Transcript Document
Photosynthesis:
Life from Light
AP Biology
Energy needs of life
All life needs a constant input of energy
Heterotrophs
get their energy from “eating others”
consumers of other organisms
consume organic molecules
Autotrophs
get their energy from “self”
get their energy from sunlight
use light energy to synthesize organic
molecules
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How are they connected?
Heterotrophs
making energy & organic molecules from ingesting organic molecules
glucose + oxygen carbon + water + energy
dioxide
C6H12O6 +
6O2
6CO2 + 6H2O + ATP
Autotrophs
making energy & organic molecules from light energy
carbon + water + energy glucose + oxygen
dioxide
6CO2 + 6H2O + light C6H12O6 + 6O2
energy
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2005-2006
Energy cycle
sun
Photosynthesis
CO2
H 2O
glucose
Cellular Respiration
The Great Circle
of Life!
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ATP
O2
What does it mean to be a plant
Need to…
collect light energy
transform it into chemical energy
store light energy
in a stable form to be moved around the plant
& also saved for a rainy day
need to get building block atoms from
the environment
C,H,O,N,P,S
produce all organic molecules needed for
growth
carbohydrates, proteins, lipids, nucleic acids
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Plant structure
Obtaining raw materials
sunlight
leaves = solar collectors
CO2
stomates = gas exchange
regulation
Found under leaves
H2O
uptake from roots
nutrients
uptake from roots
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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 performs work only with
absorbed wavelengths of light
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chlorophyll a — the dominant pigment —
absorbs best in red & blue wavelengths & least
in green
other pigments with different structures have
different absorption spectra
Photosystems
Photosystems
collections of chlorophyll molecules
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
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Transfer of Electrons in PSII & PSI
In both PSII and PSI, the energy from the
excited e- pumps H+ into the thylakoid as
it moves through the ETC.
Electrons from PSII are transferred to PSI.
After electrons have moved through PSI,
an intermediary molecule (embedded in
the membrane and adjacent to PSI)
transfers the e- to NADP+. A H+ is
attracted to this molecule and NADPH is
formed.
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Chemiosmosis in Photosynthesis
**(similar in Cell Respiration)
proton (H+)
gradient across
inner membrane
drive ATP formation
ATP synthase
enzyme
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2005-2006
Summary of the LDR
PS II absorbs light
excited electron passes from chlorophyll to
“primary electron acceptor” at the REACTION
CENTER.
splits H2O (Photolysis!!)
O2 released to atmosphere
PS I absorbs light
Produces NADPH (stored energy) which will be
used by the Calvin cycle
Chemiosmosis produces ATP from light
energy
ATP will be used by the Calvin Cycle
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ETC of Photosynthesis
Chloroplasts transform light
energy into chemical energy
of ATP
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split H2O
use electron carrier NADPH
2 Photosystems
Light reactions
elevate electrons in
2 steps (PS II & PS I)
PS II helps generate
energy as ATP (H+
pumps)
PS I generates
reducing power as
NADPH
This shows Noncyclic
photophosphorylation.
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ETC of Photosynthesis
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ETC of Photosynthesis
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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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coordinates light
reactions to Calvin
cycle
Calvin cycle uses
more ATP than
NADPH
Do Now: Light Reactions Summary Questions
Where did the energy come from?
Where did the H2O come from?
Where did the electrons come from?
Where did the O2 come from?
Where did the H+ come from?
Where did the ATP come from?
Where did the O2 go?
What will the ATP be used for?
What will the NADPH be used for?
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Calvin Cycle Overview
Calvin cycle
uses chemical energy
(NADPH & ATP)
to reduce CO2 to
build C6H12O6 (sugars)
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From Light reactions to Calvin cycle
Calvin cycle
Occurs in the stroma of the chloroplast
Need products of light reactions to
drive synthesis reactions
ATP
NADPH
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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
1C
ribulose bisphosphate
3. Regeneration
RuBP
3 ATP
PGAL
to make
glucose
5C
1. Carbon fixation
Rubisco
ribulose
bisphosphate
carboxylase
3 ADP
PGAL
sucrose
cellulose
etc.
CO2
6C
unstable
intermediate
2x 3C
3C x2
PGA
2. Reduction
6 ATP
6 NADPH
6 NADP
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2x
3C
6 ADP
Rubisco
Enzyme which fixes carbon from
atmosphere
ribulose bisphosphate carboxylase
the most important enzyme in the world!
it makes life out of air!
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definitely the most abundant enzyme
Calvin cycle
PGAL
end product of Calvin cycle
energy rich sugar
3 carbon compound
“C3 photosynthesis”
PGAL important intermediate
PGAL
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glucose carbohydrates
lipids
amino acids
nucleic acids
Photosynthesis summary
Light reactions
produced ATP
produced NADPH
consumed H2O
produced O2 as byproduct
Calvin cycle
consumed CO2
produced PGAL
regenerated ADP
regenerated NADP
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Summary of photosynthesis
6CO2 + 6H2O + light C6H12O6 + 6O2
energy
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