermis

stoma leaf vein air space

Basswood leaf, cross-section.

Fig. 7-11a2, p.116

C3 Plants

6 PGA + 6 glycolate

6 PGAL

1 PGAL

Twelve turns of the cycle, not just six, to make one 6-carbon sugar

RuBPCalvin-Benson

Cycle

CO2+

water

5 PGAL

Stomata closed: CO2 can’t get in; O2 can’t get out

Rubisco fixes oxygen, not carbon, in mesophyll cells in leaf

Fig. 7-11a3, p.117

C3 Plants

C4 PLANTS Carbon dioxide is fixed twice

In mesophyll cells, carbon dioxide is fixed to form four-carbon oxaloacetate

Oxaloacetate is transferred to bundle-sheath cells

Carbon dioxide is released and fixed again in Calvin-Benson cycle

Fig. 7-11b1, p.117

C4 Plants

upperepidermis

mesophyllcell

bundle-sheath cell

lowerepidermis

Basswood leaf, cross-section.Fig. 7-11b2, p.117

C4 Plants

oxaloacetate

malateC4

cycle

pyruvateCO2

12 PGAL

10 PGAL

2 PGAL

1 sugar

RuBPCalvin-Benson

Cycle

Carbon fixed in the mesophyll cell, malate diffuses into adjacent bundle-sheath cell

In bundle-sheath cell, malate gets converted to pyruvate with release of CO2, which enters Calvin-Benson cycle

12 PGAL

PEP

Stomata closed: CO2 can’t get in; O2 can’t get out

Fig. 7-11b3, p.117

C4 Plants

CAM PLANTS Carbon is fixed twice (in same cells) Night

Carbon dioxide is fixed to form organic acids Day

Carbon dioxide is released and fixed in Calvin-Benson cycle

Fig. 7-11c1, p.117

CAM Plants

Fig. 7-11c2, p.117

epidermis with thick cuticlemesophyll cellair space

stoma

CAM Plants

Stomata stay closed during day, open for CO2 uptake at

night only.

C4 CYCLE

Calvin-Benson

Cycle

C4 cycle operates at night when CO2 from aerobic respiration fixed

1 sugar

CO2 that accumulated overnight used in C3 cycle during the day

Fig. 7-11c3, p.117

CAM Plants

SUMMARY OF PHOTOSYNTHESIS

Figure 7-14Page 120

light 6O212H2O

CALVIN-BENSON CYCLE

C6H12O6

(phosphorylated glucose)

NADPHNADP+ATPADP + Pi

PGA PGAL

RuBP

P

6CO2

end product (e.g., sucrose, starch, cellulose)

LIGHT-DEPENDENT REACTIONS

6H2O

LIGHT-INDEPENDENT REACTIONS

CARBON AND ENERGY SOURCES Photoautotrophs

Carbon source is carbon dioxideEnergy source is sunlight

HeterotrophsGet carbon and energy by eating

autotrophs or one another

Fig. 7-12, p.118

sunlight

energyPhotosynthes

is1. H2O is split by light energy. Its oxygen diffuses away; its electrons, hydrogen enter transfer chains with roles in ATP formation. Coenzymes pick up the electrons and hydrogen2. ATP energy drives the synthesis of glucose from hydrogen and electrons (delivered by coenzymes), plus carbon and oxygen (from carbon dioxide).

glucose

(stored energy, buildin

g blocks)

carbon dioxide,water

oxygen

Aerobic Respiration1. Glucose is broken down completely to carbon dioxide and water. Coenzymes pick up the electrons, hydrogens.2. The coenzymes give up the electrons and hydrogen atoms to oxygen-requiring transfer chains that have roles in forming many ATP molecules.ATP available to drive

nearly all cellular tasks

Carbon and Energy Sources

PHOTOAUTOTROPHS Capture sunlight energy and use it to carry

out photosynthesis Plants Some bacteria Many protistans

SATELLITE IMAGES SHOW PHOTOSYNTHESIS

 Photosynthetic activity in spring

Atlantic Ocean

Figure 7-13Page 119

sunlight

Calvin-Benson cycle

Light-DependentReactions

end products (e.g., sucrose, starch, cellulose)

ATP

12 PGAL

Light-Independent

Reactionsphosphorylated glucose

6H2O

6 RuBP

12H2O 6O2

NADPH NADP+

6CO2

ADP + Pi

Fig. 7-14, p.120

HTTP://WWW.YOUTUBE.COM/WATCH?FEATURE=PLAYER_DETAILPAGE&V=0IJMRSTCWCG&LIST=PLFCE4D99C4124A27A