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PHOTOSYNTHESIS
Photosynthesis:
Life from Light and
Air
CAPTURING THE ENERGY
IN LIGHT

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The process by which
organisms obtain energy
directly from sunlight is
called photosynthesis.
CO2 + H2O → C6H12O6 + O2
ENERGY FOR LIFE
PROCESSES
Autotrophs: most Plants,
Algae, and some Bacteria.
 Autotrophs store energy in
various organic
compounds, primarily
carbohydrates.

The Basic
By McGraw
Hill
Photosynthesis involves a
complex series of chemical
reactions: Biochemical
Pathway
 Products used in cellular
respiration in both plants
and animals.

Redox Reactions:
OIL RIG
Oxidation is Loss
Reduction is Gain (of e-)
or
Oxidation is loss of hydrogen.
Reduction is gain of hydrogen.
How are they connected?
Heterotroph and….
glucose + oxygen  carbon + water + energy
dioxide
C6H12O6 +
6O2
 6CO2 + 6H2O + ATP
oxidation = exergonic
carbon + water + energy  glucose + oxygen
dioxide
6CO2 + 6H2O + light  C6H12O6 + 6O2
energy
Autotroph
reduction = endergonic
What does it mean to be a plant

Need to…

collect light energy

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glucose

transform it into chemical energy
store light energy

in a stable form to be moved around
the plant or stored
need to get building block atoms
from the environment

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ATP
C,H,O,N,P,K,S,Mg
produce all organic molecules
needed for growth

carbohydrates, proteins, lipids, nucleic acids
CO2
N
K P
…
H2O
LIGHT ABSORPTION IN
CHLOROPLASTS
Light Reactions or Light
Dependent Reactions
 They begin with the
absorption of light
in chloroplasts.

Review of the
Light Reaction
With All
Details!
CHLOROPLASTS
LIGHT AND PIGMENTS
chlorophylls accessory pigments carotenoids
Photosynthesis gets energy by
absorbing wavelengths of light.
Accessory pigments with
different structures absorb light
of different wavelengths:
chlorophyll a & b, carotenoids,
xanthophylls, antenna pigments
What is Photosynthesis?

Light reactions

light-dependent reactions

convert solar energy to chemical energy

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ATP & NADPH
Calvin cycle
light-independent reactions
 sugar building reactions


uses chemical energy (ATP & NADPH) to
reduce CO2 & synthesize C6H12O6
It’s not the
Dark Reactions!
Virtual Cell
Photo.
LIGHT REACTIONS
ELECTRON TRANSPORT CHAIN:
PHOTOSYSTEMS II AND I.
1.
1.
2.
3.
chlorophyll a
P680 = absorbs 680nm
wavelength red light
chlorophyll b
P700 = absorbs 700nm
wavelength red light
Photosystem
I
REPLENISHING PHOTOSYSTEM
II
CHEMIOSMOSIS
Go to: D-Drive
Virtual Cell:Photosynthesis
Youtube Streaming Video
Photosystem I file b
ELECTRON TRANSPORT CHAIN
The Basic
Biochemical
Pathway
RESTORING PHOTOSYSTEM II
CHEMIOSMOSIS
What is Photophosphorylation?
cyclic
photophosphorylation
NADP
NONcyclic
photophosphorylation
ATP
Why Cyclic Phosphorolation?

Calvin cycle uses more ATP than NADPH
18 ATP +
12 NADPH
1 C6H12O6
PUTTING IT ALL TOGETHER
Overview
Of the
Light Reaction
Review of the
Light Reaction
With All
Details!
Photosynthesis Animation

http://www.stolaf.edu/people/giannini/flashani
mat/metabolism/photosynthesis.swf
Experimental evidence

Where did the O2 come from?

radioactive tracer = O18
Experiment 1
6CO2 + 6H2O + light  C6H12O6 + 6O2
energy
Experiment 2
6CO2 + 6H2O + light  C6H12O6 + 6O2
energy
Proved O2 came from H2O not CO2 = plants split H2O!
Photosynthesis summary
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?
So where does CO2 fit in?
How do plants use it?
Why do they need it?
LIGHT INDEPENDENT
to the Dark
REACTIONS Welcome
Side, Lord Calvin
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KNOWN AS THE CALVIN CYCLE =
C3 Photosynthesis.
do
CO2 IS FIXED INTO ORGANIC How
Plants
Capture
COMPOUNDS: CARBON
CO2?
FIXATION.
THREE MAJOR STEPS, WHICH
OCCUR WITHIN THE STROMA.
Calvin
Reduction Reaction= C gains H+ Cycle
P.S. The Dark Cycle Does
Not Happen in the Dark
It is dependent on the products of the light
reaction (ATP and NADPH) So when the
lights go out…it has no energy to continue.
NOVA
Capturing C
Think…

Why can’t we blow carbon emissions into
forests and solve global warming?
ALTERNATIVE PATHWAYS
TO FIX CARBON

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These alternative pathways are
generally found in plants that
evolved in hot, dry climates.
Stomata: passageways FOR CO2
and O2.
C-4: Photosynthesis

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Intense Sunlight and Hot (e.g. corn and
crabgrass)
Stomata are Partly Closed During Day= CO2
falls and O2 rises

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We don’t want photorespiration.
In the Mesophyll PEP carboxylase grabs CO2
not O2.
Sends CO2 to the Calvin cycle
The C4 Pathway
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FIXES CO2 INTO A FOUR CARBON
COMPOUND OXALOACETATE.
HENSE THE NAME: C4
Oxaloacetate in the mesophyll
turns into Malate, an acid.
Malate is shipped through
plasmodesmata into bundle
sheath cells and release CO2
Calvin Cycle Starts
The CAM Plants
Crassulacean Acid Metabolism
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Adaptation to Dry Conditions
Stomata Closed during Day Open at Night
Mesophyll stores CO2 at night
Makes Sugar during Day
All 3 (C3, C-4, and CAM) use the Calvin
Cycle
The CAM Pathway
 Plants that use the CAM
pathway open their
stomata at night and close
them during the day—just
the opposite of what other
plants do.
RATE OF PHOTOSYNTHESIS
Review