Chapter 10: Photosynthesis1. What is photosynthesis & what organisms do photosynthesis?

- Photosynthesis – conversion of light energy to chemical energy- Photoautotrophs

Figure 10.2 Photoautotrophs

(a) Plants

(b) Multicellular algae

(c) Unicellular protist 10 m

40 m(c) Cyanobacteria

1.5 m(d) Pruple sulfurbacteria

These organisms use light energy to drive the synthesis 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).

Chapter 10: Photosynthesis1. What is photosynthesis & what organisms do photosynthesis?

- Photosynthesis – conversion of light energy to chemical energy- Photoautotrophs

2. Where does photosynthesis occur?- Chloroplasts

Fig. 10.3 Focusing in on the location of photosynthesis in a plant

Mesophyll cell

Mesophyll

Vein

Stomata

CO2 O2

Chloroplast

5 µm

1 µm

Outermembrane

Intermembranespace

Inner membrane

Thylakoid ThylakoidSpace

GranumStroma

Leaf cross section

½ million chloroplasts / mm2 of leaf

30 – 40 chloroplasts / mesophyll cell

Chapter 10: Photosynthesis1. What is photosynthesis & what organisms do photosynthesis?2. Where does photosynthesis occur?3. How did chloroplasts evolve?

- Endosymbiosis- Chemoheterotroph engulfed a photoautotroph (Ch 26)

4. What is the chemical equation for photosynthesis?

CO2 + H2O + light energy → C6H12O6 + O2 + H2O (+ energy)

6 CO2 12 H2OReactants:

Products: C6H12O66 H2O 6 O2

Let’s see where this occurs in the chloroplast….The light reactions & the Calvin Cycle

Figure 10.5 An overview of photosynthesis: cooperation of the light reactions and the Calvin cycle

Light

LIGHT REACTIONS

Chloroplast

H2O

Light rxns require light – light-dependent

Figure 10.5 An overview of photosynthesis: cooperation of the light reactions and the Calvin cycle

ATP

NADPH

O2

H2O

Light

LIGHT REACTIONS

Chloroplast

Figure 10.5 An overview of photosynthesis: cooperation of the light reactions and the Calvin cycle

Calvin Cycle – light-independent rxns

CO2

CALVINCYCLE

O2

[CH2O](sugar)

NADP

ADP+ P i

H2O

Light

LIGHT REACTIONS

Chloroplast

ATP

NADPH

Chapter 10: Photosynthesis1. What is photosynthesis & what organisms do photosynthesis?2. Where does photosynthesis occur?3. How did chloroplasts evolve?4. What is the chemical equation for photosynthesis?5. What are the colors of the rainbow (in order)?

ROY G BIV

Gammarays X-rays UV Infrared

Micro-waves

Radiowaves

10–5 nm 10–3 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 energy

Chapter 10: Photosynthesis1. What is photosynthesis & what organisms do photosynthesis?2. Where does photosynthesis occur?3. How did chloroplasts evolve?4. What is the chemical equation for photosynthesis?5. What are the colors of the rainbow (in order)?6. What 3 things can happen to light when it “hits” an object?

Light

ReflectedLight

Chloroplast

Absorbedlight

Granum

Transmittedlight

Figure 10.7 Why leaves are green: interaction of light with chloroplasts

What absorbs the light?- Photosynthetic pigments- chlorophyll a & b- carotenoids – broaden the spectrum of usable light

Figure 10.9 Inquiry Which wavelengths of light are most effective in driving photosynthesis?

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

EXPERIMENT

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

RESULTSA

bso

rptio

n o

f lig

ht

by

chlo

rop

last

pig

me

nts

400 500 600 700

Chlorophyll a

Chlorophyll b

Carotenoids

Wavelength of light (nm)

Rat

e o

f ph

otos

ynth

esis

(mea

sure

d by

O2 r

elea

se)

Action spectrum. This graph plots the rate of photosynthesis versus wavelength. The resulting action spectrum resembles the absorption spectrum for chlorophyll a but does not match exactly (see part a). This is partly due to the absorption of light by accessory pigments such as chlorophyll b and carotenoids.

(b)

400 500 600 700

Aerobic bacteria

Filamentof alga

Engelmann‘s experiment. In 1883, Theodor W. Engelmann illuminated a filamentous alga with light that had been passed through a prism, exposing different segments of the alga to different wavelengths. He used aerobic bacteria, which concentrate near an oxygen source, to determine which segments of the alga were releasing the most 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 driving photosynthesis.CONCLUSION

Rat

e o

f ph

otos

ynth

esis

(mea

sure

d by

O2 r

elea

se)

Action spectrum. This graph plots the rate of photosynthesis versus wavelength. The resulting action spectrum resembles the absorption spectrum for chlorophyll a but does not match exactly (see part a). This is partly due to the absorption of light by accessory pigments such as chlorophyll b and carotenoids.

(b)

400 500 600 700

Aerobic bacteria

Filamentof alga

Chapter 10: Photosynthesis1. What is photosynthesis & what organisms do photosynthesis?2. Where does photosynthesis occur?3. How did chloroplasts evolve?4. What is the chemical equation for photosynthesis?5. What are the colors of the rainbow (in order)?6. What 3 things can happen to light when it “hits” an object?7. What is the structure of chlorophyll?

Fig. 10.10 Structure of chlorophyll molecules in chloroplasts of plants

C

CH

CH2

CC

CC

C

CNNC

H3C

C

C

C

C C

C

C

C

N

CC

C

C N

MgH

H3C

H

C CH2CH3

H

CH3C

HHCH2

CH2

CH2

H CH3

C O

O

O

O

O

CH3

CH3

CHO

in chlorophyll a

in chlorophyll b

Porphyrin ring:Light-absorbing“head” of molecule;note magnesiumatom at center

Hydrocarbon tail:interacts with hydrophobicregions of proteins insidethylakoid membranes ofchloroplasts: H atoms notshown

Amphipathic – both polar & non-polar

Chapter 10: Photosynthesis1. What is photosynthesis & what organisms do photosynthesis?2. Where does photosynthesis occur?3. How did chloroplasts evolve?4. What is the chemical equation for photosynthesis?5. What are the colors of the rainbow (in order)?6. What 3 things can happen to light when it “hits” an object?7. What is the structure of chlorophyll?8. How do the photosystems harvest light energy?

Figure 10.11 Excitation of isolated chlorophyll by light

Excitedstate

Ene

rgy

of e

lect

ion

e–

Heat

Photon(fluorescence)

Chlorophyllmolecule

GroundstatePhoton

(a) Excitation of isolated chlorophyll molecule (b) Fluorescence

e–

Figure 10.12 How a photosystem harvests light

Primary electronacceptor

Photon

Thylakoid

Light-harvestingcomplexes

Reactioncenter

PhotosystemSTROMA

Thy

lako

id m

embr

ane

Transferof energy

Specialchlorophyll amolecules

Pigmentmolecules

THYLAKOID SPACE(INTERIOR OF THYLAKOID)

Figure 10.13 How noncyclic electron flow during the light reactions generates ATP and NADPH

H2O CO2

Light

LIGHT REACTIONS

CALVIN CYCLE

O2

NADP+

ADP

ATP

NADPH

[CH2O] (sugar)

Light

Photosystem II (PS II)

e

Primary acceptor

P6801

2

Ene

rgy

of e

lect

rons

Figure 10.13 How noncyclic electron flow during the light reactions generates ATP and NADPH

H2O CO2

Light

LIGHT REACTIONS

CALVIN CYCLE

O2

NADP+

NADPH

[CH2O] (sugar)

Light

Photosystem II (PS II)

e

Primary acceptor

ADP

ATP

2 H+

+

O21⁄2

H2O

e

e

1

3

2

Ene

rgy

of e

lect

rons

P680

Figure 10.13 How noncyclic electron flow during the light reactions generates ATP and NADPH

1

3O2

+

H2O CO2

Light

LIGHT REACTIONS

CALVIN CYCLE

O2

NADP+

NADPH

[CH2O] (sugar)

Light

Photosystem II (PS II)

e

Primary acceptor

ATP

2 H+

1⁄2

H2O2

Ene

rgy

of e

lect

rons

ADP

Pq

Cytochromecomplex

Pc

ATP

Electron transport chain

5

4

P680

e

e

Figure 10.13 How noncyclic electron flow during the light reactions generates ATP and NADPH

O2

H2O CO2

Light

LIGHT REACTIONS

CALVIN CYCLE

O2

NADPH

[CH2O] (sugar)

Light

Photosystem II (PS II)

e

Primary acceptor

2 H+

1⁄2

H2O2

Ene

rgy

of e

lect

rons

ADP

Pq

Cytochromecomplex

Pc

ATP

Electron transport chain

5

NADP+

ATP

Primary acceptor

e

Photosystem I (PS I)

Light

6

1

3

4

P680

P700

+

e

e

Figure 10.13 How noncyclic electron flow during the light reactions generates ATP and NADPH

P700

+

CO2

Photosystem II (PS II)

H2O

Light

LIGHT REACTIONS

CALVIN CYCLE

O2

NADPH

[CH2O] (sugar)

e

Primary acceptor

2 H+

1⁄2

H2O

e

e

1

Ene

rgy

of e

lect

rons

Pq

Cytochromecomplex

Pc

ATP

Electron transport chain

NADP+

Primary acceptor

e

Photosystem I (PS I)

Light

66

2

Light

ADP

ATP

5

Fd

ElectronTransportchain

7

NADP+

reductaseNADPH

NADP+

+ 2 H+

8

+ H+

1

3

4

P680

O2

e

e

Chapter 10: Photosynthesis1. What is photosynthesis & what organisms do photosynthesis?2. Where does photosynthesis occur?3. How did chloroplasts evolve?4. What is the chemical equation for photosynthesis?5. What are the colors of the rainbow (in order)?6. What 3 things can happen to light when it “hits” an object?7. What is the structure of chlorophyll?8. How do the photosystems harvest light energy?9. What’s the difference re: chemiosmosis in mitochondria & chloroplasts?

Figure 10.16 Comparison of chemiosmosis in mitochondria and chloroplasts

Key

Higher [H+]

Lower [H+]

Mitochondrion Chloroplast

MITOCHONDRIONSTRUCTURE

Intermembrancespace

Membrance

Matrix

Electrontransport

chain

H+ DiffusionThylakoidspace

Stroma

ATPH+

PADP+

ATPSynthase

CHLOROPLASTSTRUCTURE

Figure 10.17 The light reactions and chemiosmosis: the organization of the thylakoid membrane

LIGHTREACTOR

NADP+

ADP

ATP

NADPH

CALVINCYCLE

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

Photosystem II

LIGHT

H2O CO2

Cytochromecomplex

O2

H2OO2

1

1⁄2

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+

Chapter 10: Photosynthesis1. What is photosynthesis & what organisms do photosynthesis?2. Where does photosynthesis occur?3. How did chloroplasts evolve?4. What is the chemical equation for photosynthesis?5. What are the colors of the rainbow (in order)?6. What 3 things can happen to light when it “hits” an object?7. What is the structure of chlorophyll?8. How do the photosystems harvest light energy?9. What’s the difference chemiosmosis in mitochondria & chloroplasts?10. How do plants make “sugar?”

- Calvin Cycle

Figure 10.18 The Calvin cycle

LightH2O CO2

LIGHTREACTIONS

ATP

NADPH

NADP+

[CH2O] (sugar)

CALVINCYCLE

ADP

(Entering oneat a time)CO2

3

Phase 1: Carbon fixation

Rubisco

Short-livedintermediate

3 P P

3 P P

Ribulose bisphosphate(RuBP)

P

3-Phosphoglycerate6 ATP

6 ADP

Input

CALVINCYCLE

O2

6

Figure 10.18 The Calvin cycle

(Entering oneat a time)CO2

3

Phase 1: Carbon fixation

Rubisco

Short-livedintermediate

3 P P

3 P P

Ribulose bisphosphate(RuBP)

P

3-Phosphoglycerate

P6 P

1,3-Bisphosphoglycerate

6 NADPH

6 NADP+

6 P i

P6

Glyceraldehyde-3-phosphate(G3P)

Phase 2:Reduction

6 ATP

CALVINCYCLE

P1

G3P(a sugar)Output

Glucose andother organiccompounds

6 ADP

InputLightH2O CO2

LIGHTREACTIONS

ATP

NADP+

[CH2O] (sugar)

CALVINCYCLE

NADPH

ADP

O2

6

Figure 10.18 The Calvin cycle

(Entering oneat a time)CO2

3

Phase 1: Carbon fixation

Rubisco

Short-livedintermediate

3 P P

3 P P

Ribulose bisphosphate(RuBP)

P

3-Phosphoglycerate

P6 P

1,3-Bisphosphoglycerate

6 NADPH

6 NADP+

6 P i

P6

Glyceraldehyde-3-phosphate(G3P)

Phase 2:Reduction

6 ATP

3 ATP

3 ADP CALVINCYCLE

P5

Phase 3:Regeneration ofthe CO2 acceptor(RuBP)

P1

G3P(a sugar)Output

Glucose andother organiccompounds

G3P

6 ADP

LightH2O CO2

LIGHTREACTIONS

NADPH

NADP+

[CH2O] (sugar)

CALVINCYCLE

Input

ATP

ADP

O2

6

Chapter 10: Photosynthesis1. What is photosynthesis & what organisms do photosynthesis?2. Where does photosynthesis occur?3. How did chloroplasts evolve?4. What is the chemical equation for photosynthesis?5. What are the colors of the rainbow (in order)?6. What 3 things can happen to light when it “hits” an object?7. What is the structure of chlorophyll?8. How do the photosystems harvest light energy?9. What’s the difference chemiosmosis in mitochondria & chloroplasts?10. How do plants make “sugar?”11. How do plants get out of ATP debt?

- Cyclic electron flow

Figure 10.15 Cyclic electron flow

Primaryacceptor

Pq

Fd

Cytochromecomplex

Pc

Primaryacceptor

Fd

NADP+

reductase

NADPH

ATPPhotosystem II

(PS II)Photosystem I

(PS I)

NADP+

Chapter 10: Photosynthesis1. What is photosynthesis & what organisms do photosynthesis?2. Where does photosynthesis occur?3. How did chloroplasts evolve?4. What is the chemical equation for photosynthesis?5. What are the colors of the rainbow (in order)?6. What 3 things can happen to light when it “hits” an object?7. What is the structure of chlorophyll?8. How do the photosystems harvest light energy?9. What’s the difference chemiosmosis in mitochondria & chloroplasts?10. How do plants make “sugar?”11. How do plants get out of ATP debt?12. What is the difference between C3 & C4 photosynthesis?

Figure 10.19 C4 leaf anatomy and the C4 pathway

CO2

Mesophyll 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

CO2

Chapter 10: Photosynthesis1. What is photosynthesis & what organisms do photosynthesis?2. Where does photosynthesis occur?3. How did chloroplasts evolve?4. What is the chemical equation for photosynthesis?5. What are the colors of the rainbow (in order)?6. What 3 things can happen to light when it “hits” an object?7. What is the structure of chlorophyll?8. How do the photosystems harvest light energy?9. What’s the difference chemiosmosis in mitochondria & chloroplasts?10. How do plants make “sugar?”11. How do plants get out of ATP debt?12. What is the difference between C3 & C4 photosynthesis?13. How do CAM plants differ from C4 plants?

-Crassulacean Acid Metabolism

Figure 10.20 C4 and CAM photosynthesis compared

Organic acidsrelease CO2 toCalvin cycle

Spatial separation of steps. In C4 plants, carbon fixation and the Calvin cycle occur in differenttypes of cells.

(a) Temporal separation of steps. In CAM plants, carbon fixation and the Calvin cycle occur in the same cellsat different times.

(b)

PineappleSugarcane

Bundle-sheath cell

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

CO2

Figure 10.21 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 reactions Calvin cycle

NADP+

ADP

ATP

NADPH

+ P 1

RuBP 3-Phosphoglycerate

Amino acidsFatty acids

Starch(storage)

Sucrose (export)

G3P

Photosystem IIElectron transport chain

Photosystem I

Chloroplast