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CHAPTER 10: PHOTOSYNTHESIS, recycle-1730163_640, recycle-1730163_640,…
CHAPTER 10: PHOTOSYNTHESIS
Concepts
Organisms are ordered
(Islands of order in sea of chaos)
Universe is not
Entropy increases
Autotrophs (producers)
Green plants and cyanobacyeria
Photoautotrophs
Chemoautotrophs
Heterotrophs (consumers)
animals, completely parasitic plants,
nonphotosynthetic prokaryotes,fungi.
Sun is source of energy
#
Maintains and increases orderliness
Indirectly: Respiration
Directly: Photosynthesis
Energy and Reducing Power
Reducing Power
(or Redox Reactions)
Many compounds are oxidized
Atom does not carry as many electrons as it could
oxidation reaction = increases positive charge
Complimentary and happen together
Redox reactions
Opposite of oxidized is reduced
Electrons are added to atom
reduction reaction = reduces posiitve charge
Most compounds in the environment are oxidized
Most compounds in organisms are reduced.
Organisms need reducing power
forces electrons onto compounds
NAD+ and NADP+ are oxidizing agents
#
take electrons and become reduced
NADH and NADPH are reducing agents
give electrons and become oxidized
Other Electron Carriers
Cytochromes
Small proteins that hold an iron atom which carries electrons
Carry within thylakoid membrane
Plastoquinones
within chloroplast membranes
long tail, two ketone groups
picks up two electrons then binds two protons
Plastocyanin
carries electrons on copper atom
moves short distance along surface of chloroplast membrane
Energy Carriers
Energy enters through Photosynthesis:
light energy to chemical energy
Light energizes pigments
Energy used in chemical reactions
Option B) Pigments make intermediates
Photosynthesis produces ATP
ATP used in most reactions
High energy phosphate bonds
Constantly recycled (ADP <---> ATP)
#
ADP phosphorylations
Photophosphorylation
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Substrate-level phosphorylation
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Oxidation Phosphorylation
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Option A) Pigments used in all reactions
Impractical
Pigment too large, energetic, and immobile.
Photosynthesis
Light-Dependent Reactions
light has photons
Plants use 350-760 nm for photosynthesis
Pigments absorb some light and reflect others
Photosynthetic pigments transfer energy to electrons
Photon excites electron
can be used in chemical reactions
chlorophyll
a
absorbs some red and blue light (reflects green)
action spectrum of process matches absorption spectrum of pigment
accessory pigments help out
chlorophyll
b
and carotenoids
Pigments are held in place by light-harvesting complex proteins
energy is transferred through antenna complex
to reaction center
chlorophyll
a
dimer
Photosystem I
Photosynthetic unit with little chlorophyll
b
dimer is P700
#
absorbs red light at 700 nm most efficiently
energy excites electron
Fx
ferredoxin
ferredoxin-NADP+ reductase (carries two electrons)
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reduces with one electron at a time
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Photosystem II
Photosynthetic unit with almost equal chlorophyll
a
and
b
reduces P700
dimer is P680
gets new electrons from water
energy excites electron
phaeophytin
Q
Plastoquinone
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(electron transport chain)
ATP Synthesis
proton concentration increases in lumen
protons escape lumen through channels
proton flow powers ATP synthesis
cyclic electron transport
doesn't make more NADPH
makes correct ratio
makes more ATP
proton concentration decreases in stroma
Stroma reactions
acceptor molecule (RuBP)
RUBISCO
3-phosphoglycerate
energized to 1,3-diphosphoglycerate
reduced to 3-phosphoglyceraldehyde (PGAL)
used to build sugars
converted back to RuBP
6CO2 + 6H2O -> C6H12O6 + 6O2
Reactants and products are abundant, stable, and nontoxic
Carbon is reduced into carbohydrate
Water is source of electrons
Light is source of energy
Light-dependent reactions
create intermediates
ATP and NADPH
Stroma reactions
produces carbohydrates
anabolism
anabolic reactions
storage
Intermediate-term
glucose and sucrose
long-term
starch and lipids
short-term
ATP and NADPH
#
#
gluconeogenesis
PGAL
dihydroxyacetone phosphate
fructose-1,6-biphosphate
fructose-6-phosphate
glucose-6-phosphate
amylopectin
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cellulose
amylose
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phosphate
Environmental and Internal Factors
Leaf Structure
Balance between H2O conservation and CO2 absorption
#
different for each ecosystem and plant
Water
stomata open during day to let CO2 in
closed at night to keep H2O in
solutions to preserve water
C4 Metabolism (Spacial Seperation)
Photorespiration wastes energy
compartmentalizes CO2 away from O2
Kranz anatomy
PEP carboxylase
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Used in hot climates
19 plant families
Crassulacean Acid Metabolism (CAM) (Temporal Seperation)
similar to C4 - produces malate
malate accumulates
stores CO2 at night
stomata open at night and closed during dauy
keeps CO2 from escaping
Advantageous in hot, very dry climates
Light
Quantity (How much)
intensity
clouds
shadows
latitude
Both light and CO2 can be limiting factors
Light compensation point
respiration=photosynthesis
Too much light can be damaging
protections
wax
accessory pigments
trichomes
vertical leaves
Duration (How Long)
Time light is available
Seasons
Summer=more
Winter=less
Latitude
Poles=more extreme
Equator=more consitent
Quality (What kind)
colors
sunset, noon
understory and deep water photosynthesizers need more accessory pigments
Box 10-1
Atmospheric concentrations today are thanks to photosynthesis
Mollusks
Humans
Fire
Combustion
Greenhouse Effect
Global Warming
Surface water warmer
increased rainfall
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snow, glacier, ice cap melting
Ocean levels rising
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Warmer water expands
Not all areas affected equally
Global Climate change
Coccoliths
Calcium carbonate shells in the ocean
Kyoto Protocol
Aims to reduce greenhouse gas production
Chlorofluorocarbons
Hole in Ozone layer
Increased UV rays reaching surface
Box 10-2
cyanobacteria
chloroplasts = endosymbiotic cyanobacteria
Almost identical photosynthesis
accessory pigments = phycobilins
oxygenic photosynthesis
no chloroplasts
purple and green bacteria
no chlorophyll
bacteriochlorophylls
accessory pigments (carotenoids)
No PS II
original electron comes back
anoxygenic photosynthesis
