AP Exam Review:
Photosynthesis and Respiration
AP Biology
Photosynthesis:
Life from Light and Air
AP Biology
2007-2008
Chloroplasts
leaves
cross section absorb
of leaf
sunlight & CO2
CO2
chloroplasts
in plant cell
chloroplast
AP Biology
chloroplasts
contain
chlorophyll
make
energy & sugar
chloroplast
H+
Plant structure
ATP
+
+ H+ H H+
+
H
H
+ H+ H+ H+
+
H
H
 Chloroplasts


double membrane
stroma
outer membrane
thylakoid
inner membrane
 fluid-filled interior


thylakoid sacs
grana stacks
stroma
 Thylakoid membrane
contains



chlorophyll molecules
electron transport chain
ATP synthase
 H+ gradient built up within
AP Biology
thylakoid sac
thylakoid
granum
Photosynthesis
 Light reactions
light-dependent reactions
 energy conversion reactions

 convert solar energy to chemical energy
 ATP & NADPH
 Calvin cycle
It’s not the
Dark Reactions!
light-independent reactions
 sugar building reactions

 uses chemical energy (ATP & NADPH) to
reduce CO2 & synthesize C6H12O6
AP Biology
thylakoid
chloroplast
+H+ H+ H+
+ + +
H+ H+H
+H+ H H H
H
Light reactions
 Electron Transport Chain
 like in cellular respiration
proteins in organelle membrane
 electron acceptors

 NADPH

proton (H+)
gradient across
inner membrane
 find the double membrane!

ATP synthase
enzyme
AP Biology
ATP
+H+ H+ H+
H+ H+H
+ + + +
H+H H H H
ETC of Photosynthesis
Chloroplasts transform light energy
into chemical energy of ATP

generates O2
AP Biology
use electron carrier NADPH
The ATP that “Jack” built
photosynthesis
respiration
sunlight
breakdown of C6H12O6
H+
H+
H+
 moves the electrons
H+
H+
H+
H+
H+
 runs the pump
 pumps the protons
 builds the gradient
 drives the flow of protons
through ATP synthase
 bonds Pi to ADP
 generates the ATP
ADP + Pi
… that evolution built
ATP
H+
AP Biology
Pigments of photosynthesis
How does this
molecular structure
fit its function?
 Chlorophylls & other pigments


embedded in thylakoid membrane
arranged in a “photosystem”
 collection of molecules
AP Biology

structure-function relationship
A Look at Light
 The spectrum of color
V
AP Biology
I
B
G
Y
O
R
Light: absorption spectra
 Photosynthesis gets energy by absorbing
wavelengths of light

chlorophyll a
 absorbs best in red & blue wavelengths & least in green

accessory pigments with different structures
absorb light of different wavelengths
 chlorophyll b, carotenoids, xanthophylls
Why are
plants green?
AP Biology
Photosystems of photosynthesis
 2 photosystems in thylakoid membrane
collections of chlorophyll molecules
 act as light-gathering molecules
 Photosystem II
reaction

 chlorophyll a
center
 P680 = absorbs 680nm
wavelength red light

Photosystem I
 chlorophyll b
 P700 = absorbs 700nm
wavelength red light
AP Biology
antenna
pigments
chlorophyll a
ETC of Photosynthesis
Photosystem II
chlorophyll b
Photosystem I
AP Biology
ETC of Photosynthesis
sun
1
e
e
AP Biology
Photosystem II
P680
chlorophyll a
Inhale, baby!
ETC of Photosynthesis
thylakoid
chloroplast
+H+ H+ H+
+ + +
H+ H+H
+H+ H H H
H
ATP
H+
+H+ H+ H+
+
H
H + + H+H+ H+
HH
Plants SPLIT water!
O
H H
2
1
e
e
O
O
H
H
e
e
fill the e– vacancy
AP Biology
Photosystem II
P680
chlorophyll a
+H
e-
H+
e-
ETC of Photosynthesis
thylakoid
chloroplast
H+
+H+ H+ H+
+
H
H + + H+H+ H+
HH
+H+ H+ H+
H+ H+H
+ + + +
H+H H H H
ATP
3
2
1
e
e
H+
4
ATP
H+
to Calvin Cycle
H+
H+
H+
AP Biology
Photosystem II
P680
chlorophyll a
H+
H+
+
H+ H
ADP + Pi
ATP
H+
H+
energy to build
carbohydrates
ETC of Photosynthesis
e
e
sun
5
e
AP Biology
Photosystem II
P680
chlorophyll a
e
Photosystem I
P700
chlorophyll b
ETC of Photosynthesis
electron carrier
6
e
e
5
sun
AP Biology
Photosystem II
P680
chlorophyll a
Photosystem I
P700
chlorophyll b
$$ in the bank…
reducing power!
ETC of Photosynthesis
sun
sun
+
+
+ H
H
+
+
H+ H +
H H
H+H+ H+ H
+
H
to Calvin Cycle
O
split H2O
ATP
AP Biology
ETC of Photosynthesis
 ETC uses light energy to produce

ATP & NADPH
 go to Calvin cycle
 PS II absorbs light



AP Biology
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!
Photosynthesis:
The Calvin Cycle
Life from Air
AP Biology
2007-2008
Light reactions
 Convert solar energy to chemical
energy
ATP

ATP  energy

NADPH  reducing power
 What can we do now?
  build stuff !!
AP Biology
photosynthesis
How is that helpful?
 Want to make C6H12O6
synthesis
 How? From what?
What raw materials are available?

CO2
NADPH
carbon fixation
reduces CO2
NADP
C6H12O6
AP Biology
NADP
From CO2  C6H12O6
 CO2 has very little chemical energy

fully oxidized
 C6H12O6 contains a lot of chemical energy

highly reduced
 Synthesis = endergonic process

put in a lot of energy
 Reduction of CO2  C6H12O6 proceeds in
many small uphill steps
each catalyzed by a specific enzyme
 using energy stored in ATP & NADPH

AP Biology
From Light reactions to Calvin cycle
 Calvin cycle

chloroplast stroma
 Need products of light reactions to
drive synthesis reactions
stroma
ATP
 NADPH

ATP
thylakoid
AP Biology
C
C
Calvin cycle
C C C C C
3. Regeneration
of RuBP
C C C C C
RuBP
3 ATP
C= C= C
H H H
|
| |
C– C– C
AP Biology
C
C
C
C
C
C
C
C
C
C
C
C
C
C
C
C
C
C
1. Carbon fixation
5C
C C C C C C
RuBisCo
ribulose
bisphosphate
carboxylase
3 ADP
used
to make
glucose
CO2
C C C C C
ribulose bisphosphate
starch,
sucrose,
cellulose
& more
1C
C
C C C C C C
6C
C C C C C C
5C
glyceraldehyde-3-P
G3P
C C C
PGA
phosphoglycerate
3C
6 NADP
C
C
C
C
C
C
6 ATP
2. Reduction
6 NADPH
3C
C
C
C
C
C
C
3C
6 ADP
C
C
C
C
C
C
H
|
H
|
H
|
Light Reactions
H2O + light

energy
H2O
Energy Building
Reactions
NADPH
ATP
O2
+
NADPH
+ O2
 produces ATP
 produces NADPH
 releases O2 as a
waste product
sunlight
AP Biology
ATP
Calvin Cycle
CO2 +
ATP
+
NADPH

C6H12O6
CO2
ADP
NADP Sugar
Building
Reactions
NADPH
ATP
AP Biology
sugars
+
ADP
+
NADP
 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
NADP Sugar
Energy
Building
Building
Reactions
Reactions
NADPH
ATP
AP Biology
O2
sugars
Plants make both:
 energy
 ATP & NADPH
 sugars
Cellular Respiration
Harvesting Chemical Energy
ATP
AP Biology
2006-2007
Harvesting stored energy
 Glucose is the model
respiration

catabolism of glucose to produce ATP
glucose + oxygen  energy + water + carbon
dioxide
C6H12O6 +
6O2
 ATP + 6H2O + 6CO2 + heat
COMBUSTION = making a lot of heat energy
by burning fuels in one step
uel
AP Biology
carbohydrates)
RESPIRATION = making ATP (& some heat)
by burning fuels in many small steps
ATP
enzymes
O2
ATP
O2
CO2 + H2O + ATP (+ heat)
glucose
CO2 + H2O + heat
How do we harvest energy from fuels?
 Digest large molecules into smaller ones

break bonds & move electrons from one
molecule to another
 as electrons move they “carry energy” with them
 that energy is stored in another bond,
released as heat or harvested to make ATP
loses e-
gains e-
+
oxidized
reduced
+
+
e-
oxidation
AP Biology
–
e-
reduction
e-
redox
How do we move electrons in biology?
 Moving electrons in living systems

electrons cannot move alone in cells
 electrons move as part of H atom
e
p
 move H = move electrons
loses e-
gains e-
oxidized
+
+
oxidation
reduced
+
–
H
reduction
H
oxidation
C6H12O6 +
AP Biology
H e-
6O2
 6CO2 + 6H2O + ATP
reduction
Coupling oxidation & reduction
 REDOX reactions in respiration

release energy as breakdown organic molecules
 break C-C bonds
 strip off electrons from C-H bonds by removing H atoms
 C6H12O6  CO2 = the fuel has been oxidized
 electrons attracted to more electronegative atoms
 in biology, the most electronegative atom?
 O2  H2O = oxygen has been reduced

O
couple REDOX reactions &
2
use the released energy to synthesize ATP
oxidation
C6H12O6 +
AP Biology
6O2
 6CO2 + 6H2O + ATP
reduction
Oxidation & reduction
 Oxidation
 Reduction
adding O
 removing H
 loss of electrons
 releases energy
 exergonic

removing O
 adding H
 gain of electrons
 stores energy
 endergonic

oxidation
C6H12O6 +
6O2
 6CO2 + 6H2O + ATP
reduction
AP Biology
like $$
in the bank
Moving electrons in respiration
 Electron carriers move electrons by
shuttling H atoms around
 NAD+  NADH (reduced)
 FAD+2  FADH2 (reduced)
NAD+
nicotinamide
Vitamin B3
niacin
O–
O– P
O
–O
NADH
O
H
C
H
–O
AP Biology
reduction
oxidation
adenine
ribose sugar
O
C
phosphates
O–
O– P
O
H H
NH2
N+
+
reducing power!
carries electrons as
a reduced molecule
N+
O–
O– P
O
–O
O–
O– P
O
–O
NH
How efficient!
Build once,
use many ways
Overview of cellular respiration
 4 metabolic stages

Anaerobic respiration
1. Glycolysis
 respiration without O2
 in cytosol

Aerobic respiration
 respiration using O2
 in mitochondria
2. Pyruvate oxidation
3. Krebs cycle
4. Electron transport chain
C H O6 +
AP Biology
6 12
6O2
 ATP + 6H2O + 6CO2 (+ heat)
H+
And how do we do that?
H+
H+
H+
H+
H+
H+
H+
 ATP synthase enzyme

H+ flows through it
 conformational
changes
 bond Pi to ADP to
make ATP

set up a H+ gradient
 allow the H+ to flow
ADP
down concentration
gradient through ATP
synthase
 ADP + Pi  ATP
But…
How is the proton (H+) gradient formed?
AP Biology
+ P
ATP
H+
Cellular Respiration
Stage 1:
Glycolysis
AP Biology
2007-2008
Glycolysis
 Breaking down glucose

“glyco – lysis” (splitting sugar)
glucose      pyruvate
2x 3C
6C

ancient pathway which harvests energy
 where energy transfer first evolved
 transfer energy from organic molecules to ATP
 still is starting point for ALL cellular respiration

but it’s inefficient
 generate only 2 ATP for every 1 glucose

occurs in cytosol
AP Biology
That’s not enough
ATP for me!
In the
cytosol?
Why does
that make
evolutionary
sense?
Cellular Respiration
Stage 2 & 3:
Oxidation of Pyruvate
Krebs Cycle
AP Biology
2006-2007
Glycolysis is only the start
 Glycolysis
glucose      pyruvate
6C
2x 3C
 Pyruvate has more energy to yield



3 more C to strip off (to oxidize)
if O2 is available, pyruvate enters mitochondria
enzymes of Krebs cycle complete the full
oxidation of sugar to CO2
pyruvate       CO2
AP Biology
3C
1C
Cellular respiration
AP Biology
Mitochondria — Structure
 Double membrane energy harvesting organelle


smooth outer membrane
highly folded inner membrane
 cristae

intermembrane space
 fluid-filled space between membranes

matrix
 inner fluid-filled space


DNA, ribosomes
enzymes
 free in matrix &
What cells would have
AP
Biology
a lot
of mitochondria?
outer
intermembrane
membrane
inner
space
membrane-bound
membrane
cristae
matrix
mitochondrial
DNA
Mitochondria – Function
Oooooh!
Form fits
function!
Dividing mitochondria
Membrane-bound proteins
Who else divides like that? Enzymes & permeases
bacteria!
What does this tell us about
the evolution of eukaryotes?
Endosymbiosis!
AP Biology
Advantage of highly folded inner
membrane?
More surface area for membranebound enzymes & permeases
Oxidation of pyruvate
 Pyruvate enters mitochondrial matrix
[
2x pyruvate    acetyl CoA + CO2
3C
2C
1C
NAD
Where
does the
CO2 go?
Exhale!
3 step oxidation process
 releases 2 CO2 (count the carbons!)
 reduces 2 NAD  2 NADH (moves e )
 produces 2 acetyl CoA


Acetyl CoA enters Krebs cycle
AP Biology
]
Pyruvate oxidized to Acetyl CoA
NAD+
Pyruvate
C-C-C
[
reduction
Coenzyme A
CO2
Acetyl CoA
C-C
oxidation
2 x Yield = 2C sugar + NADH + CO2
AP Biology
]
Krebs cycle
1937 | 1953
 aka Citric Acid Cycle
in mitochondrial matrix
 8 step pathway

 each catalyzed by specific enzyme
Hans Krebs
1900-1981
 step-wise catabolism of 6C citrate molecule
 Evolved later than glycolysis

does that make evolutionary sense?
 bacteria 3.5 billion years ago (glycolysis)
 free O2 2.7 billion years ago (photosynthesis)
 eukaryotes 1.5 billion years ago (aerobic
AP Biology
respiration = organelles  mitochondria)
Count the carbons!
pyruvate
3C
2C
6C
4C
This happens
twice for each
glucose
molecule
4C
citrate
oxidation
of sugars
4C
6C
CO2
x2
4C
AP Biology
acetyl CoA
5C
4C
CO2
Count the electron carriers!
pyruvate
3C
6C
4C
NADH
This happens
twice for each
glucose
molecule
2C
4C
citrate
reduction
of electron
carriers
x2
4C
FADH2
4C
AP Biology
acetyl CoA
NADH
6C
CO2
NADH
5C
4C
ATP
CO2
CO2
NADH
Value of Krebs cycle?
 If the yield is only 2 ATP then how was the
Krebs cycle an adaptation?

value of NADH & FADH2
 electron carriers & H carriers
 reduced molecules move electrons
 reduced molecules move H+ ions
 to be used in the Electron Transport Chain
like $$
in the
bank
AP Biology
ATP accounting so far…
 Glycolysis  2 ATP
 Kreb’s cycle  2 ATP
 Life takes a lot of energy to run, need to
extract more energy than 4 ATP!
There’s got to be a better way!
I need a lot
more ATP!
AP Biology
A working muscle recycles over
10 million ATPs per second
There is a better way!
 Electron Transport Chain

series of proteins built into
inner mitochondrial membrane
 along cristae
 transport proteins & enzymes
transport of electrons down ETC linked to
pumping of H+ to create H+ gradient
 yields ~36 ATP from 1 glucose!
 only in presence of O2 (aerobic respiration)

AP Biology
That
sounds more
like it!
O2
Mitochondria
 Double membrane
outer membrane
 inner membrane

 highly folded cristae
 enzymes & transport
proteins

intermembrane space
 fluid-filled space
between membranes
AP Biology
Oooooh!
Form fits
function!
Electron Transport Chain
Inner
mitochondrial
membrane
Intermembrane space
C
Q
NADH
dehydrogenase
cytochrome
bc complex
Mitochondrial matrix
AP Biology
cytochrome c
oxidase complex
Remember the Electron Carriers?
Glycolysis
glucose
Krebs cycle
G3P
2 NADH
Time to
break open
the piggybank!
AP Biology
8 NADH
2 FADH2
Electron Transport Chain
Building proton gradient!
NADH  NAD+ + H
e
p
intermembrane
space
H+
H+
H  e- + H+
C
e–
NADH H
FADH2
NAD+
NADH
dehydrogenase
inner
mitochondrial
membrane
e–
Q
AP Biology
H+
e–
H
FAD
2H+ +
cytochrome
bc complex
1
O2
H 2O
2
cytochrome c
oxidase complex
mitochondrial
matrix
What powers the proton (H+) pumps?…
Stripping H from Electron Carriers
 Electron carriers pass electrons & H+ to ETC


H cleaved off NADH & FADH2
electrons stripped from H atoms  H+ (protons)
 electrons passed from one electron carrier to next in
mitochondrial membrane (ETC)
 flowing electrons = energy to do work

transport proteins in membrane pump H+ (protons)
across inner membrane to intermembrane space
H+
+
H
H+
TA-DA!!
Moving electrons
do the work!
+
H
H+
H+
+
H+ H+ H
+
H+ H H+
C
e–
NADH
AP Biology
+
H
H+
Q
e–
FADH2
FAD
NAD+
NADH
dehydrogenase
e–
2H+
cytochrome
bc complex
+
1
H2O
2 O2
cytochrome c
oxidase complex
ADP
+ Pi
ATP
H+
But what “pulls” the
electrons down the ETC?
H2O
O2
AP Biology
electrons
flow downhill
to O2
oxidative phosphorylation
Electrons flow downhill
 Electrons move in steps from
carrier to carrier downhill to oxygen
each carrier more electronegative
 controlled oxidation
 controlled release of energy

make ATP
instead of
fire!
AP Biology
“proton-motive” force
We did it!
 Set up a H+


H+
H+
H+
gradient
Allow the protons
to flow through
ATP synthase
Synthesizes ATP
ADP + Pi  ATP
Are we
there yet?
AP Biology
H+
H+
H+
H+
H+
ADP + Pi
ATP
H+
Chemiosmosis
 The diffusion of ions across a membrane

build up of proton gradient just so H+ could flow
through ATP synthase enzyme to build ATP
Chemiosmosis
links the Electron
Transport Chain
to ATP synthesis
So that’s
the point!
AP Biology
Pyruvate from
cytoplasm
Inner
+
mitochondrial H
membrane
H+
Intermembrane
space
Electron
transport
C system
Q
NADH
Acetyl-CoA
1. Electrons are harvested
and carried to the
transport system.
NADH
Krebs
cycle
e-
e-
FADH2
e-
2. Electrons
provide energy
to pump
protons across
the membrane.
e-
H2O
3. Oxygen joins
with protons to
form water.
1 O
2 +2
2H+
O2
H+
CO2
ATP
Mitochondrial
matrix
AP Biology
H+
ATP
ATP
4. Protons diffuse back in
down their concentration
gradient, driving the
synthesis of ATP.
H+
ATP
synthase
even though
this equation
is a bit of a lie…
it makes a
better story
Energy cycle
sun
Photosynthesis
light
CO2 + H2O + energy  C6H12O6 + O2
plants
CO2
glucose
H2O
animals, plants
ATP
C6H12O6 + O2  energy + CO2 + H2O
Cellular Respiration
AP Biology
The Great Circle
of Life,Mufasa!
ATP
O2