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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.)
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
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
NADPH
• Made from NADP+; electrons and hydrogen ions
• Made during light reaction
• Stores high energy electrons for use during light-Independent reaction (Calvin Cycle)
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