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Photosynthesis:
Nature’s Greatest
Gift to Life
I. A Historical Perspective:
CO2 + H2O
C6H12 O6 + O2
A. Old View: CO2 is Split, H2O stays intact
Why this Explanation Made Sense
CO2 +
H2O
C6H12O6
+
1.
Oxygen stays as a gas
in the same ratio
2.
Water has a 2:1 ratio as the
carbohydrate
O2
B. New View: Water is Split, CO2 stays intact
CO2 + H2 O
C6H12O6 + O2
Why the change in views?
1.
When water was tagged with an O2 isotope , the tag was on the released O2, not the glucose
CO2 + H2O
2.
C6H12O6 + O2
When CO2 was tagged with the O2 isotope, the tag was found in the glucose, not the released O2
CO2 + H2O
C6H12O6 + O2
The Structure Leaf and Photosynthesis
SO . . …
Tissue
What’s The Point?
light
chlorophyll
enzymes
Organ
Cell
Organelle
1. The structures of a leaf must
provide for the function of
photosynthesis
2. The chloroplast is the functional unit of photosynthesis
II. The 2 Stage Process of Building Glucose
The “Dark”
Reactions are
CO2 building
Glucose from
CO2
H2O
Light
ADP
NADP
Light
reactions
provide
Raw
Materials
for the
“Dark”
reaction
Light Dependent
reactions
Light
Independent
Reactions
Calvin
Cycle
ATP
Stage #1
NADPH
Stage #2
1. ATP
2. H+ (NADP)
O2
C6H12O6
III. Energy from Light (I hope you remember your physics)
SO . . …
What’s The Point?
1. Visible light comes
in different wave
lengths and energy
levels
2. The pigments seen
are due to different
wavelengths and
energy levels
“Not all wavelengths are created equal”
SO . . …
What’s The Point?
1. The color observed is
the color reflected
(transmitted)
2. All other colors are
absorbed
3. Reflected light cannot
be used for photosynthesis because it
does not absorb any
light energy
Related Questions
Why does a dark car heat up
faster in the sun than a light?
What would be the worst
color light to use as a plant
growth light?
SO . . …
What’s The Point?
1. ________ color is the best
light for photosynthesis.
The runner-up is ________
2. The advantage to having
yellow and red pigments in
leaves and not just green
is________
Go to Socrative on your cell
phone. My room # is
BRADYAPBIO
1. What leaf structure allows for gas exchange?
a. chloroplast
c. inner membrane
b. stomata
d. chlorophyll
2. What is the source of oxygen that is released from plant
cells as a result of photosynthesis?
a. carbon dioxide
c. glucose
b. ATP
d. water
3. Based on the absorption spectrum in your notes, what
wavelength of light is absorbed the most during
photosynthesis?
a. 700 nm
c. 450 nm
b. 600 nm
d. 550 nm
4. Carbon dioxide becomes ______ in photosynthesis,
forming glucose.
a. reduced
c. charged
b. oxidized
d. broken down
5. Photosynthesis converts _______ energy into chemical
energy in the form of glucose.
a. light
c. electrical
b. chemical
d. thermal
IV. How pigments react to light energy
SO . . …
What’s The Point?
EHeat
E-
1. Photosynthesis captures
the energy from the excited
electron to make ATP
Fluorescence
Light
ATP
EGreen Light
ReflectedPigment
2. The ATP is then used
to build Glucose
V. The Light Dependent Reactions
Chloroplast
Thylakoid
Grana
Stroma
Stroma
Light
H+
Light
H+
E-
H+
Fd
E-
Thylakoid
E-
Pq
NADPH
PC
PS I NADP
H2O
PS II H+ Pump
Reductase
(P700)
Thylakoid
O2 (P680) Proton Motive Force H+ H+
space
H+
Chemiosomosis H+
H+
Stroma
ADP ADP
Photophosphorylation
1. Cyclic
2. Non-Cyclic
ADP
ATP Synthase
ATP
Calvin
Cycle
Cyclic verses Non-Cyclic Photophosphorylation
Non-Cyclic
1. Electron from water never “recycles”
2. Electron used to make NADPH
3. Requires Photosystem I and II
4. Takes place when plenty of H+ and ATP
available (H20 is plentiful)
Cyclic
1. Electron recycles
2. Electron used to fill the empty
electron hole
3. Only uses Photosystem I
4. Makes ATP even though H2O is
unavailable
VI. The Calvin Cycle- Building Compounds 1 Carbon at a Time
Making the numbers
balance
CO2
(3 CO2 molecules enter)
(3 - 6C Unstable
compounds)
Rubisco
(Ribulose BiPhosphate Carboxylase)
(3 - 5C
RubBP)
Unstable 6 Carbon
compound(6 - 3C Stable
Carbon dioxide
acceptor
5c
RuBP
Ribulose
BiPhosphate
compounds)
(2) PGA
Phase 1
Carbon
Fixation
3c
ATP
ADP
ADP
Phase 3
Regeneration
of CO2
Acceptor
ATP
Rearrangement
of carbons
Phase 2
Reduction
(2)
3c
(2) PGAL/G3P
PGAL
NADPH
NADP
Pi
3c
(5 - 3C Stable
compounds)
Photosynthesis fills the PGAL
Bucket for many metabolic
products
3c
Krebs Cycle
1. Amino Acids - Proteins
Bucket O’
PGAL
2. Glycerol & Fatty Acids- Lipids
2PGAL = C6H12O6
How Photosystems Harvest Light
Slide 11
Plasmodesmata
Note: All C4 plants are easy to identify by the
presence of the unique Bundle Sheaths and
Mesophyll cells
Slide 13
Photosystem II sends electrons to a higher energy level
Slide 9
Electron Acceptor
Light
Reaction Center
1. Pq (Plastiquione)
2. FD (Ferredoxin)
EE-
Chlorophyll a
E-
E-
E-
EE-
E-
Photosystem
Donates the electron
How does chlorophyll
“a” refill its electrons?
Antenna Pigments
1. Chlorophyll “b”
2. Carotene
3. Xanthophyll
The Structure of Chlorophyll
On membrane
surface
Embedded in
the membrane
Metal that
allows
transfer of
electrons
Slide 11
Slide 8
Slide 8
Slide 7
SLIDE 11
The Metabolic
Possibilities
of PGAL
Slide 11
Cell Respiration (Glycolysis)
Vs.
Photosynthesis (Calvin Cycle)
PGAL
PGAL
H
H
ATP
1,3-Biphosphoglycerate
PGA
Pyruvic Acid
ATP
1,3-Biphosphoglycerate
2PGA
Unstable 6 Carbon
CO2 + Ribulose Bi Phosphate
Slide 11
Slide 9