Transcript Chapter 8:

Chapter 8: Photosynthesis
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8-1
Radiant Energy
Photosynthesis converts solar energy
into the chemical energy of a
carbohydrate :
Solar energy + 6CO2 + 6H2O → C6H12O6 + 6O2
Reduced Oxidized
Carbohydrate
(glucose)
Electrons from H2O are energized by the sun.
The oxygen given off comes from water – 18O experiments.
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Photosynthetic organisms
Plant
Algae
Cyanobacteria
These organisms are called producers;
they synthesize organic molecules from
raw materials.
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Nearly all life is dependent on solar
energy because photosynthetic
organisms:
1) use solar energy to produce organic
nutrients.
2) provide food (producers) for other
organisms (consumers).
And,
3) The bodies of plants became the coal
or other fossil fuels used today.
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Visible Light
Fig 8.2
Pigments (chlorophylls and carotenoids) found within
photosynthesizing cells, are capable of absorbing various
portions of visible light.
Both chlorophyll a and chlorophyll b absorb violet, blue,
and red light best and green least.3
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Fig 8.3
Leaf Structure
Mesophyll cells of a leaf
contain chloroplasts
Water reaches mesophyll
cells from vessels that
extend to the roots.
Pores called stomata
allow CO2 and O2 to
enter the leaf.
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Chloroplast structure
Double membrane
Fig 8.3
Thylakoids are interconnected
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Chlorophyll and other pigments are found in the thylakoids
Two Sets of Reactions for
Photosynthesis
Light Dependant Reactions ‘Photo-’
Cyclic and Noncyclic electron pathways
-Captures energy from the sun
Light Independent Reactions ‘-Synthesis’
Calvin Cycle
-Produces carbohydrate
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The light-dependent reactions: the cyclic
electron pathway
Fig. 8.4
-Produces only ATP!
Solar Energy
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The light-dependent reactions: the noncyclic
electron pathway
Fig. 8.5
-Splits
water
(yielding
H+, e-, and
O2)
-Produces
ATP
-Reduces
NADP+ to
NADPH
Calvin Cycle
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Light-Dependant ATP Production and the
Electron Transport System
Fig. 8.6
Hydrogen builds up
concentration gradient
in the thylakoid space.
The flow of H+ through
an ATP synthase
complex back into the
stroma drives the
chemiosmotic
production of ATP.
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Light-Dependant Reactions of Photosynthesis
produce O2, ATP, and NADPH – not glucose.
Solar energy + 6CO2 + 6H2O → C6H12O6 + 6O2
ADP + P  ATP
NADP + H  NADPH
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Carbohydrate Synthesis
Light-independent reactions
-NADPH and ATP  are used to reduce
CO2 to carbohydrate.
-This occurs in the stroma of a
chloroplast by a series of reactions
called the Calvin cycle.
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Stages of the Calvin Cycle
The Calvin cycle can be divided into:
1) Fixation of CO2;
2) Reduction of CO2; and
3) Regeneration of RuBP (ribulase
biphosphate).
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The Calvin cycle (simplified)
3CO2 + 3RuBp (C5)
6(C6)
6PGA (C3)
ATP
ADP
NADPH
NADP
6PGAL (C3)
C6H12O6
RuBp
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The light-independent reactions of the
Calvin cycle (detailed) Fig. 8.8
Fixation of CO2
From lightdependant
reactions
From lightdependant
reactions
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Photosynthesis Efficiency
Ideal laboratory conditions: 25% of solar
energy transferred.
Under natural conditions: the efficiency
ranges from less than 1% to a
maximum of 8%.
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Photosynthesis in Chloroplast
Light Independent Reactions Light Dependant Reactions
CO2
Calvin Cycle
RuBP
PGAL
H 2O
Solar Energy
Electron Pathways
ATP O2
NADPH
Glucose
Aerobic Cellular Respiration in
Mitochondria makes new ATP
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Photosynthetic organisms carry on both photosynthesis
and cellular respiration and rely on solar energy.
Solar Energy + CO2 + H20  C6H12O6 + O2
C6H12O6 + O2  CO2 + H20 + chemical energy(ATP)
Non-photosynthetic organisms only carry on cellular
respiration and must rely on an external source of
energy.
C6H12O6 + O2  CO2 + H20 + chemical energy(ATP)
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Figure 6.10 from Chapter 6
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Solar
Energy
Animal Cell
Plant Cell
Chloroplast
(Photosynthesis)
CO2
O2 and Glucose
CO2
Mitochondria
(Respiration)
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Other Types of Photosynthesis
Plants are able to live under many
environmental conditions in part
because various modes of
photosynthesis have evolved.
The photosynthesis considered so far is
called C3 photosynthesis because a C3
molecule is formed immediately
following CO2 fixation.
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C3 Versus C4 Photosynthesis
C4 plants fix CO2 by forming a C4
molecule prior to the the Calvin cycle.
In C4 plants, CO2 is taken up in mesophyll
cells, and then a C4 molecule
(oxaloacetate) is pumped into bundle
sheath cells where it releases CO2 to
the Calvin cycle.
Thus, O2 cannot accumulate when
stomata close.
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In C4 plants, bundle sheath cells also
contain chloroplasts, and mesophyll
cells are arranged concentrically
around bundle sheath cells:
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CAM Photosynthesis
CAM plants also fix CO2 by forming a C4
molecule, but this occurs at night when
stomata can open without water loss.
CAM stands for crassulacean-acid
metabolism after the Crassulaceae, a
family of succulent plants from arid
regions.
C4 represents a partitioning in space,
whereas CAM is a partitioning in time.
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Photosynthesis Versus Cellular
Respiration
Both plant and animal cells carry on
cellular respiration in mitochondria;
photosynthesis occurs in plant
chloroplasts.
Photosynthesis is the building up of
glucose, while cellular respiration is the
breaking down of glucose.
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