Transcript PHOTOSYNTHESIS2011K

Photosynthesis
Chapter 8-2 & 8-3
The Equation
 Photosynthesis uses the energy of
sunlight to convert water and carbon
dioxide into high-energy sugars and
oxygen.
Sunlight
6CO2
+
Carbon Dioxide +
6H20

Water

C6H12O6 +
sugars
6O2
+ oxygen
Light and Pigments
 Plants capture the sun’s energy with light
absorbing molecules called pigments.
 Chlorophyll = principal pigment in green plants
 Found in chloroplasts
How does chlorophyll work?
 It absorbs light
 The energy from the
light energizes
electrons in the
chlorophyll
 Energized electrons
are used to transfer
energy to other
molecules
Light and Pigments
 Chlorophyll does NOT absorb
light in the green region of the
visible spectrum
 Absorbs all other colors and
REFLECTS green
THIS IS WHY YOU SEE THE
GREEN!
Inside a Chloroplast
 Inside a Chloroplast
 In plants, photosynthesis takes place
inside chloroplasts.
Plant
Chloroplast
Plant cells
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8-3 The Reactions of Photosynthesis
Inside a Chloroplast
Chloroplasts contain thylakoids—saclike
photosynthetic membranes.
Single
thylakoid
Chloroplast
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8-3 The Reactions of Photosynthesis
Inside a Chloroplast
Thylakoids are arranged in stacks known as
grana. A singular stack is called a granum.
Granum
Chloroplast
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8-3 The Reactions of Photosynthesis
Inside a Chloroplast
Proteins in the thylakoid membrane organize
chlorophyll and other pigments into clusters called
photosystems, which are the light-collecting units
of the chloroplast.
Photosystems
Chloroplast
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The Reactions
 The reactions of photosynthesis include: the
light-dependent reactions and the lightindependent reactions, or Calvin cycle.
 The light-dependent reactions take place within
the thylakoid membranes.
 The Calvin cycle takes place in the stroma,
which is the region outside the thylakoid
membranes.
stroma
8-3 The Reactions of Photosynthesis
Light-Dependent
Reactions
Photosynthesis begins when pigments in
photosystem II absorb light, increasing their
energy level.
Photosystem II
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8-3 The Reactions of Photosynthesis
Light-Dependent
Reactions
As plants remove electrons from water, oxygen is
left behind and is released into the air.
Photosystem II
+
O2
2H2O
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High-energy
electron
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8-3 The Reactions of Photosynthesis
Light-Dependent
Reactions
High-energy electrons move through the electron
transport chain from photosystem II to
photosystem I.
Photosystem II
+
O2
2H2O
Photosystem I
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8-3 The Reactions of Photosynthesis
Light-Dependent
Reactions
The cell membrane contains a protein called ATP
synthase that allows H+ ions to pass through it
ATP synthase
+
O2
2H2O
2 NADP+
2
2
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NADPH
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8-3 The Reactions of Photosynthesis
Light-Dependent
Reactions
Because of this system, light-dependent electron
transport produces not only high-energy electrons
but ATP as well.
ATP synthase
+
O2
2H2O
ADP
2 NADP+
2
2
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NADPH
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Light Dependent Reactions
 Requires H2O
Produces Oxygen
 Sunlight excites electrons
 Excited electrons carried by NADP+ creating
NADPH (when electrons and hydrogen
added).
 ADP is converted to ATP.
The Calvin Cycle (Light
Independent Reaction)
 Requires 6CO2
Produces 6 carbon sugars (as well as
lipids and amino acids)
 Uses ATP and NADPH from the lightdependent reactions.
 After it is used, ADP and NADP+ is
returned to the thylakoids
8-3 The Reactions of Photosynthesis
H2O
Inside a Chloroplast
CO2
Light
NADP+
ADP + P
Lightdependent
reactions
Calvin
Calvin
cycle
Cycle
Chloroplast
O2
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Sugars
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Factors Affecting
Photosynthesis
 Amount of Water
 Too little can slow or
stop it
 Some plants have
waxy coatings to
reduce water loss
Factors Affecting
Photosynthesis
 Temperature
 Enzymes work best between 0 and 35C
 Too high or too low will slow or stop photosynthesis
Factors Affecting
Photosynthesis
 Light Intensity
 Greater intensity increases rate of photosynthesis
 Will level off at some point (when max level has been
reached)
Create a Flow Chart or Mind
Map of Photosynthesis
 It must include:
 Processes – step by step beginning with the Sun
 Locations of each process and organelle structures
involved
 Chemical reactants and products at each step
 Descriptions of how energy changes from one form
to another
You may use words and/or pictures