AP Biology
Warm-up
 Objective:

Explain how photosynthesis converts
light energy into chemical energy.
 Warm-up:

In the light reactions, what is the
electron donor? Where do the electrons
end up?
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2006-2007
Photosynthesis:
Life from Light and Air
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Energy needs of life
 All life needs a constant input of energy

Energy needs of life

Autotrophs (Plants)
Heterotrophs
 consumers
Heterotrophs (Animals)
 animals
 fungi
 get their energy from “eating others”
 eat food = other organisms = organic molecules
 make energy through respiration

2006-2007
 most bacteria

Autotrophs
 producers
 plants
 get their energy from “self”
 get their energy from sunlight
 photosynthetic bacteria
 build organic molecules (food) from CO2
(blue-green algae)
 make energy & synthesize sugars through
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photosynthesis
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How are they connected?
Energy cycle
sun
Heterotrophs
making energy & organic molecules from ingesting organic molecules
glucose + oxygen  carbon + water + energy
dioxide
C6H12O6 +
6O2
Photosynthesis
plants
 6CO2 + 6H2O + ATP
exergonic
Where’s
the
ATP?
Autotrophs
making energy & organic molecules from light energy
CO2
Cellular Respiration
6CO2 + 6H2O + light  C6H12O6 + 6O2
energy
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endergonic
What does it mean to be a plant
 Need to…


ATP
the plant & also saved for a rainy day



sunlight

CO2

H2O

nutrients
glucose
need to get building block atoms
from the environment
CO2
 C,H,O,N,P,K,S,Mg
produce all organic molecules
needed for growth
 stomates = gas exchange
 uptake from roots
H2O
 N, P, K, S, Mg, Fe…
N
K P
…
 uptake from roots
 carbohydrates, proteins, lipids, nucleic acids
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ATP
 leaves = solar collectors
store light energy
 in a stable form to be moved around
The Great Circle
of Life,Mufasa!
Plant structure
 Obtaining raw materials
collect light energy
 transform it into chemical energy
O2
animals, plants
carbon + water + energy  glucose + oxygen
dioxide
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glucose
H2O
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Chloroplasts
Leaf
Leaf
absorb
sunlight & CO2
CO2
Chloroplasts
stomate
Chloroplast
transpiration
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Chloroplasts
contain
Chlorophyll
make
energy & sugar
2
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Plant structure
Photosynthesis
 Chloroplasts


 Light reactions
double membrane
stroma

 fluid-filled interior



thylakoid sacs
grana stacks
 convert solar energy to chemical energy
 ATP & NADPH
 Thylakoid membrane



chlorophyll molecules
electron transport chain
ATP synthase

+
+ H+ H
+
H+ H+ H + H+ H+ HH+
H+ H
 H+ gradient built up within
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thylakoid sac
Light Reactions
 uses chemical energy (ATP & NADPH) to
reduce CO2 & synthesize C6H12O6
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Calvin Cycle
H2O
CO2 + ATP + NADPH  C6H12O6 + ADP + NADP
 produces ATP
 produces NADPH
 releases O2 as a
waste product
sunlight
Energy Building
Reactions
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light-independent reactions
sugar production reactions
light  ATP + NADPH + O
2
energy
H2O +
It’s the
Dark Reactions!
 Calvin cycle
contains

light-dependent reactions
energy production reactions
CO2
ADP
NADP
NADPH
NADPH
ATP
ATP
sugars
C6H12O6
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O2
Sugar
Building
Reactions
 builds sugars
 uses ATP &
NADPH
 recycles ADP
& NADP back
to make more
ATP & NADPH
+
Putting it all together
light
CO2 + H2O + energy  C6H12O6 + O2
H2O
CO2
sunlight
ADP
Energy NADP
Building
Reactions
Sugar
Building
Reactions
Plants make both:
 energy
ATP & NADPH
 sugars
Light reactions
 Electron Transport Chain
 like in cellular respiration
membrane-bound proteins in organelle
 electron acceptors

 NADPH

membrane?
ATP
O2
proton (H+)
gradient across
inner membrane
 Where’s the double
NADPH
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+
+H H H+
H+ H+H
+ + + +
H+H H H H
+H+ H+ H+
H+ H+H
+ + + +
H+H H H H

sugars
C6H12O6
ATP synthase
enzyme
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ETC of Respiration
 Mitochondria transfer chemical
The ATP …..
photosynthesis
energy from food molecules
into chemical energy of ATP
respiration
sunlight
breakdown of C6H12O6
H+
H+
H+
 moves the electrons
H+

use electron carrier NADH
H+
H+
H+
H+
 runs the pump
 pumps the protons
 forms the gradient
 drives the flow of protons
through ATP synthase
ADP + Pi
 attaches Pi to ADP
 forms the ATP
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ATP
… that evolution built
ETC of Photosynthesis
generate H2O
H+
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 Chloroplasts transform light
energy into chemical energy
of ATP

Pigments of photosynthesis
use electron carrier NADPH
Why does this
molecular
structure make
sense?
 Chlorophyll & other pigments
embedded in thylakoid membrane
arranged in a “photosystem”
structure-function relationship
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Biology


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A Look at Light
 The spectrum of color
Light: absorption spectra
 Photosynthesis gets energy by absorbing
wavelengths of light

chlorophyll a
 absorbs best in red & blue wavelengths & least in
green

other pigments with different structures
absorb light of different wavelengths
Why are
plants green?
V
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I
B
G
Y
O
R
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ETC of Photosynthesis
Photosystems of photosynthesis
Photosystem II
 2 photosystems in thylakoid membrane



Photosystem I
collections of chlorophyll molecules
act as light-gathering “antenna complex”
Photosystem II
reaction
 chlorophyll a
center
 P680 = absorbs 680nm
wavelength red light

Photosystem I
 chlorophyll b
 P700 = absorbs 700nm
wavelength red light
antenna
pigments
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ETC of Photosynthesis
ETC of Photosynthesis
3
3
1
2
H+
to the
Calvin
Cycle
4
H+
H+
H+
H+
H+
H+
+
H+ H
H+
ATP
H+
4
H+
H+
H+
H+
ADP + Pi
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H+
H+
+
H+ H
H+
to the
Calvin
Cycle
ADP + Pi
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H+
ATP
H+
ETC of Photosynthesis
ETC of Photosynthesis
electron
carrier
6
5
to the
Calvin
Cycle
split H2O
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$$ in the bank…
reducing power
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ETC of Photosynthesis
 ETC produces from light energy

ATP & NADPH
Experimental evidence
 Where did the O2 come from?

 go to Calvin cycle
 PS II absorbs light



excited electron passes from chlorophyll to
“primary electron acceptor”
need to replace electron in chlorophyll
enzyme extracts electrons from H2O &
supplies them to chlorophyll
 splits H2O
 O combines with another O to form O2
 O2 released to atmosphere
 and we breathe easier!
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6CO2 + 6H2O + light  C6H12O6 + 6O2
energy
Experiment 2
6CO2 + 6H2O + light  C6H12O6 + 6O2
energy
Proved O2 came from H2O not CO2 = plants split H2O
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Noncyclic Photophosphorylation
 Light reactions

PS II generates
energy as ATP

PS I generates
reducing power as
NADPH
Cyclic photophosphorylation
 If PS I can’t pass
electron to NADP…
it cycles back to PS II &
makes more ATP, but
no NADPH
elevate electrons in
2 steps (PS II & PS I)
X
coordinates light
reactions to Calvin
cycle
 Calvin cycle uses more
ATP than NADPH

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Photophosphorylation
Photosynthesis summary
cyclic
photophosphorylation
noncyclic
photophosphorylation
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radioactive tracer = O18
Experiment 1
Where did the energy come from?
Where did the electrons come from?
Where did the H2O come from?
Where did the O2 come from?
Where did the O2 go?
Where did the H+ come from?
Where did the ATP come from?
What will the ATP be used for?
Where did the NADPH come from?
What will the NADPH be used for?
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…stay tuned for the Calvin cycle
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Stomates
Any Questions??
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2006-2007
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