biol1003 -9_photosynthesis - fall2014
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BIOL 1003
INTRODUCTORY
BIOLOGY I9. Greenhouses, global warming and photosynthesis - FALL2014
Iain McKinnellDept. Biology
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Sunlight
Atmosphere
Some heat
energy escapes
into space
Radiant heat
trapped by CO2
and other gases
The gases in the atmosphere that absorb heat radiation arecalled greenhouse gases. These include
water vapor
carbon dioxide
methane
ozone
The Greenhouse effect
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Antarctica
Southern tip of
South America
Solar radiation converts O2high inthe atmosphere to ozone (O3),
which shields organisms from
damaging UV radiation.
Industrial chemicals called CFCs
have caused dangerous thinning of
the ozone layer, but international
restrictions on CFC use are
allowing a slow recovery.
Study of Earths atmospheric composition has global significance
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Greenhouse effect and global climate change
Increasing concentrations of greenhouse gaseshave been linked to global climate change(also
called global warming), a slow but steady rise in
Earths surface temperature.
Since 1850, the atmospheric concentration of CO2
has increased by about 40%, mostly due to the
combustion of fossil fuels including
coal oil
gasoline.
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The carbon cycle
http://earthobservatory.nasa.gov/Features/CarbonCycle/
http://earthobservatory.nasa.gov/Features/CarbonCycle/http://earthobservatory.nasa.gov/Features/CarbonCycle/ -
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Photosynthesis & CO2- Introduction
Autotrophs make their own food through the process of
photosynthesis,
sustain themselves, and
do not usually consume organic molecules derivedfrom other organisms.
Photosynthesis in plants
converts carbon dioxide and water into organic
molecules,
releases oxygen,
takes place in chloroplasts.
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Leaf Cross
Section
Mesophyll
CO2
O2
Vein
Leaf
Stoma
Mesophyll Cell
Chloroplast
Photosynthesis occurs in chloroplasts in plant cells
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Chloroplast
Thylakoid
Thylakoid space
Stroma
Granum
Inner and outer
membranes
Photosynthesis occurs in chloroplasts in plant cells
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Becomes reduced
Becomes oxidized
Photosynthesis, like respiration, is a redox (oxidation-reduction) process.
CO2becomes reduced to sugar as electrons along with
hydrogen ions from water are added to it.
Water molecules are oxidized when they lose electronsalong with hydrogen ions.
Photosynthesis is a redox process, as is cellularrespiration
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LightReactions
(in thylakoids)
Calvin
Cycle(in stroma)
SugarO2
NADPH
ATP
NADP+
ADP
P
H2O CO2
Light
Chloroplast
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Increasing energy
105nm 103nm 1 nm 103nm 106nm 1 m 103m
650nm
380 400 500 600 700 750
Wavelength (nm)
Visible light
Gamma
rays
Micro-
waves
Radio
wavesX-rays UV Infrared
Visible radiation absorbed by pigments drives the light reactions
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Excited
state
Heat
Ground state
Photon
of light
Photon
(fluorescence)
Chlorophyll
molecule
Pigments in chloroplastsabsorb photons (capturing
solar power), which
increases the potential
energy of the pigmentselectrons and
sends the electrons into an
unstable state.
These unstable electrons drop back down to their
ground state, and as they do,
release their excess energy as
heat.
Visible radiation absorbed by pigments drivesthe light reactions
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Photosystem
Light Light-harvestingcomplexes
Reaction-centercomplex
Primary electron
acceptor
Pigment
moleculesPair ofchlorophyll amoleculesTransferof energy
Thyla
koidmembrane
Photosystems capture solar energy
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Two types of photosystems (photosystem I and
photosystem II) cooperate in the light reactions.
Each type of photosystem has a characteristic
reaction center. Photosystem II, which functions first, is called P680
because its pigment absorbs light with a
wavelength of 680 nm.
Photosystem I, which functions second, is calledP700 because it absorbs light with a wavelength of
700 nm.
Photosystems capture solar energy
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Light
StromaPhotosystem II
Thylakoid
space
Thylakoidmembrane Primary
acceptor
Primary
acceptor
P680 P700
Photosystem I
Light NADP NADPHElectron transport chain
Provides energy for
synthesis of ATP
by chemiosmosis
21
H2O
3
1
2
45
6
H
O2 H2
Two photosystems connected by an electron transport
chain generate ATP and NADPH
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Photosystem IPhotosystem II
NADPH
ATP
Mill
makes
ATP
The products of the lightreactions are
NADPH,
ATP, and
oxygen.
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H+
ATP synthasePhotosystem IPhotosystem IIElectron
transport chain
ATPPADP
NADPHNADP+
Light Light
Chloroplast
To Calvin
Cycle
Stroma(low H+
concentration)
Thylakoid
membrane
Thylakoid space
(high H+
concentration)
H2O
O2 + 212
H+ H+
H+
H+
H+
H+ H+
H+
H+
H+
H+
H+
H+
H+
H+
H+
H+
H+
Chemiosmosis powers ATP synthesis in the light reactions
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Input
Output: G3P
Calvin
Cycle
CO2
ATP
NADPH
ATP and NADPH power sugar synthesis in theCalvin cycle
The Calvin cycle makes sugar within achloroplast.
To produce sugar, the necessaryingredients are
atmospheric CO2and ATP and NADPH generated by the
light reactions.
The Calvin cycle uses these threeingredients to produce an energy-rich,three-carbon sugar calledglyceraldehyde-3-phosphate (G3P).
A plant cell may then use G3P to makeglucose and other organic molecules.
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The steps of the Calvin cycle include
carbon fixation,
reduction, release of G3P, and
regeneration of the starting molecule
ribulose bisphosphate (RuBP).
ATP and NADPH power sugar synthesis in theCalvin cycle
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2
2
1
1
3
4
4
3
Glucose
and other
compounds
P
P
P
P
P
PP
ATP
ATP
ADP
3
ADP3
3
3
5
1
6
6
6
6
6
6
NADPH
NADP
G3P
G3P
G3P
3-PGARuBP
CO2
Rubisco
Input:
Output:Step Regeneration of RuBP
Step Release of one
molecule of G3P
Step Reduction
Step Carbon fixation
CalvinCycle
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Other methods of carbon fixation have evolved in
hot, dry climates
Most plants use CO2directly from the air,
and carbon fixation occurs when the
enzyme rubisco adds CO2to RuBP.
Such plants are called C3plants because
the first product of carbon fixation is a
three-carbon compound, 3-PGA.
Oth th d f b fi ti h l d i h t
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Calvin
Cycle
Mesophyllcell
Bundle-sheathcell
CO2
4-C compound
CO2
3-C sugar
C4plant
C4plants have evolved a means
of carbon fixation that saves water
during photosynthesis while
optimizing the Calvin cycle.
C4plants are so named becausethey first fix CO2into a four-carboncompound.
When the weather is hot and dry,C4plants keep their stomatamostly closed, thus conserving
water.
Other methods of carbon fixation have evolved in hot,dry climates
Oth th d f b fi ti h l d i h t
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Calvin
Cycle
CO2
3-C sugar
CAM plantDay
CO2
4-C compound
Night Another adaptation to hot and dry
environments has evolved in theCAM plants, such as pineapples andcacti.
CAM plants conserve water byopening their stomata and admittingCO2only at night.
CO2is fixed into a four-carboncompound,
which banks CO2at night and
releases it to the Calvin cycle during
the day.
Other methods of carbon fixation have evolved in hot,dry climates
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Light
Thylakoids
H2O CO2
O2
NADP
ADP
P
ATP
NADPHG3P
3-PGA
RuBP
Chloroplast
Sugars
Photosystem II
PhotosystemI
LightReactions
Electron
transport chain
Calvin
Cycle
(in stroma)
Stroma
Cellular
respiration
Other organiccompounds
Cellulose
Starch
Review: The chloroplast integrates the two stages of photosynthesis
Photosynthesis possible moderator of global climate
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Photosynthesispossible moderator of global climate
change
Root cause of climate change is build up of CO2 Photosynthesizing organisms are carbon sinks
Widespread deforestation has aggravated the global
warming problem by reducing an effective CO2sink.
Global warming caused by increasing CO2levels may be
reduced by
limiting deforestation,
reducing fossil fuel consumption,
growing biofuel crops that remove
CO2from the atmosphere.
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Summary
Understand significance of photosynthesis to all organisms.
Ultimately, how is light energy turned into carbohydrate?
Understand the structure & function of the chloroplasts
Why are the photosystems so important? What are the key steps in the light & light-independent
processes?
What is the significance of ATP, NADPH, Rubisco to the
entire process? What are alternative methods of carbon fixation?
Next upChapter 8.1-8.5 & Chapter 10.1-10.3
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