Where it Starts--Photosynthesis
 Obtain


energy
Autotrophs
Heterotrophs
 Metabolism—biochemical
energy


Photosynthesis
Cellular Respiration
processes release
 Food


energy stored in chemical bonds
Exergonic (cellular respiration)
Endergonic (photosynthesis)
 Energy
transfers from endergonic to
exergonic through ATP
 Chlorophyll



Plants
Algae
Some bacteria
 Transfer
sun’s energy into chemical bonds
 Three



stages
Light-capturing
Light-dependent
Light-independent
 CO2
+ H2O => C6H12O6 (glucose) + O2
 Wavelength
 Spectrum
 Photons


Packets of particle-like light
Fixed energy
 Energy

Low energy = long wavelength


level
Microwaves, radio waves
High energy = short wavelength

Gamma rays, x-rays
 The
light that you see is REFLECTED, not
absorbed.
 Therefore,
a green plant is reflecting the
green part of the spectrum (and photons of
that energy), not absorbing them.
 Molecules
that absorb photons of only a
particular wavelength
 Chlorophyll a



Absorbs red, blue, violet light
Reflects green, yellow light
Major pigment in almost all photoautotrophs
 Chlorophyll


b
Absorbs red-orange, some blue
Reflects green, some blue
 Carotenoids




Absorb blue-violet, blue-green light
Reflect red, orange, yellow light
Give color to many flowers, fruits, vegetables
Color leaves in Autumn
 Anthocyanins




Absorb green, yellow, some orange light
Reflect red, purple light
Cherries, many flowers
Color leaves in Autumn
 Phycobilins



Absorb green, yellow, orange light
Reflect red, blue-green light
Some algae & bacteria
 Pigment

absorbs light of specific wavelentgh
Corresponds to energy of photon
 Electron
absorbs energy from photon
 Energy boosts electron to higher level
 Electron then returns to original level
 When it returns, emits some energy (heat or
photon)
 Stage



Light energy converted to bond energy of ATP
Water molecules split, helping to form NADPH
Oxygen atoms escape
 Stage

1 (Light-Dependent)
2 (Light-Independent)
ATP energy used to synthesize glucose & other
carbohydrates
 Occurs
in thylakoids
 Electrons transfer light energy in electron
transport chain
 Electron
transfers pump H+ into inner
thylakoid compartment
 Repeats, building up concentration and
electric gradients
 H+
can only pass through channels inside ATP
Synthase
 Ion flow through channel makes protein turn,
forcing Phosphate onto ADP
 Electrons
continue until bonding NADP+ to
form NADPH
 NADPH used in next part of cycle
 CO2
in air attaches to rubisco (RuBP)
 Splits to form PGA
 PGA gets phosphate from ATP, then H+ and
electrons from NADPH
 Forms PGAL
 Two PGAL combine to form glucose plus
phosphate group
 Some
PGAL recycles to form more RuBP
 Takes 6 “turns” of cycle to form one glucose
molecule
 6 CO2 must be fixed and 12 PGAL must form
to produce one glucose molecule and keep
the cycle running
*(G3P = PGAL)
 Stomata



Close when hot & dry
Keeps water inside
Prevents CO2 & O2 exchange
 Basswood,
beans, peas, evergreens
 3-Carbon PGA is first stable intermediate in
Calvin-Benson cycle
 Stomata close, O2 builds up
 Increased O2 levels compete w/ CO2 in cycle
 Rubisco attaches oxygen, NOT carbon to
RuBP
 This yields 1 PGA rather than 2
 Lowers sugar production & growth of plant

12 “turns” rather than 6 to make sugars
 Better
adapted to cold & wet
 Corn,
tropical plants
 Also close stomata on hot, dry days
 Pumps carbon through cycles in 2 cells


Mesophyll cells: create 4-carbon molecule
(oxaloacetate)
Bundle-sheath cells: take 4-carbon molecule
(malate), releases CO2 to Calvin-Benson cycle
 This
allows CO2 to remain high for C-B cycle
 Requires 1 more ATP than C3, but less water
lost & more sugar produced
 Adapted to higher light & temp, lower water
 Desert
plants (cactus)
 Crassulcean Acid Metabolism
 Opens stomata at night, uses C4 cycle
 Cells store malate & organic acids
 During day when stomata close, malate
releases CO2 for C-B cycle