Transcript Photosynthesis

Photosynthesis:
Life from Light
AP Biology
How are they connected?
Heterotrophs and Autotrophs
making energy & organic molecules from ingesting organic molecules
glucose + oxygen  carbon + water + energy
dioxide
C6H12O6 +
6O2
 6CO2 + 6H2O + ATP
exergonic
Autotrophs
making energy & organic molecules from light energy
Where’s
the
ATP?
carbon + water + energy  glucose + oxygen
dioxide
6CO2 + 6H2O + light  C6H12O6 + 6O2
energy
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endergonic
Plant structure
 Obtaining raw materials

sunlight
 leaves = solar collectors

CO2
 stomates = gas exchange
 Found under leaves

H2O
 uptake from roots

Nutrients
 N, P, K, S, Mg, Fe…
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 uptake from roots
2005-2006
Plant structure
 Chloroplasts
double membrane
 stroma
 thylakoid sacs
 grana stacks

 Chlorophyll & ETC in
thylakoid membrane

H+ gradient built up
within thylakoid sac
H+
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+
+ H + H H+
+
H
H
+ H+ H+ H+
+
H
H
Pigments of photosynthesis
 chlorophyll & accessory
Why does this
structure
make sense?
pigments
“photosystem”
 embedded in thylakoid
membrane
 structure  function
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
2005-2006
Light: absorption spectra
 Photosynthesis gets energy by absorbing
wavelengths of light

chlorophyll a (dominant pigment)
 absorbs best in red & blue wavelengths & least in
green

other pigments with different structures
absorb light of different wavelengths
Why are
plants green?
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Photosynthesis
 Light reactions
light-dependent reactions
 energy production reactions

 convert solar energy to chemical energy
 ATP & NADPH
 Calvin cycle
It’s the
Dark Reactions!
light-independent reactions
 sugar production reactions

 uses chemical energy (ATP & NADPH) to
reduce CO2 & synthesize C6H12O6
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Light reactions
 Electron Transport Chain (like cell respiration!)
membrane-bound proteins in organelle
 electron acceptor

 NADPH
proton (H+)
gradient across
inner membrane
 ATP synthase
enzyme

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2005-2006
Photosystems
 2 photosystems in thylakoid membrane


act as light-gathering “antenna complex”
Photosystem II
 chlorophyll a
 P680 = absorbs 680nm
wavelength red light

Photosystem I
 chlorophyll b
 P700 = absorbs 700nm
wavelength red light
AP Biology
reaction
center
ETC of Photosynthesis
 ETC produces from light energy

ATP & NADPH
 NADPH (stored energy) goes to Calvin cycle
 PS II absorbs light

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excited electron passes from chlorophyll to
“primary electron acceptor” at the REACTION
CENTER.
 splits H2O (Photolysis!!)
 O2 released to atmosphere
 ATP is produced for later use
ETC of Photosynthesis
Photosystem II
Photosystem I
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Noncyclic Photophosphorylation
 Light reactions
elevate electrons in
2 steps (PS II & PS I)

PS II generates
energy as ATP

PS I generates
reducing power as
NADPH
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2005-2006
Cyclic photophosphorylation
 If PS I can’t pass
electron to NADP,
it cycles back to
PS II & makes
more ATP, but no
NADPH


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X
coordinates light
reactions to Calvin
cycle
Calvin cycle uses
more ATP than
NADPH
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From Light reactions to Calvin cycle
 Calvin cycle

Chloroplast stroma
 Need products of light reactions to
drive synthesis reactions
ATP
 NADPH

What is there
left to do?
Make sugar!
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2005-2006
From CO2  C6H12O6
 CO2 has very little chemical energy

fully oxidized
 C6H12O6 contains a lot of chemical energy
reduced
 endergonic

 Reduction of CO2  C6H12O6 proceeds in
many small uphill steps
each catalyzed by specific enzyme
 using energy stored in ATP & NADPH

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Calvin cycle
3. Regeneration
of RuBP
ribulose
bisphosphate
RuBP
3 ATP
PGAL
to make
glucose
5C
1C
1. Carbon fixation
Rubisco
-enzyme that
Binds CO2
to RuBP
3 ADP
PGAL
sucrose
cellulose
etc.
CO2
6C
2x 3C
3C x2
PGA
2. Reduction
6 ATP
6 NADPH
6 NADP
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2x
3C
6 ADP
Calvin cycle
 PGAL   important intermediate
 Six turns of Calvin Cycle = 1 glucose
PGAL  



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glucose   carbohydrates
lipids
amino acids
nucleic acids
Summary
 Light reactions
produced ATP
 produced NADPH
 consumed H2O
 produced O2 as by product

 Calvin cycle
consumed CO2
 produced PGAL
 regenerated ADP
 regenerated NADP

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ADP
NADP
Factors that affect Photosynthesis
 Enzymes are responsible for several
photosynthetic processes, therefore,
temperature and pH can affect the rate of
photosynthesis.
 The amount and type of light can affect the
rate.
 A shortage of any of the reactants,CO2 and/or
H2O, can affect the rate.
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Supporting a biosphere
 On global scale,
photosynthesis is the
most important process
for the continuation of life on Earth
each year photosynthesis synthesizes
160 billion tons of carbohydrate
 heterotrophs are dependent on plants
as food source for fuel & raw materials

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Energy cycle
sun
Photosynthesis
CO2
H 2O
glucose
Cellular Respiration
The Great Circle
of Life!
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ATP
O2
Summary of photosynthesis
6CO2 + 6H2O + light  C6H12O6 + 6O2
energy
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Where did the CO2 come from?
Where did the CO2 go?
Where did the H2O come from?
Where did the H2O go?
Where did the energy come from?
What’s the energy used for?
What will the C6H12O6 be used for?
Where did the O2 come from?
Where will the O2 go?
What else is involved that is not listed in this
equation?
AP Biology
2005-2006