Ch. 10
PHOTOSYNTHESIS
History
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Jan Van Helmont
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Joseph Priestley
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Plants only produce oxygen if in the light
Melvin Calvin
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Mint plant keeps candle lit inside jar, plants produce oxygen
Also discovered/named oxygen
Jan Ingenhousz
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Mass of plant, container and soil, document mass of water –
new growth was greater
Steps of dark reactions using radioactive tracers
CARBON DIOXIDE COMING INTO PLANT –
CREATING CARBOHYDRATES ….. BIOMASS
Energy Flow
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Energy flow is one directional
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Elements/ nutrients/ matter cycles
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From sun (solar energy) to chemical then
mechanical energy….. Eventually heat
C cycle, N cycle, Water cycle, etc.
Food webs
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Autotrophs = self feeding; photoautotrophic and
chemoautotrophic
Heterotrophs = other feeding; herbivores,
carnivores, omnivores, detritivores, decomposers,
parasites, etc.
Leaf Structure
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Chlorophyll is a
chemical/ pigment
Chloroplasts are
structures that contain
chlorophyll
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Other plastids
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Many layers (Membranes)
chromoplast
leukoplast
amyloplasts
Specialized cells/
tissues
From chloroplast to leaf
Light Reactions
Require light to occur
 Require water
 Light energy is used to split a water
molecule
 Thylakoid is site of reaction
 Provides H for NADPH, e- and
 Generates oxygen that is released
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Light Reaction Details
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Photons (units of light), at l just below 500
reach chloroplast and strike chlorophyll on
thylakoid membrane
e- on chlorophyll are excited
e- are passed to primary acceptor
Heat is given off
Water is split
Oxygen helps oxidize reaction, O loses H and
e- returns to chlorophyll
NADPH and ATP are generated
Noncyclic electron flow
Cyclic electron flow
Dark Reactions
Occurs in stroma of chloroplast
 Does not require dark ( or light )
 Needs NADPH and ATP from light
reactions
 Uses CO2
 Generates glycerol 3 phosphate (1/2 of a
glucose…. aka PGAl )
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Details of Calvin cycle
Phase 1: CO2 is incorporated, called
‘carbon fixation’
 Phase 2: phosphorylation, ATP spent, efrom NADPH reduce the C chain so it
stores more potential energy
 6 molecules with 3 C are made – 5 are
recycled and one is released as a future
glucose
 Phase 3: cycles
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Summary
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Rubisco is the enzyme that catalyzes the
first step of Calvin cycle – since in all
chloroplasts of all cells of all leaves, it’s
the most abundant protein on Earth.
sunlight
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6CO2 + 6H2O
C6H12O6 + 6O2
chlorophyll
Compare and contrast
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PHOTOSYNTHESIS
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Chloroplast
stroma and inner
membrane
ETC and cycle
ETC first
CO2 in, O2 out
Fixes C into chains
Stores energy
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RESPIRATION
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Mitochondria
matrix and inner
membrane
ETC and cycle
ETC last
C cpd in, CO2 out
Breaks C bonds
Releases energy
Alternatives
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C3 plants ( rice and wheat; grasses)
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Close stomata, hot dry weather,
less sugar – do photorespiration
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Photorespiration – process adds O2
by rubisco and this product then
splits releasing CO2
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C4 plants
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Sugar cane and corn
Make 4 C cpd first then Calvin –
making PEP that can fix CO2
easily, even when hot.
CAM
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Succulent plants like cactus and
pineapples
Crassulacean Acid Metabolism
make and store organic acids to
be broken down to CO2 and used
over night when cooler