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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