Photosynthesis
Energy & Life
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Overview of
Photosynthesis
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Autotrophs
Plants and some
other types of
organisms that
contain
chlorophyll are
able to use light
energy from the
sun to produce
food.
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Autotrophs
• Autotrophs
include
organisms that
make their own
food
• Autotrophs can
use the sun’s
energy directly
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Euglena
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Heterotrophs
• Heterotrophs
are organisms
that can NOT
make their own
food
• Heterotrophs
can NOT
directly use
the sun’s
energy
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Energy
• Energy Takes Many
Forms such as light,
heat, electrical,
chemical, mechanical
• Energy can be changed
from one form to
another
• Energy can be stored in
chemical bonds & then
released later
Candles release
energy as HEAT & LIGHT
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ATP – Cellular Energy
• Adenosine Triphosphate
• Contains two, high-energy phosphate
bonds
• Also contains the nitrogen base adenine
& a ribose sugar
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ADP
• Adenosine Diphosphate
• ATP releases energy, a free
phosphate, & ADP when cells take
energy from ATP
One phosphatecopyright
bond
has been removed
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Sugar in ADP & ATP
• Called ribose
• Pentose
sugar
• Also found
on RNA
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Importance of ATP
Principal
Compound
Used To
Store
Energy In
Living
Organisms
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Releasing Energy From ATP
• ATP is constantly being used and
remade by cells
• ATP provides all of the energy for
cell activities
• The high energy phosphate bonds
can be BROKEN to release energy
• The process of releasing ATP’s
energy & reforming the molecule
is called phosphorylation
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Releasing Energy From ATP
• Adding A
Phosphate Group
To ADP stores
Energy in ATP
• Removing A
Phosphate Group
From ATP
Releases Energy
& forms ADP
Loose
Gain
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Cells Using Biochemical Energy
Cells Use ATP For:
• Active transport
• Movement
• Photosynthesis
• Protein Synthesis
• Cellular respiration
• All other cellular
reactions
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More on ATP
• Cells Have Enough ATP To
Last For A Few Seconds
• ATP must constantly be
made
• ATP Transfers Energy
Very Well
• ATP Is NOT Good At
Energy Storage
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Glucose
• Glucose is a
monosaccharide
• C6H12O6
• One Molecule of glucose
Stores 90 Times More
Chemical Energy Than
One Molecule of ATP
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History of
Photosynthesis &
Plant Pigments
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Photosynthesis
• Involves the Use Of light
Energy to convert Water (H20)
and Carbon Dioxide (CO2) into
Oxygen (O2) and High Energy
Carbohydrates (sugars, e.g.
Glucose) & Starches
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Investigating Photosynthesis
• Many Scientists Have
Contributed To
Understanding
Photosynthesis
• Early Research Focused On
The Overall Process
• Later Researchers
Investigated The Detailed
Chemical Pathways
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Early Questions on Plants
Several Centuries Ago, The
Question Was:
Does the increase in mass
of a plant come from the
air? The soil? The Water?
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Van Helmont’s Experiment
1643
•
•
•
Planted a seed into A
pre-measured amount
of soil and watered
for 5 years
Weighed Plant &
Soil. Plant Was 75
kg, Soil The Same.
Concluded Mass Came
From Water
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Priestley’s Experiment 1771
•
•
•
•
Burned Candle In Bell
Jar Until It Went Out.
Placed Sprig Of Mint In
Bell Jar For A Few
Days.
Candle Could Be Relit
And Burn.
Concluded Plants
Released Substance (O2)
Necessary For
burning.
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Ingenhousz’s Experiment
1779
Repeated Priestly experiment
with & without sunlight22
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Results of Ingenhousz’s
Experiment
• Showed That Priestley’s
Results Only Occurred In
The Presence Of Sunlight.
• Light Was Necessary For
Plants To Produce The
“Burning Gas” or oxygen
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Julius Robert Mayer 1845
Proposed That
Plants can
Convert Light
Energy Into
Chemical
Energy
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Samuel Ruben & Martin Kamen
1941
Used Isotopes
To Determine
That The
Oxygen
Liberated In
Photosynthesis
Comes From
Water
RUBIN
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KAMEN
Melvin Calvin 1948
•First to trace the path
that carbon (CO2) takes
in forming Glucose
•Does NOT require
sunlight
•Called the Calvin Cycle
or Light Independent
Reaction
•Also known as the Dark
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Reaction
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Rudolph Marcus 1992
•Studied the
Light
Independent
Reactions
•First to
describe the
Electron
transport Chain
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The Photosynthesis
Equation
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Pigments
• In addition to water,
carbon dioxide, and
light energy,
photosynthesis requires
Pigments
• Chlorophyll is the
primary light-absorbing
pigment in autotrophs
• Chlorophyll is found
inside chloroplasts
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Light and Pigments
• Energy From The Sun
Enters Earth’s Biosphere
As Photons
• Photon = Light Energy
Unit
• Light Contains A Mixture
Of Wavelengths
• Different Wavelengths
Have Different Colors
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Light & Pigments
• Different pigments absorb
different wavelengths of light
• Photons of light “excite” electrons
in the plant’s pigments
• Excited electrons carry the
absorbed energy
• Excited electrons move to
HIGHER energy levels
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Chlorophyll
There are 2 main types
of chlorophyll
molecules:
Chlorophyll a
Chlorophyll b
A third type, chlorophyll
c, is found in
dinoflagellates
Magnesium atom at the
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Chlorophyll a and b
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Chlorophyll a
•Found in all plants, algae, &
cyanobacteria
•Makes photosynthesis possible
•Participates directly in the
Light Reactions
•Can accept energy from
chlorophyll b
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Chlorophyll b
• Chlorophyll b is an
accessory pigment
• Chlorophyll b acts indirectly
in photosynthesis by
transferring the light it
absorbs to chlorophyll a
• Like chlorophyll a, it
absorbs red & blue light
and REFLECTS GREEN
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The Biochemical
Reactions
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It Begins with Sunlight!
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Photoautotrophs Absorb Light
Energy
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Inside A Chloroplast
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Structure of the Chloroplast
• Double membrane organelle
• Outer membrane smooth
• Inner membrane forms
stacks of connected sacs
called thylakoids
• Thylakoid stack is called the
granun (grana-plural)
• Gel-like material around
grana called stroma
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Function of the Stroma
• Light Independent
reactions occur here
• ATP used to make
carbohydrates like glucose
• Location of the Calvin
Cycle
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Thylakoid membranes
• Light Dependent reactions
occur here
• Photosystems are made up of
clusters of chlorophyll
molecules
• Photosystems are embedded
in the thylakoid membranes
• The two photosystems are:
Photosytem I
Photosystem II
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Photosynthesis Overview
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Energy Carriers
• Nicotinamide Adenine Dinucleotide
Phosphate (NADP+)
• NADP+ = Reduced Form
• Picks Up 2 high-energy
electrons and H+ from the Light
Reaction to form NADPH
• NADPH carries energy to be
passed on to another molecule
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NADPH
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Light Dependent Reactions
• Occurs across the thylakoid
membranes
• Uses light energy
• Produce Oxygen from water
• Convert ADP to ATP
• Also convert NADP+ into
the energy carrier
NADPH
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Light Dependent Reaction
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Light Dependent Reaction
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Photosystem I
•Discovered First
•Active in the final stage of
the Light Dependent Reaction
•Made of 300 molecules of
Chlorophyll
•Almost completely chlorophyll
a
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Photosystem II
•Discovered Second
•Active in the beginning stage
Of the Light Dependent
Reaction
•Contains about equal amounts
of chlorophyll a and
chlorophyll b
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Photosynthesis Begins
Photosystem II absorbs light
energy
Electrons are energized and passed
to the Electron Transport Chain
Lost electrons are replaced from
the splitting of water into 2H+,
free electrons, and Oxygen
2H+ pumped across thylakoid
membrane
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Photosystem I
High-energy electrons are
moved to Photosystem I
through the Electron
Transport Chain
Energy is used to transport H+
from stroma to inner
thylakoid membrane
NADP+ converted to NADPH
when it picks up 2 electrons &
H+
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Phosphorylation
Enzyme in thylakoid
membrane called ATP
Synthase
As H+ ions passed through
thylakoid membrane,
enzyme binds them to ADP
Forms ATP for cellular
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Light Reaction Summary
Reactants:
• H2O
• Light Energy
Energy Products:
• ATP
• NADPH
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Light Independent Reaction
• ATP & NADPH from light
reactions used as energy
• Atmospheric C02 is used to
make sugars like glucose and
fructose
• Six-carbon Sugars made
during the Calvin Cycle
• Occurs in the stroma
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The Calvin Cycle
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The Calvin Cycle
• Two turns of the Calvin Cycle
are required to make one
molecule of glucose
• 3-CO2 molecules enter the cycle
to form several intermediate
compounds (PGA)
• A 3-carbon molecule called
Ribulose Biphosphate (RuBP) is
used to regenerate the Calvin
cycle
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Factors Affecting the Rate
of Photosynthesis
• Amount of
available water
• Temperature
• Amount of
available light
energy
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