PhotosynthesisLife Is Solar Powered!

What Would Plants Look Like On Alien Planets? Why?

Why Would They Look Different?

• Different Stars Give off Different types of light or Electromagnetic Waves

• The color of plants depends on the spectrum of the star’s light, which astronomers can easily observe. (Our Sun is a type “G” star.)

Anatomy of a Wave• Wavelength

– Is the distance between the crests of waves– Determines the type of electromagnetic

energy

Electromagnetic Spectrum• Is the entire range of electromagnetic

energy, or radiation

• The longer the wavelength the lower the energy associated with the wave.

Visible Light

• Light is a form of electromagnetic energy, which travels in waves

• When white light passes through a prism the individual wavelengths are separated out.

Visible Light Spectrum

• Light travels in waves• Light is a form of radiant energy• Radiant energy is made of tiny packets of

energy called photons• The red end of the spectrum has the lowest

energy (longer wavelength) while the blue end is the highest energy (shorter wavelength).

• The order of visible light is ROY-G-BIV• This is the same order you will see in a rainbow

b/c water droplets in the air act as tiny prisms

Light Options When It Strikes A Leaf

• Reflect – a small amount of light is reflected off of the leaf. Most leaves reflect the color green, which means that it absorbs all of the other colors or wavelengths.

• Absorbed – most of the light is absorbed by plants providing the energy needed for the production of Glucose (photosynthesis)

• Transmitted – some light passes through the leaf

Light

ReflectedLight

Chloroplast

Absorbedlight

Granum

Transmittedlight

Figure 10.7

Photosynthesis Overview

Photosynthesis

includes

of

occur inoccurs in uses

to produce to produce

uses

Lightdependentreactions

Thylakoidmembranes Stroma NADPHATPLight

Energy

ATP NADPH O2 Chloroplasts Glucose

Lightindependent

reactions

Concept Map

Anatomy of a Leaf

Vein

Leaf cross section

Figure 10.3

Mesophyll

CO2 O2Stomata

Chloroplast

Chloroplast

Mesophyll

5 µm

Outermembrane

IntermembranespaceInner

membrane

Thylakoidspace

ThylakoidGranumStroma

1 µm

Chloroplast• Are located within the palisade layer of the leaf• Stacks of membrane sacs called Thylakoids

– Contain pigments on the surface• Pigments absorb certain wavelenghts of light

• A Stack of Thylakoids is called a Granum

Pigments

• Are molecules that absorb light• Chlorophyll, a green pigment, is the primary

absorber for photosynthesis– There are two types of cholorophyll

• Chlorophyll a• Chlorophyll b

• Carotenoids, yellow & orange pigments, are those that produce fall colors. Lots of Vitamin A for your eyes!

• Chlorophyll is so abundant that the other pigments are not visible so the plant is green…Then why do leaves change color in the fall?

Color Change

• In the fall when the temperature drops plants stop making Chrlorophyll and the Carotenoids and other pigments are left over (that’s why leaves change color in the fall).

• The absorption spectra of three types of pigments in chloroplasts

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

EXPERIMENT

RESULTSA

bso

rptio

n o

f lig

ht

by

chlo

rop

last

pig

me

nts

Chlorophyll a

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

Wavelength of light (nm)

Chlorophyll b

Carotenoids

Figure 10.9

• The action spectrum of a pigment– Profiles the relative effectiveness of different

wavelengths of radiation in driving photosynthesis

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)

• The action spectrum for photosynthesis– Was first demonstrated by Theodor W.

Engelmann

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

Chlorophyll• Chlorophyll a

– Is the main photosynthetic pigment

• Chlorophyll b– Is an accessory pigment C

CH

CH2

CC

CC

C

CNNC

H3C

C

CC

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 moleculenote magnesiumatom at center

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

Figure 10.10

PHOTOSYNTHESIS

• Comes from Greek Word “photo” meaning “Light” and “syntithenai” meaning “to put together”– Photosynthesis puts together sugar molecules

using water, carbon dioxide, & energy from light.

Happens in two phases

• Light-Dependent Reaction– Converts light energy into chemical energy

• Light-Independent Reaction– Produces simple sugars (glucose)

• General Equation– 6 CO2 + 12 H2O + light energy C6H12O6 + 6 O2 + 6 H2O

First Phase

• Requires Light = Light Dependent Reaction– Sun’s energy energizes an electron in

chlorophyll molecule– Electron is passed to nearby protein

molecules in the thylakoid membrane of the chloroplast

Excitation of Chlorophyll by Light• When a pigment absorbs light

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

Excitedstate

Ene

rgy

of e

lect

ion

Heat

Photon(fluorescence)

Chlorophyllmolecule

GroundstatePhoton

e–

Figure 10.11 A

• If an isolated solution of chlorophyll is illuminated– It will fluoresce, giving off light and heat

Figure 10.11 B

ETC

• Electron from Chlorophyll is passed from protein to protein along an Electron Transport Chain– Electrons lose energy (energy changes form)– Finally bonded with electron carrier called

NADP+ to form NADPH or ATP• Energy is stored for later use

Two Photosystems

• Photosystem II: Clusters of pigments boost e- by absorbing light w/ wavelength of ~680 nm

• Photosystem I: Clusters boost e- by absorbing light w/ wavelength of ~760 nm.

• Reaction Center: Both PS have it. Energy is passed to a special Chlorophyll a molecule which boosts an e-

• A mechanical analogy for the light reactions

MillmakesATP

ATP

e–

e–e–

e–

e–

Pho

ton

Photosystem II Photosystem I

e–

e–

NADPH

Pho

ton

Figure 10.14 

Photosystem• A photosystem

– Is composed of a reaction center surrounded by a number of light-harvesting complexes

Primary electionacceptor

Photon

Thylakoid

Light-harvestingcomplexes

Reactioncenter

Photosystem

STROMAT

hyla

koid

mem

bran

e

Transferof energy

Specialchlorophyll amolecules

Pigmentmolecules

THYLAKOID SPACE(INTERIOR OF THYLAKOID)Figure 10.12

e–

Where those electrons come from

• Water

• Electrons from the splitting of water (photolysis) supply the chlorophyll molecules with the electrons they need

• The left over oxygen is given off as gas

The Splitting of Water• Chloroplasts split water into

– Hydrogen and oxygen, incorporating the electrons of hydrogen into sugar molecules

6 CO2 12 H2OReactants:

Products: C6H12O66 H2O 6 O2

Figure 10.4

High Quality H2O

• Photolysis – Splitting of water with light energy

• Hydrogen ions (H+) from water are used to power ATP formation with the electrons

• Hydrogen ions (charged particle) actually move from one side of the thylakoid membrane to the other

• Chemiosmosis – Coupling the movement of Hydrogen Ions to ATP production

• Animation – takes a min. to load…be patient

• Animation II – Does not take as long to load but it is not as good

• 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

H2O O21

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+

Figure 10.17

Vocabulary Review

• Light-Dependent • Pigment• Chlorophyll• Electron Transport Chain• ATP• NADPH• Photolysis• Chemiosmosis

MillmakesATP

ATP

e–

e–e–

e–

e–

Pho

ton

Photosystem II Photosystem I

e–

e–

NADPH

Pho

ton

Figure 10.14 

Light-Dependent

• Converts light into chemical energy (ATP & NADPH are the chemical products). Oxygen is a by-product

Pigment

• Molecules that absorb specific wavelengths of light– Chlorophyll absorbs reds & blues and reflects

green– Xanthophyll absorbs red, blues, greens &

reflects yellow– Carotenoids reflect orange

Chlorophyll

• Green pigment in plants

• Traps sun’s energy

• Sunlight energizes electron in chlorophyll

Electron Transport Chain

• Series of Proteins embedded in a membrane that transports electrons to an electron carrier

ATP

• Adenosine Triphosphate

• Stores energy in high energy bonds between phosphates

NADPH

• Made from NADP+; electrons and hydrogen ions

• Made during light reaction

• Stores high energy electrons for use during light-Independent reaction (Calvin Cycle)

Chemiosmosis

• The combination of moving hydrogen ions across a membrane to make ATP

H2O CO2

Light

LIGHT REACTIONS

CALVINCYCLE

Chloroplast

[CH2O](sugar)

NADPH

NADP

ADP

+ P

O2Figure 10.5

ATP

PART II

• LIGHT INDEPENDENT REACTION– Also called the Calvin Cycle– No Light Required– Takes place in the stroma of the chloroplast– Takes carbon dioxide & converts into sugar– It is a cycle because it ends with a chemical

used in the first step– Calvin Cycle uses ATP & NADPH to make

Glucose (C6H12O6)

Begins & Ends

• The Calvin Cycle begins and ends with RuBP

• CO2 is added to RuBP; “fixing” the CO2 in a compound

• One compound made along the way is PGAL– PGAL can be made into sugars or RuBP– Calvin Cycle uses ATP & NADPH

• The Calvin cycle

(G3P)

Input(Entering one

at a time)CO2

3

Rubisco

Short-livedintermediate

3 P P

3 P P

Ribulose bisphosphate(RuBP)

P

3-Phosphoglycerate

P6 P

6

1,3-Bisphoglycerate

6 NADPH

6 NADPH+

6 P

P6

Glyceraldehyde-3-phosphate(G3P)

6 ATP

3 ATP

3 ADP CALVINCYCLE

P5

P1

G3P(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)

Chloroplast – Where the Magic Chloroplast – Where the Magic Happens!Happens!

HH22OO COCO22

OO22 CC66HH1212OO66

Light Light ReactionReaction

Dark ReactionDark Reaction

Light is AdsorbedLight is AdsorbedBy By

ChlorophyllChlorophyll

Which splitsWhich splitswaterwater

ChloroplastChloroplast

ATP andATP andNADPHNADPH22

ADPADPNADPNADP

Calvin CycleCalvin Cycle

EnergyEnergy

Used Energy and is Used Energy and is recycled.recycled.

++

++

6 CO2 + 12 H2O + Light energy C6H12O6 + 6 O2 + 6 H2 O