Photosynthesis

Copyright 2005 Pearson Education, Inc. publishing as Benjamin Cummings

PowerPoint Lectures forBiology, Seventh Edition

Neil Campbell and Jane Reece

Lectures by Chris Romero

Chapter 10Chapter 10

Photosynthesis


Photosynthesis

Occurs in plants, algae, certain other protists,and some prokaryotes

These organisms use light energy to drive thesynthesis of organic molecules from carbon dioxideand (in most cases) water. They feed not onlythemselves, but the entire living world. (a) Onland, plants are the predominant producers offood. In aquatic environments, photosyntheticorganisms include (b) multicellular algae, suchas this kelp; (c) some unicellular protists, suchas Euglena; (d) the prokaryotes calledcyanobacteria; and (e) other photosyntheticprokaryotes, such as these purple sulfurbacteria, which produce sulfur (sphericalglobules) (c, d, e: LMs).

(a) Plants

(b) Multicellular algae

(c) Unicellular protist 10 m

40 m(d) Cyanobacteria

1.5 m(e) Pruple sulfurbacteria

Figure 10.2


Chloroplasts: The Sites of Photosynthesis in Plants

Vein

Leaf cross section

Figure 10.3

Mesophyll

CO2 O2Stomata


Chloroplast

Mesophyll

5 m

Outermembrane

Intermembranespace

Innermembrane

Thylakoidspace

ThylakoidGranumStroma

1 m


Tracking Atoms Through Photosynthesis:Scientific Inquiry Photosynthesis is summarized as

6 CO2 + 6 H2O + Light energy C6H12O6 + 6 O2


The Splitting of Water Chloroplasts split water into

Hydrogen and oxygen, incorporating theelectrons of hydrogen into sugar molecules

6 CO2 12 H2OReactants:

Products: C6H12O66

H2O6

O2

Figure 10.4


The Two Stages of Photosynthesis: A Preview Photosynthesis consists of two processes

The light reactions

The Calvin cycle


An overview of photosynthesis

H2O CO2

Light

LIGHTREACTIONS

CALVINCYCLE

Chloroplast

[CH2O](sugar)

NADPH

NADP

ADP+ P

O2Figure 10.5

ATP


Concept 10.2: The light reactions convert solarenergy to the chemical energy of ATP andNADPH


The electromagnetic spectrum

Is the entire range of electromagnetic energy, orradiation

Gammarays X-rays UV Infrared

Micro-waves

Radiowaves

105 nm 103 nm 1 nm 103 nm 106 nm1 m

106 nm 103 m

380 450 500 550 600 650 700 750 nm

Visible light

Shorter wavelength

Higher energy

Longer wavelength

Lower energyFigure 10.6


Reflect light, which include the colors we see

Light

ReflectedLight

Chloroplast

Absorbedlight

Granum

Transmittedlight

Figure 10.7


The absorption spectra of three types of pigmentsin chloroplasts

Three different experiments helped reveal which wavelengths of light are photosyntheticallyimportant. The results are shown below.

EXPERIMENT

RESULTS

Abs

orpt

ion

of li

ght b

ych

loro

plas

t pig

men

tsChlorophyll a

(a) Absorption spectra. The three curves show the wavelengths of light best absorbed bythree types of chloroplast pigments.

Wavelength of light (nm)

Chlorophyll b

Carotenoids

Figure 10.9


The action spectrum for photosynthesis

Was first demonstrated by Theodor W. Engelmann

400 500 600 700

Aerobic bacteria

Filamentof alga

Engelmanns experiment. In 1883, Theodor W. Engelmann illuminated a filamentous alga with light that hadbeen passed through a prism, exposing different segments of the alga to different wavelengths. He used aerobicbacteria, which concentrate near an oxygen source, to determine which segments of the alga were releasing themost O2 and thus photosynthesizing most.Bacteria congregated in greatest numbers around the parts of the alga illuminated with violet-blue or red light.Notice the close match of the bacterial distribution to the action spectrum in part b.

(c)

Light in the violet-blue and red portions of the spectrum are most effective in drivingphotosynthesis.CONCLUSION


Excitation of Chlorophyll by Light When a pigment absorbs light

It goes from a ground state to an excited state,which is unstable

Excitedstate

Heat

Photon(fluorescence)

Chlorophyllmolecule

GroundstatePhoton

e

Figure 10.11 A


A photosystem

Primary electionacceptor

Photon

Thylakoid

Light-harvestingcomplexes

Reactioncenter

Photosystem

STROMATh

ylak

oid

mem

bran

e

Transferof energy

Specialchlorophyll amolecules

Pigmentmolecules

THYLAKOID SPACE(INTERIOR OF THYLAKOID)Figure 10.12

e


Produces NADPH, ATP, and oxygen

Figure 10.13 Photosystem II(PS II)Photosystem-I

(PS I)

ATP

NADPH

NADP+

ADPCALVINCYCLE

CO2H2O

O2 [CH2O] (sugar)

LIGHTREACTIONS

Light

Primaryacceptor

Pq

Cytochromecomplex

PC

e

P680

e

e

O2+

H2O2 H+

Light

ATP

Primaryacceptor

Fd

ee

NADP+reductase

P700

Light

NADPH

NADP++ 2 H+

+ H+

1

5

7

2

3

4

6

8


A mechanical analogy for the light reactions

MillmakesATP

ATP

e

ee

e

e

Photosystem II Photosystem I

e

e

NADPH

Figure 10.14


The light reactions and chemiosmosis: theorganization of the thylakoid membrane

LIGHTREACTOR

NADP+ADP

ATP

NADPH

CALVINCYCLE

[CH2O] (sugar)STROMA(Low H+ concentration) Photosystem II

LIGHTH2O CO2

Cytochromecomplex

O2

H2O O21

12

2

Photosystem ILight

THYLAKOID SPACE(High H+ concentration)

STROMA(Low H+ concentration)

Thylakoidmembrane

ATPsynthase

PqPc

Fd

NADP+reductase

NADPH + H+

NADP+ + 2H+

ToCalvincycle

ADP

PATP

3

H+

2 H++2 H+

2 H+

Figure 10.17


Key

Higher [H+]Lower [H+]

Mitochondrion Chloroplast

MITOCHONDRIONSTRUCTURE

Intermembrancespace

Membrance

Matrix

Electrontransport

chain

H+ DiffusionThylakoidspace

Stroma

ATPH+

PADP+

ATPSynthase

CHLOROPLASTSTRUCTURE

Figure 10.16


Cyclic Electron Flow Under certain conditions

Photoexcited electrons take an alternative path


In cyclic electron flow

Only photosystem I is used

Only ATP is produced

Primaryacceptor

Pq

Fd

Cytochromecomplex

Pc

Primaryacceptor

Fd

NADP+reductase

NADPH

ATPFigure 10.15 Photosystem II

Photosystem I

NADP+


Objective: You will be able to discuss how theenergy from the light reactions helps build acarbohydrate in the Calvin cycle.


The Calvin cycle has three phases

Carbon fixation

Reduction

Regeneration of the CO2 acceptor


The Calvin cycle

(G3P)

Input(Entering one

at a time)CO23

Rubisco

Short-livedintermediate

3 P P

3 P PRibulose bisphosphate

(RuBP)

P

3-Phosphoglycerate

P6 P

6

1,3-Bisphoglycerate6 NADPH

6 NADPH+

6 P

P6

Glyceraldehyde-3-phosphate(G3P)

6 ATP

3 ATP

3 ADP CALVINCYCLE

P5

P1G3P

(a sugar)Output

LightH2O CO2

LIGHTREACTION

ATP

NADPH

NADP+ADP

[CH2O] (sugar)

CALVINCYCLE

Figure 10.18

O2

6 ADP

Glucose andother organiccompounds

Phase 1: Carbon fixation

Phase 2:Reduction

Phase 3:Regeneration ofthe CO2 acceptor(RuBP)


Objective: You will be able to differentiatebetween photorespiration adaptations.


Photorespiration: An Evolutionary Relic? In photorespiration

O2 substitutes for CO2 in the active site of theenzyme rubisco

The photosynthetic rate is reduced


C4 leaf anatomy and the C4 pathway

CO2Mesophyll cell

Bundle-sheathcell

Vein(vascular tissue)

Photosyntheticcells of C4 plantleaf

Stoma

Mesophyllcell

C4 leaf anatomy

PEP carboxylase

Oxaloacetate (4 C) PEP (3 C)

Malate (4 C)

ADP

ATP

Bundle-Sheathcell CO2

Pyruate (3 C)

CALVINCYCLE

Sugar

Vasculartissue

Figure 10.19

CO2


The CAM pathway

Spatial separationof steps. In C4plants, carbon fixationand the Calvin cycleoccur in differenttypes of cells.

(a) Temporal separationof steps. In CAMplants, carbon fixationand the Calvin cycleoccur in the same cellsat different times.

(b)

PineappleSugarcane

Bundle-sheathcell

Mesophyll Cell

Organic acid

CALVINCYCLE

Sugar

CO2 CO2

Organic acid

CALVINCYCLE

Sugar

C4 CAM

CO2 incorporatedinto four-carbonorganic acids(carbon fixation)

Night

Day

1

2 Organic acidsrelease CO2 toCalvin cycle

Figure 10.20


The Importance of Photosynthesis: A Review A review of photosynthesis

Light reactions: Are carried out by molecules in the

thylakoid membranes Convert light energy to the chemical

energy of ATP and NADPH Split H2O and release O2 to the

atmosphere

Calvin cycle reactions: Take place in the stroma Use ATP and NADPH to convert

CO2 to the sugar G3P Return ADP, inorganic phosphate,and

NADP+ to the light reactions

O2

CO2H2O

Light

Light reaction Calvin cycle

NADP+ADP

ATP

NADPH

+ P 1RuBP 3-Phosphoglycerate

Amino acidsFatty acids

Starch(storage)

Sucrose (export)

G3P

Photosystem IIElectron transport chain

Photosystem I

Chloroplast

Figure 10.21

Photosynthesis

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