Photosynthesis

Ch 7

Autotrophs

Chloroplasts

• Contain chlorophyll– Green

• Site of photosynthesis• Concentrated in leaves

Chloroplast Structure

Overview of Photosynthesis

• Light Reaction (stage 1)– Thylakoid membranes of granna– Converts light energy to chemical energy– O2 produced as waste product

• Calvin Cycle (stage 2)– Stroma – Synthesizes sugar molecules with CO2 &

energy produced in light reactions

Fig. 7-5-3

H2O

ADP

P

LIGHTREACTIONS

(in thylakoids)

Light

Chloroplast

NADPH

ATP

O2

CALVINCYCLE

(in stroma)

Sugar

CO2

NADP+

Redox (again)

• Recall– Oxidation- loss of e-– Reduction- addition of e-

6 CO2 + 6 H2O C6H12O6 + 6 O2

Reduction

Oxidation

Light Reactions

Wavelength (nm)

10–5 nm

Increasing energy

Visible light

650nm

10–3 nm 1 nm 103 nm 106 nm 1 m

380400 500 600 700 750

Radiowaves

Micro-waves

InfraredX-rays UVGammarays

Light Absorbing Pigments

• Chlorophyll A• Chlorophyll B• Carotenoids

Chlorophyll is excited

Chlorophyllmolecule

Excited state

Ground state

Heat

PhotonPhoton

(fluorescence)

e–

PhotosystemsReactioncenter complex

e–

Primary electronacceptor

Light-harvestingcomplexes

Photon

Transferof energy

Pigmentmolecules

Pair ofChlorophyll a molecules

Th

yla

ko

id m

em

bra

ne

Photosystems

Fig. 7-8a

Stroma

O2

H2O 12 H+

NADP+ NADPHPhoton

Photosystem II

Electron transport chainProvides energy forsynthesis of

by chemiosmosis

+ 2

Primaryacceptor

1

Thylakoidmem-brane

P680

2

4

3Thylakoidspace

e–e–

5

Primaryacceptor

P700

6

Photon

Photosystem IATP

H++

Fig. 7-9

+

O2

H2O12 H+

NADP+ H+ NADPH

+ 2

H+

H+

H+ H+

H+

H+

H+

H+

H+H+

H+

H+

H+ H+

Photosystem II Photosystem IElectrontransport

chain

ATP synthase

LightLight

Stroma (low H+

concentration)

Chloroplast

Thylakoidmembrane

Thylakoid space(high H+ concentration)

ADP + P ATP

Calvin CycleCO2

ATPNADPH

Input

CALVINCYCLE

G3POutput:

Carbon Fixation - Stomata

NADPH

ATP

RuBP

3

P

G3P

P

Input:CO2

1

Rubisco

3 P

Step Carbon fixation

3-PGA6 P

CALVINCYCLE

6

6

6

6

P

Step Reduction

2

2

G3P5 P

3

3

G3P1 P

Glucoseand othercompounds

Output:

Step Release of one

molecule of G3P

1

Step Regeneration of RuBP4

4ATP3

3 ADP

NADP+

6 ADP +

Adaptations

CO2

CALVINCYCLE

Bundle-sheathcell

3-C sugar

C4 plant

4-C compound

CO2

CALVINCYCLE

3-C sugar

CAM plant

4-C compound

Night

Day

Mesophyllcell

CO2 CO2

Photosynthesis and cellular respiration provide energy for life

– Photosynthesis uses solar energy to produce glucose and O2 from CO2 and H2O

– Cellular respiration makes ATP and consumes O2 during the oxidation of glucose to CO2 and H2O

CO2

H2O

Glucose

O2

ATP

ECOSYSTEM

Sunlight energy

Photosynthesis in chloroplasts

Cellular respiration in mitochondria

(for cellular work)

Heat energy

Figure 6.1