Transcript Photosynthesis_Bio rev.3-8



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.)

Wavelength


Is the distance between the crests of waves
Determines the type of electromagnetic energy
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
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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
Light is a form of electromagnetic energy,
which travels in waves
When white light passes through a prism the
individual wavelengths are separated out.
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



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
Reflect – a small amount
of light is reflected off
Reflected
of the leaf. Most leaves reflect
Light the color green,
Chloroplast
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)
Absorbed
Granum
Transmittedlight
– some light passes
through the
leaf
Transmitted
light
Figure 10.7
Concept Map
Photosynthesis
includes
Light
independent
reactions
Light
dependent
reactions
uses
Light
Energy
Thylakoid
membranes
to produce
ATP
NADPH
occurs in
occur in
Stroma
of
O2
Chloroplasts
uses
ATP
NADPH
to produce
Glucose
Leaf cross section
Vein
Mesophyll
Stomata
Figure 10.3
CO2
O2


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
Mesophyll
Chloroplast
5 µm
Outer
membrane
Stroma Granum
Intermembrane
space
Thylakoid Thylakoid
space
Inner
membrane
1 µm


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
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
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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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
Chlorophyll a
Absorption of light by
chloroplast pigments

Chlorophyll b
Carotenoids
Wavelength of light (nm)
(a) Absorption spectra. The three curves show the wavelengths of light best absorbed by
three types of chloroplast pigments.
Figure 10.9
The action spectrum of a pigment

Profiles the relative effectiveness of different
wavelengths of radiation in driving photosynthesis
Rate of photosynthesis
(measured by O2 release)

(b) 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.
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The action spectrum for photosynthesis

Was first demonstrated by Theodor W. Engelmann
Aerobic bacteria
Filament
of alga
500
600
700
400
(c) 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.
CONCLUSION
photosynthesis.
Light in the violet-blue and red portions of the spectrum are most effective in driving
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Similar- both have two peaks. For both graphs the
peak is the higher in the blue end. Both have a
valley in the green part of the spectrum.
Different- Chlorophyll B peaks more in blue,
whereas chlorophyll a has its peak to the left in
violet. (they are at different wavelengths of light)
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(2) Any reasonable explanation accepted that
connects to the data…Chlorophyll absorbs light
in the red and blue ends of the light spectrum
but not green. So green is reflected back to our
eyes and that is what we see.
 (2)
reasonable
explanation…Reflected
and/or transmitted (goes
through)
1. Explain why leaves are green. Begin your
explanation with white light coming from the sun
and ending in your eye. (4)
 White Light from the sun  hits leaf  all
wavelengths (colors) absorbed but green 
green reflected to our eyes
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X-axis: Wavelength (2) units: nanometers (1)
Y -axis: % absorption (2)
Line graph for carotenoids (2)
Appropriate title- Absorption of carotenoids at
various wavelengths in the visible light
spectrum (2)

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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
Green pigment in plants
Traps sun’s energy
Sunlight energizes electron in chlorophyll
What is beta carotene? Where is it found? What
does it do for plants? Why is it beneficial in a
human diet? (4 extra credit)
 Beta-carotene is one of a group of natural
chemicals known as carotenes or carotenoids.
Carotenes are responsible for the orange color
of many fruits and vegetables such as carrots,
pumpkins, and sweet potatoes.
 Beta carotene is converted in the body to
vitamin A. It is an antioxidant, like vitamins E
and C.
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Chlorophyll a


Is the main photosynthetic pigment
Chlorophyll b

Is an accessory pigment
CH3
in chlorophyll a
CHO
in chlorophyll b
CH2
CH
C
H3C
C
H
C
C
C
C
C
N
C
N
C
Mg
N
C
C
C
H
C
N
C
H3C
CH3
H
CH2
H
H
C
C
C
O
C
H
C
CH3
CH3
Porphyrin ring:
Light-absorbing
“head” of molecule
note magnesium
atom at center
C
O
O
CH2
C
C
CH2
C
O
O
CH3
CH2
Figure 10.10
Hydrocarbon tail:
interacts with hydrophobic
regions of proteins inside
thylakoid membranes of
chloroplasts: H atoms not
shown

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.

Light-Dependent Reaction


Light-Independent Reaction


Converts light energy into chemical energy
Produces simple sugars (glucose)
General Equation

6 CO2 + 6 H2O  C6H12O6 + 6 O2
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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

When a pigment absorbs light

It goes from a ground state to an excited state, which is
unstable
e–
Excited
state
Heat
Photon
(fluorescence)
Photon
Figure 10.11 A
Chlorophyll
molecule
Ground
state

If an isolated solution of chlorophyll is
illuminated

It will fluoresce, giving off light and heat
Figure 10.11 B

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
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Photosystem II: Clusters of pigments boost eby 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
e–
ATP
e–
e–
NADPH
e–
e–
e–
Mill
makes
ATP
e–
Figure 10.14
Photosystem II
Photosystem I
A photosystem

Is composed of a reaction center surrounded by a
number of light-harvesting complexes
Thylakoid
Photosystem
Photon
Light-harvesting
complexes
Thylakoid membrane

STROMA
Primary election
acceptor
e–
Transfer
of energy
Figure 10.12
Reaction
center
Special
chlorophyll a
molecules
Pigment
molecules
THYLAKOID SPACE
(INTERIOR OF THYLAKOID)



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
Reactants:
Products:
Figure 10.4
12 H2O
6 CO2
C6H12O6
6
H2O
6
O2




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
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
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
H2O
CO2
LIGHT
NADP+
ADP
LIGHT
REACTOR
CALVIN
CYCLE
ATP
NADPH
STROMA
(Low H+ concentration)
O2
[CH2O] (sugar)
Cytochrome
Photosystem II
complex
Photosystem I
NADP+
reductase
Light
2 H+
Fd
3
NADP+ + 2H+
NADPH + H+
Pq
Pc
2
H2O
THYLAKOID SPACE
1
(High H+ concentration)
1⁄
2
O2
+2 H+
2 H+
To
Calvin
cycle
STROMA
(Low H+ concentration)
Thylakoid
membrane
ATP
synthase
ADP
ATP
P
Figure 10.17
H+

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





Light-Dependent
Pigment
Chlorophyll
Electron Transport Chain
ATP
NADPH
Photolysis
Chemiosmosis

Converts light into chemical energy (ATP &
NADPH are the chemical products). Oxygen is
a by-product
e–
ATP
e–
e–
NADPH
e–
e–
e–
Mill
makes
ATP
e–
Figure 10.14
Photosystem II
Photosystem I

Series of Proteins embedded in a membrane
that transports electrons to an electron carrier


Adenosine Triphosphate
Stores energy in high energy bonds between
phosphates



Made from NADP+; electrons and hydrogen
ions
Made during light reaction
Stores high energy electrons for use during
light-Independent reaction (Calvin Cycle)

The combination of moving hydrogen ions
across a membrane to make ATP
H2O
CO2
Light
NADP 
ADP
+ P
LIGHT
REACTIONS
CALVIN
CYCLE
ATP
NADPH
Chloroplast
Figure 10.5
O2
[CH2O]
(sugar)

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




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
Light
H2 O
CO2
Input
3 (Entering one
CO2 at a time)
NADP+
ADP
CALVIN
CYCLE
LIGHT
REACTION
ATP
Phase 1: Carbon fixation
NADPH
O2
Rubisco
[CH2O] (sugar)
3 P
3 P
P
Short-lived
intermediate
P
Ribulose bisphosphate
(RuBP)
P
6
3-Phosphoglycerate
6
ATP
6 ADP
CALVIN
CYCLE
3 ADP
3
ATP
Phase 3:
Regeneration of
the CO2 acceptor
(RuBP)
6 P
6 NADPH
6 NADPH+
6 P
P
5
(G3P)
6
P
Glyceraldehyde-3-phosphate
(G3P)
P
1
Figure 10.18
P
1,3-Bisphoglycerate
G3P
(a sugar)
Output
Glucose and
other organic
compounds
Phase 2:
Reduction
Chloroplast – Where the Magic
Happens!
+
H2 O
CO2
Energy
Which splits
water
ATP and
NADPH2
Light is Adsorbed
By
Chlorophyll
ADP
NADP
Chloroplast
O2
Light Reaction
Calvin Cycle
Used Energy and is
recycled.
+
C6H12O6
Dark Reaction
6 CO2 + 12 H2O + Light energy  C6H12O6 + 6 O2 + 6 H2 O