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Photosynthesis Life Is Solar Powered!

What Would Plants Look Like On

Alien Planets?

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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.)

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Anatomy of a Wave

• Wavelength

– Is the distance between the crests of waves

– Determines the type of electromagnetic

energy

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Electromagnetic Spectrum

• Is the entire range of electromagnetic

energy, or radiation

• The longer the wavelength the lower the

energy associated with the wave.

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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

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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

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Photosynthesis Overview

Photosynthesis

includes

of

occur in occurs in uses

to produce to produce

uses

Light dependent reactions

Thylakoid membranes

Stroma NADPH ATP Light Energy

ATP NADPH O2 Chloroplasts Glucose

Light independent

reactions

Concept Map

Anatomy of a Leaf

Vein

Leaf cross section

Figure 10.3

Mesophyll

CO2 O2 Stomata

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Chloroplast

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Chloroplast

Mesophyll

5 µm

Outer

membrane

Intermembrane

space Inner

membrane

Thylakoid

space

Thylakoid Granum Stroma

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?

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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

RESULTS

Ab

so

rptio

n o

f lig

ht b

y

ch

loro

pla

st p

igm

en

ts

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

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• The action spectrum of a pigment

– Profiles the relative effectiveness of different

wavelengths of radiation in driving

photosynthesis R

ate

of

photo

syn

thesis

(measure

d b

y O

2 r

ele

ase)

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

Filament

of 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

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Chlorophyll • Chlorophyll a

– Is the main photosynthetic pigment

• Chlorophyll b

– Is an accessory pigment C

CH

CH2

C C

C C

C

C N N C

H3C

C

C

C

C C

C

C

C

N

C C

C

C N

Mg H

H3C

H

C CH2 CH3

H

CH3 C

H H

CH2

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 magnesium

atom at center

Hydrocarbon tail:

interacts with hydrophobic

regions of proteins inside

thylakoid membranes of

chloroplasts: H atoms not

shown 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.

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Happens in two phases

• Light-Dependent Reaction

– Converts light energy into chemical energy

• Light-Independent Reaction

– Produces simple sugars (glucose)

• General Equation

– 6 CO2 + 6 H2O C6H12O6 + 6 O2

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

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Excitation of Chlorophyll by Light • When a pigment absorbs light

– It goes from a ground state to an excited state,

which is unstable

Excited

state

Heat

Photon

(fluorescence)

Chlorophyll

molecule

Ground

state Photon

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

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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-

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• A mechanical analogy for the light reactions

Mill

makes

ATP

ATP

e–

e– e–

e–

e–

Photosystem II Photosystem I

e–

e–

NADPH

Figure 10.14

Photosystem • A photosystem

– Is composed of a reaction center surrounded by

a number of light-harvesting complexes

Primary election

acceptor

Photon

Thylakoid

Light-harvesting

complexes

Reaction

center

Photosystem

STROMA

Thyla

koid

mem

bra

ne

Transfer

of energy

Special

chlorophyll a

molecules

Pigment

molecules

THYLAKOID SPACE

(INTERIOR OF THYLAKOID) Figure 10.12

e–

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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 H2O Reactants:

Products: C6H12O6 6

H2O

6

O2

Figure 10.4

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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

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• The light reactions and chemiosmosis: the

organization of the thylakoid membrane

LIGHT

REACTOR

NADP+

ADP

ATP

NADPH

CALVIN

CYCLE

[CH2O] (sugar) STROMA

(Low H+ concentration) Photosystem II

LIGHT

H2O CO2

Cytochrome

complex

O2

H2O O2

1

1⁄2

2

Photosystem I Light

THYLAKOID SPACE

(High H+ concentration)

STROMA

(Low H+ concentration)

Thylakoid

membrane

ATP

synthase

Pq Pc

Fd

NADP+

reductase

NADPH + H+

NADP+ + 2H+

To

Calvin

cycle

ADP

P ATP

3

H+

2 H+ +2 H+

2 H+

Figure 10.17

Vocabulary Review

• Light-Dependent

• Pigment

• Chlorophyll

• Electron Transport Chain

• ATP

• NADPH

• Photolysis

• Chemiosmosis

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Mill

makes

ATP

ATP

e–

e– e–

e–

e–

Photosystem II Photosystem I

e–

e–

NADPH

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

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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

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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)

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Chemiosmosis

• The combination of moving hydrogen ions

across a membrane to make ATP

H2O CO2

Light

LIGHT

REACTIONS CALVIN

CYCLE

Chloroplast

[CH2O]

(sugar)

NADPH

NADP

ADP

+ P

O2 Figure 10.5

ATP

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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

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

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• The Calvin cycle

(G3P)

Input

(Entering one

at a time) CO2 3

Rubisco

Short-lived

intermediate

3 P P

3 P P

Ribulose bisphosphate

(RuBP)

P

3-Phosphoglycerate

P 6 P

6

1,3-Bisphoglycerate

6 NADPH

6 NADPH+

6 P

P 6

Glyceraldehyde-3-phosphate

(G3P)

6 ATP

3 ATP

3 ADP CALVIN

CYCLE

P 5

P 1

G3P

(a sugar)

Output

Light H2O CO2

LIGHT

REACTION ATP

NADPH

NADP+

ADP

[CH2O] (sugar)

CALVIN

CYCLE

Figure 10.18

O2

6 ADP

Glucose and

other organic

compounds

Phase 1: Carbon fixation

Phase 2:

Reduction

Phase 3:

Regeneration of

the CO2 acceptor

(RuBP)

Chloroplast – Where the Magic

Happens! H2O CO2

O2 C6H12O6

Light Reaction Dark Reaction

Light is Adsorbed

By

Chlorophyll

Which splits

water

Chloroplast

ATP and

NADPH2

ADP

NADP

Calvin Cycle

Energy

Used Energy and is

recycled.

+

+

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